DoD 5200.28-STD
                                                                    Supersedes
                                                 CSC-STD-00l-83, dtd l5 Aug 83
                                                          Library No. S225,7ll









                        DEPARTMENT OF DEFENSE STANDARD




                                 DEPARTMENT OF

                                    DEFENSE

                               TRUSTED COMPUTER

                               SYSTEM EVALUATION

                                   CRITERIA




















                                 DECEMBER l985


                                                             December 26, l985 

                                   FOREWORD


This publication, DoD 5200.28-STD, "Department of Defense Trusted Computer
System Evaluation Criteria," is issued under the authority of an in accordance
with DoD Directive 5200.28, "Security Requirements for Automatic Data
Processing (ADP) Systems," and in furtherance of responsibilities assigned by
DoD Directive 52l5.l, "Computer Security Evaluation Center."  Its purpose is to
provide technical hardware/firmware/software security criteria and associated
technical evaluation methodologies in support of the overall ADP system
security policy, evaluation and approval/accreditation responsibilities
promulgated by DoD Directive 5200.28.

The provisions of this document apply to the Office of the Secretary of Defense
(ASD), the Military Departments, the Organization of the Joint Chiefs of Staff,
the Unified and Specified Commands, the Defense Agencies and activities
administratively supported by OSD (hereafter called "DoD Components").

This publication is effective immediately and is mandatory for use by all DoD
Components in carrying out ADP system technical security evaluation activities
applicable to the processing and storage of classified and other sensitive DoD
information and applications as set forth herein.

Recommendations for revisions to this publication are encouraged and will be
reviewed biannually by the National Computer Security Center through a formal
review process.  Address all proposals for revision through appropriate
channels to:  National Computer Security Center, Attention:  Chief, Computer
Security Standards.

DoD Components may obtain copies of this publication through their own
publications channels.  Other federal agencies and the public may obtain copies
from:  Office of Standards and Products, National Computer Security Center,
Fort Meade, MD  20755-6000, Attention:  Chief, Computer Security Standards.




_________________________________

Donald C. Latham
Assistant Secretary of Defense
(Command, Control, Communications, and Intelligence)


                               ACKNOWLEDGEMENTS


Special recognition is extended to Sheila L. Brand, National Computer Security
Center (NCSC), who integrated theory, policy, and practice into and directed
the production of this document.

Acknowledgment is also given for the contributions of: Grace Hammonds and
Peter S. Tasker, the MITRE Corp., Daniel J. Edwards, NCSC, Roger R. Schell,
former Deputy Director of NCSC, Marvin Schaefer, NCSC, and Theodore M. P. Lee,
Sperry Corp., who as original architects formulated and articulated the
technical issues and solutions presented in this document; Jeff Makey, formerly
NCSC, Warren F. Shadle, NCSC, and Carole S. Jordan, NCSC, who assisted in the
preparation of this document; James P. Anderson, James P. Anderson & Co.,
Steven B. Lipner, Digital Equipment Corp., Clark Weissman, System Development
Corp., LTC Lawrence A. Noble, formerly U.S. Air Force, Stephen T. Walker,
formerly DoD, Eugene V. Epperly, DoD, and James E. Studer, formerly Dept. of
the Army, who gave generously of their time and expertise in the review and
critique of this document; and finally, thanks are given to the computer
industry and others interested in trusted computing for their enthusiastic
advice and assistance throughout this effort.



                                   CONTENTS


          FOREWORD. . . . . . . . . . . . . . . . . . . . . . . . . . . .i

          ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . ii

          PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . .v

          INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . .1


                             PART I:  THE CRITERIA

          1.0  DIVISION D:  MINIMAL PROTECTION. . . . . . . . . . . . . .9

          2.0  DIVISION C:  DISCRETIONARY PROTECTION. . . . . . . . . . 11
               2.1   Class (C1):  Discretionary Security Protection . . 12
               2.2   Class (C2):  Controlled Access Protection. . . . . 15

          3.0  DIVISION B:  MANDATORY PROTECTION. . . . . . . . . . . . 19
               3.1   Class (B1):  Labeled Security Protection . . . . . 20
               3.2   Class (B2):  Structured Protection . . . . . . . . 26
               3.3   Class (B3):  Security Domains. . . . . . . . . . . 33

          4.0  DIVISION A:  VERIFIED PROTECTION . . . . . . . . . . . . 41
               4.1   Class (A1):  Verified Design . . . . . . . . . . . 42
               4.2   Beyond Class (A1). . . . . . . . . . . . . . . . . 51


                      PART II:  RATIONALE AND GUIDELINES

          5.0  CONTROL OBJECTIVES FOR TRUSTED COMPUTER SYSTEMS. . . . . 55
               5.1   A Need for Consensus . . . . . . . . . . . . . . . 56
               5.2   Definition and Usefulness. . . . . . . . . . . . . 56
               5.3   Criteria Control Objective . . . . . . . . . . . . 56

          6.0  RATIONALE BEHIND THE EVALUATION CLASSES. . . . . . . . . 63
               6.1   The Reference Monitor Concept. . . . . . . . . . . 64
               6.2   A Formal Security Policy Model . . . . . . . . . . 64
               6.3   The Trusted Computing Base . . . . . . . . . . . . 65
               6.4   Assurance. . . . . . . . . . . . . . . . . . . . . 65
               6.5   The Classes. . . . . . . . . . . . . . . . . . . . 66

          7.0  THE RELATIONSHIP BETWEEN POLICY AND THE CRITERIA . . . . 69
               7.1   Established Federal Policies . . . . . . . . . . . 70
               7.2   DoD Policies . . . . . . . . . . . . . . . . . . . 70
               7.3   Criteria Control Objective For Security Policy . . 71
               7.4   Criteria Control Objective for Accountability. . . 74
               7.5   Criteria Control Objective for Assurance . . . . . 76

          8.0  A GUIDELINE ON COVERT CHANNELS . . . . . . . . . . . . . 79


          9.0  A GUIDELINE ON CONFIGURING MANDATORY ACCESS CONTROL
               FEATURES . . . . . . . . . . . . . . . . . . . . . . . . 81

          10.0  A GUIDELINE ON SECURITY TESTING . . . . . . . . . . . . 83
                10.1 Testing for Division C . . . . . . . . . . . . . . 84
                10.2 Testing for Division B . . . . . . . . . . . . . . 84
                10.3 Testing for Division A . . . . . . . . . . . . . . 85


          APPENDIX A:  Commercial Product Evaluation Process. . . . . . 87

          APPENDIX B:  Summary of Evaluation Criteria Divisions . . . . 89
          
          APPENDIX C:  Sumary of Evaluation Criteria Classes. . . . . . 91

          APPENDIX D:  Requirement Directory. . . . . . . . . . . . . . 93

          GLOSSARY. . . . . . . . . . . . . . . . . . . . . . . . . . .109

          REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . .115



                                    PREFACE


The trusted computer system evaluation criteria defined in this document
classify systems into four broad hierarchical divisions of enhanced security
protection.  They provide a basis for the evaluation of effectiveness of
security controls built into automatic data processing system products.  The
criteria were developed with three objectives in mind: (a) to provide users
with a yardstick with which to assess the degree of trust that can be placed
in computer systems for the secure processing of classified or other sensitive
information; (b) to provide guidance to manufacturers as to what to build into
their new, widely-available trusted commercial products in order to satisfy
trust requirements for sensitive applications; and (c) to provide a basis for
specifying security requirements in acquisition specifications.  Two types of
requirements are delineated for secure processing: (a) specific security
feature requirements and (b) assurance requirements.  Some of the latter
requirements enable evaluation personnel to determine if the required features
are present and functioning as intended.  The scope of these criteria is to be
applied to the set of components comprising a trusted system, and is not
necessarily to be applied to each system component individually.  Hence, some
components of a system may be completely untrusted, while others may be
individually evaluated to a lower or higher evaluation class than the trusted
product considered as a whole system.  In trusted products at the high end of
the range, the strength of the reference monitor is such that most of the
components can be completely untrusted.  Though the criteria are intended to be
application-independent, the specific security feature requirements may have to
be interpreted when applying the criteria to specific systems with their own
functional requirements, applications or special environments (e.g.,
communications processors, process control computers, and embedded systems in
general).  The underlying assurance requirements can be applied across the
entire spectrum of ADP system or application processing environments without
special interpretation.


                                 INTRODUCTION

Historical Perspective

In October 1967, a task force was assembled under the auspices of the Defense
Science Board to address computer security safeguards that would protect
classified information in remote-access, resource-sharing computer systems.
The Task Force report, "Security Controls for Computer Systems," published in
February 1970, made a number of policy and technical recommendations on
actions to be taken to reduce the threat of compromise of classified
information processed on remote-access computer systems.[34]  Department of
Defense Directive 5200.28 and its accompanying manual DoD 5200.28-M, published
in 1972 and 1973 respectively, responded to one of these recommendations by
establishing uniform DoD policy, security requirements, administrative
controls, and technical measures to protect classified information processed
by DoD computer systems.[8;9]  Research and development work undertaken by the
Air Force, Advanced Research Projects Agency, and other defense agencies in
the early and mid 70's developed and demonstrated solution approaches for the
technical problems associated with controlling the flow of information in
resource and information sharing computer systems.[1]  The DoD Computer
Security Initiative was started in 1977 under the auspices of the Under
Secretary of Defense for Research and Engineering to focus DoD efforts
addressing computer security issues.[33]

Concurrent with DoD efforts to address computer security issues, work was
begun under the leadership of the National Bureau of Standards (NBS) to define
problems and solutions for building, evaluating, and auditing secure computer
systems.[17]  As part of this work NBS held two invitational workshops on the
subject of audit and evaluation of computer security.[20;28]  The first was
held in March 1977, and the second in November of 1978.  One of the products
of the second workshop was a definitive paper on the problems related to
providing criteria for the evaluation of technical computer security
effectiveness.[20]  As an outgrowth of recommendations from this report, and in
support of the DoD Computer Security Initiative, the MITRE Corporation began
work on a set of computer security evaluation criteria that could be used to
assess the degree of trust one could place in a computer system to protect
classified data.[24;25;31]  The preliminary concepts for computer security
evaluation were defined and expanded upon at invitational workshops and
symposia whose participants represented computer security expertise drawn from
industry and academia in addition to the government.  Their work has since
been subjected to much peer review and constructive technical criticism from
the DoD, industrial research and development organizations, universities, and
computer manufacturers.

The DoD Computer Security Center (the Center) was formed in January 1981 to
staff and expand on the work started by the DoD Computer Security
Initiative.[15]  A major goal of the Center as given in its DoD Charter is to
encourage the widespread availability of trusted computer systems for use by
those who process classified or other sensitive information.[10]  The criteria
presented in this document have evolved from the earlier NBS and MITRE
evaluation material.

Scope

The trusted computer system evaluation criteria defined in this document apply
primarily to trusted commercially available automatic data processing (ADP)
systems.  They are also applicable, as amplified below, the the evaluation of
existing systems and to the specification of security requirements for ADP
systems acquisition.  Included are two distinct sets of requirements: 1)
specific security feature requirements; and 2) assurance requirements.  The
specific feature requirements encompass the capabilities typically found in
information processing systems employing general-purpose operating systems that
are distinct from the applications programs being supported.  However, specific
security feature requirements may also apply to specific systems with their own
functional requirements, applications or special environments (e.g.,
communications processors, process control computers, and embedded systems in
general).  The assurance requirements, on the other hand, apply to systems that
cover the full range of computing environments from dedicated controllers to
full range multilevel secure resource sharing systems.


Purpose

As outlined in the Preface, the criteria have been developedto serve a number
of intended purposes:

           * To provide a standard to manufacturers as to what security
           features to build into their new and planned, commercial 
           products in order to provide widely available systems that
           satisfy trust requirements (with particular emphasis on preventing
           the disclosure of data) for sensitive applications.

           * To provide DoD components with a metric with which to evaluate
           the degree of trust that can be placed in computer systems for
           the secure processing of classified and other sensitive
           information.

           * To provide a basis for specifying security requirements in
           acquisition specifications.

With respect to the second purpose for development of the criteria, i.e.,
providing DoD components with a security evaluation metric, evaluations can be
delineated into two types: (a) an evaluation can be performed on a computer
product from a perspective that excludes the application environment; or, (b)
it can be done to assess whether appropriate security measures have been taken
to permit the system to be used operationally in a specific environment.  The
former type of evaluation is done by the Computer Security Center through the
Commercial Product Evaluation Process.  That process is described in Appendix
A.

The latter type of evaluation, i.e., those done for the purpose of assessing a
system's security attributes with respect to a specific operational mission,
is known as a certification evaluation.  It must be understood that the
completion of a formal product evaluation does not constitute certification or
accreditation for the system to be used in any specific application
environment.  On the contrary, the evaluation report only provides a trusted
computer system's evaluation rating along with supporting data describing the
product system's strengths and weaknesses from a computer security point of
view.  The system security certification and the formal approval/accreditation
procedure, done in accordance with the applicable policies of the issuing
agencies, must still be followed-before a system can be approved for use in
processing or handling classified information.[8;9]  Designated Approving
Authorities (DAAs) remain ultimately responsible for specifying security of
systems they accredit.

The trusted computer system evaluation criteria will be used directly and
indirectly in the certification process.  Along with applicable policy, it
will be used directly as technical guidance for evaluation of the total system
and for specifying system security and certification requirements for new
acquisitions.  Where a system being evaluated for certification employs a
product that has undergone a Commercial Product Evaluation, reports from that
process will be used as input to the certification evaluation.  Technical data
will be furnished to designers, evaluators and the Designated Approving
Authorities to support their needs for making decisions.


Fundamental Computer Security Requirements

Any discussion of computer security necessarily starts from a statement of
requirements, i.e., what it really means to call a computer system "secure."
In general, secure systems will control, through use of specific security
features, access to information such that only properly authorized
individuals, or processes operating on their behalf, will have access to read,
write, create, or delete information.  Six fundamental requirements are
derived from this basic statement of objective: four deal with what needs to
be provided to control access to information; and two deal with how one can
obtain credible assurances that this is accomplished in a trusted computer
system.

                                    Policy

          Requirement 1 - SECURITY POLICY - There must be an explicit and
well-defined security policy enforced by the system.  Given identified subjects
and objects, there must be a set of rules that are used by the system to
determine whether a given subject can be permitted to gain access to a specific
object.  Computer systems of interest must enforce a mandatory security policy
that can effectively implement access rules for handling sensitive (e.g.,
classified) information.[7]  These rules include requirements such as: No
person lacking proper personnel security clearance shall obtain access to
classified
information.  In addition, discretionary security controls are required to
ensure that only selected users or groups of users may obtain access to data
(e.g., based on a need-to-know). 

          Requirement 2 - MARKING - Access control labels must be associated
with objects.  In order to control access to information stored in a computer,
according to the rules of a mandatory security policy, it must be possible to
mark every object with a label that reliably identifies the object's
sensitivity level (e.g., classification), and/or the modes of access accorded
those subjects who may potentially access the object.

                                Accountability

          Requirement 3 - IDENTIFICATION - Individual subjects must be
identified.  Each access to information must be mediated based on who is
accessing the information and what classes of information they are authorized
to deal with.  This identification and authorization information must be
securely maintained by the computer system and be associated with every active
element that performs some security-relevant action in the system.

          Requirement 4 - ACCOUNTABILITY - Audit information must be
selectively kept and protected so that actions affecting security can be traced
to the responsible party.  A trusted system must be able to record the
occurrences of security-relevant events in an audit log.  The capability to
select the audit events to be recorded is necessary to minimize the expense of
auditing and to allow efficient analysis.  Audit data must be protected from
modification and unauthorized destruction to permit detection and
after-the-fact investigations of security violations.

                                   Assurance

          Requirement 5 - ASSURANCE - The computer system must contain
hardware/software mechanisms that can be independently evaluated to provide
sufficient assurance that the system enforces requirements 1 through 4 above. 
In order to assure that the four requirements of Security Policy, Marking,
Identification, and Accountability are enforced by a computer system, there
must be some identified and unified collection of hardware and software
controls that perform those functions.  These mechanisms are typically embedded
in the operating system and are designed to carry out the assigned tasks in a
secure manner.  The basis for trusting such system mechanisms in their
operational setting must be clearly documented such that it is possible to
independently examine the evidence to evaluate their sufficiency.

          Requirement 6 - CONTINUOUS PROTECTION - The trusted mechanisms that
enforce these basic requirements must be continuously protected against
tampering and/or unauthorized changes.  No computer system can be considered
truly secure if the basic hardware and software mechanisms that enforce the
security policy are themselves subject to unauthorized modification or
subversion.  The continuous protection requirement has direct implications
throughout the computer system's life-cycle.

These fundamental requirements form the basis for the individual evaluation
criteria applicable for each evaluation division and class.  The interested
reader is referred to Section 5 of this document, "Control Objectives for
Trusted Computer Systems," for a more complete discussion and further
amplification of these fundamental requirements as they apply to
general-purpose information processing systems and to Section 7 for
amplification of the relationship between Policy and these requirements.


Structure of the Document

The remainder of this document is divided into two parts, four appendices, and
a glossary.  Part I (Sections 1 through 4) presents the detailed criteria
derived from the fundamental requirements described above and relevant to the
rationale and policy excerpts contained in Part II.

Part II (Sections 5 through 10) provides a discussion of basic objectives,
rationale, and national policy behind the development of the criteria, and
guidelines for developers pertaining to: mandatory access control rules
implementation, the covert channel problem, and security testing.  It is
divided into six sections.  Section 5 discusses the use of control objectives
in general and presents the three basic control objectives of the criteria.
Section 6 provides the theoretical basis behind the criteria.  Section 7 gives
excerpts from pertinent regulations, directives, OMB Circulars, and Executive
Orders which provide the basis for many trust requirements for processing
nationally sensitive and classified information with computer systems.
Section 8 provides guidance to system developers on expectations in dealing
with the covert channel problem.  Section 9 provides guidelines dealing with
mandatory security.  Section 10 provides guidelines for security testing.
There are four appendices, including a description of the Trusted Computer
System Commercial Products Evaluation Process (Appendix A), summaries of the
evaluation divisions (Appendix B) and classes (Appendix C), and finally a
directory of requirements ordered alphabetically.  In addition, there is a
glossary.


Structure of the Criteria

The criteria are divided into four divisions: D, C, B, and A ordered in a
hierarchical manner with the highest division (A) being reserved for systems
providing the most comprehensive security.  Each division represents a major
improvement in the overall confidence one can place in the system for the
protection of sensitive information.  Within divisions C and B there are a
number of subdivisions known as classes.  The classes are also ordered in a
hierarchical manner with systems representative of division C and lower
classes of division B being characterized by the set of computer security
mechanisms that they possess.  Assurance of correct and complete design and
implementation for these systems is gained mostly through testing of the
security- relevant portions of the system.  The security-relevant portions of
a system are referred to throughout this document as the Trusted Computing
Base (TCB).  Systems representative of higher classes in division B and
division A derive their security attributes more from their design and
implementation structure.  Increased assurance that the required features are
operative, correct, and tamperproof under all circumstances is gained through
progressively more rigorous analysis during the design process.

Within each class, four major sets of criteria are addressed.  The first three
represent features necessary to satisfy the broad control objectives of
Security Policy, Accountability, and Assurance that are discussed in Part II,
Section 5.  The fourth set, Documentation, describes the type of written
evidence in the form of user guides, manuals, and the test and design
documentation required for each class.

A reader using this publication for the first time may find it helpful to
first read Part II, before continuing on with Part I.



                             PART I:  THE CRITERIA


Highlighting (UPPERCASE) is used in Part I to indicate criteria not contained
in a lower class or changes and additions to already defined criteria.  Where
there is no highlighting, requirements have been carried over from lower
classes without addition or modification.
     


                     1.0  DIVISION D:  MINIMAL PROTECTION


This division contains only one class.  It is reserved for those systems that
have been evaluated but that fail to meet the requirements for a higher
evaluation class.



                   2.0 DIVISION C:  DISCRETIONARY PROTECTION


Classes in this division provide for discretionary (need-to-know) protection
and, through the inclusion of audit capabilities, for accountability of
subjects and the actions they initiate.

    

2.1  CLASS (C1):  DISCRETIONARY SECURITY PROTECTION

The Trusted Computing Base (TCB) of a class (C1) system nominally satisfies
the discretionary security requirements by providing separation of users and
data.  It incorporates some form of credible controls capable of enforcing
access limitations on an individual basis, i.e., ostensibly suitable for
allowing users to be able to protect project or private information and to
keep other users from accidentally reading or destroying their data.  The
class (C1) environment is expected to be one of cooperating users processing
data at the same level(s) of sensitivity.  The following are minimal
requirements for systems assigned a class (C1) rating:

2.1.1  Security Policy

     2.1.1.1   Discretionary Access Control

               The TCB shall define and control access between named users and
               named objects (e.g., files and programs) in the ADP system.  The
               enforcement mechanism (e.g., self/group/public controls, access
               control lists) shall allow users to specify and control sharing
               of those objects by named individuals or defined groups or both.

2.1.2  Accountability

     2.1.2.1   Identification and Authentication

               The TCB shall require users to identify themselves to it before
               beginning to perform any other actions that the TCB is expected
               to mediate.  Furthermore, the TCB shall use a protected 
               mechanism (e.g., passwords) to authenticate the user's identity.
               The TCB shall protect authentication data so that it cannot be
               accessed by any unauthorized user.

2.1.3  Assurance

     2.1.3.1   Operational Assurance

          2.1.3.1.1  System Architecture

                     The TCB shall maintain a domain for its own execution
                     protects it from external interference or tampering
                     (e.g., by modification of its code or data strucutres).
                     Resources controlled by the TCB may be a defined subset
                     of the subjects and objects in the ADP system.

          2.1.3.1.2  System Integrity

                     Hardware and/or software features shall be provided that
                     can be used to periodically validate the correct operation
                     of the on-site hardware and firmware elements of the TCB.

     2.1.3.2   Life-Cycle Assurance

          2.1.3.2.1  Security Testing

                     The security mechanisms of the ADP system shall be tested
                     and found to work as claimed in the system documentation.
                     Testing shall be done to assure that there are no obvious
                     ways for an unauthorized user to bypass or otherwise
                     defeat the security protection mechanisms of the TCB.
                     (See the Security Testing Guidelines.)

2.1.4  Documentation

     2.1.4.1   Security Features User's Guide

               A single summary, chapter, or manual in user documentation
               shall describe the protection mechanisms provided by the TCB,
               guidelines on their use, and how they interact with one another.

     2.1.4.2   Trusted Facility Manual

               A manual addressed to the ADP System Administrator shall
               present cautions about functions and privileges that should be
               controlled when running a secure facility.

     2.1.4.3   Test Documentation

               The system developer shall provide to the evaluators a document
               that describes the test plan, test procedures that show how the
               the security mechanisms were tested, and results of the
               security mechanisms' functional testing.

     2.1.4.4   Design Documentation

               Documentation shall be available that provides a description of
               the manufacturer's philosophy of protection and an explanation
               of how this philosophy is translated into the TCB.  If the TCB
               is composed of distinct modules, the interfaces between these
               modules shall be described.




2.2  CLASS (C2):  CONTROLLED ACCESS PROTECTION

Systems in this class enforce a more finely grained discretionary access
control than (C1) systems, making users individually accountable for their
actions through login procedures, auditing of security-relevant events, and
resource isolation.  The following are minimal requirements for systems
assigned a class (C2) rating:

2.2.1  Security Policy

     2.2.1.1   Discretionary Access Control

               The TCB shall define and control access between named users and
               named objects (e.g., files and programs) in the ADP system.  The
               enforcement mechanism (e.g., self/group/public controls, access
               control lists) shall allow users to specify and control sharing
               of those objects by named individuals, or defined groups of 
               individuals, or by both, and shall provide controls to limit
               propagation of access rights.  The discretionary access control
               mechanism shall, either by explicit user action or by default,
               provide that objects are protected from unauthorized access.
               These access controls shall be capable of including or excluding
               access to the granularity of a single user.  Access permission
               to an object by users not already possessing access permission
               shall only be assigned by authorized users.

     2.2.1.2   Object Reuse

               All authorizations to the information contained within a
               storage object shall be revoked prior to initial assignment,
               allocation or reallocation to a subject from the TCB's pool
               of unused storage objects.  No information, including encrypted
               representations of information, produced by a prior subject's
               actions is to be available to any subject that obtains access
               to an object that has been released back to the system.

2.2.2  Accountability

     2.2.2.1   Identification and Authentication

               The TCB shall require users to identify themselves to it before
               beginning to perform any other actions that the TCB is expected
               to mediate.  Furthermore, the TCB shall use a protected 
               mechanism (e.g., passwords) to authenticate the user's identity.
               The TCB shall protect authentication data so that it cannot be
               accessed by any unauthorized user.  The TCB shall be able to
               enforce individual accountability by providing the capability to
               uniquely identify each individual ADP system user.  The TCB
               shall also provide the capability of associating this identity
               with all auditable actions taken by that individual.

     2.2.2.2   Audit

               The TCB shall be able to create, maintain, and protect from
               modification or unauthorized access or destruction an audit
               trail of accesses to the objects it protects.  The audit data
               shall be protected by the TCB so that read access to it is
               limited to those who are authorized for audit data.  The TCB
               shall be able to record the following types of events:  use of
               identification and authentication mechanisms, introduction or
               objects into a user's address space (e.g., file open, program
               initiation), deletion of objects, and actions taken by 
               computer operators and system administrators and/or system
               security officers, and other security relevant events.  For
               each recorded event, the audit record shall identify:  date and
               time of the event, user, type of event, and success or failure
               of the event.  For identification/authentication events the
               origin of request (e.g., terminal ID) shall be included in the
               audit record.  For events that introduce an object into a user's
               address space and  for object deletion events the audit record
               shall include the name of the object.  The ADP system
               administrator shall be able to selectively audit the actions of
               any one or more users based on individual identity.

2.2.3  Assurance

     2.2.3.1   Operational Assurance

          2.2.3.1.1  System Architecture

                     The TCB shall maintain a domain for its own execution
                     that protects it from external interference or tampering
                     (e.g., by modification of its code or data structures). 
                     Resources controlled by the TCB may be a defined subset
                     of the subjects and objects in the ADP system.  The TCB
                     shall isolate the resources to be protected so that they
                     are subject to the access control and auditing
                     requirements.

          2.2.3.1.2  System Integrity

                     Hardware and/or software features shall be provided that
                     can be used to periodically validate the correct operation
                     of the on-site hardware and firmware elements of the TCB.

     2.2.3.2   Life-Cycle Assurance

          2.2.3.2.1  Security Testing

                     The security mechanisms of the ADP system shall be tested
                     and found to work as claimed in the system documentation.
                     Testing shall be done to assure that there are no obvious
                     ways for an unauthorized user to bypass or otherwise
                     defeat the security protection mechanisms of the TCB.
                     Testing shall also include a search for obvious flaws that
                     would allow violation of resource isolation, or that would
                     permit unauthorized access to the audit or authentication
                     data.  (See the Security Testing guidelines.)

2.2.4  Documentation

     2.2.4.1   Security Features User's Guide

               A single summary, chapter, or manual in user documentation
               shall describe the protection mechanisms provided by the TCB, 
               guidelines on their use, and how they interact with one another.

     2.2.4.2   Trusted Facility Manual

               A manual addressed to the ADP system administrator shall
               present cautions about functions and privileges that should be
               controlled when running a secure facility.  The procedures for
               examining and maintaining the audit files as well as the 
               detailed audit record structure for each type of audit event
               shall be given.


     2.2.4.3   Test Documentation

               The system developer shall provide to the evaluators a document
               that describes the test plan, test procedures that show how the
               security mechanisms were tested, and results of the security 
               mechanisms' functional testing.

     2.2.4.4   Design Documentation

               Documentation shall be available that provides a description of
               the manufacturer's philosophy of protection and an explanation
               of how this philosophy is translated into the TCB.  If the TCB
               is composed of distinct modules, the interfaces between these
               modules shall be described.

    

                    3.0  DIVISION B:  MANDATORY PROTECTION


The notion of a TCB that preserves the integrity of sensitivity labels and
uses them to enforce a set of mandatory access control rules is a major
requirement in this division.  Systems in this division must carry the
sensitivity labels with major data structures in the system.  The system
developer also provides the security policy model on which the TCB is based
and furnishes a specification of the TCB.  Evidence must be provided to
demonstrate that the reference monitor concept has been implemented.



3.1  CLASS (B1):  LABELED SECURITY PROTECTION

Class (B1) systems require all the features required for class (C2).  In
addition, an informal statement of the security policy model, data labeling,
and mandatory access control over named subjects and objects must be present.
The capability must exist for accurately labeling exported information.  Any
flaws identified by testing must be removed.  The following are minimal
requirements for systems assigned a class (B1) rating:

3.1.1  Security Policy

     3.1.1.1   Discretionary Access Control

               The TCB shall define and control access between named users and
               named objects (e.g., files and programs) in the ADP system.  
               The enforcement mechanism (e.g., self/group/public controls, 
               access control lists) shall allow users to specify and control
               sharing of those objects by named individuals, or defined groups
               of individuals, or by both, and shall provide controls to limit
               propagation of access rights.  The discretionary access control
               mechanism shall, either by explicit user action or by default,
               provide that objects are protected from unauthorized access. 
               These access controls shall be capable of including or excluding
               access to the granularity of a single user.  Access permission
               to an object by users not already possessing access permission
               shall only be assigned by authorized users.

     3.1.1.2   Object Reuse

               All authorizations to the information contained within a
               storage object shall be revoked prior to initial assignment,
               allocation or reallocation to a subject from the TCB's pool
               of unused storage objects.  No information, including encrypted
               representations of information, produced by a prior subject's
               actions is to be available to any subject that obtains access
               to an object that has been released back to the system.

     3.1.1.3   Labels

               Sensitivity labels associated with each subject and storage
               object under its control (e.g., process, file, segment, device)
               shall be maintained by the TCB.  These labels shall be used as
               the basis for mandatory access control decisions.  In order to
               import non-labeled data, the TCB shall request and receive from
               an authorized user the security level of the data, and all such
               actions shall be auditable by the TCB.

          3.1.1.3.1  Label Integrity

                     Sensitivity labels shall accurately represent security
                     levels of the specific subjects or objects with which they
                     are associated.  When exported by the TCB, sensitivity
                     labels shall accurately and unambiguously represent the
                     internal labels and shall be associated with the
                     information being exported.

          3.1.1.3.2  Exportation of Labeled Information

                     The TCB shall designate each communication channel and
                     I/O device as either single-level or miltilevel.  Any
                     change in this designation shall be done manually and
                     shall be auditable by the TCB.  The TCB shall maintain
                     and be able to audit any change in the security level
                     or levels associated with a communication channel or 
                     I/O device.

               3.1.1.3.2.1  Exportation to Multilevel Devices

                          When the TCB exports an object to a multilevel I/O
                          device, the sensitivity label associated with that
                          object shall also be exported and shall reside on
                          the same physical medium as the exported
                          information and shall be in the same form
                          (i.e., machine-readable or human-readable form).
                          When the TCB exports or imports an object over a 
                          multilevel communication channel, the protocol
                          used on that channel shall provide for the
                          unambiguous pairing between the sensitivity labels
                          and the associated information that is sent or
                          received.

               3.1.1.3.2.2  Exportation to Single-Level Devices

                          Single-level I/O devices and single-level
                          communication channels are not required to
                          maintain the sensitivity labels of the information
                          they process.  However, the TCB shall include a
                          mechanism by which the TCb and an authorized user 
                          reliably communicate to designate the single
                          security level of information imported or exported
                          via single-level communication channels or I/O
                          devices.

               3.1.1.3.2.3  Labeling Human-Readable Output

                          The ADP system administrator shall be able to
                          specify the printable label names associated with
                          exported sensitivity labels.  The TCB shall mark
                          the beginning and end of all human-readable, paged,
                          hardcopy output (e.g., line printer output) with
                          human-readable sensitivity labels that properly*
                          represent the sensitivity of the output.  The TCB
                          shall, be default, mark the top and bottom of each
                          page of human-readable, paged, hardcopy output
                          (e.g., line printer output) with human-readable
                          sensitivity labels that properly* represent the
                          overall sensitivity of the output or that properly*
                          represent the sensitivity of the information on the
                          page.  The TCB shall, by default and in an
                          appropriate manner, mark other forms of human-
                          readable output (e.g., maps, graphics) with human-
                          readable sensitivity labels that properly*
                          represent the sensitivity of the touput.  Any
                          override of these marking defaults shall be
                          auditable by the TCB.

     3.1.1.4  Mandatory Access Control

               The TCB shall enforce a mandatory access control policy over
               all subjects and storage objects under its control (e.g.,
               processes, files, segments, devices).  These subjects and
               objects shall be assigned sensitivity labels that are a
               combination of hierarchical classification levels and
               non-hierarchical categories, and the labels shall be used as
               the basis for mandatory access control decisions.  The TCB
               shall be able to support two or more such security levels.
               (See the Mandatory Access Control Guidelines.)  The following
               requirements shall hold for all accesses between subjects and
               objects controlled by the TCB:  a subject can read an object
               only if the hierarchical classification in the subject's
               security level is greater than or equal to the hierarchical
               classification in the object's security level and the non-
               hierarchical categories in the subject's security level include
               all the non-hierarchical categories in the object's security
               level.  A subject can write an object only if the hierarchical
               classification in the subject's security level is less than or
               equal to the hierarchical classification in the object's 
               security level and all the non-hierarchical categories in the
               subject's security level are included in the non-hierarchical
               categories in the object's security level.  Identification 
               and authentication data shall be used by the TCB to authenti-
               cate the user's identity and to ensure that the security level
               and authorization of subjects external to the TCB that may be
               created to act on behalf of the individual user are dominated
               by the clearance and authorization of that user.

3.1.2  Accountability

     3.1.2.1  Identification and Authentication

               The TCB shall require users to identify themselves to it before
               beginning to perform any other actions that the TCB is expected
               to mediate.  Furthermore, the TCB shall maintain authentication
               data that includes information for verifying the identity of
               individual users (e.g., passwords) as well as information for
               determining the clearance and authorizations or individual
_____________________________
* The hierarchical classification component in human-readable sensitivity
labels shall be equal to the greatest hierarchical classification or any of the
information in the output that the labels refer to; the non-hierarchical
category component shall include all of the non-hierarchical categories of the
information in the output the labels refer to, but no other non-hierarchical
categories.

               users.  This data shall be used by the TCB to authenticate the
               user's identity and to ensure that the security level and
               authorizations of subjects external to the TCB that may be
               created to act on behalf of the individual user are dominated
               by the clearance and authorization of that user.  The TCB shall
               protect authentication data so that it cannot be accessed by any
               unauthorized user.  The TCB shall be able to enforce individual
               accountability by providing the capability to uniquely identify
               each individual ADP system user.  The TCB shall also provide the
               capability of associating this identity with all auditable
               actions taken by that individual.

     3.1.2.2   Audit

               The TCB shall be able to create, maintain, and protect from
               modification or unauthorized access or destruction an audit
               trail of accesses to the objects it protects.  The audit data
               shall be protected by the TCB so that read access to it is
               limited to those who are authorized for audit data.  The TCB
               shall be able to record the following types of events: use of
               identification and authentication mechanisms, introduction of
               objects into a user's address space (e.g., file open, program
               initiation), deletion of objects, and actions taken by computer
               operators and system administrators and/or system security
               officers and other security relevant events.  The TCB shall also
               be able to audit any override of human-readable output markings.
               For each recorded event, the audit record shall identify: date
               and time of the event, user, type of event, and success or
               failure of the event.  For identification/authentication events
               the origin of request (e.g., terminal ID) shall be included in
               the audit record.  For events that introduce an object into a
               user's address space and for object deletion events the audit
               record shall include the name of the object and the object's
               security level.  The ADP system administrator shall be able to
               selectively audit the actions of any one or more users based on
               individual identity and/or object security level.

3.1.3  Assurance

     3.1.3.1   Operational Assurance

          3.1.3.1.1  System Architecture

                     The TCB shall maintain a domain for its own execution
                     that protects it from external interference or tampering
                     (e.g., by modification of its code or data structures). 
                     Resources controlled by the TCB may be a defined subset
                     of the subjects and objects in the ADP system.  The TCB
                     shall maintain process isolation through the provision of
                     distinct address spaces under its control.  The TCB shall
                     isolate the resources to be protected so that they are
                     subject to the access control and auditing requirements.

          3.1.3.1.2  System Integrity

                     Hardware and/or software features shall be provided that
                     can be used to periodically validate the correct operation
                     of the on-site hardware and firmware elements of the TCB.

     3.1.3.2   Life-Cycle Assurance

          3.1.3.2.1  Security Testing

                     The security mechanisms of the ADP system shall be tested
                     and found to work as claimed in the system documentation.
                     A team of individuals who thoroughly understand the
                     specific implementation of the TCB shall subject its
                     design documentation, source code, and object code to
                     thorough analysis and testing.  Their objectives shall be:
                     to uncover all design and implementation flaws that would
                     permit a subject external to the TCB to read, change, or
                     delete data normally denied under the mandatory or
                     discretionary security policy enforced by the TCB; as well
                     as to assure that no subject (without authorization to do
                     so) is able to cause the TCB to enter a state such that
                     it is unable to respond to communications initiated by
                     other users.  All discovered flaws shall be removed or
                     neutralized and the TCB retested to demonstrate that they
                     have been eliminated and that new flaws have not been
                     introduced.  (See the Security Testing Guidelines.)

          3.1.3.2.2  Design Specification and Verification

                     An informal or formal model of the security policy
                     supported by the TCB shall be maintained over the life
                     cycle of the ADP system and demonstrated to be consistent
                     with its axioms.

3.1.4  Documentation

     3.1.4.1   Security Features User's Guide

               A single summary, chapter, or manual in user documentation
               shall describe the protection mechanisms provided by the TCB,
               guidelines on their use, and how they interact with one another.

     3.1.4.2   Trusted Facility Manual

               A manual addressed to the ADP system administrator shall
               present cautions about functions and privileges that should be
               controlled when running a secure facility.  The procedures for
               examining and maintaining the audit files as well as the
               detailed audit record structure for each type of audit event
               shall be given.  The manual shall describe the operator and
               administrator functions related to security, to include changing
               the security characteristics of a user.  It shall provide
               guidelines on the consistent and effective use of the protection
               features of the system, how they interact, how to securely
               generate a new TCB, and facility procedures, warnings, and
               privileges that need to be controlled in order to operate the
               facility in a secure manner.

     3.1.4.3   Test Documentation

               The system developer shall provide to the evaluators a document
               that describes the test plan, test procedures that show how the
               security mechanisms were tested, and results of the security 
               mechanisms' functional testing.

     3.1.4.4   Design Documentation

               Documentation shall be available that provides a description of
               the manufacturer's philosophy of protection and an explanation
               of how this philosophy is translated into the TCB.  If the TCB
               is composed of distinct modules, the interfaces between these
               modules shall be described.  An informal or formal description
               of the security policy model enforced by the TCB shall be
               available and an explanation provided to show that it is
               sufficient to enforce the security policy.  The specific TCB
               protection mechanisms shall be identified and an explanation
               given to show that they satisfy the model.


3.2  CLASS (B2):  STRUCTURED PROTECTION

In class (B2) systems, the TCB is based on a clearly defined and documented
formal security policy model that requires the discretionary and mandatory
access control enforcement found in class (B1) systems be extended to all
subjects and objects in the ADP system.  In addition, covert channels are
addressed.  The TCB must be carefully structured into protection-critical and
non- protection-critical elements.  The TCB interface is well-defined and the
TCB design and implementation enable it to be subjected to more thorough
testing and more complete review.  Authentication mechanisms are strengthened,
trusted facility management is provided in the form of support for system
administrator and operator functions, and stringent configuration management
controls are imposed.  The system is relatively resistant to penetration.  The
following are minimal requirements for systems assigned a class (B2) rating:

3.2.1  Security Policy

     3.2.1.1   Discretionary Access Control

               The TCB shall define and control access between named users and
               named objects (e.g., files and programs) in the ADP system.
               The enforcement mechanism (e.g., self/group/public controls,
               access control lists) shall allow users to specify and control
               sharing of those objects by named individuals, or defined
               groups of individuals, or by both, and shall provide controls 
               to limit propagation of access rights.  The discretionary access
               control mechanism shall, either by explicit user action or by
               default, provide that objects are protected from unauthorized
               access.  These access controls shall be capable of including
               or excluding access to the granularity of a single user.
               Access permission to an object by users not already possessing
               access permission shall only be assigned by authorized users.

     3.2.1.2   Object Reuse

               All authorizations to the information contained within a
               storage object shall be revoked prior to initial assignment,
               allocation or reallocation to a subject from the TCB's pool of 
               unused storage objects.  No information, including encrypted
               representations of information, produced by a prior subject's
               actions is to be available to any subject that obtains access
               to an object that has been released back to the system.

     3.2.1.3   Labels

               Sensitivity labels associated with each ADP system resource
               (e.g., subject, storage object, ROM) that is directly or
               indirectly accessible by subjects external to the TCB shall be
               maintained by the TCB.  These labels shall be used as the basis
               for mandatory access control decisions.  In order to import 
               non-labeled data, the TCB shall request and receive from an
               authorized user the security level of the data, and all such
               actions shall be auditable by the TCB.

          3.2.1.3.1  Label Integrity

                     Sensitivity labels shall accurately represent security
                     levels of the specific subjects or objects with which
                     they are associated.  When exported by the TCB,
                     sensitivity labels shall accurately and unambiguously
                     represent the internal labels and shall be associated
                     with the information being exported.

          3.2.1.3.2  Exportation of Labeled Information

                     The TCB shall designate each communication channel and
                     I/O device as either single-level or multilevel.  Any
                     change in this designation shall be done manually and
                     shall be auditable by the TCB.  The TCB shall maintain
                     and be able to audit any change in the security level
                     or levels associated with a communication channel or 
                     I/O device.

               3.2.1.3.2.1  Exportation to Multilevel Devices

                          When the TCB exports an object to a multilevel I/O
                          device, the sensitivity label associated with that
                          object shall also be exported and shall reside on
                          the same physical medium as the exported 
                          information and shall be in the same form (i.e., 
                          machine-readable or human-readable form).  When
                          the TCB exports or imports an object over a
                          multilevel communication channel, the protocol
                          used on that channel shall provide for the
                          unambiguous pairing between the sensitivity labels
                          and the associated information that is sent or
                          received.

               3.2.1.3.2.2  Exportation to Single-Level Devices

                          Single-level I/O devices and single-level
                          communication channels are not required to 
                          maintain the sensitivity labels of the
                          information they process.  However, the TCB shall
                          include a mechanism by which the TCB and an
                          authorized user reliably communicate to designate
                          the single security level of information imported
                          or exported via single-level communication 
                          channels or I/O devices.

               3.2.1.3.2.3  Labeling Human-Readable Output

                          The ADP system administrator shall be able to
                          specify the printable label names associated with
                          exported sensitivity labels.  The TCB shall mark
                          the beginning and end of all human-readable, paged,
                          hardcopy output (e.g., line printer output) with
                          human-readable sensitivity labels that properly*
                          represent the sensitivity of the output.  The TCB
                          shall, by default, mark the top and bottom of each
                          page of human-readable, paged, hardcopy output
                          (e.g., line printer output) with human-readable
                          sensitivity labels that properly* represent the
                          overall sensitivity of the output or that 
                          properly* represent the sensitivity of the
                          information on the page.  The TCB shall, by
                          default and in an appropriate manner, mark other
                          forms of human-readable output (e.g., maps,
                          graphics) with human-readable sensitivity labels
                          that properly* represent the sensitivity of the
                          output.  Any override of these marking defaults
                          shall be auditable by the TCB.

          3.2.1.3.3  Subject Sensitivity Labels

                     The TCB shall immediately notify a terminal user of each
                     change in the security level associated with that user
                     during an interactive session.  A terminal user shall be
                     able to query the TCB as desired for a display of the
                     subject's complete sensitivity label.

          3.2.1.3.4  Device Labels

                     The TCB shall support the assignment of minimum and
                     maximum security levels to all attached physical devices.
                     These security levels shall be used by the TCB to enforce
                     constraints imposed by the physical environments in which
                     the devices are located.

     3.2.1.4   Mandatory Access Control

               The TCB shall enforce a mandatory access control policy over
               all resources (i.e., subjects, storage objects, and I/O devices
               that are directly or indirectly accessible by subjects external
               to the TCB.  These subjects and objects shall be assigned
               sensitivity labels that are a combination of hierarchical
               classification levels and non-hierarchical categories, and the
               labels shall be used as the basis for mandatory access control
               decisions.  The TCB shall be able to support two or more such
               security levels.  (See the Mandatory Access Control guidelines.)
               The following requirements shall hold for all accesses between
               All subjects external to the TCB and all objects directly or
               indirectly accessible by these subjects:  A subject can read an
               object only if the hierarchical classification in the subject's
               security level is greater than or equal to the hierarchical
               classification in the object's security level and the non-
               hierarchical categories in the subject's security level include
               all the non-hierarchical categories in the object's security
               level.  A subject can write an object only if the hierarchical
               classification in the subject's security level is less than or
               equal to the hierarchical classification in the object's
               security level and all the non-hierarchical categories in the
               subject's security level are included in the non-hierarchical
               categories in the object's security level.  Identification and
               authentication data shall be used by the TCB to authenticate
               the user's identity and to ensure that the security level and
               authorization of subjects external to the TCB that may be
               created to act on behalf of the individual user are dominated
               by the clearance and authorization of that user.

3.2.2  Accountability

     3.2.2.1   Identification and Authentication

               The TCB shall require users to identify themselves to it before
               beginning to perform any other actions that the TCB is expected
               to mediate.  Furthermore, the TCB shall maintain authentication
               data that includes information for verifying the identity of
               individual users (e.g., passwords) as well as information for
               determining the clearance and authorizations of individual
               users.  This data shall be used by the TCB to authenticate the
               user's identity and to ensure that the security level and
               authorizations of subjects external to the TCB that may be
               created to act on behalf of the individual user are dominated by
               the clearance and authorization of that user.  The TCB shall
               protect authentication data so that it cannot be accessed by any
               unauthorized user.  The TCB shall be able to enforce individual
               accountability by providing the capability to uniquely identify
               each individual ADP system user.  The TCB shall also provide the
               capability of associating this identity with all auditable
               actions taken by that individual.

          3.2.2.1.1  Trusted Path

                     The TCB shall support a trusted communication path
                     between itself and user for initial login and
                     authentication.  Communications via this path shall be
                     initiated exclusively by a user.

     3.2.2.2   Audit

               The TCB shall be able to create, maintain, and protect from
               modification or unauthorized access or destruction an audit
               trail of accesses to the objects it protects.  The audit data
               shall be protected by the TCB so that read access to it is
               limited to those who are authorized for audit data.  The TCB
               shall be able to record the following types of events: use of
               identification and authentication mechanisms, introduction of
               objects into a user's address space (e.g., file open, program
               initiation), deletion of objects, and actions taken by computer
               operators and system administrators and/or system security
               officers, and other security relevant events.  The TCB shall
               also be able to audit any override of human-readable output
               markings.  For each recorded event, the audit record shall
               identify:  date and time of the event, user, type of event, and
               success or failure of the event.  For identification/
               authentication events the origin of request (e.g., terminal ID)
               shall be included in the audit record.  For events that
               introduce an object into a user's address space and for object
               deletion events the audit record shall include the name of the
               object and the object's security level.  The ADP system
               administrator shall be able to selectively audit the actions of
               any one or more users based on individual identity and/or object
               security level.  The TCB shall be able to audit the identified
               events that may be used in the exploitation of covert storage
               channels.

3.2.3  Assurance

     3.2.3.1   Operational Assurance

          3.2.3.1.1  System Architecture

                     The TCB shall maintain a domain for its own execution
                     that protects it from external interference or tampering
                     (e.g., by modification of its code or data structures).
                     The TCB shall maintain process isolation through the
                     provision of distinct address spaces under its control.
                     The TCB shall be internally structured into well-defined
                     largely independent modules.  It shall make effective use
                     of available hardware to separate those elements that are
                     protection-critical from those that are not.  The TCB
                     modules shall be designed such that the principle of least
                     privilege is enforced.  Features in hardware, such as
                     segmentation, shall be used to support logically distinct
                     storage objects with separate attributes (namely:
                     readable, writeable).  The user interface to the TCB
                     shall be completely defined and all elements of the TCB
                     identified.

          3.2.3.1.2  System Integrity

                     Hardware and/or software features shall be provided that
                     can be used to periodically validate the correct 
                     operation of the on-site hardware and firmware elements 
                     of the TCB.

          3.2.3.1.3  Covert Channel Analysis

                     The system developer shall conduct a thorough search for
                     covert storage channels and make a determination (either
                     by actual measurement or by engineering estimation) of
                     the maximum bandwidth of each identified channel.  (See
                     the covert channels guideline section.)

          3.2.3.1.4  Trusted Facility Management

                     The TCB shall support separate operator and administrator
                     functions.

     3.2.3.2   Life-Cycle Assurance

          3.2.3.2.1  Security Testing

                     The security mechanisms of the ADP system shall be tested
                     and found to work as claimed in the system documentation. 
                     A team of individuals who thoroughly understand the
                     specific implementation of the TCB shall subject its
                     design documentation, source code, and object code to
                     thorough analysis and testing.  Their objectives shall be:
                     to uncover all design and implementation flaws that would
                     permit a subject external to the TCB to read, change, or
                     delete data normally denied under the mandatory or
                     discretionary security policy enforced by the TCB; as well
                     as to assure that no subject (without authorization to do
                     so) is able to cause the TCB to enter a state such that it
                     is unable to respond to communications initiated by other
                     users.  The TCB shall be found relatively resistant to
                     penetration.  All discovered flaws shall be corrected and
                     the TCB retested to demonstrate that they have been
                     eliminated and that new flaws have not been introduced.
                     Testing shall demonstrate that the TCB implementation is
                     consistent with the descriptive top-level specification.
                     (See the Security Testing Guidelines.)

          3.2.3.2.2  Design Specification and Verification

                     A formal model of the security policy supported by the
                     TCB shall be maintained over the life cycle of the ADP
                     system that is proven consistent with its axioms.  A
                     descriptive top-level specification (DTLS) of the TCB
                     shall be maintained that completely and accurately
                     describes the TCB in terms of exceptions, error messages,
                     and effects.  It shall be shown to be an accurate
                     description of the TCB interface.

          3.2.3.2.3  Configuration Management

                     During development and maintenance of the TCB, a
                     configuration management system shall be in place that
                     maintains control of changes to the descriptive top-level
                     specification, other design data, implementation
                     documentation, source code, the running versionof the
                     object code, and test fixtures and documentation.  The
                     configuration management system shall assure a consistent
                     mapping among all documentation and code associated with 
                     the current version of the TCB.  Tools shall be provided
                     for generation of a new version of the TCB from source
                     code.  Also available shall be tools for comparing a
                     newly generated version with the previous TCB version in
                     order to ascertain that only the intended changes have
                     been made in the code that will actually be used as the
                     new version of the TCB.

3.2.4  Documentation

     3.2.4.1   Security Features User's Guide

               A single summary, chapter, or manual in user documentation
               shall describe the protection mechanisms provided by the TCB,
               guidelines on their use, and how they interact with one another.

     3.2.4.2   Trusted Facility Manual

               A manual addressed to the ADP system administrator shall
               present cautions about functions and privileges that should be
               controlled when running a secure facility.  The procedures for
               examining and maintaining the audit files as well as the
               detailed audit record structure for each type of audit event
               shall be given.  The manual shall describe the operator and
               administrator functions related to security, to include 
               changing the security characteristics of a user.  It shall
               provide guidelines on the consistent and effective use of the
               protection features of the system, how they interact, how to
               securely generate a new TCB, and facility procedures, warnings,
               and privileges that need to be controlled in order to operate
               the facility in a secure manner.  The TCB modules that contain
               the reference validation mechanism shall be identified.  The
               procedures for secure generation of a new TCB from source after
               modification of any modules in the TCB shall be described.

     3.2.4.3   Test Documentation

               The system developer shall provide to the evaluators a document
               that describes the test plan, test procedures that show how the
               security mechanisms were tested, and results of the security
               mechanisms' functional testing.  It shall include results of
               testing the effectiveness of the methods used to reduce covert
               channel bandwidths.

     3.2.4.4   Design Documentation

               Documentation shall be available that provides a description of
               the manufacturer's philosophy of protection and an explanation
               of how this philosophy is translated into the TCB.  The
               interfaces between the TCB modules shall be described.  A
               formal description of the security policy model enforced by the
               TCB shall be available and proven that it is sufficient to
               enforce the security policy.  The specific TCB protection 
               mechanisms shall be identified and an explanation given to show
               that they satisfy the model.  The descriptive top-level
               specification (DTLS) shall be shown to be an accurate
               description of the TCB interface.  Documentation shall describe
               how the TCB implements the reference monitor concept and give
               an explanation why it is tamper resistant, cannot be bypassed,
               and is correctly implemented.  Documentation shall describe how
               the TCB is structured to facilitate testing and to enforce least
               privilege.  This documentation shall also present the results
               of the covert channel analysis and the tradeoffs involved in
               restricting the channels.  All auditable events that may be
               used in the exploitation of known covert storage channels shall
               be identified.  The bandwidths of known covert storage channels
               the use of which is not detectable by the auditing mechanisms,
               shall be provided.  (See the Covert Channel Guideline section.)


3.3  CLASS (B3):  SECURITY DOMAINS

The class (B3) TCB must satisfy the reference monitor requirements that it
mediate all accesses of subjects to objects, be tamperproof, and be small
enough to be subjected to analysis and tests.  To this end, the TCB is
structured to exclude code not essential to security policy enforcement, with
significant system engineering during TCB design and implementation directed
toward minimizing its complexity.  A security administrator is supported,
audit mechanisms are expanded to signal security- relevant events, and system
recovery procedures are required.  The system is highly resistant to
penetration.  The following are minimal requirements for systems assigned a
class (B3) rating:

3.1.1  Security Policy

     3.3.1.1   Discretionary Access Control

               The TCB shall define and control access between named users and
               named objects (e.g., files and programs) in the ADP system.
               The enforcement mechanism (e.g., access control lists) shall
               allow users to specify and control sharing of those objects,
               and shall provide controls to limit propagation of access
               rights.  The discretionary access control mechanism shall,
               either by explicit user action or by default, provide that
               objects are protected from unauthorized access.  These access
               controls shall be capable of specifying, for each named object,
               a list of named individuals and a list of groups of named
               individuals with their respective modes of access to that
               object.  Furthermore, for each such named object, it shall be
               possible to specify a list of named individuals and a list of
               groups of named individuals for which no access to the object is
               to be given.  Access permission to an object by users not
               already possessing access permission shall only be assigned by
               authorized users.

     3.3.1.2   Object Reuse

               All authorizations to the information contained within a
               storage object shall be revoked prior to initial assignment,
               allocation or reallocation to a subject from the TCB's pool
               of unused storage objects.  No information, including 
               encrypted representations of information, produced by a prior
               subjects actions is to be available to any subject that obtains
               access to an object that has been released back to the system.

     3.3.1.3   Labels

               Sensitivity labels associated with each ADP system resource
               (e.g., subject, storage object, ROM) that is directly or
               indirectly accessible by subjects external to the TCB shall be
               maintained by the TCB.  These labels shall be used as the basis
               for mandatory access control decisions.  In order to import 
               non-labeled data, the TCB shall request and receive from an
               authorized user the security level of the data, and all such
               actions shall be auditable by the TCB.

          3.3.1.3.1  Label Integrity

                     Sensitivity labels shall accurately represent security
                     levels of the specific subjects or objects with which
                     they are associated.  When exported by the TCB,
                     sensitivity labels shall accurately and unambiguously
                     represent the internal labels and shall be associated
                     with the information being exported.

          3.3.1.3.2  Exportation of Labeled Information

                     The TCB shall designate each communication channel and
                     I/O device as either single-level or multilevel.  Any
                     change in this designation shall be done manually and
                     shall be auditable by the TCB.  The TCB shall maintain
                     and be able to audit any change in the security level
                     or levels associated with a communication channel or
                     I/O device.

               3.3.1.3.2.1  Exportation to Multilevel Devices

                            When the TCB exports an object to a multilevel I/O
                            device, the sensitivity label associated with that
                            object shall also be exported and shall reside on
                            the same physical medium as the exported 
                            information and shall be in the same form (i.e., 
                            machine-readable or human-readable form).  When
                            the TCB exports or imports an object over a
                            multilevel communication channel, the protocol 
                            used on that channel shall provide for the
                            unambiguous pairing between the sensitivity labels
                            and the associated information that is sent or
                            received.

               3.3.1.3.2.2  Exportation to Single-Level Devices

                            Single-level I/O devices and single-level
                            communication channels are not required to 
                            maintain the sensitivity labels of the information
                            they process.  However, the TCB shall include a 
                            mechanism by which the TCB and an authorized user
                            reliably communicate to designate the single
                            security level of information imported or exported
                            via single-level communication channels or I/O
                            devices.

               3.3.1.3.2.3  Labeling Human-Readable Output

                            The ADP system administrator shall be able to
                            specify the printable label names associated with
                            exported sensitivity labels.  The TCB shall mark
                            the beginning and end of all human-readable, paged,
                            hardcopy output (e.g., line printer output) with
                            human-readable sensitivity labels that properly*
                            represent the sensitivity of the output.  The TCB
                            shall, by default, mark the top and bottom of each
                            page of human-readable, paged, hardcopy output
                            (e.g., line printer output) with human-readable
                            sensitivity labels that properly* represent the
                            overall sensitivity of the output or that
                            properly* represent the sensitivity of the 
                            information on the page.  The TCB shall, by
                            default and in an appropriate manner, mark other
                            forms of human-readable output (e.g., maps,
                            graphics) with human-readable sensitivity labels
                            that properly* represent the sensitivity of the 
                            output.  Any override of these marking defaults
                            shall be auditable by the TCB.

          3.3.1.3.3  Subject Sensitivity Labels

                     The TCB shall immediately notify a terminal user of each
                     change in the security level associated with that user
                     during an interactive session.  A terminal user shall be
                     able to query the TCB as desired for a display of the
                     subject's complete sensitivity label.

          3.3.1.3.4  Device Labels

                     The TCB shall support the assignment of minimum and
                     maximum security levels to all attached physical devices.
                     These security levels shall be used by the TCB to enforce
                     constraints imposed by the physical environments in which
                     the devices are located.

     3.3.1.4   Mandatory Access Control

               The TCB shall enforce a mandatory access control policy over
               all resources (i.e., subjects, storage objects, and I/O 
               devices) that are directly or indirectly accessible by subjects
               external to the TCB.  These subjects and objects shall be
               assigned sensitivity labels that are a combination of
               hierarchical classification levels and non-hierarchical
               categories, and the labels shall be used as the basis for 
               mandatory access control decisions.  The TCB shall be able to
               support two or more such security levels.  (See the Mandatory
______________________________
* The hierarchical classification component in human-readable sensitivity
labels shall be equal to the greatest hierarchical classification of any of the
information in the output that the labels refer to; the non-hierarchical
category component shall include all of the non-hierarchical categories of the
information in the output the labels refer to, but no other non-hierarchical
categories.

               Access Control guidelines.)  The following requirements shall
               hold for all accesses between all subjects external to the TCB
               and all objects directly or indirectly accessible by these 
               subjects: A subject can read an object only if the hierarchical
               classification in the subject's security level is greater than
               or equal to the hierarchical classification in the object's
               security level and the non-hierarchical categories in the
               subject's security level include all the non-hierarchical
               categories in the object's security level.  A subject can write
               an object only if the hierarchical classification in the 
               subject's security level is less than or equal to the
               hierarchical classification in the object's security level and
               all the non-hierarchical categories in the subject's security 
               level are included in the non- hierarchical categories in the 
               object's security level.  Identification and authentication 
               data shall be used by the TCB to authenticate the user's
               identity and to ensure that the security level and authori-
               zation of subjects external to the TCB that may be created 
               to act on behalf of the individual user are dominated by the
               clearance and authorization of that user.

3.3.2  Accountability

     3.3.2.1   Identification and Authentication

               The TCB shall require users to identify themselves to it before
               beginning to perform any other actions that the TCB is expected
               to mediate.  Furthermore, the TCB shall maintain authentication
               data that includes information for verifying the identity of
               individual users (e.g., passwords) as well as information for
               determining the clearance and authorizations of individual
               users.  This data shall be used by the TCB to authenticate the
               user's identity and to ensure that the security level and 
               authorizations of subjectsexternal to the TCB that may be
               created to act on behalf of the individual user are dominated
               by the clearance and authorization of that user.  The TCB shall
               protect authentication data so that it cannot be accessed by any
               unauthorized user.  The TCB shall be able to enforce individual
               accountability by providing the capability to uniquely identify
               each individual ADP system user.  The TCB shall also provide the
               capability of associating this identity with all auditable
               actions taken by that individual.

          3.3.2.1.1  Trusted Path

                     The TCB shall support a trusted communication path
                     between itself and users for use when a positive TCB-to-
                     user connection is required (e.g., login, change subject
                     security level).  Communications via this trusted path
                     shall be activated exclusively by a user of the TCB and
                     shall be logically isolated and unmistakably
                     distinguishable from other paths.

     3.3.2.2   Audit

               The TCB shall be able to create, maintain, and protect from
               modification or unauthorized access or destruction an audit 
               trail of accesses to the objects it protects.  The audit data
               shall be protected by the TCB so that read access to it is
               limited to those who are authorized for audit data.  The TCB
               shall be able to record the following types of events: use of
               identification and authentication mechanisms, introduction of
               objects into a user's address space (e.g., file open, program
               initiation), deletion of objects, and actions taken by computer
               operators and system administrators and/or system security
               officers and other security relevant events.  The TCB shall also
               be able to audit any override of human-readable output markings.
               For each recorded event, the audit record shall identify:  date
               and time of the event, user, type of event, and success or
               failure of the event.  For identification/authentication events
               the origin of request (e.g., terminal ID) shall be included in
               the audit record.  For events that introduce an object into a
               user's address space and for object deletion events the audit
               record shall include the name of the object and the object's
               security level.  The ADP system administrator shall be able to
               selectively audit the actions of any one or more users based on
               individual identity and/or object security level.  The TCB shall
               be able to audit the identified events that may be used in the
               exploitation of covert storage channels.  The TCB shall contain
               a mechanism that is able to monitor the occurrence or
               accumulation of security auditable events that may indicate an
               imminent violation of security policy.  This mechanism shall be
               able to immediately notify the security administrator when
               thresholds are exceeded, and if the occurrence or accumulation
               of these security relevant events continues, the system shall
               take the least disruptive action to terminate the event.

3.3.3  Assurance

     3.3.3.1   Operational Assurance

          3.3.3.1.1  System Architecture

                     The TCB shall maintain a domain for its own execution
                     that protects it from external interference or tampering
                     (e.g., by modification of its code or data structures).
                     The TCB shall maintain process isolation through the
                     provision of distinct address spaces under its control.
                     The TCB shall be internally structured into well-defined
                     largely independent modules.  It shall make effective use
                     of available hardware to separate those elements that are
                     protection-critical from those that are not.  The TCB
                     modules shall be designed such that the principle of 
                     least privilege is enforced.  Features in hardware, such
                     as segmentation, shall be used to support logically
                     distinct storage objects with separate attributes (namely:
                     readable, writeable).  The user interface to the TCB shall
                     be completely defined and all elements of the TCB
                     identified.  The TCB shall be designed and structured to
                     use a complete, conceptually simple protection mechanism
                     with precisely defined semantics.  This mechanism shall
                     play a central role in enforcing the internal structuring
                     of the TCB and the system.  The TCB shall incorporate
                     significant use of layering, abstraction and data hiding.
                     Significant system engineering shall be directed toward
                     minimizing the complexity of the TCB and excluding from 
                     the TCB modules that are not protection-critical.

          3.3.3.1.2  System Integrity

                     Hardware and/or software features shall be provided that
                     can be used to periodically validate the correct 
                     operation of the on-site hardware and firmware elements 
                     of the TCB.

          3.3.3.1.3  Covert Channel Analysis

                     The system developer shall conduct a thorough search for
                     covert channels and make a determination (either by 
                     actual measurement or by engineering estimation) of the
                     maximum bandwidth of each identified channel.  (See the
                     Covert Channels Guideline section.)

          3.3.3.1.4  Trusted Facility Management

                     The TCB shall support separate operator and administrator
                     functions.  The functions performed in the role of a
                     security administrator shall be identified.  The ADP
                     system administrative personnel shall only be able to
                     perform security administrator functions after taking a
                     distinct auditable action to assume the security
                     administrator role on the ADP system.  Non-security
                     functions that can be performed in the security
                     administration role shall be limited strictly to those
                     essential to performing the security role effectively.

          3.3.3.1.5  Trusted Recovery

                     Procedures and/or mechanisms shall be provided to assure
                     that, after an ADP system failure or other discontinuity,
                     recovery without a protection compromise is obtained.

     3.3.3.2   Life-Cycle Assurance

          3.3.3.2.1  Security Testing

                     The security mechanisms of the ADP system shall be tested
                     and found to work as claimed in the system documentation.
                     A team of individuals who thoroughly understand the
                     specific implementation of the TCB shall subject its
                     design documentation, source code, and object code to
                     thorough analysis and testing.  Their objectives shall 
                     be: to uncover all design and implementation flaws that
                     would permit a subject external to the TCB to read,
                     change, or delete data normally denied under the 
                     mandatory or discretionary security policy enforced by
                     the TCB; as well as to assure that no subject (without
                     authorization to do so) is able to cause the TCB to enter
                     a state such that it is unable to respond to 
                     communications initiated by other users.  The TCB shall
                     be found resistant to penetration.  All discovered flaws
                     shall be corrected and the TCB retested to demonstrate 
                     that they have been eliminated and that new flaws have
                     not been introduced.  Testing shall demonstrate that the
                     TCB implementation is consistent with the descriptive
                     top-level specification.  (See the Security Testing 
                     Guidelines.)  No design flaws and no more than a few
                     correctable implementation flaws may be found during 
                     testing and there shall be reasonable confidence that
                     few remain.

          3.3.3.2.2  Design Specification and Verification

                     A formal model of the security policy supported by the
                     TCB shall be maintained over the life cycle of the ADP
                     system that is proven consistent with its axioms.  A
                     descriptive top-level specification (DTLS) of the TCB
                     shall be maintained that completely and accurately
                     describes the TCB in terms of exceptions, error messages,
                     and effects.  It shall be shown to be an accurate
                     description of the TCB interface.  A convincing argument
                     shall be given that the DTLS is consistent with the model.

          3.3.3.2.3  Configuration Management

                     During development and maintenance of the TCB, a
                     configuration management system shall be in place that 
                     maintains control of changes to the descriptive top-level
                     specification, other design data, implementation
                     documentation, source code, the running version of the
                     object code, and test fixtures and documentation.  The
                     configuration management system shall assure a consistent
                     mapping among all documentation and code associated with
                     the current version of the TCB.  Tools shall be provided
                     for generation of a new version of the TCB from source 
                     code.  Also available shall be tools for comparing a
                     newly generated version with the previous TCB version in
                     order to ascertain that only the intended changes have 
                     been made in the code that will actually be used as the
                     new version of the TCB.

3.3.4  Documentation

     3.3.4.1   Security Features User's Guide

               A single summary, chapter, or manual in user documentation
               shall describe the protection mechanisms provided by the TCB,
               guidelines on their use, and how they interact with one another.

     3.3.4.2   Trusted Facility Manual

               A manual addressed to the ADP system administrator shall
               present cautions about functions and privileges that should be
               controlled when running a secure facility.  The procedures for
               examining and maintaining the audit files as well as the
               detailed audit record structure for each type of audit event
               shall be given.  The manual shall describe the operator and
               administrator functions related to security, to include 
               changing the security characteristics of a user.  It shall
               provide guidelines on the consistent and effective use of the
               protection features of the system, how they interact, how to
               securely generate a new TCB, and facility procedures, warnings,
               and privileges that need to be controlled in order to operate
               the facility in a secure manner.  The TCB modules that contain
               the reference validation mechanism shall be identified.  The
               procedures for secure generation of a new TCB from source after
               modification of any modules in the TCB shall be described.  It
               shall include the procedures to ensure that the system is
               initially started in a secure manner.  Procedures shall also be
               included to resume secure system operation after any lapse in
               system operation.

     3.3.4.3   Test Documentation

               The system developer shall provide to the evaluators a document
               that describes the test plan, test procedures that show how the
               security mechanisms were tested, and results of the security 
               mechanisms' functional testing.  It shall include results of
               testing the effectiveness of the methods used to reduce covert
               channel bandwidths.

     3.3.4.4   Design Documentation

               Documentation shall be available that provides a description of
               the manufacturer's philosophy of protection and an explanation
               of how this philosophy is translated into the TCB.  The
               interfaces between the TCB modules shall be described.  A
               formal description of the security policy model enforced by the
               TCB shall be available and proven that it is sufficient to
               enforce the security policy.  The specific TCB protection 
               mechanisms shall be identified and an explanation given to show
               that they satisfy the model.  The descriptive top-level
               specification (DTLS) shall be shown to be an accurate 
               description of the TCB interface.  Documentation shall describe
               how the TCB implements the reference monitor concept and give 
               an explanation why it is tamper resistant, cannot be bypassed,
               and is correctly implemented.  The TCB implementation (i.e., in
               hardware, firmware, and software) shall be informally shown to
               be consistent with the DTLS.  The elements of the DTLS shall be
               shown, using informal techniques, to correspond to the elements
               of the TCB.  Documentation shall describe how the TCB is
               structured to facilitate testing and to enforce least privilege.
               This documentation shall also present the results of the covert
               channel analysis and the tradeoffs involved in restricting the
               channels.  All auditable events that may be used in the 
               exploitation of known covert storage channels shall be 
               identified.  The bandwidths of known covert storage channels,
               the use of which is not detectable by the auditing mechanisms,
               shall be provided.  (See the Covert Channel Guideline section.)


                     4.0  DIVISION A:  VERIFIED PROTECTION

This division is characterized by the use of formal security verification
methods to assure that the mandatory and discretionary security controls
employed in the system can effectively protect classified or other sensitive
information stored or processed by the system.  Extensive documentation is
required to demonstrate that the TCB meets the security requirements in all
aspects of design, development and implementation.



4.1  CLASS (A1):  VERIFIED DESIGN

Systems in class (A1) are functionally equivalent to those in class (B3) in
that no additional architectural features or policy requirements are added.
The distinguishing feature of systems in this class is the analysis derived
from formal design specification and verification techniques and the resulting
high degree of assurance that the TCB is correctly implemented.  This
assurance is developmental in nature, starting with a formal model of the
security policy and a formal top-level specification (FTLS) of the design.
Independent of the particular specification language or verification system
used, there are five important criteria for class (A1) design verification:

          * A formal model of the security policy must be clearly
          identified and documented, including a mathematical proof
          that the model is consistent with its axioms and is
          sufficient to support the security policy.

          * An FTLS must be produced that includes abstract definitions
          of the functions the TCB performs and of the hardware and/or
          firmware mechanisms that are used to support separate
          execution domains.

          * The FTLS of the TCB must be shown to be consistent with the
          model by formal techniques where possible (i.e., where
          verification tools exist) and informal ones otherwise.

          * The TCB implementation (i.e., in hardware, firmware, and
          software) must be informally shown to be consistent with the
          FTLS.  The elements of the FTLS must be shown, using
          informal techniques, to correspond to the elements of the
          TCB.  The FTLS must express the unified protection mechanism
          required to satisfy the security policy, and it is the
          elements of this protection mechanism that are mapped to the
          elements of the TCB.

          * Formal analysis techniques must be used to identify and
          analyze covert channels.  Informal techniques may be used to
          identify covert timing channels.  The continued existence of
          identified covert channels in the system must be justified.

In keeping with the extensive design and development analysis of the TCB
required of systems in class (A1), more stringent configuration management is
required and procedures are established for securely distributing the system
to sites.  A system security administrator is supported.

The following are minimal requirements for systems assigned a class (A1)
rating:

4.1.1  Security Policy

     4.1.1.1   Discretionary Access Control

               The TCB shall define and control access between named users and
               named objects (e.g., files and programs) in the ADP system.  
               The enforcement mechanism (e.g., access control lists) shall 
               allow users to specify and control sharing of those objects,
               and shall provide controls to limit propagation of access
               rights.  The discretionary access control mechanism shall,
               either by explicit user action or by default, provide that
               objects are protected from unauthorized access.  These access
               controls shall be capable of specifying, for each named object,
               a list of named individuals and a list of groups of named
               individuals with their respective modes of access to that
               object.  Furthermore, for each such named object, it shall be
               possible to specify a list of named individuals and a list of
               groups of named individuals for which no access to the object is
               to be given.  Access permission to an object by users not
               already possessing access permission shall only be assigned by
               authorized users.

     4.1.1.2   Object Reuse

               All authorizations to the information contained within a
               storage object shall be revoked prior to initial assignment,
               allocation or reallocation to a subject from the TCB's pool
               of unused storage objects.  No information, including encrypted
               representations of information, produced by a prior subject's
               actions is to be available to any subject that obtains access
               to an object that has been released back to the system.

     4.1.1.3   Labels

               Sensitivity labels associated with each ADP system resource
               (e.g., subject, storage object, ROM) that is directly or
               indirectly accessible by subjects external to the TCB shall be
               maintained by the TCB.  These labels shall be used as the basis
               for mandatory access control decisions.  In order to import 
               non-labeled data, the TCB shall request and receive from an 
               authorized user the security level of the data, and all such
               actions shall be auditable by the TCB.

          4.1.1.3.1  Label Integrity

                     Sensitivity labels shall accurately represent security
                     levels of the specific subjects or objects with which 
                     they are associated.  When exported by the TCB,
                     sensitivity labels shall accurately and unambiguously
                     represent the internal labels and shall be associated 
                     with the information being exported.

          4.1.1.3.2  Exportation of Labeled Information

                     The TCB shall designate each communication channel and
                     I/O device as either single-level or multilevel.  Any 
                     change in this designation shall be done manually and
                     shall be auditable by the TCB.  The TCB shall maintain
                     and be able to audit any change in the security level
                     or levels associated with a communication channel or 
                     I/O device.

               4.1.1.3.2.1  Exportation to Multilevel Devices

                            When the TCB exports an object to a multilevel I/O
                            device, the sensitivity label associated with that
                            object shall also be exported and shall reside on
                            the same physical medium as the exported 
                            information and shall be in the same form (i.e., 
                            machine-readable or human-readable form).  When
                            the TCB exports or imports an object over a
                            multilevel communication channel, the protocol 
                            used on that channel shall provide for the
                            unambiguous pairing between the sensitivity labels
                            and the associated information that is sent or 
                            received.

               4.1.1.3.2.2  Exportation to Single-Level Devices

                            Single-level I/O devices and single-level
                            communication channels are not required to 
                            maintain the sensitivity labels of the information
                            they process.  However, the TCB shall include a 
                            mechanism by which the TCB and an authorized user
                            reliably communicate to designate the single
                            security level of information imported or exported
                            via single-level communication channels or I/O 
                            devices.

               4.1.1.3.2.3  Labeling Human-Readable Output

                            The ADP system administrator shall be able to
                            specify the printable label names associated with
                            exported sensitivity labels.  The TCB shall mark
                            the beginning and end of all human-readable, paged,
                            hardcopy output (e.g., line printer output) with 
                            human-readable sensitivity labels that properly*
                            represent the sensitivity of the output.  The TCB
                            shall, by default, mark the top and bottom of each
                            page of human-readable, paged, hardcopy output
                            (e.g., line printer output) with human-readable 
                            sensitivity labels that properly* represent the
                            overall sensitivity of the output or that 
                            properly* represent the sensitivity of the 
                            information on the page.  The TCB shall, by
                            default and in an appropriate manner, mark other
                            forms of human-readable output (e.g., maps,
                            graphics) with human-readable sensitivity labels
                            that properly* represent the sensitivity of the 
                            output.  Any override of these marking defaults
                            shall be auditable by the TCB.

          4.1.1.3.3  Subject Sensitivity Labels

                     The TCB shall immediately notify a terminal user of each
                     change in the security level associated with that user 
                     during an interactive session.  A terminal user shall be
                     able to query the TCB as desired for a display of the
                     subject's complete sensitivity label.

          4.1.1.3.4  Device Labels

                     The TCB shall support the assignment of minimum and
                     maximum security levels to all attached physical devices.
                     These security levels shall be used by the TCB to enforce
                     constraints imposed by the physical environments in which
                     the devices are located.

     4.1.1.4   Mandatory Access Control

               The TCB shall enforce a mandatory access control policy over
               all resources (i.e., subjects, storage objects, and I/O 
               devices) that are directly or indirectly accessible by subjects
               external to the TCB.  These subjects and objects shall be
               assigned sensitivity labels that are a combination of
               hierarchical classification levels and non-hierarchical
               categories, and the labels shall be used as the basis for 
               mandatory access control decisions.  The TCB shall be able to
               support two or more such security levels.  (See the Mandatory
               Access Control guidelines.) The following requirements shall
               hold for all accesses between all subjects external to the TCB
               and all objects directly or indirectly accessible by these 
               subjects: A subject can read an object only if the hierarchical
               classification in the subject's security level is greater than
               or equal to the hierarchical classification in the object's
               security level and the non-hierarchical categories in the
               subject's security level include all the non-hierarchical
               categories in the object's security level.  A subject can write
______________________________
* The hierarchical classification component in human-readable sensitivity
labels shall be equal to the greatest hierarchical classification of any of the
information in the output that the labels refer to; the non-hierarchical
category component shall include all of the non-hierarchical categories of the
information in the output the labels refer to, but no other non-hierarchical
categories.

               an object only if the hierarchical classification in the 
               subject's security level is less than or equal to the
               hierarchical classification in the object's security level and
               all the non-hierarchical categories in the subject's security 
               level are included in the non- hierarchical categories in the 
               object's security level.  Identification and authentication 
               data shall be used by the TCB to authenticate the user's
               identity and to ensure that the security level and authoriza-
               tion of subjects external to the TCB that may be created to
               act on behalf of the individual user are dominated by the
               clearance and authorization of that user.

4.1.2  Accountability

     4.1.2.1   Identification and Authentication

               The TCB shall require users to identify themselves to it before
               beginning to perform any other actions that the TCB is expected
               to mediate.  Furthermore, the TCB shall maintain authentication
               data that includes information for verifying the identity of
               individual users (e.g., passwords) as well as information for
               determining the clearance and authorizations of individual
               users.  This data shall be used by the TCB to authenticate the
               user's identity and to ensure that the security level and 
               authorizations of subjects external to the TCB that may be
               created to act on behalf of the individual user are dominated by
               the clearance and authorization of that user.  The TCB shall
               protect authentication data so that it cannot be accessed by any
               unauthorized user.  The TCB shall be able to enforce individual
               accountability by providing the capability to uniquely identify
               each individual ADP system user.  The TCB shall also provide the
               capability of associating this identity with all auditable
               actions taken by that individual.

          4.1.2.1.1  Trusted Path

                     The TCB shall support a trusted communication path
                     between itself and users for use when a positive TCB-to-
                     user connection is required (e.g., login, change subject
                     security level).  Communications via this trusted path
                     shall be activated exclusively by a user or the TCB and
                     shall be logically isolated and unmistakably 
                     distinguishable from other paths.

     4.1.2.2   Audit

               The TCB shall be able to create, maintain, and protect from
               modification or unauthorized access or destruction an audit 
               trail of accesses to the objects it protects.  The audit data
               shall be protected by the TCB so that read access to it is
               limited to those who are authorized for audit data.  The TCB
               shall be able to record the following types of events: use of
               identification and authentication mechanisms, introduction of
               objects into a user's address space (e.g., file open, program
               initiation), deletion of objects, and actions taken by computer
               operators and system administrators and/or system security
               officers, and other security relevant events.  The TCB shall
               also be able to audit any override of human-readable output
               markings.  For each recorded event, the audit record shall
               identify: date and time of the event, user, type of event, and
               success or failure of the event.  For identification/
               authentication events the origin of request (e.g., terminal ID)
               shall be included in the audit record.  For events that
               introduce an object into a user's address space and for object
               deletion events the audit record shall include the name of the
               object and the object's security level.  The ADP system
               administrator shall be able to selectively audit the actions of
               any one or more users based on individual identity and/or object
               security level.  The TCB shall be able to audit the identified
               events that may be used in the exploitation of covert storage
               channels.  The TCB shall contain a mechanism that is able to
               monitor the occurrence or accumulation of security auditable
               events that may indicate an imminent violation of security
               policy.  This mechanism shall be able to immediately notify the
               security administrator when thresholds are exceeded, and, if
               the occurrence or accumulation of these security relevant
               events continues, the system shall take the least disruptive
               action to terminate the event.
     
4.1.3  Assurance

     4.1.3.1   Operational Assurance

          4.1.3.1.1  System Architecture
     
                     The TCB shall maintain a domain for its own execution
                     that protects it from external interference or tampering
                     (e.g., by modification of its code or data structures).
                     The TCB shall maintain process isolation through the
                     provision of distinct address spaces under its control.
                     The TCB shall be internally structured into well-defined
                     largely independent modules.  It shall make effective use
                     of available hardware to separate those elements that are
                     protection-critical from those that are not.  The TCB
                     modules shall be designed such that the principle of 
                     least privilege is enforced.  Features in hardware, such
                     as segmentation, shall be used to support logically 
                     distinct storage objects with separate attributes (namely:
                     readable, writeable).  The user interface to the TCB 
                     shall be completely defined and all elements of the TCB 
                     identified.  The TCB shall be designed and structured to
                     use a complete, conceptually simple protection mechanism
                     with precisely defined semantics.  This mechanism shall 
                     play a central role in enforcing the internal structuring
                     of the TCB and the system.  The TCB shall incorporate
                     significant use of layering, abstraction and data hiding.
                     Significant system engineering shall be directed toward 
                     minimizing the complexity of the TCB and excluding from
                     the TCB modules that are not protection-critical.

          4.1.3.1.2  System Integrity

                     Hardware and/or software features shall be provided that
                     can be used to periodically validate the correct 
                     operation of the on-site hardware and firmware elements
                     of the TCB.

          4.1.3.1.3  Covert Channel Analysis

                     The system developer shall conduct a thorough search for
                     covert channels and make a determination (either by 
                     actual measurement or by engineering estimation) of the
                     maximum bandwidth of each identified channel.  (See the
                     Covert Channels Guideline section.)  Formal methods shall
                     be used in the analysis.

          4.1.3.1.4  Trusted Facility Management

                     The TCB shall support separate operator and administrator
                     functions.  The functions performed in the role of a 
                     security administrator shall be identified.  The ADP
                     system administrative personnel shall only be able to
                     perform security administrator functions after taking a 
                     distinct auditable action to assume the security
                     administrator role on the ADP system.  Non-security
                     functions that can be performed in the security 
                     administration role shall be limited strictly to those
                     essential to performing the security role effectively.

          4.1.3.1.5  Trusted Recovery

                     Procedures and/or mechanisms shall be provided to assure
                     that, after an ADP system failure or other discontinuity,
                     recovery without a protection compromise is obtained.

     4.1.3.2   Life-Cycle Assurance

          4.1.3.2.1  Security Testing

                     The security mechanisms of the ADP system shall be tested
                     and found to work as claimed in the system documentation.
                     A team of individuals who thoroughly understand the
                     specific implementation of the TCB shall subject its
                     design documentation, source code, and object code to
                     thorough analysis and testing.  Their objectives shall 
                     be: to uncover all design and implementation flaws that
                     would permit a subject external to the TCB to read,
                     change, or delete data normally denied under the 
                     mandatory or discretionary security policy enforced by 
                     the TCB; as well as to assure that no subject (without
                     authorization to do so) is able to cause the TCB to enter
                     a state such that it is unable to respond to 
                     communications initiated by other users.  The TCB shall 
                     be found resistant to penetration.  All discovered flaws
                     shall be corrected and the TCB retested to demonstrate 
                     that they have been eliminated and that new flaws have
                     not been introduced.  Testing shall demonstrate that the
                     TCB implementation is consistent with the formal top-
                     level specification.  (See the Security Testing 
                     Guidelines.)  No design flaws and no more than a few
                     correctable implementation flaws may be found during
                     testing and there shall be reasonable confidence that few
                     remain.  Manual or other mapping of the FTLS to the
                     source code may form a basis for penetration testing.

          4.1.3.2.2  Design Specification and Verification

                     A formal model of the security policy supported by the
                     TCB shall be maintained over the life-cycle of the ADP
                     system that is proven consistent with its axioms.  A
                     descriptive top-level specification (DTLS) of the TCB
                     shall be maintained that completely and accurately
                     describes the TCB in terms of exceptions, error messages,
                     and effects. A formal top-level specification (FTLS) of
                     the TCB shall be maintained that accurately describes the
                     TCB in terms of exceptions, error messages, and effects. 
                     The DTLS and FTLS shall include those components of the
                     TCB that are implemented as hardware and/or firmware if
                     their properties are visible at the TCB interface.  The
                     FTLS shall be shown to be an accurate description of the
                     TCB interface.  A convincing argument shall be given that
                     the DTLS is consistent with the model and a combination of
                     formal and informal techniques shall be used to show that
                     the FTLS is consistent with the model.  This verification
                     evidence shall be consistent with that provided within the
                     state-of-the-art of the particular computer security
                     center-endorsed formal specification and verification
                     system used.  Manual or other mapping of the FTLS to the
                     TCB source code shall be performed to provide evidence of
                     correct implementation.

          4.1.3.2.3  Configuration Management

                     During the entire life-cycle, i.e., during the design,
                     development, and maintenance of the TCB, a configuration
                     management system shall be in place for all security-
                     relevant hardware, firmware, and software that maintains
                     control of changes to the formal model, the descriptive 
                     and formal top-level specifications, other design data, 
                     implementation documentation, source code, the running
                     version of the object code, and test fixtures and
                     documentation.  The configuration management system shall
                     assure a consistent mapping among all documentation and 
                     code associated with the current version of the TCB.
                     Tools shall be provided for generation of a new version
                     of the TCB from source code.  Also available shall be 
                     tools, maintained under strict configuration control, for
                     comparing a newly generated version with the previous TCB
                     version in order to ascertain that only the intended
                     changes have been made in the code that will actually be
                     used as the new version of the TCB.  A combination of
                     technical, physical, and procedural safeguards shall be
                     used to protect from unauthorized modification or
                     destruction the master copy or copies of all material
                     used to generate the TCB.

          4.1.3.2.4  Trusted Distribution

                     A trusted ADP system control and distribution facility
                     shall be provided for maintaining the integrity of the
                     mapping between the master data describing the current
                     version of the TCB and the on-site master copy of the
                     code for the current version.  Procedures (e.g., site
                     security acceptance testing) shall exist for assuring 
                     that the TCb software, firmware, and hardware updates
                     distributed to a customer are exactly as specified by
                     the master copies.

4.1.4  Documentation

     4.1.4.1   Security Features User's Guide

               A single summary, chapter, or manual in user documentation
               shall describe the protection mechanisms provided by the TCB,
               guidelines on their use, and how they interact with one another.

     4.1.4.2   Trusted Facility Manual

               A manual addressed to the ADP system administrator shall
               present cautions about functions and privileges that should be
               controlled when running a secure facility.  The procedures for
               examining and maintaining the audit files as well as the
               detailed audit record structure for each type of audit event
               shall be given.  The manual shall describe the operator and
               administrator functions related to security, to include 
               changing the security characteristics of a user.  It shall
               provide guidelines on the consistent and effective use of the
               protection features of the system, how they interact, how to
               securely generate a new TCB, and facility procedures, warnings,
               and privileges that need to be controlled in order to operate
               the facility in a secure manner.  The TCB modules that contain
               the reference validation mechanism shall be identified.  The 
               procedures for secure generation of a new TCB from source after
               modification of any modules in the TCB shall be described.  It
               shall include the procedures to ensure that the system is 
               initially started in a secure manner.  Procedures shall also be
               included to resume secure system operation after any lapse in 
               system operation.  

     4.1.4.3   Test Documentation

               The system developer shall provide to the evaluators a document
               that describes the test plan, test procedures that show how the
               security mechanisms were tested, and results of the security
               mechanisms' functional testing.  It shall include results of 
               testing the effectiveness of the methods used to reduce covert
               channel bandwidths.  The results of the mapping between the
               formal top-level specification and the TCB source code shall be
               given.

     4.1.4.4   Design Documentation

               Documentation shall be available that provides a description of
               the manufacturer's philosophy of protection and an explanation
               of how this philosophy is translated into the TCB.  The 
               interfaces between the TCB modules shall be described.  A
               formal description of the security policy model enforced by the
               TCB shall be available and proven that it is sufficient to 
               enforce the security policy.  The specific TCB protection 
               mechanisms shall be identified and an explanation given to show
               that they satisfy the model.  The descriptive top-level speci-
               fication (DTLS) shall be shown to be an accurate description of
               the TCB interface.  Documentation shall describe how the TCB
               implements the reference monitor concept and give an explana-
               tion why it is tamper resistant, cannot be bypassed, and
               is correctly implemented.  The TCB implementation (i.e., in
               hardware, firmware, and software) shall be informally shown to
               be consistent with the formal top-level specification (FTLS).
               The elements of the FTLS shall be shown, using informal 
               techniques, to correspond to the elements of the TCB.  
               Documentation shall describe how the TCB is structured to
               facilitate testing and to enforce least privilege.  This
               documentation shall also present the results of the covert 
               channel analysis and the tradeoffs involved in restricting the
               channels.  All auditable events that may be used in the
               exploitation of known covert storage channels shall be 
               identified.  The bandwidths of known covert storage channels,
               the use of which is not detectable by the auditing mechanisms,
               shall be provided.  (See the Covert Channel Guideline section.)
               Hardware, firmware, and software mechanisms not dealt with in
               the FTLS but strictly internal to the TCB (e.g., mapping
               registers, direct memory access I/O) shall be clearly described.


4.2  BEYOND CLASS (A1)

Most of the security enhancements envisioned for systems that will provide
features and assurance in addition to that already provided by class (Al)
systems are beyond current technology.  The discussion below is intended to
guide future work and is derived from research and development activities
already underway in both the public and private sectors.  As more and better
analysis techniques are developed, the requirements for these systems will
become more explicit.  In the future, use of formal verification will be
extended to the source level and covert timing channels will be more fully
addressed.  At this level the design environment will become important and
testing will be aided by analysis of the formal top-level specification.
Consideration will be given to the correctness of the tools used in TCB
development (e.g., compilers, assemblers, loaders) and to the correct
functioning of the hardware/firmware on which the TCB will run.  Areas to be
addressed by systems beyond class (A1) include:

           * System Architecture

           A demonstration (formal or otherwise) must be given showing
           that requirements of self-protection and completeness for
           reference monitors have been implemented in the TCB.

           * Security Testing

           Although beyond the current state-of-the-art, it is
           envisioned that some test-case generation will be done
           automatically from the formal top-level specification or
           formal lower-level specifications.

           * Formal Specification and Verification

           The TCB must be verified down to the source code level,
           using formal verification methods where feasible.  Formal
           verification of the source code of the security-relevant
           portions of an operating system has proven to be a difficult
           task.  Two important considerations are the choice of a
           high-level language whose semantics can be fully and
           formally expressed, and a careful mapping, through
           successive stages, of the abstract formal design to a
           formalization of the implementation in low-level
           specifications.    Experience has shown that only when the
           lowest level specifications closely correspond to the actual
           code can code proofs be successfully accomplished.

           * Trusted Design Environment

           The TCB must be designed in a trusted facility with only
           trusted (cleared) personnel.





                                   PART II:

                           RATIONALE AND GUIDELINES



             5.0  CONTROL OBJECTIVES FOR TRUSTED COMPUTER SYSTEMS

The criteria are divided within each class into groups of requirements.  These
groupings were developed to assure that three basic control objectives for
computer security are satisfied and not overlooked.  These control objectives
deal with:

                      * Security Policy
                      * Accountability
                      * Assurance

This section provides a discussion of these general control objectives and
their implication in terms of designing trusted systems.


5.1  A NEED FOR CONSENSUS

A major goal of the DoD Computer Security Center is to encourage the Computer
Industry to develop trusted computer systems and products, making them widely
available in the commercial market place.  Achievement of this goal will
require recognition and articulation by both the public and private sectors of
a need and demand for such products.

As described in the introduction to this document, efforts to define the
problems and develop solutions associated with processing nationally sensitive
information, as well as other sensitive data such as financial, medical, and
personnel information used by the National Security Establishment, have been
underway for a number of years.  The criteria, as described in Part I,
represent the culmination of these efforts and describe basic requirements for
building trusted computer systems.  To date, however, these systems have been
viewed by many as only satisfying National Security needs.  As long as this
perception continues the consensus needed to motivate manufacture of trusted
systems will be lacking.

The purpose of this section is to describe in detail the fundamental control
objectives.  These objectives lay the foundation for the requirements outlined
in the criteria.  The goal is to explain the foundations so that those outside
the National Security Establishment can assess their universality and, by
extension, the universal applicability of the criteria requirements to
processing all types of sensitive applications whether they be for National
Security or the private sector.


5.2  DEFINITION AND USEFULNESS

The term "control objective" refers to a statement of intent with respect to
control over some aspect of an organization's resources, or processes, or
both.  In terms of a computer system, control objectives provide a framework
for developing a strategy for fulfilling a set of security requirements for
any given system.  Developed in response to generic vulnerabilities, such as
the need to manage and handle sensitive data in order to prevent compromise,
or the need to provide accountability in order to detect fraud, control
objectives have been identified as a useful method of expressing security
goals.[3]

Examples of control objectives include the three basic design requirements for
implementing the reference monitor concept discussed in Section 6.  They are:

     * The reference validation mechanism must be tamperproof.

     * The reference validation mechanism must always be invoked.

     * The reference validation mechanism must be small enough to be
       subjected to analysis and tests, the completeness of which can 
       be assured.[1]


5.3  CRITERIA CONTROL OBJECTIVES

The three basic control objectives of the criteria are concerned with security
policy, accountability, and assurance.  The remainder of this section provides
a discussion of these basic requirements.

5.3.1  Security Policy

       In the most general sense, computer security is concerned with
       controlling the way in which a computer can be used, i.e., 
       controlling how information processed by it can be accessed and 
       manipulated.  However, at closer examination, computer security 
       can refer to a number of areas.  Symptomatic of this, FIPS PUB 39,
       Glossary For Computer Systems Security, does not have a unique
       definition for computer security.[16]  Instead there are eleven
       separate definitions for security which include: ADP systems 
       security, administrative security, data security, etc.  A common 
       thread running through these definitions is the word "protection."
       Further declarations of protection requirements can be found in
       DoD Directive 5200.28 which describes an acceptable level of
       protection for classified data to be one that will "assure that
       systems which process, store, or use classified data and produce
       classified information will, with reasonable dependability, 
       prevent: a. Deliberate or inadvertent access to classified 
       material by unauthorized persons, and b.  Unauthorized 
       manipulation of the computer and its associated peripheral 
       devices."[8]

       In summary, protection requirements must be defined in terms of
       the perceived threats, risks, and goals of an organization.  This
       is often stated in terms of a security policy.  It has been 
       pointed out in the literature that it is external laws, rules, 
       regulations, etc.  that establish what access to information is to
       be permitted, independent of the use of a computer.  In particular,
       a given system can only be said to be secure with respect to its
       enforcement of some specific policy.[30]  Thus, the control 
       objective for security policy is:

       SECURITY POLICY CONTROL OBJECTIVE

       A statement of intent with regard to control over access to and
       dissemination of information, to be known as the security policy
       must be precisely defined and implemented for each system that is
       used to process sensitive information.  The security policy must
       accurately reflect the laws, regulations, and general policies
       from which it is derived.

     5.3.1.1   Mandatory Security Policy
               
               Where a security policy is developed that is to be applied
               to control of classified or other specifically designated 
               sensitive information, the policy must include detailed 
               rules on how to handle that information throughout its
               life-cycle.  These rules are a function of the various
               sensitivity designations that the information can assume 
               and the various forms of access supported by the system.
               Mandatory security refers to the enforcement of a set of
               access control rules that constrains a subject's access to
               information on the basis of a comparison of that 
               individual's clearance/authorization to the information,
               the classification/sensitivity designation of the
               information, and the form of access being mediated.
               Mandatory policies either require or can be satisfied by 
               systems that can enforce a partial ordering of 
               designations, namely, the designations must form what is
               mathematically known as a "lattice."[5]
 
               A clear implication of the above is that the system must
               assure that the designations associated with sensitive data
               cannot be arbitrarily changed, since this could permit 
               individuals who lack the appropriate authorization to 
               access sensitive information.  Also implied is the
               requirement that the system control the flow of information
               so that data cannot be stored with lower sensitivity 
               designations unless its "downgrading" has been authorized.
               The control objective is:

               MANDATORY SECURITY CONTROL OBJECTIVE

               Security policies defined for systems that are used to
               process classified or other specifically categorized
               sensitive information must include provisions for the 
               enforcement of mandatory access control rules.  That is,
               they must include a set of rules for controlling access
               based directly on a comparison of the individual's
               clearance or authorization for the information and the
               classification or sensitivity designation of the
               information being sought, and indirectly on considerations
               of physical and other environmental factors of control.
               The mandatory access control rules must accurately reflect
               the laws, regulations, and general policies from which
               they are derived.

     5.3.1.2   Discretionary Security Policy

               Discretionary security is the principal type of access
               control available in computer systems today.  The basis of
               this kind of security is that an individual user, or
               program operating on his behalf, is allowed to specify
               explicitly the types of access other users may have to
               information under his control.  Discretionary security
               differs from mandatory security in that it implements an
               access control policy on the basis of an individual's
               need-to-know as opposed to mandatory controls which are
               driven by the classification or sensitivity designation of
               the information.

               Discretionary controls are not a replacement for mandatory
               controls.  In an environment in which information is 
               classified (as in the DoD) discretionary security provides
               for a finer granularity of control within the overall
               constraints of the mandatory policy.  Access to classified
               information requires effective implementation of both types
               of controls as precondition to granting that access.  In 
               general, no person may have access to classified
               information unless: (a) that person has been determined to
               be trustworthy, i.e., granted a personnel security 
               clearance -- MANDATORY, and (b) access is necessary for the
               performance of official duties, i.e., determined to have a
               need-to-know -- DISCRETIONARY.  In other words, 
               discretionary controls give individuals discretion to 
               decide on which of the permissible accesses will actually
               be allowed to which users, consistent with overriding
               mandatory policy restrictions.  The control objective is:

               DISCRETIONARY SECURITY CONTROL OBJECTIVE

               Security policies defined for systems that are used to
               process classified or other sensitive information must
               include provisions for the enforcement of discretionary
               access control rules.  That is, they must include a
               consistent set of rules for controlling and limiting access
               based on identified individuals who have been determined to
               have a need-to-know for the information.

     5.3.1.3   Marking

               To implement a set of mechanisms that will put into effect
               a mandatory security policy, it is necessary that the 
               system mark information with appropriate classification or
               sensitivity labels and maintain these markings as the
               information moves through the system.  Once information is
               unalterably and accurately marked, comparisons required by
               the mandatory access control rules can be accurately and
               consistently made.  An additional benefit of having the
               system maintain the classification or sensitivity label
               internally is the ability to automatically generate 
               properly "labeled" output.  The labels, if accurately and
               integrally maintained by the system, remain accurate when
               output from the system.  The control objective is:

               MARKING CONTROL OBJECTIVE

               Systems that are designed to enforce a mandatory security
               policy must store and preserve the integrity of
               classification or other sensitivity labels for all
               information.  Labels exported from the system must be 
               accurate representations of the corresponding internal
               sensitivity labels being exported.

5.3.2  Accountability

       The second basic control objective addresses one of the
       fundamental principles of security, i.e., individual 
       accountability.  Individual accountability is the key to securing
       and controlling any system that processes information on behalf
       of individuals or groups of individuals.  A number of requirements
       must be met in order to satisfy this objective.

       The first requirement is for individual user identification.
       Second, there is a need for authentication of the identification.
       Identification is functionally dependent on authentication.  
       Without authentication, user identification has no credibility.  
       Without a credible identity, neither mandatory nor discretionary
       security policies can be properly invoked because there is no
       assurance that proper authorizations can be made.

       The third requirement is for dependable audit capabilities.  That
       is, a trusted computer system must provide authorized personnel 
       with the ability to audit any action that can potentially cause
       access to, generation of, or effect the release of classified or
       sensitive information.  The audit data will be selectively 
       acquired based on the auditing needs of a particular installation
       and/or application.  However, there must be sufficient granularity
       in the audit data to support tracing the auditable events to a
       specific individual who has taken the actions or on whose behalf
       the actions were taken.  The control objective is:

       ACCOUNTABILITY CONTROL OBJECTIVE

       Systems that are used to process or handle classified or other 
       sensitive information must assure individual accountability
       whenever either a mandatory or discretionary security policy is
       invoked.  Furthermore, to assure accountability, the capability
       must exist for an authorized and competent agent to access and
       evaluate accountability information by a secure means, within a
       reasonable amount of time, and without undue difficulty.

5.3.3  Assurance

       The third basic control objective is concerned with guaranteeing
       or providing confidence that the security policy has been 
       implemented correctly and that the protection-relevant elements of
       the system do, indeed, accurately mediate and enforce the intent
       of that policy.  By extension, assurance must include a guarantee
       that the trusted portion of the system works only as intended.  To
       accomplish these objectives, two types of assurance are needed.
       They are life-cycle assurance and operational assurance.

       Life-cycle assurance refers to steps taken by an organization to
       ensure that the system is designed, developed, and maintained 
       using formalized and rigorous controls and standards.[17]  
       Computer systems that process and store sensitive or classified
       information depend on the hardware and software to protect that
       information.  It follows that the hardware and software themselves
       must be protected against unauthorized changes that could cause
       protection mechanisms to malfunction or be bypassed completely.  
       For this reason trusted computer systems must be carefully 
       evaluated and tested during the design and development phases and
       reevaluated whenever changes are made that could affect the
       integrity of the protection mechanisms.  Only in this way can
       confidence be provided that the hardware and software 
       interpretation of the security policy is maintained accurately 
       and without distortion.

       While life-cycle assurance is concerned with procedures for
       managing system design, development, and maintenance; operational
       assurance focuses on features and system architecture used to
       ensure that the security policy is uncircumventably enforced
       during system operation.  That is, the security policy must be
       integrated into the hardware and software protection features of
       the system.  Examples of steps taken to provide this kind of
       confidence include: methods for testing the operational hardware 
       and software for correct operation, isolation of protection-
       critical code, and the use of hardware and software to provide
       distinct domains.  The control objective is:

       ASSURANCE CONTROL OBJECTIVE

       Systems that are used to process or handle classified or other
       sensitive information must be designed to guarantee correct and
       accurate interpretation of the security policy and must not
       distort the intent of that policy.  Assurance must be provided
       that correct implementation and operation of the policy exists
       throughout the system's life-cycle.



                 6.0  RATIONALE BEHIND THE EVALUATION CLASSES



6.1  THE REFERENCE MONITOR CONCEPT

In October of 1972, the Computer Security Technology Planning Study, conducted
by James P.  Anderson & Co., produced a report for the Electronic Systems
Division (ESD) of the United States Air Force.[1]  In that report, the concept
of "a reference monitor which enforces the authorized access relationships
between subjects and objects of a system" was introduced.  The reference
monitor concept was found to be an essential element of any system that would
provide multilevel secure computing facilities and controls.

The Anderson report went on to define the reference validation mechanism as
"an implementation of the reference monitor concept .  .  .  that validates
each reference to data or programs by any user (program) against a list of
authorized types of reference for that user." It then listed the three design
requirements that must be met by a reference validation mechanism:

     a. The reference validation mechanism must be tamper proof.

     b. The reference validation mechanism must always be invoked.

     c. The reference validation mechanism must be small enough to be
        subject to analysis and tests, the completeness of which can 
        be assured."[1]

Extensive peer review and continuing research and development activities have
sustained the validity of the Anderson Committee's findings.  Early examples
of the reference validation mechanism were known as security kernels.  The
Anderson Report described the security kernel as "that combination of hardware
and software which implements the reference monitor concept."[1]  In this vein,
it will be noted that the security kernel must support the three reference
monitor requirements listed above.


6.2  A FORMAL SECURITY POLICY MODEL

Following the publication of the Anderson report, considerable research was
initiated into formal models of security policy requirements and of the
mechanisms that would implement and enforce those policy models as a security
kernel.  Prominent among these efforts was the ESD-sponsored development of
the Bell and LaPadula model, an abstract formal treatment of DoD security
policy.[2]  Using mathematics and set theory, the model precisely defines the
notion of secure state, fundamental modes of access, and the rules for
granting subjects specific modes of access to objects.  Finally, a theorem is
proven to demonstrate that the rules are security-preserving operations, so
that the application of any sequence of the rules to a system that is in a
secure state will result in the system entering a new state that is also
secure.  This theorem is known as the Basic Security Theorem.

A subject can act on behalf of a user or another subject.  The subject is
created as a surrogate for the cleared user and is assigned a formal security
level based on their classification.  The state transitions and invariants of
the formal policy model define the invariant relationships that must hold
between the clearance of the user, the formal security level of any process
that can act on the user's behalf, and the formal security level of the devices
and other objects to which any process can obtain specific modes of access. 
The Bell and LaPadula model, for example, defines a relationship between formal 
security levels of subjects and objects, now referenced as the "dominance
relation." From this definition, accesses permitted between subjects and
objects are explicitly defined for the fundamental modes of access, including
read-only access, read/write access, and write-only access.  The model defines
the Simple Security Condition to control granting a subject read access to a
specific object, and the *-Property (read "Star Property") to control granting
a subject write access to a specific object.  Both the Simple Security
Condition and the *-Property include mandatory security provisions based on the
dominance relation between formal security levels of subjects and objects the
clearance of the subject and the classification of the object.  The
Discretionary Security Property is also defined, and requires that a specific
subject be authorized for the particular mode of access required for the state
transition.  In its treatment of subjects (processes acting on behalf of a
user), the model distinguishes between trusted subjects (i.e., not constrained
within the model by the *-Property) and untrusted subjects (those that are
constrained by the *-Property).

From the Bell and LaPadula model there evolved a model of the method of proof
required to formally demonstrate that all arbitrary sequences of state
transitions are security-preserving.  It was also shown that the *- Property
is sufficient to prevent the compromise of information by Trojan Horse
attacks.


6.3  THE TRUSTED COMPUTING BASE

In order to encourage the widespread commercial availability of trusted
computer systems, these evaluation criteria have been designed to address
those systems in which a security kernel is specifically implemented as well
as those in which a security kernel has not been implemented.  The latter case
includes those systems in which objective (c) is not fully supported because
of the size or complexity of the reference validation mechanism.  For
convenience, these evaluation criteria use the term Trusted Computing Base to
refer to the reference validation mechanism, be it a security kernel,
front-end security filter, or the entire trusted computer system.

The heart of a trusted computer system is the Trusted Computing Base (TCB)
which contains all of the elements of the system responsible for supporting
the security policy and supporting the isolation of objects (code and data) on
which the protection is based.  The bounds of the TCB equate to the "security
perimeter" referenced in some computer security literature.  In the interest
of understandable and maintainable protection, a TCB should be as simple as
possible consistent with the functions it has to perform.  Thus, the TCB
includes hardware, firmware, and software critical to protection and must be
designed and implemented such that system elements excluded from it need not
be trusted to maintain protection.  Identification of the interface and
elements of the TCB along with their correct functionality therefore forms the
basis for evaluation.

For general-purpose systems, the TCB will include key elements of the
operating system and may include all of the operating system.  For embedded
systems, the security policy may deal with objects in a way that is meaningful
at the application level rather than at the operating system level.  Thus, the
protection policy may be enforced in the application software rather than in
the underlying operating system.  The TCB will necessarily include all those
portions of the operating system and application software essential to the
support of the policy.  Note that, as the amount of code in the TCB increases,
it becomes harder to be confident that the TCB enforces the reference monitor
requirements under all circumstances.


6.4  ASSURANCE

The third reference monitor design objective is currently interpreted as
meaning that the TCB "must be of sufficiently simple organization and
complexity to be subjected to analysis and tests, the completeness of which
can be assured."

Clearly, as the perceived degree of risk increases (e.g., the range of
sensitivity of the system's protected data, along with the range of clearances
held by the system's user population) for a particular system's operational
application and environment, so also must the assurances be increased to
substantiate the degree of trust that will be placed in the system.  The
hierarchy of requirements that are presented for the evaluation classes in the
trusted computer system evaluation criteria reflect the need for these
assurances.

As discussed in Section 5.3, the evaluation criteria uniformly require a
statement of the security policy that is enforced by each trusted computer
system.  In addition, it is required that a convincing argument be presented
that explains why the TCB satisfies the first two design requirements for a
reference monitor.  It is not expected that this argument will be entirely
formal.  This argument is required for each candidate system in order to
satisfy the assurance control objective.

The systems to which security enforcement mechanisms have been added, rather
than built-in as fundamental design objectives, are not readily amenable to
extensive analysis since they lack the requisite conceptual simplicity of a
security kernel.  This is because their TCB extends to cover much of the
entire system.  Hence, their degree of trustworthiness can best be ascertained
only by obtaining test results.  Since no test procedure for something as
complex as a computer system can be truly exhaustive, there is always the
possibility that a subsequent penetration attempt could succeed.  It is for
this reason that such systems must fall into the lower evaluation classes.

On the other hand, those systems that are designed and engineered to support
the TCB concepts are more amenable to analysis and structured testing.  Formal
methods can be used to analyze the correctness of their reference validation
mechanisms in enforcing the system's security policy.  Other methods,
including less-formal arguments, can be used in order to substantiate claims
for the completeness of their access mediation and their degree of
tamper-resistance.  More confidence can be placed in the results of this
analysis and in the thoroughness of the structured testing than can be placed
in the results for less methodically structured systems.  For these reasons,
it appears reasonable to conclude that these systems could be used in
higher-risk environments.  Successful implementations of such systems would be
placed in the higher evaluation classes.


6.5  THE CLASSES

It is highly desirable that there be only a small number of overall evaluation
classes.  Three major divisions have been identified in the evaluation
criteria with a fourth division reserved for those systems that have been
evaluated and found to offer unacceptable security protection.  Within each
major evaluation division, it was found that "intermediate" classes of trusted
system design and development could meaningfully be defined.  These
intermediate classes have been designated in the criteria because they
identify systems that:

     * are viewed to offer significantly better protection and assurance
       than would systems that satisfy the basic requirements for their
       evaluation class; and

     * there is reason to believe that systems in the intermediate
       evaluation classes could eventually be evolved such that they 
       would satisfy the requirements for the next higher evaluation 
       class.

Except within division A it is not anticipated that additional "intermediate"
evaluation classes satisfying the two characteristics described above will be
identified.

Distinctions in terms of system architecture, security policy enforcement, and
evidence of credibility between evaluation classes have been defined such that
the "jump" between evaluation classes would require a considerable investment
of effort on the part of implementors.  Correspondingly, there are expected to
be significant differentials of risk to which systems from the higher
evaluation classes will be exposed.


             7.0  THE RELATIONSHIP BETWEEN POLICY AND THE CRITERIA


Section 1 presents fundamental computer security requirements and Section 5
presents the control objectives for Trusted Computer Systems.  They are
general requirements, useful and necessary, for the development of all secure
systems.  However, when designing systems that will be used to process
classified or other sensitive information, functional requirements for meeting
the Control Objectives become more specific.  There is a large body of policy
laid down in the form of Regulations, Directives, Presidential Executive
Orders, and OMB Circulars that form the basis of the procedures for the
handling and processing of Federal information in general and classified
information specifically.  This section presents pertinent excerpts from these
policy statements and discusses their relationship to the Control Objectives.
These excerpts are examples to illustrate the relationship of the policies to
criteria and may not be complete.


7.1  ESTABLISHED FEDERAL POLICIES

A significant number of computer security policies and associated requirements
have been promulgated by Federal government elements.  The interested reader
is referred to reference [32] which analyzes the need for trusted systems in
the civilian agencies of the Federal government, as well as in state and local
governments and in the private sector.  This reference also details a number
of relevant Federal statutes, policies and requirements not treated further
below.

Security guidance for Federal automated information systems is provided by the
Office of Management and Budget.  Two specifically applicable Circulars have
been issued.  OMB Circular No.  A-71, Transmittal Memorandum No.  1, "Security
of Federal Automated Information Systems,"[26] directs each executive agency
to establish and maintain a computer security program.  It makes the head of
each executive branch, department and agency responsible "for assuring an
adequate level of security for all agency data whether processed in-house or
commercially.  This includes responsibility for the establishment of physical,
administrative and technical safeguards required to adequately protect
personal, proprietary or other sensitive data not subject to national security
regulations, as well as national security data."[26, para. 4 p. 2]

OMB Circular No.  A-123, "Internal Control Systems,"[27] issued to help
eliminate fraud, waste, and abuse in government programs requires: (a) agency
heads to issue internal control directives and assign responsibility, (b)
managers to review programs for vulnerability, and (c) managers to perform
periodic reviews to evaluate strengths and update controls.  Soon after
promulgation of OMB Circular A-123, the relationship of its internal control
requirements to building secure computer systems was recognized.[4] While not
stipulating computer controls specifically, the definition of Internal
Controls in A-123 makes it clear that computer systems are to be included:

     "Internal Controls - The plan of organization and all of the methods and
      measures adopted within an agency to safeguard its resources, assure the
      accuracy and reliability of its information, assure adherence to 
      applicable laws, regulations and policies, and promote operational 
      economy and efficiency."[27, sec. 4.C]

The matter of classified national security information processed by ADP
systems was one of the first areas given serious and extensive concern in
computer security.  The computer security policy documents promulgated as a
result contain generally more specific and structured requirements than most,
keyed in turn to an authoritative basis that itself provides a rather clearly
articulated and structured information security policy.  This basis, Executive
Order 12356, "National Security Information," sets forth requirements for the
classification, declassification and safeguarding of "national security
information" per se.[14]


7.2  DOD POLICIES

Within the Department of Defense, these broad requirements are implemented and
further specified primarily through two vehicles: 1) DoD Regulation 5200.1-R
[7], which applies to all components of the DoD as such, and 2) DoD 5220.22-M,
"Industrial Security Manual for Safeguarding Classified Information" [11],
which applies to contractors included within the Defense Industrial Security
Program.  Note that the latter transcends DoD as such, since it applies not
only to any contractors handling classified information for any DoD component,
but also to the contractors of eighteen other Federal organizations for whom
the Secretary of Defense is authorized to act in rendering industrial security
services.*

______________________________
* i.e., NASA, Commerce Department, GSA, State Department, Small Business
Administration, National Science Foundation, Treasury Department,
Transportation Department, Interior Department, Agriculture Department, U.S.
Information Agency, Labor Department, Environmental Protection Agency, Justice
Department, U.S. Arms Control and Disarmament Agency, Federal Emergency
Management Agency, Federal Reserve System, and U.S. General Accounting Office.

For ADP systems, these information security requirements are further amplified
and specified in: 1) DoD Directive 5200.28 [8] and DoD Manual 5200.28-M [9],
for DoD components; and 2) Section XIII of DoD 5220.22-M [11] for contractors.
DoD Directive 5200.28, "Security Requirements for Automatic Data Processing
(ADP) Systems," stipulates: "Classified material contained in an ADP system
shall be safeguarded by the continuous employment of protective features in
the system's hardware and software design and configuration .  .  .  ."[8,
sec.  IV] Furthermore, it is required that ADP systems that "process, store,
or use classified data and produce classified information will, with
reasonable dependability, prevent:

     a.  Deliberate or inadvertent access to classified material by
         unauthorized persons, and

     b.  Unauthorized manipulation of the computer and its associated
         peripheral devices."[8, sec. I B.3]

Requirements equivalent to these appear within DoD 5200.28-M [9] and in DoD
5220.22-M [11].

DoD Directove 5200.28 provides the security requirements for ADP systems.  For
some types of information, such as Sensitive Compartmented Information (SCI),
DoD Directive 5200.28 states that other minimum security requirements also
apply.  These minima are found in DCID l/l6 (new reference number 5) which is
implemented in DIAM 50-4 (new reference number 6) for DoD and DoD contractor
ADP systems.

From requirements imposed by these regulations, directives and circulars, the
three components of the Security Policy Control Objective, i.e., Mandatory and
Discretionary Security and Marking, as well as the Accountability and
Assurance Control Objectives, can be functionally defined for DoD
applications.  The following discussion provides further specificity in Policy
for these Control Objectives.


7.3  CRITERIA CONTROL OBJECTIVE FOR SECURITY POLICY

7.3.1  Marking

       The control objective for marking is: "Systems that are designed
       to enforce a mandatory security policy must store and preserve the
       integrity of classification or other sensitivity labels for all 
       information.  Labels exported from the system must be accurate 
       representations of the corresonding internal sensitivity labels
       being exported."

       DoD 5220.22-M, "Industrial Security Manual for Safeguarding
       Classified Information," explains in paragraph 11 the reasons for 
       marking information:

            "a.  General.  Classification designation by physical 
            marking, notation or other means serves to warn and to
            inform the holder what degree of protection against 
            unauthorized disclosure is reqired for that information
            or material."  (14)

       Marking requirements are given in a number of policy statements.

       Executive Order 12356 (Sections 1.5.a and 1.5.a.1) requires that
       classification markings "shall be shown on the face of all 
       classified documents, or clearly associated with other forms of 
       classified information in a manner appropriate to the medium 
       involved."[14]

       DoD Regulation 5200.1-R (Section 1-500) requires that: ".  .  .
       information or material that requires protection against 
       unauthorized disclosure in the interest of national security shall
       be classified in one of three designations, namely: 'Top Secret,'
       'Secret' or 'Confidential.'"[7] (By extension, for use in computer
       processing, the unofficial designation "Unclassified" is used to
       indicate information that does not fall under one of the other
       three designations of classified information.)

       DoD Regulation 5200.1-R (Section 4-304b) requires that: "ADP
       systems and word processing systems employing such media shall 
       provide for internal classification marking to assure that 
       classified information contained therein that is reproduced or 
       generated, will bear applicable classification and associated
       markings." (This regulation provides for the exemption of certain
       existing systems where "internal classification and applicable
       associated markings cannot be implemented without extensive system
       modifications."[7]  However, it is clear that future DoD ADP 
       systems must be able to provide applicable and accurate labels for
       classified and other sensitive information.)

       DoD Manual 5200.28-M (Section IV, 4-305d) requires the following:
       "Security Labels - All classified material accessible by or within
       the ADP system shall be identified as to its security 
       classification and access or dissemination limitations, and all
       output of the ADP system shall be appropriately marked."[9]

7.3.2  Mandatory Security

       The control objective for mandatory security is: "Security
       policies defined for systems that are used to process classified
       or other specifically categorized sensitive information must 
       include provisions for the enforcement of mandatory access control
       rules.  That is, they must include a set of rules for controlling
       access based directly on a comparison of the individual's
       clearance or authorization for the information and the 
       classification or sensitivity designation of the information being
       sought, and indirectly on considerations of physical and other 
       environmental factors of control.  The mandatory access control
       rules must accurately reflect the laws, regulations, and general
       policies from which they are derived."

       There are a number of policy statements that are related to
       mandatory security.

       Executive Order 12356 (Section 4.1.a) states that "a person is
       eligible for access to classified information provided that a 
       determination of trustworthiness has been made by agency heads or
       designated officials and provided that such access is essential
       to the accomplishment of lawful and authorized Government
       purposes."[14]

       DoD Regulation 5200.1-R (Chapter I, Section 3) defines a Special
       Access Program as "any program imposing 'need-to-know' or access
       controls beyond those normally provided for access to 
       Confidential, Secret, or Top Secret information.  Such a program
       includes, but is not limited to, special clearance, adjudication,
       or investigative requirements, special designation of officials
       authorized to determine 'need-to-know', or special lists of persons
       determined to have a 'need-to- know.'"[7, para.  1-328] This
       passage distinguishes between a 'discretionary' determination of
       need-to-know and formal need-to-know which is implemented through
       Special Access Programs.  DoD Regulation 5200.1-R, paragraph 7-100
       describes general requirements for trustworthiness (clearance) and
       need-to-know, and states that the individual with possession,
       knowledge or control of classified information has final
       responsibility for determining if conditions for access have been
       met.  This regulation further stipulates that "no one has a right
       to have access to classified information solely by virtue of rank
       or position." [7, para. 7-100])

       DoD Manual 5200.28-M (Section II 2-100) states that, "Personnel
       who develop, test (debug), maintain, or use programs which are 
       classified or which will be used to access or develop classified
       material shall have a personnel security clearance and an access
       authorization (need-to-know), as appropriate for the highest
       classified and most restrictive category of classified material
       which they will access under system constraints."[9]

       DoD Manual 5220.22-M (Paragraph 3.a) defines access as "the
       ability and opportunity to obtain knowledge of classified 
       information.  An individual, in fact, may have access to 
       classified information by being in a place where such information
       is kept, if the security measures which are in force do not
       prevent him from gaining knowledge of the classified 
       information."[11]

       The above mentioned Executive Order, Manual, Directives and
       Regulations clearly imply that a trusted computer system must 
       assure that the classification labels associated with sensitive
       data cannot be arbitrarily changed, since this could permit
       individuals who lack the appropriate clearance to access
       classified information.  Also implied is the requirement that a
       trusted computer system must control the flow of information so 
       that data from a higher classification cannot be placed in a 
       storage object of lower classification unless its "downgrading" 
       has been authorized.

7.3.3  Discretionary Security

       The term discretionary security refers to a computer system's
       ability to control information on an individual basis.  It stems
       from the fact that even though an individual has all the formal 
       clearances for access to specific classified information, each
       individual's access to information must be based on a demonstrated
       need-to-know.  Because of this, it must be made clear that this
       requirement is not discretionary in a "take it or leave it" sense.
       The directives and regulations are explicit in stating that the
       need-to-know test must be satisfied before access can be granted 
       to the classified information.  The control objective for 
       discretionary security is: "Security policies defined for systems
       that are used to process classified or other sensitive information
       must include provisions for the enforcement of discretionary
       access control rules.  That is, they must include a consistent set
       of rules for controlling and limiting access based on identified
       individuals who have been determined to have a need-to-know for the
       information."

       DoD Regulation 5200.1-R (Paragraph 7-100) In addition to excerpts
       already provided that touch on need-to- know, this section of the
       regulation stresses the need- to-know principle when it states "no
       person may have access to classified information unless .  .  .  
       access is necessary for the performance of official duties."[7]

       Also, DoD Manual 5220.22-M (Section III 20.a) states that "an
       individual shall be permitted to have access to classified
       information only . . . when the contractor determines that access
       is necessary in the performance of tasks or services essential to
       the fulfillment of a contract or program, i.e., the individual has
       a need-to-know."[11]


7.4  CRITERIA CONTROL OBJECTIVE FOR ACCOUNTABILITY

The control objective for accountability is: "Systems that are used to process
or handle classified or other sensitive information must assure individual
accountability whenever either a mandatory or discretionary security policy is
invoked.  Furthermore, to assure accountability the capability must exist for
an authorized and competent agent to access and evaluate accountability
information by a secure means, within a reasonable amount of time, and without
undue difficulty."

This control objective is supported by the following citations:

     DoD Directive 5200.28 (VI.A.1) states: "Each user's identity shall be
     positively established, and his access to the system, and his activity in
     the system (including material accessed and actions taken) controlled and
     open to scrutiny."[8]

     DoD Manual 5200.28-M (Section V 5-100) states: "An audit log or file
     (manual, machine, or a combination of both) shall be maintained as a 
     history of the use of the ADP System to permit a regular security review
     of system activity.  (e.g., The log should record security related 
     transactions, including each access to a classified file and the nature 
     of the access, e.g., logins, production of accountable classified 
     outputs, and creation of new classified files.  Each classified file
     successfully accessed [regardless of the number of individual references]
     during each 'job' or 'interactive session' should also be recorded in the
     audit log.  Much of the material in this log may also be required to 
     assure that the system preserves information entrusted to it.)"[9]

     DoD Manual 5200.28-M (Section IV 4-305f) states: "Where needed to assure
     control of access and individual accountability, each user or specific 
     group of users shall be identified to the ADP System by appropriate 
     administrative or hardware/software measures.  Such identification 
     measures must be in sufficient detail to enable the ADP System to provide
     the user only that material which he is authorized."[9]

     DoD Manual 5200.28-M (Section I 1-102b) states: 

     "Component's Designated Approving Authorities, or their designees
      for this purpose .  .  .  will assure:

                 .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .

           (4) Maintenance of documentation on operating systems (O/S)
           and all modifications thereto, and its retention for a
           sufficient period of time to enable tracing of security-
           related defects to their point of origin or inclusion in the
           system.

                 .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .

           (6) Establishment of procedures to discover, recover,
           handle, and dispose of classified material improperly
           disclosed through system malfunction or personnel action.

           (7) Proper disposition and correction of security
           deficiencies in all approved ADP Systems, and the effective
           use and disposition of system housekeeping or audit records,
           records of security violations or security-related system
           malfunctions, and records of tests of the security features
           of an ADP System."[9]

     DoD Manual 5220.22-M (Section XIII 111) states: "Audit Trails

           a. The general security requirement for any ADP system audit
           trail is that it provide a documented history of the use of
           the system.  An approved audit trail will permit review of
           classified system activity and will provide a detailed
           activity record to facilitate reconstruction of events to
           determine the magnitude of compromise (if any) should a
           security malfunction occur.  To fulfill this basic
           requirement, audit trail systems, manual, automated or a
           combination of both must document significant events
           occurring in the following areas of concern: (i) preparation
           of input data and dissemination of output data (i.e.,
           reportable interactivity between users and system support
           personnel), (ii) activity involved within an ADP environment
           (e.g., ADP support personnel modification of security and
           related controls), and (iii) internal machine activity.

           b. The audit trail for an ADP system approved to process
           classified information must be based on the above three
           areas and may be stylized to the particular system.  All
           systems approved for classified processing should contain
           most if not all of the audit trail records listed below. The
           contractor's SPP documentation must identify and describe
           those applicable:

                      1. Personnel access;

                      2. Unauthorized and surreptitious entry into the
           central computer facility or remote terminal areas;

                      3. Start/stop time of classified processing indicating
           pertinent systems security initiation and termination events
           (e.g., upgrading/downgrading actions pursuant to paragraph
           107);

                      4. All functions initiated by ADP system console
           operators;

                      5. Disconnects of remote terminals and peripheral
           devices (paragraph 107c);

                      6. Log-on and log-off user activity;

                      7. Unauthorized attempts to access files or programs,
           as well as all open, close, create, and file destroy
           actions;

                      8. Program aborts and anomalies including
           identification information (i.e., user/program name, time
           and location of incident, etc.);

                      9. System hardware additions, deletions and maintenance
           actions;

                      10. Generations and modifications affecting the
           security features of the system software.

           c. The ADP system security supervisor or designee shall
           review the audit trail logs at least weekly to assure that
           all pertinent activity is properly recorded and that
           appropriate action has been taken to correct any anomaly.
           The majority of ADP systems in use today can develop audit
           trail systems in accord with the above; however, special
           systems such as weapons, communications, communications
           security, and tactical data exchange and display systems,
           may not be able to comply with all aspects of the above and
           may require individualized consideration by the cognizant
           security office.

           d. Audit trail records shall be retained for a period of one
           inspection cycle."[11]


7.5  CRITERIA CONTROL OBJECTIVE FOR ASSURANCE

The control objective for assurance is: "Systems that are used to process or
handle classified or other sensitive information must be designed to guarantee
correct and accurate interpretation of the security policy and must not distort
the intent of that policy.  Assurance must be provided that correct
implementation and operation of the policy exists throughout the system's
life-cycle."

A basis for this objective can be found in the following sections of DoD     
Directive 5200.28:

     DoD Directive 5200.28 (IV.B.1) stipulates: "Generally, security of an ADP
     system is most effective and economical if the system is designed 
     originally to provide it.  Each Department of Defense Component 
     undertaking design of an ADP system which is expected to process, store,
     use, or produce classified material shall:  From the beginning of the 
     design process, consider the security policies, concepts, and measures
     prescribed in this Directive."[8]

     DoD Directive 5200.28 (IV.C.5.a) states: "Provision may be made to permit
     adjustment of ADP system area controls to the level of protection 
     required for the classification category and type(s) of material actually
     being handled by the system, provided change procedures are developed and
     implemented which will prevent both the unauthorized access to classified
     material handled by the system and the unauthorized manipulation of the
     system and its components.  Particular attention shall be given to the
     continuous protection of automated system security measures, techniques
     and procedures when the personnel security clearance level of users
     having access to the system changes."[8]

     DoD Directive 5200.28 (VI.A.2) states: "Environmental Control.  The ADP
     System shall be externally protected to minimize the likelihood of
     unauthorized access to system entry points, access to classified 
     information in the system, or damage to the system."[8]

     DoD Manual 5200.28-M (Section I 1-102b) states: 

     "Component's Designated Approving Authorities, or their designees
     for this purpose .  .  .  will assure:

                  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .

              (5) Supervision, monitoring, and testing, as appropriate, of
          changes in an approved ADP System which could affect the
          security features of the system, so that a secure system is
          maintained.

                  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .

              (7) Proper disposition and correction of security
          deficiencies in all approved ADP Systems, and the effective
          use and disposition of system housekeeping or audit records,
          records of security violations or security-related system
          malfunctions, and records of tests of the security features
          of an ADP System.

              (8) Conduct of competent system ST&E, timely review of
          system ST&E reports, and correction of deficiencies needed
          to support conditional or final approval or disapproval of
          an ADP System for the processing of classified information.

              (9) Establishment, where appropriate, of a central ST&E
          coordination point for the maintenance of records of
          selected techniques, procedures, standards, and tests used
          in the testing and evaluation of security features of ADP
          Systems which may be suitable for validation and use by
          other Department of Defense Components."[9]

     DoD Manual 5220.22-M (Section XIII 103a) requires: "the initial approval,
     in writing, of the cognizant security office prior to processing any
     classified information in an ADP system.  This section requires 
     reapproval by the cognizant security office for major system 
     modifications made subsequent to initial approval.  Reapprovals will be 
     required because of (i) major changes in personnel access requirements,
     (ii) relocation or structural modification of the central computer
     facility, (iii) additions, deletions or changes to main frame, storage or
     input/output devices, (iv) system software changes impacting security
     protection features, (v) any change in clearance, declassification, audit
     trail or hardware/software maintenance procedures, and (vi) other system
     changes as determined by the cognizant security office."[11]

     A major component of assurance, life-cycle assurance, as described in DoD
     Directive 7920.l, is concerned with testing ADP systems both in the
     development phase as well as during operation (17).  DoD Directive 5215.1
     (Section F.2.C.(2)) requires "evaluations of selected industry and
     government-developed trusted computer systems against these criteria."[10]


                      8.0  A GUIDELINE ON COVERT CHANNELS


A covert channel is any communication channel that can be exploited by a
process to transfer information in a manner that violates the system's
security policy.  There are two types of covert channels: storage channels and
timing channels.  Covert storage channels include all vehicles that would
allow the direct or indirect writing of a storage location by one process and
the direct or indirect reading of it by another.  Covert timing channels
include all vehicles that would allow one process to signal information to
another process by modulating its own use of system resources in such a way
that the change in response time observed by the second process would provide
information.

From a security perspective, covert channels with low bandwidths represent a
lower threat than those with high bandwidths.  However, for many types of
covert channels, techniques used to reduce the bandwidth below a certain rate
(which depends on the specific channel mechanism and the system architecture)
also have the effect of degrading the performance provided to legitimate
system users.  Hence, a trade-off between system performance and covert
channel bandwidth must be made.  Because of the threat of compromise that
would be present in any multilevel computer system containing classified or
sensitive information, such systems should not contain covert channels with
high bandwidths.  This guideline is intended to provide system developers with
an idea of just how high a "high" covert channel bandwidth is.

A covert channel bandwidth that exceeds a rate of one hundred (100) bits per
second is considered "high" because 100 bits per second is the approximate
rate at which many computer terminals are run.  It does not seem appropriate
to call a computer system "secure" if information can be compromised at a rate
equal to the normal output rate of some commonly used device.

In any multilevel computer system there are a number of relatively
low-bandwidth covert channels whose existence is deeply ingrained in the
system design.  Faced with the large potential cost of reducing the bandwidths
of such covert channels, it is felt that those with maximum bandwidths of less
than one (1) bit per second are acceptable in most application environments.
Though maintaining acceptable performance in some systems may make it
impractical to eliminate all covert channels with bandwidths of 1 or more bits
per second, it is possible to audit their use without adversely affecting
system performance.  This audit capability provides the system administration
with a means of detecting -- and procedurally correcting -- significant
compromise.  Therefore, a Trusted Computing Base should provide, wherever
possible, the capability to audit the use of covert channel mechanisms with
bandwidths that may exceed a rate of one (1) bit in ten (10) seconds.

The covert channel problem has been addressed by a number of authors.  The
interested reader is referred to references [5], [6], [19], [21], [22], [23],
and [29].


       9.0  A GUIDELINE ON CONFIGURING MANDATORY ACCESS CONTROL FEATURES


The Mandatory Access Control requirement includes a capability to support an
unspecified number of hierarchical classifications and an unspecified number
of non-hierarchical categories at each hierarchical level.  To encourage
consistency and portability in the design and development of the National
Security Establishment trusted computer systems, it is desirable for all such
systems to be able to support a minimum number of levels and categories.  The
following suggestions are provided for this purpose:

     * The number of hierarchical classifications should be greater than or
       equal to sixteen (16).

     * The number of non-hierarchical categories should be greater than or
       equal to sixty-four (64).



                     10.0  A GUIDELINE ON SECURITY TESTING


These guidelines are provided to give an indication of the extent and
sophistication of testing undertaken by the DoD Computer Security Center
during the Formal Product Evaluation process.  Organizations wishing to use
"Department of Defense Trusted Computer System Evaluation Criteria" for
performing their own evaluations may find this section useful for planning
purposes.

As in Part I, highlighting is used to indicate changes in the guidelines from
the next lower division.


10.1  TESTING FOR DIVISION C

10.1.1  Personnel

        The security testing team shall consist of at least two
        individuals with bachelor degrees in Computer Science or the
        equivalent.  Team members shall be able to follow test plans
        prepared by the system developer and suggest additions, shall
        be familiar with the "flaw hypothesis" or equivalent security
        testing methodology, and shall have assembly level programming
        experience.  Before testing begins, the team members shall have
        functional knowledge of, and shall have completed the system 
        developer's internals course for, the system being evaluated.

10.1.2  Testing

        The team shall have "hands-on" involvement in an independent run
        of the tests used by the system developer.  The team shall 
        independently design and implement at least five system-specific
        tests in an attempt to circumvent the security mechanisms of the
        system.  The elapsed time devoted to testing shall be at least
        one month and need not exceed three months.  There shall be no
        fewer than twenty hands-on hours spent carrying out system
        developer-defined tests and test team-defined tests.


10.2  TESTING FOR DIVISION B

10.2.1  Personnel

        The security testing team shall consist of at least two
        individuals with bachelor degrees in Computer Science or the 
        equivalent and at least one individual with a master's degree in
        Computer Science or equivalent.  Team members shall be able to
        follow test plans prepared by the system developer and suggest
        additions, shall be conversant with the "flaw hypothesis" or
        equivalent security testing methodology, shall be fluent in the
        TCB implementation language(s), and shall have assembly level 
        programming experience.  Before testing begins, the team members
        shall have functional knowledge of, and shall have completed the
        system developer's internals course for, the system being
        evaluated.  At least one team member shall have previously
        completed a security test on another system.

10.2.2  Testing

        The team shall have "hands-on" involvement in an independent run
        of the test package used by the system developer to test 
        security-relevant hardware and software.  The team shall
        independently design and implement at least fifteen system-
        specific tests in an attempt to circumvent the security
        mechanisms of the system.  The elapsed time devoted to testing 
        shall be at least two months and need not exceed four months.  
        There shall be no fewer than thirty hands-on hours per team
        member spent carrying out system developer-defined tests and
        test team-defined tests.


10.3  TESTING FOR DIVISION A

10.3.1  Personnel

        The security testing team shall consist of at least one
        individual with a bachelor's degree in Computer Science or the 
        equivalent and at least two individuals with masters' degrees in
        Computer Science or equivalent.  Team members shall be able to 
        follow test plans prepared by the system developer and suggest
        additions, shall be conversant with the "flaw hypothesis" or
        equivalent security testing methodology, shall be fluent in the
        TCB implementation language(s), and shall have assembly level 
        programming experience.  Before testing begins, the team members
        shall have functional knowledge of, and shall have completed the
        system developer's internals course for, the system being
        evaluated.  At least one team member shall be familiar enough
        with the system hardware to understand the maintenance diagnostic
        programs and supporting hardware documentation.  At least two 
        team members shall have previously completed a security test on
        another system.  At least one team member shall have 
        demonstrated system level programming competence on the system
        under test to a level of complexity equivalent to adding a device
        driver to the system.

10.3.2  Testing

        The team shall have "hands-on" involvement in an independent run
        of the test package used by the system developer to test 
        security-relevant hardware and software.  The team shall 
        independently design and implement at least twenty-five system-
        specific tests in an attempt to circumvent the security
        mechanisms of the system.  The elapsed time devoted to testing 
        shall be at least three months and need not exceed six months.  
        There shall be no fewer than fifty hands-on hours per team 
        member spent carrying out system developer-defined tests and
        test team-defined tests.


                                  APPENDIX A

                     COMMERCIAL PRODUCE EVALUATION PROCESS


"Department of Defense Trusted Computer System Evaluation Criteria" forms the
basis upon which the Computer Security Center will carry out the commercial
computer security evaluation process.  This process is focused on commercially
produced and supported general-purpose operating system products that meet the
needs of government departments and agencies.  The formal evaluation is aimed
at "off-the-shelf" commercially supported products and is completely divorced
from any consideration of overall system performance, potential applications,
or particular processing environments.  The evaluation provides a key input to
a computer system security approval/accreditation.  However, it does not
constitute a complete computer system security evaluation.  A complete study
(e.g., as in reference [18]) must consider additional factors dealing with the
system in its unique environment, such as it's proposed security mode of
operation, specific users, applications, data sensitivity, physical and
personnel security, administrative and procedural security, TEMPEST, and
communications security.

The product evaluation process carried out by the Computer Security Center has
three distinct elements:

     * Preliminary Product Evaluation - An informal dialogue between a vendor
       and the Center in which technical information is exchanged to create a
       common understanding of the vendor's product, the criteria, and the 
       rating that may be expected to result from a formal product evaluation.

     * Formal Product Evaluation - A formal evaluation, by the Center, of a
       product that is available to the DoD, and that results in that product
       and its assigned rating being placed on the Evaluated Products List.

     * Evaluated Products List - A list of products that have been subjected
       to formal product evaluation and their assigned ratings.


Preliminary Product Evaluation

Since it is generally very difficult to add effective security measures late
in a product's life cycle, the Center is interested in working with system
vendors in the early stages of product design.  A preliminary product
evaluation allows the Center to consult with computer vendors on computer
security issues found in products that have not yet been formally announced.

A preliminary evaluation is typically initiated by computer system vendors who
are planning new computer products that feature security or major
security-related upgrades to existing products.  After an initial meeting
between the vendor and the Center, appropriate non-disclosure agreements are
executed that require the Center to maintain the confidentiality of any
proprietary information disclosed to it.  Technical exchange meetings follow
in which the vendor provides details about the proposed product (particularly
its internal designs and goals) and the Center provides expert feedback to the
vendor on potential computer security strengths and weaknesses of the vendor's
design choices, as well as relevant interpretation of the criteria.  The
preliminary evaluation is typically terminated when the product is completed
and ready for field release by the vendor.  Upon termination, the Center
prepares a wrap-up report for the vendor and for internal distribution within
the Center.  Those reports containing proprietary information are not
available to the public.

During preliminary evaluation, the vendor is under no obligation to actually
complete or market the potential product.  The Center is, likewise, not
committed to conduct a formal product evaluation.  A preliminary evaluation
may be terminated by either the Center or the vendor when one notifies the
other, in writing, that it is no longer advantageous to continue the
evaluation.


Formal Product Evaluation

The formal product evaluation provides a key input to certification of a
computer system for use in National Security Establishment applications and is
the sole basis for a product being placed on the Evaluated Products List.

A formal product evaluation begins with a request by a vendor for the Center
to evaluate a product for which the product itself and accompanying
documentation needed to meet the requirements defined by this publication are
complete.  Non-disclosure agreements are executed and a formal product
evaluation team is formed by the Center.  An initial meeting is then held with
the vendor to work out the schedule for the formal evaluation.  Since testing
of the implemented product forms an important part of the evaluation process,
access by the evaluation team to a working version of the system is negotiated
with the vendor.  Additional support required from the vendor includes
complete design documentation, source code, and access to vendor personnel who
can answer detailed questions about specific portions of the product.  The
evaluation team tests the product against each requirement, making any
necessary interpretations of the criteria with respect to the product being
evaluated.

The evaluation team writes a final report on their findings about the system. 
The report is publicly available (containing no proprietary or sensitive
information) and contains the overall class rating assigned to the system and
the details of the evalution team's findings when comparing the product against
the evaluation criteria.  Detailed information concerning vulnerabilities found
by the evaluation team is furnished to the system developers and designers as
each is found so that the vendor has a chance to eliminate as many of them as
possible prior to the completion of the Formal Product Evaluation. 
Vulnerability analyses and other proprietary or sensitive information are
controlled within the Center through the Vulnerability Reporting Program and
are distributed only within the U.S. Government on a strict need-to-know and
non-disclosure basis, and to the vendor.

                                  APPENDIX B

                   SUMMARY OF EVALUATION CRITERIA DIVISIONS


The divisions of systems recognized under the trusted computer system
evaluation criteria are as follows.  Each division represents a major
improvement in the overall confidence one can place in the system to protect
classified and other sensitive information.

Division (D):  Minimal Protection

This division contains only one class.  It is reserved for those systems that
have been evaluated but that fail to meet the requirements for a higher
evaluation class.

Division (C):  Discretionary Protection

Classes in this division provide for discretionary (need-to-know) protection
and, through the inclusion of audit capabilities, for accountability of
subjects and the actions they initiate.

Division (B):  Mandatory Protection

The notion of a TCB that preserves the integrity of sensitivity labels and
uses them to enforce a set of mandatory access control rules is a major
requirement in this division.  Systems in this division must carry the
sensitivity labels with major data structures in the system.  The system
developer also provides the security policy model on which the TCB is based
and furnishes a specification of the TCB.  Evidence must be provided to
demonstrate that the reference monitor concept has been implemented.

Division (A):  Verified Protection

This division is characterized by the use of formal security verification
methods to assure that the mandatory and discretionary security controls
employed in the system can effectively protect classified or other sensitive
information stored or processed by the system.  Extensive documentation is
required to demonstrate that the TCB meets the security requirements in all
aspects of design, development and implementation.



                                  APPENDIX C

                    SUMMARY OF EVALUATION CRITERIA CLASSES


The classes of systems recognized under the trusted computer system evaluation
criteria are as follows.  They are presented in the order of increasing
desirablity from a computer security point of view.

Class (D):  Minimal Protection

This class is reserved for those systems that have been evaluated but that
fail to meet the requirements for a higher evaluation class.

Class (C1):  Discretionary Security Protection

The Trusted Computing Base (TCB) of a class (C1) system nominally satisfies
the discretionary security requirements by providing separation of users and
data.  It incorporates some form of credible controls capable of enforcing
access limitations on an individual basis, i.e., ostensibly suitable for
allowing users to be able to protect project or private information and to
keep other users from accidentally reading or destroying their data.  The
class (C1) environment is expected to be one of cooperating users processing
data at the same level(s) of sensitivity.

Class (C2):  Controlled Access Protection

Systems in this class enforce a more finely grained discretionary access
control than (C1) systems, making users individually accountable for their
actions through login procedures, auditing of security-relevant events, and
resource isolation.

Class (B1):  Labeled Security Protection

Class (B1) systems require all the features required for class (C2).  In
addition, an informal statement of the security policy model, data labeling,
and mandatory access control over named subjects and objects must be present.
The capability must exist for accurately labeling exported information.  Any
flaws identified by testing must be removed.

Class (B2):  Structured Protection

In class (B2) systems, the TCB is based on a clearly defined and documented
formal security policy model that requires the discretionary and mandatory
access control enforcement found in class (B1) systems be extended to all
subjects and objects in the ADP system.  In addition, covert channels are
addressed.  The TCB must be carefully structured into protection-critical and
non- protection-critical elements.  The TCB interface is well-defined and the
TCB design and implementation enable it to be subjected to more thorough
testing and more complete review.  Authentication mechanisms are strengthened,
trusted facility management is provided in the form of support for system
administrator and operator functions, and stringent configuration management
controls are imposed.  The system is relatively resistant to penetration.

Class (B3):  Security Domains

The class (B3) TCB must satisfy the reference monitor requirements that it
mediate all accesses of subjects to objects, be tamperproof, and be small
enough to be subjected to analysis and tests.  To this end, the TCB is
structured to exclude code not essential to security policy enforcement, with
significant system engineering during TCB design and implementation directed
toward minimizing its complexity.  A security administrator is supported,
audit mechanisms are expanded to signal security- relevant events, and system
recovery procedures are required.  The system is highly resistant to
penetration.

Class (A1):  Verified Design

Systems in class (A1) are functionally equivalent to those in class (B3) in
that no additional architectural features or policy requirements are added.
The distinguishing feature of systems in this class is the analysis derived
from formal design specification and verification techniques and the resulting
high degree of assurance that the TCB is correctly implemented.  This
assurance is developmental in nature, starting with a formal model of the
security policy and a formal top-level specification (FTLS) of the design.  In
keeping with the extensive design and development analysis of the TCB required
of systems in class (A1), more stringent configuration management is required
and procedures are established for securely distributing the system to sites.
A system security administrator is supported.



                                  APPENDIX D

                             REQUIREMENT DIRECTORY


This appendix lists requirements defined in "Department of Defense Trusted
Computer System Evaluation Criteria" alphabetically rather than by class.  It
is provided to assist in following the evolution of a requirement through the
classes.  For each requirement, three types of criteria may be present.  Each
will be preceded by the word: NEW, CHANGE, or ADD to indicate the following:

              NEW: Any criteria appearing in a lower class are superseded
                   by the criteria that follow.

           CHANGE: The criteria that follow have appeared in a lower class
                   but are changed for this class.  Highlighting is used
                   to indicate the specific changes to previously stated
                   criteria.

              ADD: The criteria that follow have not been required for any
                   lower class, and are added in this class to the
                   previously stated criteria for this requirement.

Abbreviations are used as follows:

               NR: (No Requirement) This requirement is not included in
                   this class.

              NAR: (No Additional Requirements) This requirement does not
                   change from the previous class.

The reader is referred to Part I of this document when placing new criteria
for a requirement into the complete context for that class.

Figure 1 provides a pictorial summary of the evolution of requirements through
the classes.


Audit

     C1: NR.

     C2: NEW: The TCB shall be able to create, maintain, and protect from
         modification or unauthorized access or destruction an audit trail of
         accesses to the objects it protects.  The audit data shall be 
         protected by the TCB so that read access to it is limited to those 
         who are authorized for audit data.  The TCB shall be able to record
         the following types of events:  use of identification and
         authentication mechanisms, introduction of objects into a user's
         address space (e.g., file open, program initiation), deletion of
         objects, and actions taken by computer operators and system 
         administrators and/or system security officers and other security
         relevant events.  For each recorded event, the audit record shall
         identify: date and time of the event, user, type of event, and success
         or failure of the event.  For identification/authentication events the
         origin of request (e.g., terminal ID) shall be included in the audit
         record.  For events that introduce an object into a user's address
         space and for object deletion events the audit record shall include
         the name of the object.  The ADP system administrator shall be able to
         selectively audit the actions of any one or more users based on
         individual identity.

     B1: CHANGE: For events that introduce an object into a user's address
         space and for object deletion events the audit record shall include
         the name of the object and the object's security level.  The ADP 
         system administrator shall be able to selectively audit the actions 
         of any one or more users based on individual identity and/or object
         security level.

         ADD: The TCB shall also be able to audit any override of
         human-readable output markings.

     B2: ADD: The TCB shall be able to audit the identified events that may be
         used in the exploitation of covert storage channels.

     B3: ADD: The TCB shall contain a mechanism that is able to monitor the
         occurrence or accumulation of security auditable events that may 
         indicate an imminent violation of security policy.  This mechanism 
         shall be able to immediately notify the security administrator when
         thresholds are exceeded, and, if the occurrence or accumulation of
         these security relevant events continues, the system shall take the
         lease disruptive action to terminate the event.

     A1: NAR.

Configuration Management

     C1: NR.

     C2: NR.

     B1: NR.

     B2: NEW: During development and maintenance of the TCB, a configuration
         management system shall be in place that maintains control of changes
         to the descriptive top-level specification, other design data, 
         implementation documentation, source code, the running version of the
         object code, and test fixtures and documentation.  The configuration
         management system shall assure a consistent mapping among all
         documentation and code associated with the current version of the TCB.
         Tools shall be provided for generation of a new version of the TCB
         from source code.  Also available shall be tools for comparing a 
         newly generated version with the previous TCB version in order to
         ascertain that only the intended changes have been made in the code 
         that will actually be used as the new version of the TCB.

     B3: NAR.

     A1: CHANGE: During the entire life-cycle, i.e., during the design,
         development, and maintenance of the TCB, a configuration management
         system shall be in place for all security-relevant hardware, firmware,
         and software that maintains control of changes to the formal model, 
         the descriptive and formal top-level specifications, other design
         data, implementation documentation, source code, the running version
         of the object code, and test fixtures and documentation.  Also
         available shall be tools, maintained under strict configuration
         control, for comparing a newly generated version with the previous
         TCB version in order to ascertain that only the intended changes have
         been made in the code that will actually be used as the new version 
         of the TCB.

    ADD: A combination of technical, physical, and procedural safeguards
         shall be used to protect from unauthorized modification or 
         destruction the master copy or copies of all material used to 
         generate the TCB.

Covert Channel Analysis

     C1: NR.

     C2: NR.

     B1: NR.

     B2: NEW: The system developer shall conduct a thorough search for covert
         storage channels and make a determination (either by actual 
         measurement or by engineering estimation) of the maximum bandwidth of
         each identified channel.  (See the Covert Channels Guideline section.)

     B3: CHANGE: The system developer shall conduct a thorough search for
         covert channels and make a determination (either by actual 
         measurement or by engineering estimation) of the maximum bandwidth 
         of each identified channel.

     A1: ADD: Formal methods shall be used in the analysis.

Design Documentation

     C1: NEW: Documentation shall be available that provides a description of
         the manufacturer's philosophy of protection and an explanation of how
         this philosophy is translated into the TCB.  If the TCB is composed 
         of distinct modules, the interfaces between these modules shall be 
         described.

     C2: NAR.

     B1: ADD: An informal or formal description of the security policy model
         enforced by the TCB shall be available and an explanation provided to
         show that it is sufficient to enforce the security policy.  The 
         specific TCB protection mechanisms shall be identified and an 
         explanation given to show that they satisfy the model.

     B2: CHANGE: The interfaces between the TCB modules shall be described.  A
         formal description of the security policy model enforced by the TCB 
         shall be available and proven that it is sufficient to enforce the 
         security policy.

         ADD: The descriptive top-level specification (DTLS) shall be shown to
         be an accurate description of the TCB interface.  Documentation shall
         describe how the TCB implements the reference monitor concept and 
         give an explanation why it is tamper resistant, cannot be bypassed,
         and is correctly implemented.  Documentation shall describe how the
         TCB is structured to facilitate testing and to enforce least
         privilege.  This documentation shall also present the results of the
         covert channel analysis and the tradeoffs involved in restricting the
         channels.  All auditable events that may be used in the exploitation
         of known covert storage channels shall be identified.  The bandwidths
         of known covert storage channels, the use of which is not detectable
         by the auditing mechanisms, shall be provided.  (See the Covert 
         Channel Guideline section.)

     B3: ADD: The TCB implementation (i.e., in hardware, firmware, and
         software) shall be informally shown to be consistent with the DTLS.
         The elements of the DTLS shall be shown, using informal techniques, 
         to correspond to the elements of the TCB.

     A1: CHANGE: The TCB implementation (i.e., in hardware, firmware, and
         software) shall be informally shown to be consistent with the formal
         top-level specification (FTLS).  The elements of the FTLS shall be 
         shown, using informal techniques, to correspond to the elements of 
         the TCB.

         ADD: Hardware, firmware, and software mechanisms not dealt with in
         the FTLS but strictly internal to the TCB (e.g., mapping registers,
         direct memory access I/O) shall be clearly described.

Design Specification and Verification

     C1: NR.

     C2: NR.

     B1: NEW: An informal or formal model of the security policy supported by
         the TCB shall be maintained over the life cycle of the ADP system that
         is shown to be consistent with its axioms.

     B2: CHANGE: A formal model of the security policy supported by the TCB
         shall be maintained over the life cycle of the ADP system that is
         proven consistent with its axioms.

         ADD: A descriptive top-level specification (DTLS) of the TCB shall be
         maintained that completely and accurately describes the TCB in terms
         of exceptions, error messages, and effects.  It shall be shown to be
         an accurate description of the TCB interface.

     B3: ADD: A convincing argument shall be given that the DTLS is consistent
         with the model.

     A1: CHANGE: The FTLS shall be shown to be an accurate description of the
         TCB interface.  A convincing argument shall be given that the DTLS is
         consistent with the model and a combination of formal and informal 
         techniques shall be used to show that the FTLS is consistent with the
         model.

         ADD: A formal top-level specification (FTLS) of the TCB shall be
         maintained that accurately describes the TCB in terms of exceptions,
         error messages, and effects.  The DTLS and FTLS shall include those
         components of the TCB that are implemented as hardware and/or 
         firmware if their properties are visible at the TCB interface.  This
         verification evidence shall be consistent with that provided within
         the state-of-the-art of the particular Computer Security Center-
         endorsed formal specification and verification system used.  Manual
         or other mapping of the FTLS to the TCB source code shall be
         performed to provide evidence of correct implementation.

Device Labels

     C1: NR.

     C2: NR.

     B1: NR.

     B2: NEW: The TCB shall support the assignment of minimum and maximum
         security levels to all attached physical devices.  These security
         levels shall be used by the TCB to enforce constraints imposed by 
         the physical environments in which the devices are located.

     B3: NAR.

     A1: NAR.

Discretionary Access Control

     C1: NEW: The TCB shall define and control access between named users and
         named objects (e.g., files and programs) in the ADP system.  The 
         enforcement mechanism (e.g., self/group/public controls, access 
         control lists) shall allow users to specify and control sharing of
         those objects by named individuals or defined groups or both.

     C2: CHANGE: The enforcement mechanism (e.g., self/group/public controls,
         access control lists) shall allow users to specify and control 
         sharing of those objects by named individuals, or defined groups of
         individuals, or by both, and shall provide controls to limit
         propagation of access rights.

    ADD: The discretionary access control mechanism shall, either by explicit
         user action or by default, provide that objects are protected from
         unauthorized access.  These access controls shall be capable of 
         including or excluding access to the granularity of a single user.  
         Access permission to an object by users not already possessing access
         permission shall only be assigned by authorized users.

     B1: NAR.

     B2: NAR.

     B3: CHANGE: The enforcement mechanism (e.g., access control lists) shall
         allow users to specify and control sharing of those objects, and shall
         provide controls to limit propagation of access rights.  These 
         access controls shall be capable of specifying, for each named 
         object, a list of named individuals and a list of groups of named 
         individuals with their respective modes of access to that object.

    ADD: Furthermore, for each such named object, it shall be possible to
         specify a list of named individuals and a list of groups of named 
         individuals for which no access to the object is to be given.

     A1: NAR.

Exportation of Labeled Information

     C1: NR.

     C2: NR.

     B1: NEW: The TCB shall designate each communication channel and I/O
         device as either single-level or multilevel.  Any change in this 
         designation shall be done manually and shall be auditable by the 
         TCB.  The TCB shall maintain and be able to audit any change in the
         security level or levels associated with a communication channel or
         I/O device.

     B2: NAR.

     B3: NAR.

     A1: NAR.

Exportation to Multilevel Devices

     C1: NR.

     C2: NR.

     B1: NEW: When the TCB exports an object to a multilevel I/O device, the
         sensitivity label associated with that object shall also be exported
         and shall reside on the same physical medium as the exported 
         information and shall be in the same form (i.e., machine-readable or
         human-readable form).  When the TCB exports or imports an object over
         a multilevel communication channel, the protocol used on that channel
         shall provide for the unambiguous pairing between the sensitivity
         labels and the associated information that is sent or received.

     B2: NAR.

     B3: NAR.

     A1: NAR.

Exportation to Single-Level Devices

     C1: NR.

     C2: NR.

     B1: NEW: Single-level I/O devices and single-level communication channels
         are not required to maintain the sensitivity labels of the 
         information they process.  However, the TCB shall include a mechanism
         by which the TCB and an authorized user reliably communicate to
         designate the single security level of information imported or 
         exported via single-level communication channels or I/O devices.

     B2: NAR.

     B3: NAR.

     A1: NAR.

Identification and Authentication

     C1: NEW: The TCB shall require users to identify themselves to it before
         beginning to perform any other actions that the TCB is expected to 
         mediate.  Furthermore, the TCB shall use a protected mechanism (e.g.,
         passwords) to authenticate the user's identity.  The TCB shall 
         protect authentication data so that it cannot be accessed by any 
         unauthorized user.

     C2: ADD: The TCB shall be able to enforce individual accountability by
         providing the capability to uniquely identify each individual ADP 
         system user.  The TCB shall also provide the capability of 
         associating this identity with all auditable actions taken by that 
         individual.

     B1: CHANGE: Furthermore, the TCB shall maintain authentication data that
         includes information for verifying the identity of individual users
         (e.g., passwords) as well as information for determining the 
         clearance and authorizations of individual users.  This data shall be
         used by the TCB to authenticate the user's identity and to ensure
         that the security level and authorizations of subjects external to
         the TCB that may be created to act on behalf of the individual user
         are dominated by the clearance and authorization of that user.


     B2: NAR.

     B3: NAR.

     A1: NAR.

Label Integrity

     C1: NR.

     C2: NR.

     B1: NEW: Sensitivity labels shall accurately represent security levels of
         the specific subjects or objects with which they are associated.  When
         exported by the TCB, sensitivity labels shall accurately and 
         unambiguously represent the internal labels and shall be associated 
         with the information being exported.

     B2: NAR.

     B3: NAR.

     A1: NAR.

Labeling Human-Readable Output

     C1: NR.

     C2: NR.

     B1: NEW: The ADP system administrator shall be able to specify the
         printable label names associated with exported sensitivity labels.
         The TCB shall mark the beginning and end of all human-readable, 
         paged, hardcopy output (e.g., line printer output) with human-
         readable sensitivity labels that properly* represent the sensitivity
         of the output.  The TCB shall, by default, mark the top and bottom of
         each page of human-readable, paged, hardcopy output (e.g., line
         printer output) with human-readable sensitivity labels that
         properly* represent the overall sensitivity of the output or that 
         properly* represent the sensitivity of the information on the page.
         The TCB shall, by default and in an appropriate manner, mark other 
         forms of human-readable output (e.g., maps, graphics) with human-
         readable sensitivity labels that properly* represent the sensitivity
         of the output.  Any override of these marking defaults shall be
         auditable by the TCB.

     B2: NAR.

     B3: NAR.

     A1: NAR.

______________________________
* The hierarchical classification component in human-readable sensitivity
labels shall be equal to the greatest hierarchical classification of any of the
information in the output that the labels refer to;  the non-hierarchical
category component shall include all of the non-hierarchical categories of the
information in the output the labels refer to, but no other non-hierarchical
categories.

Labels

     C1: NR.

     C2: NR.

     B1: NEW: Sensitivity labels associated with each subject and storage
         object under its control (e.g., process, file, segment, device) shall
         be maintained by the TCB.  These labels shall be used as the basis 
         for mandatory access control decisions.  In order to import non-
         labeled data, the TCB shall request and receive from an authorized 
         user the security level of the data, and all such actions shall be
         auditable by the TCB.

     B2: CHANGE: Sensitivity labels associated with each ADP system resource
         (e.g., subject, storage object, ROM) that is directly or indirectly 
         accessible by subjects external to the TCB shall be maintained by 
         the TCB.

     B3: NAR.

     A1: NAR.

Mandatory Access Control

     C1: NR.

     C2: NR.

     B1: NEW: The TCB shall enforce a mandatory access control policy over all
         subjects and storage objects under its control (e.g., processes, 
         files, segments, devices).  These subjects and objects shall be 
         assigned sensitivity labels that are a combination of hierarchical 
         classification levels and non-hierarchical categories, and the labels
         shall be used as the basis for mandatory access control decisions.
         The TCB shall be able to support two or more such security levels.
         (See the Mandatory Access Control guidelines.)  The following
         requirements shall hold for all accesses between subjects and objects
         controlled by the TCB: A subject can read an object only if the
         hierarchical classification in the subject's security level is 
         greater than or equal to the hierarchical classification in the 
         object's security level and the non-hierarchical categories in the
         subject's security level include all the non-hierarchical categories
         in the object's security level.  A subject can write an object only
         if the hierarchical classification in the subject's security level is
         less than or equal to the hierarchical classification in the object's
         security level and all the non-hierarchical categories in the 
         subject's security level are included in the non-hierarchical 
         categories in the object's security level.  Identification and
         authentication data shall be used by the TCB to authenticate the 
         user's identity and to ensure that the security level and authori-
         zation of subjects external to the TCB that may be created to act
         on behalf of the individual user are dominated by the clearance and
         authorization of that user.

     B2: CHANGE: The TCB shall enforce a mandatory access control policy over
         all resources (i.e., subjects, storage objects, and I/O devices) that
         are directly or indirectly accessible by subjects external to the TCB.
         The following requirements shall hold for all accesses between all
         subjects external to the TCB and all objects directly or indirectly 
         accessible by these subjects:

     B3: NAR.

     A1: NAR.

Object Reuse

     C1: NR.

     C2: NEW: All authorizations to the information contained within a 
         storage object shall be revoked prior to initial assignment,
         allocation or reallocation to a subject from the TCB's pool of
         unused storage objects.  No information, including encrypted
         representations of information, produced by a prior subject's
         actions is to be available to any subject that obtains access to
         an object that has been released back to the system.

     B1: NAR.

     B2: NAR.

     B3: NAR.

     A1: NAR.

Security Features User's Guide

     C1: NEW: A single summary, chapter, or manual in user documentation shall
         describe the protection mechanisms provided by the TCB, guidelines on
         their use, and how they interact with one another.

     C2: NAR.

     B1: NAR.

     B2: NAR.

     B3: NAR.

     A1: NAR.

Security Testing

     C1: NEW: The security mechanisms of the ADP system shall be tested and
         found to work as claimed in the system documentation.  Testing shall 
         be done to assure that there are no obvious ways for an unauthorized
         user to bypass or otherwise defeat the security protection mechanisms
         of the TCB.  (See the Security Testing guidelines.)

     C2: ADD: Testing shall also include a search for obvious flaws that would
         allow violation of resource isolation, or that would permit 
         unauthorized access to the audit or authentication data.

     B1: NEW: The security mechanisms of the ADP system shall be tested and
         found to work as claimed in the system documentation.  A team of 
         individuals who thoroughly understand the specific implementation of
         the TCB shall subject its design documentation, source code, and 
         object code to thorough analysis and testing.  Their objectives shall
         be: to uncover all design and implementation flaws that would permit
         a subject external to the TCB to read, change, or delete data
         normally denied under the mandatory or discretionary security policy 
         enforced by the TCB; as well as to assure that no subject (without
         authorization to do so) is able to cause the TCB to enter a state
         such that it is unable to respond to communications initiated by 
         other users.  All discovered flaws shall be removed or neutralized 
         and the TCB retested to demonstrate that they have been eliminated 
         and that new flaws have not been introduced.  (See the Security 
         Testing Guidelines.)

     B2: CHANGE: All discovered flaws shall be corrected and the TCB retested
         to demonstrate that they have been eliminated and that new flaws have
         not been introduced.

         ADD: The TCB shall be found relatively resistant to penetration.
         Testing shall demonstrate that the TCB implementation is consistent 
         with the descriptive top-level specification.

     B3: CHANGE: The TCB shall be found resistant to penetration.

         ADD: No design flaws and no more than a few correctable
         implementation flaws may be found during testing and there shall be 
         reasonable confidence that few remain.

     A1: CHANGE: Testing shall demonstrate that the TCB implementation is
         consistent with the formal top-level specification.

         ADD: Manual or other mapping of the FTLS to the source code may form
         a basis for penetration testing.

Subject Sensitivity Labels

     C1: NR.

     C2: NR.

     B1: NR.

     B2: NEW: The TCB shall immediately notify a terminal user of each change
         in the security level associated with that user during an interactive
         session.  A terminal user shall be able to query the TCB as desired 
         for a display of the subject's complete sensitivity label.

     B3: NAR.

     A1: NAR.

System Architecture

     C1: NEW: The TCB shall maintain a domain for its own execution that
         protects it from external interference or tampering (e.g., by 
         modification of its code or data structures).  Resources controlled 
         by the TCB may be a defined subset of the subjects and objects in 
         the ADP system.

     C2: ADD: The TCB shall isolate the resources to be protected so that they
         are subject to the access control and auditing requirements.

     B1: ADD: The TCB shall maintain process isolation through the provision
         of distinct address spaces under its control.

     B2: NEW: The TCB shall maintain a domain for its own execution that
         protects it from external interference or tampering (e.g., by 
         modification of its code or data structures).  The TCB shall maintain
         process isolation through the provision of distinct address spaces 
         under its control.  The TCB shall be internally structured into well-
         defined largely independent modules.  It shall make effective use of
         available hardware to separate those elements that are protection-
         critical from those that are not.  The TCB modules shall be designed
         such that the principle of least privilege is enforced.  Features in
         hardware, such as segmentation, shall be used to support logically 
         distinct storage objects with separate attributes (namely: readable, 
         writeable).  The user interface to the TCB shall be completely 
         defined and all elements of the TCB identified.

     B3: ADD: The TCB shall be designed and structured to use a complete,
         conceptually simple protection mechanism with precisely defined 
         semantics.  This mechanism shall play a central role in enforcing the
         internal structuring of the TCB and the system.  The TCB shall
         incorporate significant use of layering, abstraction and data hiding.
         Significant system engineering shall be directed toward minimizing
         the complexity of the TCB and excluding from the TCB modules that are
         not protection-critical.

     A1: NAR.

System Integrity

     C1: NEW: Hardware and/or software features shall be provided that can be
         used to periodically validate the correct operation of the on-site 
         hardware and firmware elements of the TCB.

     C2: NAR.

     B1: NAR.

     B2: NAR.

     B3: NAR.

     A1: NAR.

Test Documentation

     C1: NEW: The system developer shall provide to the evaluators a document
         that describes the test plan, test procedures that show how the
         security mechanisms were tested and results of the security
         mechanisms' functional testing.

     C2: NAR.

     B1: NAR.

     B2: ADD: It shall include results of testing the effectiveness of the
         methods used to reduce covert channel bandwidths.

     B3: NAR.

     A1: ADD: The results of the mapping between the formal top-level
         specification and the TCB source code shall be given.

Trusted Distribution

     C1: NR.

     C2: NR.

     B1: NR.

     B2: NR.

     B3: NR.

     A1: NEW: A trusted ADP system control and distribution facility shall be
         provided for maintaining the integrity of the mapping between the 
         master data describing the current version of the TCB and the on-site
         master copy of the code for the current version.  Procedures (e.g.,
         site security acceptance testing) shall exist for assuring that the
         TCB software, firmware, and hardware updates distributed to a
         customer are exactly as specified by the master copies.

Trusted Facility Management

     C1: NR.

     C2: NR.

     B1: NR.

     B2: NEW: The TCB shall support separate operator and administrator
         functions.

     B3: ADD: The functions performed in the role of a security administrator
         shall be identified.  The ADP system administrative personnel shall 
         only be able to perform security administrator functions after taking
         a distinct auditable action to assume the security administrator role
         on the ADP system.  Non-security functions that can be performed in
         the security administration role shall be limited strictly to those
         essential to performing the security role effectively.

     A1: NAR.

Trusted Facility Manual

     C1: NEW: A manual addressed to the ADP system administrator shall present
         cautions about functions and privileges that should be controlled 
         when running a secure facility.

     C2: ADD: The procedures for examining and maintaining the audit files as
         well as the detailed audit record structure for each type of audit 
         event shall be given.

     B1: ADD: The manual shall describe the operator and administrator
         functions related to security, to include changing the 
         characteristics of a user.  It shall provide guidelines on the 
         consistent and effective use of the protection features of the
         system, how they interact, how to securely generate a new TCB, and
         facility procedures, warnings, and privileges that need to be
         controlled in order to operate the facility in a secure manner.

     B2: ADD: The TCB modules that contain the reference validation mechanism
         shall be identified.  The procedures for secure generation of a new 
         TCB from source after modification of any modules in the TCB shall 
         be described.

     B3: ADD: It shall include the procedures to ensure that the system is
         initially started in a secure manner.  Procedures shall also be 
         included to resume secure system operation after any lapse in system
         operation.

     A1: NAR.

Trusted Path

     C1: NR.

     C2: NR.

     B1: NR.

     B2: NEW: The TCB shall support a trusted communication path between
         itself and user for initial login and authentication.  Communications
         via this path shall be initiated exclusively by a user.

     B3: CHANGE: The TCB shall support a trusted communication path between
         itself and users for use when a positive TCB-to-user connection is 
         required (e.g., login, change subject security level).  
         Communications via this trusted path shall be activated exclusively
         by a user or the TCB and shall be logically isolated and unmistakably
         distinguishable from other paths.

     A1: NAR.

Trusted Recovery

     C1: NR.

     C2: NR.

     B1: NR.

     B2: NR.

     B3: NEW: Procedures and/or mechanisms shall be provided to assure that,
         after an ADP system failure or other discontinuity, recovery without a
         protection compromise is obtained.

     A1: NAR.





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                                   GLOSSARY


Access - A specific type of interaction between a subject and an object 
     that results in the flow of information from one to the other.

Approval/Accreditation - The official authorization that is
     granted to an ADP system to process sensitive information in
     its operational environment, based upon comprehensive
     security evaluation of the system's hardware, firmware, and
     software security design, configuration, and implementation
     and of the other system procedural, administrative,
     physical, TEMPEST, personnel, and communications security
     controls.

Audit Trail - A set of records that collectively provide
     documentary evidence of processing used to aid in tracing
     from original transactions forward to related records and
     reports, and/or backwards from records and reports to their
     component source transactions.

Authenticate - To establish the validity of a claimed identity.

Automatic Data Processing (ADP) System - An assembly of computer
     hardware, firmware, and software configured for the purpose
     of classifying, sorting, calculating, computing,
     summarizing, transmitting and receiving, storing, and
     retrieving data with a minimum of human intervention.

Bandwidth - A characteristic of a communication channel that is
     the amount of information that can be passed through it in a
     given amount of time, usually expressed in bits per second.

Bell-LaPadula Model - A formal state transition model of computer
     security policy that describes a set of access control
     rules.  In this formal model, the entities in a computer
     system are divided into abstract sets of subjects and
     objects.  The notion of a secure state is defined and it is
     proven that each state transition preserves security by
     moving from secure state to secure state; thus, inductively
     proving that the system is secure.  A system state is
     defined to be "secure" if the only permitted access modes of
     subjects to objects are in accordance with a specific
     security policy.  In order to determine whether or not a
     specific access mode is allowed, the clearance of a subject
     is compared to the classification of the object and a
     determination is made as to whether the subject is
     authorized for the specific access mode.  The
     clearance/classification scheme is expressed in terms of a
     lattice.  See also: Lattice, Simple Security Property, *-
     Property.

Certification - The technical evaluation of a system's security
     features, made as part of and in support of the
     approval/accreditation process, that establishes the extent
     to which a particular computer system's design and
     implementation meet a set of specified security
     requirements.

Channel - An information transfer path within a system.  May also
     refer to the mechanism by which the path is effected.

Covert Channel - A communication channel that allows a process to
     transfer information in a manner that violates the system's
     security policy.  See also:  Covert Storage Channel, Covert
     Timing Channel.

Covert Storage Channel - A covert channel that involves the
     direct or indirect writing of a storage location by one
     process and the direct or indirect reading of the storage
     location by another process.  Covert storage channels
     typically involve a finite resource (e.g., sectors on a
     disk) that is shared by two subjects at different security
     levels.

Covert Timing Channel - A covert channel in which one process
     signals information to another by modulating its own use of
     system resources (e.g., CPU time) in such a way that this
     manipulation affects the real response time observed by the
     second process.

Data - Information with a specific physical representation.

Data Integrity - The state that exists when computerized data is
     the same as that in the source documents and has not been
     exposed to accidental or malicious alteration or
     destruction.

Descriptive Top-Level Specification (DTLS) - A top-level
     specification that is written in a natural language (e.g.,
     English), an informal program design notation, or a
     combination of the two.

Discretionary Access Control - A means of restricting access to
     objects based on the identity of subjects and/or groups to
     which they belong.  The controls are discretionary in the
     sense that a subject with a certain access permission is
     capable of passing that permission (perhaps indirectly) on
     to any other subject (unless restrained by mandatory access
     control).

Domain - The set of objects that a subject has the ability to
     access.

Dominate - Security level S1 is said to dominate security level
     S2 if the hierarchical classification of S1 is greater than
     or equal to that of S2 and the non-hierarchical categories
     of S1 include all those of S2 as a subset.

Exploitable Channel - Any channel that is useable or detectable
     by subjects external to the Trusted Computing Base.

Flaw Hypothesis Methodology - A system analysis and penetration
     technique where specifications and documentation for the
     system are analyzed and then flaws in the system are
     hypothesized.  The list of hypothesized flaws is then
     prioritized on the basis of the estimated probability that a
     flaw actually exists and, assuming a flaw does exist, on the
     ease of exploiting it and on the extent of control or
     compromise it would provide.  The prioritized list is used
     to direct the actual testing of the system.

Flaw - An error of commission, omission, or oversight in a system
     that allows protection mechanisms to be bypassed.

Formal Proof - A complete and convincing mathematical argument,
     presenting the full logical justification for each proof
     step, for the truth of a theorem or set of theorems.  The
     formal verification process uses formal proofs to show the
     truth of certain properties of formal specification and for
     showing that computer programs satisfy their specifications.

Formal Security Policy Model - A mathematically precise statement
     of a security policy.  To be adequately precise, such a
     model must represent the initial state of a system, the way
     in which the system progresses from one state to another,
     and a definition of a "secure" state of the system.  To be
     acceptable as a basis for a TCB, the model must be supported
     by a formal proof that if the initial state of the system
     satisfies the definition of a "secure" state and if all
     assumptions required by the model hold, then all future
     states of the system will be secure.  Some formal modeling
     techniques include:  state transition models, temporal logic
     models, denotational semantics models, algebraic
     specification models.  An example is the model described by
     Bell and LaPadula in reference [2].  See also:  Bell-
     LaPadula Model, Security Policy Model.

Formal Top-Level Specification (FTLS) - A Top-Level Specification
     that is written in a formal mathematical language to allow
     theorems showing the correspondence of the system
     specification to its formal requirements to be hypothesized
     and formally proven.

Formal Verification - The process of using formal proofs to
     demonstrate the consistency (design verification) between a
     formal specification of a system and a formal security
     policy model or (implementation verification) between the
     formal specification and its program implementation.

Front-End Security Filter - A process that is invoked to process
     data accordint to a specified security policy prior to
     releasing the data outside the processing environment or
     upon receiving data from an external source.

Functional Testing - The portion of security testing in which the
     advertised features of a system are tested for correct
     operation.

General-Purpose System - A computer system that is designed to
     aid in solving a wide variety of problems.

Granularity - The relative fineness or coarseness by which a
     mechanism can be adjusted.  The phrase "the granularity of
     a single user" means the access control mechanism can be
     adjusted to include or exclude any single user.

Lattice - A partially ordered set for which every pair of
     elements has a greatest lower bound and a least upper bound.

Least Privilege - This principle requires that each subject in a
     system be granted the most restrictive set of privileges (or
     lowest clearance) needed for the performance of authorized
     tasks.  The application of this principle limits the damage
     that can result from accident, error, or unauthorized use.

Mandatory Access Control - A means of restricting access to
     objects based on the sensitivity (as represented by a label)
     of the information contained in the objects and the formal
     authorization (i.e., clearance) of subjects to access
     information of such sensitivity.

Multilevel Device - A device that is used in a manner that
     permits it to simultaneously process data of two or more
     security levels without risk of compromise.  To accomplish
     this, sensitivity labels are normally stored on the same
     physical medium and in the same form (i.e., machine-readable
     or human-readable) as the data being processed.

Multilevel Secure - A class of system containing information with
     different sensitivities that simultaneously permits access
     by users with different security clearances and needs-to-
     know, but prevents users from obtaining access to
     information for which they lack authorization.

Object - A passive entity that contains or receives information.
     Access to an object potentially implies access to the
     information it contains.  Examples of objects are:  records,
     blocks, pages, segments, files, directories, directory
     trees, and programs, as well as bits, bytes, words, fields,
     processors, video displays, keyboards, clocks, printers,
     network nodes, etc.

Object Reuse - The reassignment to some subject of a medium
     (e.g., page frame, disk sector, magnetic tape) that
     contained one or more objects.  To be securely reassigned,
     such media must contain no residual data from the previously
     contained object(s).

Output - Information that has been exported by a TCB.

Password - A private character string that is used to
     authenticate an identity.

Penetration Testing - The portion of security testing in which
     the penetrators attempt to circumvent the security features
     of a system.  The penetrators may be assumed to use all
     system design and implementation documentation, which may
     include listings of system source code, manuals, and circuit
     diagrams.  The penetrators work under no constraints other
     than those that would be applied to ordinary users.

Process - A program in execution.  It is completely characterized
     by a single current execution point (represented by the
     machine state) and address space.

Protection-Critical Portions of the TCB - Those portions of the
     TCB whose normal function is to deal with the control of
     access between subjects and objects.

Protection Philosophy - An informal description of the overall
     design of a system that delineates each of the protection
     mechanisms employed.  A combination (appropriate to the
     evaluation class) of formal and informal techniques is used
     to show that the mechanisms are adequate to enforce the
     security policy.

Read - A fundamental operation that results only in the flow of
     information from an object to a subject.

Read Access - Permission to read information.

Read-Only Memory (ROM) - A storage area in which the contents can
     be read but not altered during normal computer processing.

Reference Monitor Concept - An access control concept that refers
     to an abstract machine that mediates all accesses to objects
     by subjects.

Resource - Anything used or consumed while performing a function.
     The categories of resources are: time, information, objects
     (information containers), or processors (the ability to use
     information).  Specific examples are: CPU time; terminal
     connect time; amount of directly-addressable memory; disk
     space; number of I/O requests per minute, etc.

Security Kernel - The hardware, firmware, and software elements
     of a Trusted Computing Base that implement the reference
     monitor concept.  It must mediate all accesses, be protected
     from modification, and be verifiable as correct.

Security Level - The combination of a hierarchical classification
     and a set of non-hierarchical categories that represents the
     sensitivity of information.

Security Policy - The set of laws, rules, and practices that
     regulate how an organization manages, protects, and
     distributes sensitive information.

Security Policy Model - An informal presentation of a formal
     security policy model.

Security Relevant Event - Any event that attempts to change the
     security state of the system, (e.g., change discretionary
     access controls, change the security level of the subject,
     change user password, etc.).  Also, any event that attempts
     to violate the security policy of the system, (e.g., too
     many attempts to login, attempts to violate the mandatory
     access control limits of a defice, attempts to downgrade a 
     file, etc.).

Security Testing - A process used to determine that the security
     features of a system are implemented as designed and that
     they are adequate for a proposed application environment.
     This process includes hands-on functional testing,
     penetration testing, and verification.  See also: Functional
     Testing, Penetration Testing, Verification.

Sensitive Information - Information that, as determined by a
     competent authority, must be protected because its
     unauthorized disclosure, alteration, loss, or destruction
     will at least cause perceivable damage to someone or
     something.

Sensitivity Label - A piece of information that represents the
     security level of an object and that describes the
     sensitivity (e.g., classification) of the data in the
     object.   Sensitivity labels are used by the TCB as the basis
     for mandatory access control decisions.

Simple Security Condition - A Bell-LaPadula security model rule
     allowing a subject read access to an object only if the
     security level of the subject dominates the security level
     of the object.

Single-Level Device - A device that is used to process data of a
     single security level at any one time.  Since the device
     need not be trusted to separate data of different security
     levels, sensitivity labels do not have to be stored with the
     data being processed.

*-Property (Star Property) - A Bell-LaPadula security model rule
     allowing a subject write access to an object only if the
     security level of the subject is dominated by the security
     level of the object.  Also known as the Confinement
     Property.

Storage Object - An object that supports both read and write
     accesses.

Subject - An active entity, generally in the form of a person,
     process, or device that causes information to flow among
     objects or changes the system state.  Technically, a
     process/domain pair.

Subject Security Level - A subject's security level is equal to
     the security level of the objects to which it has both read
     and write access.  A subject's security level must always be
     dominated by the clearance of the user the subject is
     associated with.

TEMPEST - The study and control of spurious electronic signals
     emitted from ADP equipment.

Top-Level Specification (TLS) - A non-procedural description of
     system behavior at the most abstract level.  Typically a
     functional specification that omits all implementation
     details.

Trap Door - A hidden software or hardware mechanism that permits
     system protection mechanisms to be circumvented.  It is
     activated in some non-apparent manner (e.g., special
     "random" key sequence at a terminal).

Trojan Horse - A computer program with an apparently or actually
     useful function that contains additional (hidden) functions
     that surreptitiously exploit the legitimate authorizations
     of the invoking process to the detriment of security.  For
     example, making a "blind copy" of a sensitive file for the
     creator of the Trojan Horse.

Trusted Computer System - A system that employs sufficient
     hardware and software integrity measures to allow its use
     for processing simultaneously a range of sensitive or
     classified information.

Trusted Computing Base (TCB) - The totality of protection
     mechanisms within a computer system -- including hardware,
     firmware, and software -- the combination of which is
     responsible for enforcing a security policy.  A TCB consists
     of one or more components that together enforce a unified
     security policy over a product or system.  The ability of
     a trusted computing base to correctly enforce a
     security policy depends solely on the mechanisms within the
     TCB and on the correct input by system administrative
     personnel of parameters (e.g., a user's clearance) related
     to the security policy.

Trusted Path - A mechanism by which a person at a terminal can
     communicate directly with the Trusted Computing Base.  This
     mechanism can only be activated by the person or the Trusted
     Computing Base and cannot be imitated by untrusted software.

Trusted Software - The software portion of a Trusted Computing
     Base.

User - Any person who interacts directly with a computer system.

Verification - The process of comparing two levels of system
     specification for proper correspondence (e.g., security
     policy model with top-level specification, TLS with source
     code, or source code with object code).  This process may or
     may not be automated.

Write - A fundamental operation that results only in the flow of
     information from a subject to an object.

Write Access - Permission to write an object.


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