# Patent

## Title
Method of maintaining security in a common output means and system for

## Abstract

The invention described herein is related to that described in U.S. Pat. No. 5,388,156, entitled "Personal Computer System With Security Features and Method", to that described in U.S. application Ser. No. 07/889,325 filed May 22, 1992, entitled "Trusted Personal Computer System With Limited Accessibility" and U.S. Pat. No. 5,574,786, entitled "Securing Trusted Personal Computer System Against Unauthorized Movement," all of which are held in common ownership with this invention.

## Background
1. Field of the Invention

This invention relates to personal computer systems and, more particularly, to such systems having security features enabling control over access to data retained in the system.

2. Description of the Prior Art

Personal computer systems have attained widespread use for providing computer power to many segments of today's modern society. Personal computer systems can usually be defined as a desk top, floor standing, or portable microcomputer that consists of a system unit having at least one system processor and associated volatile and non-volatile memory, a display monitor, a keyboard, one or more diskette drives, a fixed disk storage, and an optional printer. One of the distinguishing characteristics of these systems is the use of a motherboard (also known as and occasionally mentioned herein as a system board, system planar or planar) to electrically connect these components together. These systems are designed primarily to give independent computing power to a single user and are inexpensively priced for purchase by individuals or small businesses. Examples of such personal computer systems are IBM's PERSONAL COMPUTER AT and IBM's PERSONAL SYSTEM/2 Models 90 and 95.

These systems can be classified into two general families. The first family, usually referred to as Family I Models, use a bus architecture exemplified by the IBM PERSONAL COMPUTER AT and other "IBM compatible" machines. The second family, referred to as Family II Models, use IBM's MICRO CHANNEL bus architecture exemplified by IBM's PERSONAL SYSTEM/2 Models 50 through 95. Early Family I models typically used the popular INTEL 8088 or 8086 microprocessor as the system processor. Certain later Family I and the Family II models typically use the high speed INTEL 80286, 80386, and 80486 microprocessors which can operate in a real mode to emulate the slower speed INTEL 8086 microprocessor or a protected mode which extends the addressing range from 1 megabyte to 4 Gigabytes for some models. In essence, the real mode feature of the 80286, 80386, and 80486 processors provides hardware compatibility with software written for the 8086 and 8088 microprocessors.

With the growing use of personal computers in the world in recent years, more and more data or information is being collected and retained or stored in such systems. A lot of this data is sensitive in nature. In the wrong hands, data could become embarrassing to individuals, a company could lose a competitive edge, or sensitive data could be used to force payment for silence or lead to physical violence against individuals. As more users recognize the sensitive nature of data and its value, the more it becomes desirable to protect against such misuse. To protect themselves and the persons associated with the stored data, users are requiring incorporation of security and integrity features into the personal computers that they purchase.

Users are not the only people to recognize the sensitivity of the data being collected and stored. Governments are also enacting laws to enforce protection of sensitive data. One such government is that of the United States. It has recognized and responded to the gravity of the situation. The United States federal government has defined security levels and the associated requirements it takes to meet those levels, and provides a certification agency for personal computer manufacturers to submit products in order to see if the products meet the security level claimed by the manufacturer. The source for the Federal Requirements is the Department of Defense, Trusted Computer System Evaluation Criteria, DOD 5200.28 STD, 12/85, generally referred to as The Orange Book. The government has legislated that by Jan. 1, 1992 all data related to the government must only be processed and stored on personal computers with a minimum security level of C-2. For computer system hardware, the essence of the requirements is contained in the Assurance section, Requirement 6: "trusted mechanisms must be continuously protected against tampering and/or unauthorized changes . . . "

The related U.S. Pat. No. 5,388,156 describes a personal computer providing means for limiting access to certain critical data to only those users having a proper privilege to access such data. In realizing this purpose, a specialized memory element is provided for receiving and storing a Power On Password and a Privileged Access Password (sometimes hereinafter called a "POP" and a "PAP" respectively) and for coordinating the access granted to various functions and data to the activation and usage of the passwords. A user may have choices to activate or inactivate the security provisions made available, so that the system can be adapted to varying needs or desires for securing the usage of the system. The system may be adapted to the security requirements of governmental standards if desired and yet also used in an essentially unsecured manner should the circumstances of use so permit. Thus users of such systems are given great flexibility in application of the systems. Certain of the teachings of this related Application are described in detail hereinafter in view of its relationship with the invention of the present Application.

With the foregoing in mind, the present invention contemplates a new personal computer feature which makes data stored in a personal computer system inaccessible if transportation occurs which indicates the system is in unintended hands. In particular, the invention addresses the problem of removal of the computer from an area without authorization and disables the computer in response to such removal. In a preferred implementation the computer can be made operative again by providing a correct password.

The preferred new security feature renders the personal computer system, if moved through a control zone where it is exposed to radiation with a predefined characteristic, thereafter inoperable without knowledge of a predefined password. Thus, at least, certain data contained within the system components cannot be accessed by an unauthorized user in the event that the system is transported through the control zone.

In a more sophisticated version of the present invention, a personal computer system of the type described above has a first radiation responsive system that emits a radiation signal bearing a coded serial number upon being exposed to radiation having a predefined characteristic. A receiver in the control zone then triggers a computer to do a search referencing a list of serial numbers authorized for removal through such zone, which may, for example, be a doorway to a computer room. If the serial number is not matched with one on the list, a signal is sent to trigger transmission of radiation having a second predefined characteristic, preferably different from the first characteristic, which causes a receiver in the computer to activate logic that disables the computer from completing power-on setup, thereby making the computer inoperable.

Some of the features of the invention having been stated, other features will appear as the description proceeds, when taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a personal computer system embodying this invention;

FIG. 2 is an exploded perspective view of certain elements of the personal computer of FIG. 1 including a chassis, a cover, and a planar board and illustrating certain relationships among those elements and further including certain components related to the security feature of the present invention;

FIG. 3 is a schematic view of certain components of the personal computer of FIGS. 1 and 2;

FIGS. 4 and 5 are schematic representations of certain components of the personal computer of FIGS. 1 and 2 which are related to the security features of the prior art and to the security feature of the present invention;

FIG. 6 is an enlarged scale perspective view of certain components illustrated in FIGS. 4 and 5;

FIG. 7 is a view similar to FIG. 6 of certain optional components of the personal computer of FIGS. 1, 2, 4 and 5;

FIGS. 8a-8c and 9a-9e are schematic flowcharts illustrating certain functions involved in the security options available in accordance with the tamper evident security feature of the prior art which have been modified to include functions involved in the security feature of the present invention;

FIG. 10 is a simplified diagram of a control zone, indicating a radiation field and a computer system prior to entering the radiation field.

While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the present invention is shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention.

Certain defined terms may be used herein, as follows:

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 TCB 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 SOFTWARE: The software portion of a Trusted Computing Base.

TRUSTED PROGRAM: A program included in Trusted Software.

OPEN PROGRAM: A program operable on a Trusted Computing Base and which is other than a Trusted Program.

REFERENCE MONITOR CONCEPT: An access control concept that refers to an abstract machine that mediates all accesses to objects by subjects.

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.

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.

SYSTEM OWNER: The system owner is the user who is responsible for configuring and placing a system in secure mode initially. The system owner will control configuration both initially and whenever an update needs to be made. This person will control the Privileged Access Password and be responsible for maintaining its integrity. The system owner will also maintain physical security of the tamper evident cover keylock key. The system owner will be responsible for maintaining security logs on all systems. The system owner will also have to record all attempted security breaches. The system owner may own more than one system. The system owner is considered an authorized user and can also be a normal user.

SECURE MODE: When a system owner has successfully installed the Privileged Access Password on a personal computer system to invoke security protection provided by the security and integrity elements.

AUTHORIZED USER: Any user who is given permission to use the Privileged Access Password. This person may or may not be the system owner. This person may also have a key for a particular system or a set of systems. If this person is involved in recovering a system from a security breach, they are responsible for reporting it to the system owner. An authorized user may also be a normal user.

NORMAL USER: Any user of a system authorized to use the system facilities. In order to change a system configuration or fix a problem, this user requires the assistance of either the system owner or an authorized user. The normal user does not have the Privileged Access Password or the tamper evident cover keylock key unless they belong to either the authorized user or system owner category.

UNAUTHORIZED USER: Any one not defined as a system owner, authorized user or normal user. Any use of a secured personal computer system by an unauthorized user is considered a security breach, other than an unsuccessful power on, and an audit trail must exist showing such breaches.

EEPROM: Electrically Erasable Programmable Read Only Memory. This memory technology provides for non-volatile storage of data that can be changed under control of hardware logic. Contents of storage is not lost when power is absent. Contents may be altered only when the appropriate controls signals on the module are activated in the predefined sequence.

PASSWORD DESCRIPTION: The system has the potential to be protected by two passwords: 1. Privileged Access Password (PAP) and 2. Power On Password (POP). These passwords are intended to be used independently of one another. The PAP is designed to provide protection for the system owner by protecting the Initial Program Load (IPL) device boot list, access to the password utility, and access to the System Reference Diskette or System Partition. The System Partition will only be booted in response to a POST error (or on a warm boot) if there is no PAP installed or the PAP was entered initially during the power on sequence. Initial BIOS Load (IBL) from a diskette will be secured in the same manner as booting the System Reference Diskette. The existence of the PAP will be transparent to a normal user using the POP. The PAP will be installed, changed, or deleted by a utility on the System Reference Diskette or in the System Partition. The PAP, when set and entered correctly, will give the owner access to the entire system, overriding the POP. The POP, working as on all current PS/2 systems, is used to prevent any unauthorized access to the Operating System on the DASD or the facilities of the system.

Referring now more particularly to the accompanying drawings, a microcomputer system embodying the present invention is there shown and generally indicated at 10 (FIG. 1). The computer system 10 may have an associated monitor 11, keyboard 12 and printer or plotter 14. The computer 10 has a cover 15 which cooperates with a chassis 19 in defining an enclosed, shielded volume for receiving data processing and storage components for processing and storing digital data, as shown in FIG. 2. At least certain of the system components are mounted on a multi layer planar 20 (also commonly called a motherboard or system board) which is mounted on the chassis 19 and provides a means for mounting and electrically interconnecting various components of the computer system 10 including the CPU, system memory and accessory cards or boards as is well known in the art.

The chassis 19 has a base and a rear panel 16 and defines at least one open bay 22 for receiving a data storage device such as a disk drive 23.

At the rear panel 16 or other suitable area, according to one aspect of the invention, an antenna 109 is mounted to extend outside computer 10 to collect radiation. The antenna 109 is intended to provide a signal indicating radiation in the vicinity of the computer system and is connected to a detector 110 which is tuned to trigger in response to a particular radiation characteristic, such as a predefined frequency in an allowed radio frequency band.

When triggered detector 110 creates an alarm signal by setting a flag bit in a register 114 (see also FIG. 4) to the "on" state. As will be discussed below (with reference to FIGS. 8a-c), this flag is tested by logic in the set up sequence of the computer 10 and, when in the on state, causes the setup logic to be diverted to require a password input to permit the system 10 to become operative.

In a preferred but more complex implementation of the invention, there is additionally provided a second antenna 150 which also collects radiation external of the computer 10. The signal of antenna 150 is applied to an electronic tag 154 which responds to radiation having a second predefined characteristic to emit radiation, using an antenna 152, that bears an encoded serial number. Such electronic tags are known in the art and, for example, the Texas Instruments Capsule Series, 32 mm Transponder, P/N RI-TRP-RR2B may be used. Preferably the second characteristic is a different allowed frequency in the radio band than the first frequency characteristic.

Prior to relating the above structure for the invention to the setup logic of the computer, a summary of the operation in general of the computer system 10 will be reviewed. Referring to FIG. 3, there is shown a block diagram of a personal computer system illustrating the various components of the computer system such as the system 10 in accordance with the present invention, including components mounted on the planar 20 and the connection of the planar to the I/O slots and other hardware of the personal computer system. Connected to the planar is the system processor 32. While any appropriate microprocessor can be used as the CPU 32, one suitable microprocessor is the Pentium which is sold by INTEL. The CPU 32 is connected by a high speed CPU local bus 34 to a bus interface control unit 35, to volatile random access memory (RAM) 36 here shown as Single Inline Memory Modules (SIMMs) and to BIOS ROM 38 in which is stored instructions for basic input/output operations to the CPU 32. The BIOS ROM 38 includes the BIOS that is used to interface between the I/O devices and the operating system of the microprocessor 32. Instructions stored in the BIOS ROM 38 can be copied into RAM 36 to decrease the execution time of BIOS. The system also has, as has become conventional, a circuit component which has battery backed non-volatile memory (conventionally CMOS RAM) for receiving and retaining data regarding the system configuration and a real time clock (RTC) 68 (FIGS. 3 and 4).

While the present invention is described hereinafter with particular reference to the system block diagram of FIG. 3, it is to be understood at the outset of the description which follows that it is contemplated that the apparatus and methods in accordance with the present invention may be used with other hardware configurations of the planar board. For example, the system processor could be an Intel 80286 or 80486 microprocessor.

Returning now to FIG. 3, the CPU local bus 34 (comprising data, address and control components) also provides for the connection of the microprocessor 32 with a math coprocessor 39 and a Small Computer Systems Interface (SCSI) controller 40. The SCSI controller 40 may, as is known to persons skilled in the arts of computer design and operation, be connected or connectable with Read Only Memory (ROM) 41, RAM 42, and suitable internal or external devices of a variety of types as facilitated by the I/O connection indicated to the right in the Figure. The SCSI controller 40 functions as a storage controller in controlling storage memory devices such as fixed or removable media electromagnetic storage devices (also known as hard and floppy disk drives), electro-optical, tape and other storage devices.

The bus interface controller (BIC) 35 couples the CPU local bus 34 with an I/O bus 44. By means of the bus 44, the BIC 35 is coupled with an optional feature bus such as a MICRO CHANNEL bus having a plurality of I/O slots for receiving MICRO CHANNEL adapter cards 45 which may be further connected to an I/O device or memory (not shown). The I/O bus 44 includes address, data, and control components.

Coupled along the I/O bus 44 are a variety of I/O components such as a video signal processor 46 which is associated with video RAM (VRAM) for storing graphic information (indicated at 48) and for storing image information (indicated at 49). Video signals exchanged with the processor 46 may be passed through a Digital to Analog Converter (DAC) 50 to a monitor or other display device. Provision is also made for connecting the VSP 46 directly with what is here referred to as a natural image input/output, which may take the form of a video recorder/player, camera, etc. The I/O bus 44 is also coupled with a Digital Signal Processor (DSP) 51 which has associated instruction RAM 52 and data RAM 54 available to store software instructions for the processing of signals by the DSP 51 and data involved in such processing. The DSP 51 provides for processing of audio inputs and outputs by the provision of an audio controller 55, and for handling of other signals by provision of an analog interface controller 56. Lastly, the I/O bus 44 is coupled with an input/output controller 58 with an associated Electrical Erasable Programmable Read Only Memory (EEPROM) 59 by which inputs and outputs are exchanged with conventional peripherals including floppy disk drives, a printer or plotter 14, keyboard 12, a mouse or pointing device (not shown), and by means of a serial port. The EEPROM plays a part in the security provisions described hereinafter.

In achieving certain objectives of securing a personal computer system as described herein, the personal computer system 10 has an erasable memory element mounted within the system enclosure for selective activation to active and inactive states and for receiving and storing a privileged access password (defined more fully hereinafter) when in the active state. The erasable memory element preferably is the electrically erasable programmable read only memory device or EEPROM 59 (FIG. 3) described above. The system also has an option or security switch mounted within the enclosure and operatively connected with the erasable memory element 59 for setting that memory element to the active and inactive states. The option switch (also called security switch in this disclosure) may be, for example, a jumper mounted on the system planar 20 and manually settable to two different states by a person having access to the planar. In one state (also known as the write enable state), the EEPROM 59 is set to be active and to store a PAP as described herein. In the write enable state, the PAP may be written to the EEPROM, changed or removed. In the other or inactive state, the PAP storage capability of the EEPROM is set to be inactive.

As mentioned above, the system 10 also has a second component having erasable memory capabilities, namely battery supported, non-volatile CMOS RAM and an associated real time clock (RTC), indicated at 68 in FIG. 4. The CMOS RAM stores data indicative of the system configuration including data regarding the successful entry of the PAP on power up of the system 10. At least one tamper detection switch (FIGS. 4, 5 and 6) is provided, mounted within the enclosure and operatively connected with the CMOS RAM for detecting opening of the enclosure and for clearing certain data stored in that memory element in response to any switching of the tamper detection switch.

The system processor 32, in accordance with this invention, is operatively connected with the EEPROM 59 and the CMOS RAM 68 and functions in part for controlling access to at least certain levels of data stored within the system by distinguishing between the active and inactive states of the PAP storage capability of the memory element and between entry and non-entry of any valid, stored privileged access password (PAP). By manipulating the option switch, an operator (or more specifically the person charged with supervising and maintaining the security) of the system may select between secured operation of the system and unsecured operation of the system by selecting respective active and inactive states of the EEPROM. If secured operation is desired and to be effectuated, then the system owner must also enter a PAP.

As here disclosed, the system adapted for security concerns in accordance with this invention has two separate non-volatile erasable memory elements--the EEPROM and the CMOS RAM. This is done, in part, because at the time of this invention, EEPROM have a limited life in terms of the number of cycles of erasing and writing, while the indicators of the state of the PAP and the correct entry of the PAP, as well as at least potentially the state of any unauthorized opening of the system enclosure, may need to be erased and written a large number of times. Thus the functions described herein have been separated into first and second erasable memory elements in order to adapt to presently available technology. However, it is contemplated that the two forms of related data may be stored in a single erasable memory element where either technology so permits or a system designer is willing to accept the limitations which follow.

FIG. 4 illustrates certain relationships among the conventional power control or "on/off" switch 61, the conventional power supply 62, switches which change conductive state in response to opening or removal of enclosure covers such as the main cover 15 and the cable connection cover 16, and a keylock switch 64. The switches which change state on opening or removal of enclosure covers are, as illustrated, two in number; namely a switch 65 (FIGS. 4, 5 and 6) responsive to removal of the main cover 15 and a switch 66 (FIGS. 4, 5 and 7) responsive to removal of the cable connection cover 16. Each switch has two components, one normally open (65a and 66a, respectively) and one normally closed (65b and 66b, respectively). The second switch 66 is optional, as is the cable connection cover 16. However, as will be clear from a thoughtful consideration of the disclosure here made, the presence of the optional cover and switch assures more complete security control over the system.

The normally open contact sets of the cover switches 65 and 66 are connected in series with the main power switch 61 and to the power supply 62 (FIG. 4). As a consequence, if an attempt is made to "power up" the system 10 with the covers removed, the contact sets 65a and 66a will be open and prevent system operation. With the covers in place, the contact sets are held closed and normal system operation may be initiated.

The normally closed contact sets of the cover switches 65 and 66 are connected in series with the keylock switch 64 and to the RTC and CMOS memory 68. The normally closed contact sets 65b and 66b are held open by the presence of the covers 15, 16 and will close on the removal of those covers. The keylock switch 64 is normally held closed on locking of the enclosure lock which is conventionally supplied on the computer system 10. These three contact sets provide an alternate path to ground for current otherwise energizing portions of the RTC and CMOS memory, and have the effect of setting a register 114 of that memory to a distinctive state (such as all "1"s) if energization is lost, as upon unauthorized removal of a cover while the system is in an enclosure locked state. As that segment in memory is checked by POST, setting that segment to a distinctive state will result in a configuration error signal being generated which will alert a system owner that an attempt (successful or otherwise) has been made to breach system security.

In accordance with the present invention, the radiation detector 110 (see FIG. 2) is connected through a transistor 108 to a transistor 106 which responds to the alarm signal to set the alarm flag at a register 114 which is preferably a segment of CMOS RAM 68. The polling loop logic for testing the register 114 is show in FIG. 8a. This signal stored at register 114 is tested by the security logic as will be described more specifically with reference to FIG. 8c and if the register has been set will require entry of a correct password to complete the power-up sequence (see the diagrammatic representation of this logic at FIG. 8c).

The keylock switch 64 and main enclosure cover switch 65 are preferably mounted on a front card guide member 69 (FIGS. 2 and 6) so as to be appropriately positioned relative to the lock provided in the main enclosure cover 15. The front card guide member is mounted in the computer system frame is such a position that an actuating lever 70 for the cover switch 65 protrudes through an opening in an upright front frame member, to be actuated by the cover 15 when present and positioned to close the system enclosure.

The cable cover switch 66 is preferably mounted on the rear panel of the system frame, positioned to be actuated by a latch member mounted on the cable cover 16 and rotatable under the control of a manually operable keylock similar to that provided on the enclosure cover 15. When the optional cable cover 16 is used (as will be the case where full security of the system is desired or required), latching or locking of the cover to the rear panel causes the latch member to close the associated normally open contact set 66a and open the normally closed contact set 66b.

The security and integrity features described above and hereinafter work independently of a previously offered personal computer security feature, the Power on Password (POP). These additional security and integrity features provide a secure platform for operating system certification under applicable regulations such as the Orange Book. An additional password is required to place the system in secure mode. The password is here referred to as the Privileged Access Password (PAP). To maintain compatibility with previous personal computer systems, the POP is still supported. This description so far deals with the security and integrity features as they relate to POST and the password utility executing on a personal computer system with an EEPROM, option switch, and tamper evident covers.

Password Security is implemented by system hardware features; an EEPROM, a security switch and a tamper evident cover switch, firmware, POST and the system software password utility. Once the PAP has been installed, the system is in secure mode. The PAP is saved in the EEPROM. A backup copy of the PAP is also maintained in the EEPROM. This is done to prevent accidental loss of the PAP when a power failure occurs during the installation, change, or removal of the PAP. The POP and at least certain bits indicative of the validity of the PAP (if installed) are stored in the CMOS RTC. Changes in data retained in the CMOS RTC and in the EEPROM are independent one from the other.

Two bits in the EEPROM are used as a state machine that lets POST know exactly where a power outage occurred in the update sequence and, if possible, recover from a system board replacement situation. The password utility maintains the update indicator field, a two bit state machine used during any access to the PAP. If a power outage occurred during the password modification, when power is restored POST checks the state machine (POST actually checks the state machine on all power ups.) If the PAP is updated successfully (a `00` state), POST proceeds in the normal manner. If the update has started before power is lost (a `01` state), POST will check for the presence of a valid backup PAP. If valid, POST copies the backup PAP into the storage for the primary PAP. If the primary PAP has been updated successfully (a `10` state), POST will use the primary PAP (the new PAP) to validate any attempts to use the system reference diskette or boot the system partition. POST will assume the backup PAP is invalid. POST will copy the primary PAP to the backup PAP in this case. If the option or security switch is not in the unlocked or write enable position an error will be displayed. The system owner will have to intervene by unlocking the covers and changing the position of the security switch.

If the backup PAP has been updated successfully (a `11` state), both the primary and backup PAP are considered valid and POST will verify the validity of the Primary PAP, prior to confirming the entry of the PAP by the user.

As mentioned above, the POP is maintained in CMOS memory. Two bits will be maintained in CMOS memory for use as password indicators for the PAP. One indicator is used to signify that the system is in secure mode (PAP installed). The second indicator is to signify that the PAP was entered during the initial power on, cold boot. These two indicators will be initialized and set at a cold boot only. Prior to IPL, the indicators will be write protected unless the system reference diskette or system partition is booted, which requires the successful entry of any installed PAP. Changes in the POP and in the indicators are independent of any changes in the PAP stored in the EEPROM. However, changes in the CMOS memory can indicate security violations which require entry of a valid PAP for recovery permitting the loading of an operating system.

To prevent any unauthorized access to the passwords, the IPL device boot list, the EEPROM CRC, and all the indicators will be locked prior to Initial Program Load (IPL) booting an operating system. To lock out these areas, POST will set special hardware latches that cannot be reset unless the system is powered off. At the beginning of POST Stage I (initial power on), POST will check to see if the EEPROM is locked. If it is locked, POST will display an error and halt the system because the hardware is not functional. The system owner will need to intervene to remedy the situation, which might require that the system board be replaced. In one form, when the system has been tampered with, the first 14 bytes of RAM storage in CMOS associated with the RTC and control registers are unaffected. The remaining segment of CMOS is set to all "one's" (binary value 1) as briefly described above. Upon detecting this condition, POST displays an appropriate error. In another form, as little as a single bit may be set to a state indicative of tampering. In either instance, the system owner/authorized user will need to intervene to remedy the situation which might require entry of the PAP at the password prompt to boot from the system reference diskette or the system partition or that the system board be re-configured.

If the system owner forgets the PAP, the system board(s) affected will need to be replaced. If the POP is forgotten, the system owner can open the covers and toggle another switch on the system board to destroy the contents of the POP in CMOS, and then enter the PAP (if installed) to boot the System Reference Diskette or the System Partition to run the password utility, to reinstall the POP.

When a system has been powered on with neither password installed, POST will not prompt for a password. However, if the System Reference Diskette is not present or the System Partition boot is not requested or present, POST will lock the PAP, the backup PAP, the IPL device boot list, the EEPROM CRC, and all the indicators. This is done to prevent any accidental or malicious access to these areas. If the System Reference Diskette is present or the System Partition boot is requested, these locations are left unlocked to allow the system owner to invoke secure mode. When a system has been powered on with a POP installed, but no PAP installed, POST will check the state machine and then verify the POP password checksum. If the checksum is bad, POST will erase the POP in CMOS and not prompt for a password. Otherwise, POST will prompt for a password. If the System Reference Diskette is not present or the System Partition boot is not requested, the PAP, the backup PAP, the IPL device boot list, the EEPROM CRC, and all the indicators will be locked to prevent any access.

When a system has been powered on with a valid PAP installed (Secure mode) but no POP installed, POST will verify the PAP checksum. If the checksum is good, POST will prompt the user to enter the PAP if the System Reference Diskette is present or the System Partition boot is requested. Otherwise, POST will not prompt for a password and the POP, the PAP, the backup PAP, the IPL device boot list, the EEPROM CRC, and all the indicators will be locked to prevent any access. If the PAP checksum is bad, an error is displayed and the system is halted. This is to prevent a condition where POST could accidentally give unprotected access to a user to a system which was previously in secure mode when the EEPROM failed. The system owner will need to intervene to remedy the situation which might require that the system board be replaced.

When the system has been powered on with both a valid PAP and a valid POP installed, POST will prompt the user to enter a password. If the POP is entered, POST will not boot from the System Reference Diskette or the System Partition. The system can only boot using the existing IPL device list. If the PAP is entered at the prompt rather than the POP, the user can boot from the System Reference Diskette, the System Partition, the IBL diskette, or the normal IPL device list. An indicator is set that signifies that the PAP was successfully entered at initial power up time, so that a system reference diskette or system partition boot may occur later on in this power on session. POST will not prompt the user for a password after a soft reboot, hence the need for the PAP successfully entered indicator and its protection.

In brief, if a user can boot from the System Reference Diskette or the System Partition on a cold start, the POP, the PAP, the backup PAP, the IPL device boot list, the EEPROM CRC, and all the indicators will remain unlocked. This condition gives trusted software (i.e. the System Reference Diskette) and an authorized user access to the security parameters for the system. After POST verifies that either password is entered correctly, it will acknowledge the entry by displaying a confirmation icon. POST will skip prompting for the POP as described above when Network Server (Unattended Start) Mode is active.

Flowchart logic for the scenarios just described are included within FIGS. 8a-8c and 9a-9e, where links between certain steps are indicated by process blocks occupied by single letter designations in order to simplify the charting.

A system that has a Network Server (Unattended Start) Mode installed will complete the booting process all the way through the target operating system boot but the keyboard will be locked using the POP. However, if a system reference diskette is present or the System Partition boot is requested, the password prompt will be displayed to allow the owner to enter the PAP and gain control of the system. If a system is in the secure state and the user wants to boot from the system reference diskette or the system partition after the keyboard is already locked out, the user must power the system down and initiate a cold boot, from a power-off state with the system reference diskette in the diskette drive.

In conjunction with the POST changes, the password utility must include support for the PAP. The utility will support installing, changing and removing a PAP, and will interlock these three functions with the position of the option or security switch. The security switch should remain in the locked position until an authorized user wishes to set the PAP. At that time, the user should remove the system covers and move the security switch to the unlocked (change) position; then the PAP can be set. When the security switch is placed in the unlocked position, hardware logic external to the EEPROM allows the storing of the PAP into the EEPROM. When the security switch is placed in the locked position, external hardware logic prevents any changes to the PAP locations in the EEPROM. Appropriate messages will appear if the authorized user attempts to modify the PAP when the security switch is in the locked position. Also, messages will remind the user to return the security switch to the locked position after the PAP is removed. An additional safety feature is built into the password utility that prohibits the authorized user from setting the PAP equal to the POP. Checks will be made when setting or changing the PAP to ensure that the new PAP does not equal the current POP of the system. Also, when changing or removing the PAP, the current PAP must be known.

It is contemplated that a personal computer system will initially be shipped with the security switch in the locked position and the tamper evident cover locked. This is done to prevent any person other than the system owner from setting the system into secure mode. Unlike the POP, the PAP cannot be erased through hardware manipulation. If the PAP is forgotten or an unauthorized user places the system into secure mode, the system board must be replaced.

The memory elements, switches and their interconnections described herein are referred to in this description as "security feature elements," reflecting that the components named are elements of the computer system which specifically enable the security features described.

As will be understood, a personal computer system having the security capabilities described herein will be subject to attack by unauthorized users seeking to circumvent the security provisions described. One anticipatable form of attack will be a simple physical attack through openings defined in the enclosure provided by the cover 15 and chassis 19. Such openings are provided, for example, for the flow of cooling air through the enclosure; for the insertion and removal of floppy discs and other digital signal storage media; for the attachment of cables and the like; and even for the attachment (during manufacture or thereafter) of fixtures and accessories to be bolted or screwed in place. Any such opening may present an opportunity for the insertion of a probe by an unauthorized user seeking to avoid the security features described. Thus, a knowledgeable attacker might seek to erase the PAP or POP from the memory elements in which that data is stored, or seek to supply power in a way which would defeat the interlock switch arrangements described.

The resolution of protection against such attacks is to mount the memory elements and switches disposed within the computer system enclosure at locations inaccessible to any unauthorized user of the personal computer system attempting to affect the operation of any one of the memory elements and switches by insertion of a probe through an opening. The opening probed may be aventilation opening for the passage of cooling air or, with ingenuity on the part of the attacker, any other one of the various openings described above. The probe may be a simple mechanical device such as a bent paper clip, or some more sophisticated device configured specifically to reach a security feature element such as those described or to emit some form of energy (electrical, sonic, radiation) which would so disrupt the normal operation of the security feature element as to permit an unauthorized user to gain access to otherwise protected data.

Security feature elements as described above can be protected against probing attack of the types described by being positioned either at such distances from enclosure openings as to defeat mechanical probing attack or at positions shielded by other computer elements which are of a non-sensitive nature. Signal pathways connecting security feature elements and possibly carrying digital signals related to security functions may be protected against attack by being placed in the interior of multiple layer printed circuit boards. Openings defined in the computer enclosure may be configured to restrict or prevent attacking access, as by being configured as tortuous passageways or being occluded by non-sensitive elements.

Again referring to FIG. 4, connection of battery voltage or ground potential to the CMOS RAM 68 depends upon the state of the field effect transistors 106 and 108. When transistor 106 is off, the security feature is not enabled, and battery voltage is always applied to the register 114 of CMOS RAM 68. When the user enables the security features the transistor 106 is turned on, by an en.sub.-- dect signal applied to the input 107 of transistor 106, When antenna 109 passes through the control zone where the first frequency is being transmitted (see also FIGS. 2 and 10), detector 110, triggered by the antenna 109, signals transistor 108 to turn on and with transistor 106 also on (security enabled), ground or low potential is applied to set the alarm flag at the register 114 of the CMOS RAM 68. But if radiation with the first characteristic is not present, battery voltage continues to be applied at register 114 of the CMOS RAM 68 since transistor 108 is blocking.

Preferably the register 114 is located in the same storage segment of the CMOS RAM 68 as the registers which are set by the tamper evident switches 65b, 66b when a cover is removed from the system. Thus, both unauthorized passage of the computer system through a control zone when this radiation triggered feature is enabled and unauthorized removal of a cover while the tamper evident feature is enabled both result in the same configuration error and are thereafter handled by the system in the same manner during subsequent power-off, power-on procedures as set forth above with respect to the prior art security feature of the related application, Ser. No. 07/889,325. Accordingly, the preferred embodiment contemplates one bit in the preselected segment of the storage 68 is designated as a register to indicate activation of the cover tampering switches 65, 66 with the feature enabled, and a second bit of the segment is for radiation detected flag bit to indicate activation of transistor 108 with the feature enabled. The switches 65, 66 and transistor 108 set these bits to "1"s when they are activated as shown in FIG. 4.

During a power-on after a power-off, POST determines whether or not the radiation detected flag has been set to "1" by the transistor 108 and prompts for a password(PAP). The power-on logic then only reestablishes system operation upon the successful entry of the PAP, i.e. permits booting of the Operating System from RAM storage 23 (FIG. 2). At the next power-up from a power-off state, POST will check to see if radiation detection is enabled and if the detection mechanism has been activated. If both conditions are met, POST will prompt for the PAP. After three attempts of incorrectly entering the PAP, POST will disable the system. In order to reactivate the system, it is necessary to power-off the system and then power it on to obtain the prompt for the PAP. Until the PAP is correctly entered, the system will not boot and thus renders the system inactive. POST will render the system inactive after three unsuccessful attempts at correctly entering the PAP in a single power-on session. A power-off and power-on cycle is required prior to being allowed to enter the PAP once-again. If this condition exists, it requires that the user return the system to either the system owner or an authorized user to be re-activated unless the user has knowledge of the PAP.

The present invention as described contemplates systems which include the capability to detect radiation with a predefined characteristic. Upon detection a register 114 is set and the power-on logic tests this register 114 to determine if security has been breached. If so, the normal power-on sequence is diverted but can be resumed, in a preferred implementation, by entering a correct password. Otherwise, the sequence is halted.

As an alternative (see FIG. 10), radiation normally applied to the control zone 500 by a transmitter and antenna 501 has a second characteristic. That second characteristic triggers an electronic tag 154 to emit a signal bearing an encoded serial number. An antenna 502 at the control zone 500 collects the coded signal and applies it to a detector 503 that supplies the serial number to a table-look-up computer 506 which looks for a match with a list of serial numbers in its storage 508. If no match is found a security signal is sent to a transmitter 510 which floods the control zone with radiation having the first characteristic to cause the computer system 10 to set the alarm flag as discussed above.

The instant invention has been shown and described herein in what is considered to be the most practical and preferred embodiment. It is recognized, however, that departures may be made therefrom within the scope of the invention and that obvious modifications will occur to a person skilled in the art.

## Claims

1. A computer system which stores and processes data, which computer system includes a security system to control access to that data in the event of an unauthorized movement of such system through a gate where radiation having a first distinctive characteristic is present and where radiation having a second distinctive characteristic is selective applied in response to radiation signals bearing identifying characteristics, said computer system comprising: sequencing through a power on logic that performs set up operations; which first detector upon a detection responsively produces a selection signal to indicate a detection has occurred; radiation signal bearing identifying characteristics; characteristic to produce an alarm signal; and signal and cooperating with said power-on logic to block said electronic computing apparatus from becoming operative in response to said alarm signal whereby said computer system maybe selectively disabled upon passing through said gate.

2. A computer system according to claim 1 wherein said radiation is a radio frequency signal and the distinctive characteristic is the frequency of the radiation.

3. A computer system according to claim 1 which further includes password checking logic, a display device and a user operable input device and wherein said password checking logic prompts the user for a password if an alarm signal is present and disables said security logic from preventing said electronic computing apparatus from becoming operative if a correct password is asserted at said input device.

4. A security system for user systems at an enclosure having a portal defining an exit point, said security system comprising: radiation having a first distinctive characteristic; sequences the user system through a process to become operational, said user system having an identifier device that detects radiation having said first distinctive characteristic and responsively emits radiation bearing a respective encoded identification signal; which reciver performs a search on a defined list of identifier codes to determine if the received encoded identification signal is listed and produces an alarm signal if no match is found; second distinctive characteristic into the portal; having said second distinctive characteristic to produce a system alarm signal; and security logic, cooperating with said start-up logic and responsive to said system alarm signal, to disable said start-up logic from making said computer system operative, whereby said computer system maybe selectively disabled at said portal.

5. A security system according to claim 4 wherein said first and second distinctive characteristics are first and second frequencies and the radiation is radio frequency radiation.

6. A security system according to claim 4 wherein said user system further includes password checking logic and a user operable input device and wherein said password checking logic prompts the user for a password if an alarm signal is present and disables said security logic from preventing said user system from becoming operative if a correct password is asserted at said input device.