Abstract:
A personal computer system has security features enabling control over access to data retained in such system. The system cooperates with a transmitter of radiation having a predefined characteristic. A radiation detector within the system detects such radiation and produces an alarm signal when detection fails or is lost. The alarm signal is retained and triggers security logic cooperating with power-on-sequence logic to prevent the system from becoming operative. It is preferred to also provide an erasable memory element that when switched to an active state stores a privileged-access password. Logic is provided to cooperate with such element and override the security logic when the correct password is input to the system. 
     As an added security feature the transmitter may be deactivated if an intrusion is detected at the site to shut down all systems responding to the radiation in the security zone.

Description:
RELATED APPLICATIONS 
     The invention described herein is related to that described in U.S. application Ser. No. 840,965 filed Feb. 26, 1992, and now U.S. Pat. No. 5,388,156 issued on Feb. 7, 1995, entitled &#34;Personal Computer System With Security Features and Method&#34;, to that described in U.S. application Ser. No. 07/889,325 filed May 22, 1992, entitled &#34;Trusted Personal Computer System With Limited Accessibility,&#34; and to that described in U.S. application Ser. No. 08/383,828 filed Feb. 6, 1995, and now U.S. Pat. No. 5,574,786 issued on Nov. 12, 1996, entitled &#34;Securing Trusted Personal Computer System Against Unauthorized Movement&#34; all of which are held in common ownership with this invention. 
     1. Field of the Invention 
     This invention relates to personal computer systems and, more particularly, to such a system having security features enabling control over access to data retained in such a system. 
     2. Description of the Prior Art 
     Personal computer systems have attained widespread use for providing computer power to many segments of today&#39;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. 
     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 &#34;IBM compatible&#34; machines. The second family, referred to as Family II Models, use IBM&#39;s MICRO CHANNEL bus architecture exemplified by IBM&#39;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. 
     As more users come to recognize the sensitive nature of data and its value, the more it becomes desirable to protect against misuse. To protect themselves, 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. 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: &#34;trusted mechanisms must be continuously protected against tampering and/or unauthorized changes . . . &#34; 
     Beginning with the earliest personal computer system of the Family I models, such as the IBM Personal Computer, it was recognized that software compatibility would be of utmost importance. In order to achieve this goal, an insulation layer of system resident code, also known as &#34;firmware&#34;, was established between the hardware and software. This firmware provided an operational interface between a user&#39;s application program/operating system and the device to relieve the user of the concern about the characteristics of hardware devices. Eventually, the code developed into a Basic Input/Output System (BIOS), for allowing new devices to be added to the system, while insulating the application program from the peculiarities of the hardware. The importance of BIOS was immediately evident because it freed a device driver from depending on specific device hardware characteristics while providing the device driver with an intermediate interface to the device. Since BIOS was an integral part of the system and controlled the movement of data in and out of the system processor, it was resident on the system planar and was shipped to the user in a read only memory (ROM). For example, BIOS in the original IBM Personal Computer occupied 8K of ROM resident on the planar board. 
     As new models of the personal computer family were introduced, BIOS had to be updated and expanded to include new hardware and I/O devices. As could be expected, BIOS started to increase in memory size. For example, with the introduction of the IBM PERSONAL COMPUTER AT, BIOS grew to require 32K bytes of ROM. 
     Today, with the development of new technology, personal computer systems of the Family II models are growing even more sophisticated and are being made available to consumers more frequently. Since the technology is rapidly changing and new I/O devices are being added to the personal computer systems, modification to the BIOS has become a significant problem in the development cycle of the personal computer system. 
     For instance, with the introduction of the IBM Personal System/2 with Micro Channel architecture, a new BIOS, known as advanced BIOS, or ABIOS, was developed. However, to maintain software compatibility, BIOS from the Family I models had to be included in the Family II models. The Family I BIOS became known as Compatibility BIOS or CBIOS. However, as previously explained with respect to the IBM PERSONAL COMPUTER AT, only 32K bytes of ROM were resident on the planar board. Fortunately, the system could be expanded to 96K bytes of ROM. Unfortunately, because of system constraints, this turned out to be the maximum capacity available for BIOS. Luckily, even with the addition of ABIOS, ABIOS and CBIOS could still squeeze into 96K of ROM. However, only a small percentage of the 96K ROM area remained available for expansion. It has been believed that, with the addition of future I/O devices, CBIOS and ABIOS will eventually run out of ROM space. Thus, new I/O technology will not be able to be easily integrated within CBIOS and ABIOS. 
     As the BIOS became larger, it became necessary to offload portions of BIOS from the ROM. This was accomplished by storing portions of BIOS on a mass storage device such as a fixed disk, preferably in a defined portion of such a disk known as a system partition. The system partition also stores an image of a system reference diskette, which includes certain utility programs used in establishing system configuration and the like. Since a disk provides writing as well as reading capabilities, it became feasible to modify the actual BIOS code on the disk. The disk, while providing a fast and efficient way to store BIOS code, nevertheless greatly increased the probability of the BIOS code being corrupted. Since BIOS is an integral part of the operating system, a corrupt BIOS could lead to complete failure and non-operation of the system. Thus, it became quite apparent that a means for preventing unauthorized modification of the BIOS code on the fixed disk was highly desirable. This was the subject matter of U.S. patent application Ser. No. 07/398,820, filed Aug. 25, 1989, and now U.S. Pat. No. 5,022,077 issued 4 Jun. 1991. The interested reader is referred to that patent for additional information possibly helpful in understanding of the invention here disclosed, and the disclosure of that patent is hereby incorporated by reference into this specification to any extent necessary to a full understanding of the inventions here disclosed. 
     With the introduction of IBM&#39;s PS/2 Micro Channel Systems came the removal of switches and jumpers from I/O adapter cards and planar. The Micro Channel Architecture provided for programmable registers to replace them. Utilities to configure these programmable registers or programmable option select (POS) registers were required. These, and other utilities to improve system usability characteristics along with system diagnostics, were shipped with each system on a system reference diskette. 
     Prior to initial use, each Micro Channel System requires that its POS registers be initialized. For example, if the system is booted with a new I/O card, or a slot change for an I/O card, a configuration error is generated and the system boot up procedure halts. The user is then prompted to load the system reference diskette and press the F1 key. A &#34;Set Configuration Utility&#34; can then be booted from the system reference diskette to configure the system. The Set Configuration Utility will prompt the user for the desired action. If the appropriate I/O card&#39;s descriptor files are loaded on the system reference diskette, the Set Configuration Utility will generate the correct POS or configuration data in non-volatile storage. The descriptor file contains configuration information to interface the card to the system. 
     The related application Ser. No. 840,965 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 &#34;POP&#34; and a &#34;PAP&#34; 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. The teachings of this related Application are described in detail hereinafter in view of its relationship with the invention of the present Application. 
     BRIEF DESCRIPTION OF THE INVENTION 
     With the foregoing in mind, the present invention contemplates a new personal computer feature which, when combined with other security features disclosed in the prior art, renders data stored in a personal computer system useless, i.e. inaccessible by an unauthorized user. 
     The new security feature renders the personal computer system, if moved from a control area where preselected distinctive radiation signal is constantly transmitted to an area where the signal is absent inoperable to any unauthorized user, i.e. one who does not have knowledge of the system passwords. Thus, at least certain prescribed data contained within the system components cannot be accessed by an unauthorized user in the event that the system is stolen or otherwise removed from the control area. 
     In a preferred embodiment of the present invention, a personal computer system of the type described above and hereinafter in greater detail includes the optional capability to detect the removal of radiation having a predefined distinctive characteristic. Upon such detection of a loss of the radiation, which is preferably radio frequency radiation having a particular frequency characteristic, the detection apparatus preferably activates the prior art tamper evident mechanism described above. Thereafter, the system can only be activated after a power-off by a system owner, or authorized user, properly entering the current password (PAP) in response to a prompt for a password during the power-up routine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Some of the objects of the invention having been stated, other objects 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 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 a component 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 illustrates a control zone created by radiation transmitter. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     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&#39;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 embodying the present invention is there shown and generally indicated at 10 (FIG. 1). As mentioned hereinabove, the computer 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 electrically powered data processing and storage components for processing and storing digital data, as shown in FIG. 2. In the form illustrated in FIG. 2, the computer 10 also has an optional I/O cable connection cover 16 which extends over and protects the connection points of I/O cables with the computer system. At least certain of the system components are mounted on a multilayer planar 20 (also described herein as a motherboard or system board) which is mounted on the chassis 19 and provides a means for electrically interconnecting the components of the computer 10 including those identified above and such other associated elements as floppy disk drives, various forms of direct access storage devices, accessory cards or boards, and the like. 
     The chassis 19 has a base and a rear panel (FIG. 2, and which may be covered externally by the cable connection cover 16) and defines at least one open bay for receiving a data storage device such as a disk drive for magnetic or optical disks, a tape backup drive, or the like. In the illustrated form, an upper bay 22 is adapted to receive peripheral drives of a first size (such as those known as 3.5 inch drives). A hard disk drive 23, a direct access storage device may be provided in the upper bay 22. 
     According to the invention an antenna 112 is arranged to extend externally of the cover 15 to receive radiation external to computer 10. The antenna is connected to a radiation detector 114 which in preferred form responds to radiation of a predefined radio frequency to produce a detection signal when such radiation is at a level above a threshold as is well known in the art. 
     Prior to relating the above structure to the present invention, a summary of the operation in general of the personal computer system 10 may merit review. 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 &#34;on/off&#34; 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, in the illustrated form of this invention, 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 &#34;power up&#34; 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 68, and have the effect of setting a register 117 of that memory to a distinctive state (such as all &#34;1&#34;s) if energization is lost, as upon unauthorized removal of a cover while the system is in an enclosure locked state. As that register 117 in memory is checked by POST, setting that register 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. 
     According to the invention the detector 114 supplies its output signal indicating the presence of radiation of the predefined type to a transistor 110 which is in the conducting state when radiation is present causing a transistor 108 to be in the off state to place a logic zero in the Loss of RF Detected flag in a register 118 of the RTC and CMOS memory 68. When the radiation level falls to a level at which the detector 114 turns off transistor 110 which in turn causes transistor 108 to be conducting and if the enabling signal EN 13  CONT is a one at input 107 of a transistor 106 a one is placed in the Loss of RF Detected flag at register 118. As is discussed below with respect to FIG. 8a this flag causes the POST logic to require the PAP before completing the setup sequence to make the computer 10 operable. 
     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 &#34;one&#39;s&#34; (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. As is discussed in detail below, the present invention in a preferred implementation, supplements the above described logic with logic (see in particular FIG. 8a) which triggers POST to require a PAP to be input when it is detected by detector 114 (see FIG. 4) that the computer 10 has been moved out of range of the transmitter 152 (see FIG. 10). 
     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 present invention contemplates prior art computer systems of the type described above which further includes the capability to detect a loss of a predefined distinct radiation field to trigger protection of stored data. By so responding to radiation it is possible, in effect, to establish a secured zone where normal operation is possible without resort to a password (PAP). Referring to FIG. 10, the perimeter of the zone 150 is established by the decreasing field strength as the distance from the transmitter 152 increases to a point where it no longer triggers the detector 110 to switch the transistor 108 (see again FIG. 4). Various choices of radiation may be made but it is preferred to use a fixed predefined frequency of radiation in the radio band, which satisfies Federal Communication Commission requirements. 
     In the control zone 152, the radiation transmitter 150 is constantly transmitting the chosen frequency. The transmitter 150 can be fixed in place to provide a fixed control zone 152 or can be portable which provides a temporary control field 152 that can be relocated when desired as may be desirable for a laptop computer having stored confidential information, which, for example, is taken on business trips. When a computer system with this feature enabled, is moved out of a control zone 152, the detection circuitry 114 tuned to detect the chosen frequency collected by antenna 112, and triggered when the selected frequency signal is lost. The computer system is rendered non-operational by activating the prior art tamper evident mechanism described above or a similar but separate signal activated disabling mechanism. For purpose of this invention, an unauthorized event is defined as loss of a RF signal when this new security feature is enabled. Referring to FIG. 4, when the transistor 108 is turned on as a result of a loss of detection by detector 114 a detection signal sets an Loss of RF Detected Flag in register 118 of RAM 68 if the detection feature is armed by the enabling signal (EN-CONT) 107 applying a signal turning transistor 106 to the on state. The Loss of RF Detected Flag is tested by the power on self test logic as indicated in the logic flowchart of FIG. 8 and in particular FIG. 8a. If the Loss of RF Detected Flag is not in the zero state, the logic forces the user to correctly enter the highest level password (PAP) before it permits setup to be completed to make the computer 10 usable. 
     By so arming the computer 10, to be disabled when out of range of a zone defining transmitter 152, data may be secured in areas that have no controllable perimeter or in a room where a number of people may have access. The fact that the computer 10 is so armed is not apparent should it be desirable to keep that information from others. 
     The invention has been described with reference to the presently preferred embodiment but it will be appreciated that modifications and variations within the spirit and scope of the claimed invention will be suggested to those skilled in the art. To determine the scope of the invention attention should be directed to the claims appended hereto.