Method and apparatus for controlled access to a computer system
Contents
1. dIH2 SLINOYID EZH 39v4931NI M3Q0V3M QMVO ool 621 9L3N9VW 201 1 S2 0 1 2 9 5 4300030 3 0108 553400 Quvog M 01 US Patent Aug 21 1990 Sheet 2 of 8 4 951 249 200 POWER ON CONTROL ALT DEL 201 203 204 20 25 26 217 28 OPERATING CMM BOOT li EXECUTE ISKETTE HARD EXEC BAT SYSTEM SECURITY SYSTEM INT 13 RETURN INACTIVE STATUS CODE FROM SECURITY RESTORE INTS 9 13 816 3 SYSTEM gt 0 c m z o m m BA we FIG SIMULATE INT 21 4800 TO 8 INITIATE SMP WITH RETURN TO NEXT PLP STATEMENT ee ee URITY ANY ABNORMAL REQUIRE INSERT OF PREVIOUSLY SYSTEM AN AUTHORIZED IDENTIFICATION SIGNON CARD PROGRAM xd IF INPUT IF INPUT 4 AFTER 3 TRIES 2 SMP LOG ATTEMPT 3227 VALID 248 233 229 242 _ STORE PROGRAM amp 2ND PROGRAM AUTHORIZATION IN PLP DATA AREA 243 FIG 2 US Patent Aug 21 1990 Sheet 3 of 8 4 951 249 EXECUTE NORMAL SERVICE ROUTINE 267 266 IF AUTHORIZED 254 265 2559 IF CHECK EXIT RIS Vico ay CHECK O FIG ABNORMAL TO INITIATE DOS 244 FUNCTION OR A 2ND PROGRAM SIMULATE IN2. i providing at said security system address for said critical errors a routine for blocking access to said operating system 22 The method according to claim 21 wherein said computer system includes a floppy disc drive and wherein said security system further performs steps of changing the computer systems address for said floppy disc drive to an address in the security sys tem providing at said security system address for said floppy disc drive a routine for blocking any input from said floppy disc drive which would place the computer outside the control of said security sys tem and in response to validation restoring the address for said floppy disc drive to said computer system s address for said floppy disc drive 23 The method according to claim 21 wherein said system includes a display and wherein said step g includes displaying on said display a menu of programs and functions for which the user is pre authorized 24 The method according to claim 21 further com prising the following steps prior to step a initiating operation of said computer system via the operating system s startup routine and reading a read only memory ROM containing in structions for the operating system to transfer con trol to said security system 25 The method according to claim 21 and further comprising changing the computer system s address for DOS function call routines to an address in the security system and provid
3. Tamper means detect the loosening or removal of a screw on the hous ing which would allow access to the inside of the hous ing Alarm means is coupled to the tilt detection means and the tamper detection means for sounding an alarm if the computer is tilted or a screw is loosened Means 4 951 249 3 responsive to a reset instruction from a user authorized to reset the alarm is provided the reset instruction being generated by the security program resident in the com puter system BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is an overall block diagram of the computer security system FIGS 2 and 3 are a flow diagram of the event sequen ces of the computer security program FIG 4 is a schematic diagram of the board address decoder and buffer circuits shown in FIG 1 FIG 5 is a schematic diagram of the chip select de coder and data buffering circuits shown in FIG 1 FIG 6 comprising FIGS 6A and 6B is a block diagram of the magnetic card reader interface circuits FIG 7 is a flow diagram of the magnetic card reader program FIG 8 is a schematic diagram of the alarm circuit DETAILED DESCRIPTION The present invention is illustrated herein for IBM PC XT or AT trademarks of IBM Corporation com puters or computers which are compatible with these computers The present invention is described in con nection with these computers because of their extreme popularity and this should not be taken as an implication that
4. and wherein said means for identifying all operators of said computer system comprises means for identifying all operators of said computer system via said non keyboard device 20 The security device according to claim 19 wherein said non keyboard data entry device is a mag netic card reader 21 A method for securing a computer system having keyboard entry device comprising the steps of a transferring control of said computer system to a security system interposed between an operating system and all peripheral devices and application progress and data stored in said computer system said security system performing the following steps b changing the computer system s keyboard address to an address in the security system 0 15 20 25 30 40 45 55 65 18 c providing at said security system address a routine for blocking any keyboard input which would place the operation of the computer outside the control of said security system d requiring all operators to identify themselves e validating the operator s identification f in response to validation restoring the address for said keyboard to said computer system s keyboard address g allowing a valid user access only to one or more of said programs and data and operating system for which the user has been pre authorized h changing the computer system s address for the critical error routine to an address in the security system and
5. and which define the requirements for the circuits de veloping the chip select signals are indicated in Table 3 JUMPER 1 u E As also shown in Table 2 these addresses require that lines A12 and A13 be simultaneously low Line A13 is applied to the input 411 to inverter 427 the output of which is applied by line 441 to one input of two input AND gate 461 Similiarly line A12 applied to the input 413 of inverter 429 the output of which is applied via line 443 to the other input of AND gate 461 If lines A12 and A13 are both low high signals will be applied on lines 441 and 443 which will resuit in a high signal being applied on line 463 to one input of two input NAND gate 465 The signal on line 459 is applied to the other input of NAND gate 465 If the signal on line 463 is high and the signal on line 459 is high this indicates a valid address has been selected and an active low signal on line 467 labeled board select it is generated by gate 465 This signal has two functions First of all it acts as an active low chip select signal for the one way buffers 431 and 433 for address lines A11 through A4 applied 30 35 The active low board select signal generated on line 467 on FIG 4 is applied to line 501 in FIG 5 This signal is inverted by inverter 505 and applied via line 507 to one input of two input NAND gate 523 The internal address bus 469 of FIG 4 continues as bus 503 in FIG 5 Line A11 is
6. 266 the operating system will perform the requested function and return control back to the user application program via line 271 or line 273 depending on the type of service requested A return passes control via line 267 to line 271 and hence to line 263 through the continue input of the secondary program execution block 278 An exit via line 269 passes control via line 273 to the start input of the secondary program execu tion at block 278 The secondary programs execute in the same manner as the initial program requested by the user Exits from the secondary program pass via line 275 to line 253 back to block 254 and are handled identi cally to exits from the primary program Referring now to FIG 4 the board address decoder and buffer circuits 131 shown as FIG 1 are shown in greater detail The purpose of the circuit shown in FIG 4 is to detect that the computer is addressing the com puter security system circuit and to buffer the address lines from the address lines of the computer bus so that they can be utilized in other circuits on the circuit board without loading the computer bus The address latch enable ALE signal from the computer address bus is utilized to latch addresses onto the bus at the falling edge of this signal The address enable AEN signal is low when the address lines have been driven from pro gram instructions and high when direct memory access transfers are active Consequently when the ALE and AEN
7. applied via line 517 through inverter 519 and then via line 521 to the other input of gate 523 Thus whenever the board is selected and the signal on line A11 is low the output of gate 523 will be a low on line 525 which will provide an active low chip select signal to the ROM 527 which will be selected Referring to Table 3 this will occur whenever the board is addressed and the address on line A0 A11 are in the range from hexadecimal 000 through hexadecimal 7FF As can be seen from line 2 of Table 3 line A11 does not become a digital 1 until address hexadecimal 800 is reached Therefore all addresses below this address are directed to the ROM TABLE 3 CHIP SELECT AND ALARM FUNCTION DECODE All 10 09 A08 A07 06 05 04 A03 02 AO A00 E 000 0 0 0 0 0 0 0 0 0 0 0 0 ROM 7FF 0 1 1 1 1 1 1 i 1 ROM 800 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 l 1 1 0 1 1 1 RAM FF0 1 1 1 1 1 1 1 1 0 0 0 0 Not Used FF1 1 I 1 1 1 1 1 0 0 0 1 Read Dat FF2 1 1 1 1 1 0 0 0 Disarm Alarm FF4 1 1 1 1 1 L 0 1 0 0 Arm Alarm via bus 415 and through 0 applied via bus 417 55 respectively In addition this signal operates as the chip select for the two way three state octal buffers 581 in FIG 5 which will be described below The internal address bus 469 containing buffer address lines A11 A0 corresponds to bus 109 in FIG 1 Referring now to FIG 5 the circuit block 133 shown in FIG 1 is shown in great
8. lines are in the low state the address lines are valid and are being driven by program instruc tions The ALE signal is provided to inverter 419 via line 401 and the AEN signal is provided to inverter 421 via line 403 The outputs of these inverters on lines 475 and 437 respectfully are input to a two input AND gate 445 The result of ANDing these two signals on line 447 is a signal which when high indicates that the address lines are valid This signal is applied to one input of two input NAND gate 449 The security system circuit board is designed to re spond only to addresses in the range of hexadecimal C8000 through F4000 which is the user ROM area of the computer address space Table 2 indicates the bit patterns for the circuit board general address As indi cated in the Table lines A19 and A18 must always be high for the user ROM area to be addressed Line A19 is applied to input of AND gate 423 via line 405 and line A18 is applied to the other input of AND gate 423 via line 407 A high output on line 439 labeled high mem ory indicates that both of the input lines A19 and A18 are high and that the user ROM is to be addressed The signal on line 447 and the signal on line 439 are applied to the inputs of two input NAND gate 449 If both signals are high a low signal appears on line 451 which serves as the chip select CS signal which is active low This signal serves to enable a four line to sixteen line decoder 425 such as a T
9. said validated operator access to only one or more of said programs and data and operating system for which said validated operator has been pre authorized 2 The security device according to claim 1 wherein said system includes a display and wherein said means for allowing includes means for displaying on said dis play a menu of programs and functions which the user is authorized to use 3 The security device according to claim 1 wherein said means for transferring includes a read only memory ROM read by said operating system and which tains instructions transferring control of the computer system to the security program 4 The security device according to claim 3 further comprising means under control of said security system for changing the computer system s address for DOS function call routines to an address in the security system and means at said address in said security system for said DOS function call routines for blocking execution of DOS commands unless said validated operator is pre authorized for said operating system 5 The security device according to claim 3 further comprising means under control of said security system for changing the computer system s address for the critical error routine to an address in the security system and means at said address in said security system for said critical errors for blocking access to the operating system 6 The security device of claim 1 further com
10. 44 47 Equipment Check 12 48 4B Memory 13 4C 4F Diskette Disk 14 50 53 Communications 0 40 55 65 6 TABLE 1 continued SOFTWARE INTERRUPT LISTING INT f ADDRESS IN RAM FUNCTION PERFORMED 15 54 57 Cassette 16 58 5B Keyboard 17 5C 5F Printer 18 60 63 Resident BASIC 19 64 67 Bootstrap lA 68 6B Time of Day 1B 6C 6F Keyboard Break 70 73 Timer Tick ID 74 77 Video Initialization 78 7 Diskette Parameters 7C 7F Video Graphics Chars 20 80 83 DOS PGM Term 21 84 87 DOS 22 88 8 DOS Term Address 23 8C 8F Cti break Address 24 90 93 DOS Fatal Error 25 94 97 Abs Disk Read 26 98 9B Abs Disk Write 27 9C 9F DOS Terminate 28 3F Reserved 40 SF 100 17 Reserved 60 67 180 19F User INTs 68 7F 1A0 IFF Not Used 80 FO 200 3 3 Basic F1 FF 3 4 3 Not Used The hard disk is operative and the system will look for a file known to the operating system as the AUTOEX EC BAT file which contains a user defined sequence of programs and procedures to be executed before giving control over to the operator of the computer system The operating system executes the AUTOEXEC BAT file in block 218 The PLP program must be the last program named in the AUTOEXEC BAT file The operation of the computer system passes via line 219 to block 220 In block 220 when the PLP begins execution it restores the normal diskette and keyboard interrupt addresses thus allowing normal operation of these t
11. T MEANS CLOCK 15 HIGH 7M STORE BIT 2 DATA BIT 715 717 READ DATA BB FFI AND CHECK BIT FOR LOGIC 0 CLOCK LOW NOT CHECK TIMEOUT 721 NOT TIMEOUT 4 TIMEOUT TN CONVERT NEXT 5 BITS INTO ASCII CHAR AND STORE CHECK FOR END OF BIT STRING 727 NOT END OF STRING DISPLAY ERROR MESSAGE EXIT PROGRAM 731 FIG 7 Aug 21 1990 Sheet 8 of 8 4 051 249 US Patent gt gt a gt X e 8399141 J18YN3 4013 4114 4014 4113 41081802 03 SONI WAVIN 68 KYYIV u01v 111250 188 M d ng 108 109 318 3 WuvY 17 8 914 501015 Nuviv SOW TY 81804 01 0350 0511 18311V9 WOXI AG 310N w 009 4 951 249 1 METHOD AND APPARATUS FOR CONTROLLED ACCESS TO A COMPUTER SYSTEM This is a continuation of U S Application Ser No 922 600 filed Oct 24 1986 now abandoned BACKGROUND OF THE INVENTION This invention relates to a computer security system which protects the computer software from unautho rized access and protects the computer hardware from unauthorized intrusion or unauthorized removal In a particular it pertains to a security system for the sonal computers now in wide use Since their introduction only a few years ago the number of personal computers in use in corporations and financial institutio
12. T 21 4800 TO INITIATE PROGRAM SETUP BY SMP WITH RETURN d NEXT PLP STATEMENT een AR us 245 522 gt 263 255 273 i CONTINUE START 228 CONTINUE SECONDARY PROGRAM gt EXIT PROGRAM EXECUT 275 EXECUTION 7297 US Patent Aug 21 1990 Sheet 4 of 8 4 051 249 131 JUMPER PAIR TO SET BOARD OCTAL 3 STATE BUFFER 172 OCTAL 3 STATE BUFFER INTERNAL All A ADOR BUS A3 AQ FIG 4 US Patent Aug 21 1990 Sheet 5 of 8 4 951 249 AQ INTERNAL ADOR BUS A CARD READER CLOCK CARD READER DATA CARD STATUS FROM FIG ALARM STATUS FROM FIG FIG 5 COMPUTER DATA BUS 06 07 MEMR MEM W Aug 21 1990 Sheet 6 of 8 4 051 249 US Patent 3334708 HV312 MOLVHBIALLTIQIN JISVLSONOW J409 4399181 MOLVYSIAILINW 330 38 3 18V LSONOW OVW D 629 29 OML 0130 3305 SOU3NO9VN NVOIWMSWV MOLVH8SIALLYYN 3 HVLSONOW 4399194 M3O0V3J GYV OVW US Patent Aug 21 1990 Sheet 7 of 8 4 951 249 DISPLAY INSERT CARD PROMPT 70 READ DATA AT BS FF AND CHECK BIT 3 FOR LOGIC 3 1 MEANS CARD HAS BEEN INSERTED DISPLAY REMOVE CARD PROMPT READ DATA 5 AND CHECK BIT FOR LOGIC BI
13. United States Patent 5 McClung et al 54 75 73 21 22 63 51 52 58 56 METHOD AND APPARATUS FOR CONTROLLED ACCESS TO A COMPUTER SYSTEM Inventors Charles McClung Baldwin Peter H Roberts Brooklyn N Y Assignee Harcom Security Systems Corp New York N Y Appl No 328 735 Filed Mar 23 1989 Related U S Application Data Continuation of Ser No 922 600 Oct 24 1986 aban doned 12 14 HO4L 9 00 US eicere 364 900 380 23 380 25 340 825 34 Field of Search 364 200 MS File 900 MS File 340 825 3 825 31 825 34 380 3 4 23 25 52 References Cited U S PATENT DOCUMENTS 3 643 219 2 1972 Heimann 364 200 3 764 742 10 1973 Abbott et al 340 825 3 X 3 806 882 4 1974 Clarke se 364 200 4 494 114 1 1985 Kaish 364 900 X 4 532 508 7 1985 Ruell 340 825 34 POWER ON CONTROL ALT OEL OPERATING SYSTEM securiry SYSTEM ROM TEM SECURITY SYS SECURITY SYSTEM SIGNON MENU PROGRAM SMP 231 AFTER 3 TRIES _ F INPUT ACER RR NOT 233 i Patent Number 4 951 249 4 Date of Patent Aug 21 1990 4 549 281 10 1985 Eckert et al ss 364 900 4 558 175 12 1985 Genest et al 2 380 21 4 621 334 11 1986 Garcia 340 825 3 X 4 622 651 11 1986 Eckert ss 364 900 4 667 307 5 1987 Porch
14. a prompt to the user to insert and withdraw his magnetically encoded identification card The SMP 4 951 249 7 then checks the data read from the The card reader interface hardware and the software routine necessary to read the data from the card are explained in fuller detail below in connection with FIGS 6 and 7 The information on the card is checked against the entries in the security system file of authorized users If the card is not an authorized card that is the security system does not have this card stored in its file of autho rized users control passes via line 229 and then via line 231 back to block 230 Setting up the file of authorized users is handled in the same manner as any other appli cation program If the card does match one of the previously autho rized cards in the security system file the SMP then requests the user to input his personal identification number PIN via the keyboard The purpose of the PIN is to guarantee that the user of the card is its owner Magnetically encoded identification cards can be lost or otherwise used by persons that are not their owner The secret PIN which is known only to the owner and to those authorized to enter such information into the computer s file greatly reduces a chance of unautho rized entry or entry into portions of the computer for which the user is not authorized If the PIN entered by the user does not match the one stored with the card identification nu
15. address of the security system circuit board The alarm enable signal is gen erated by ANDing line AI in gate 807 via line 801 with the alarm control signal via line 803 When both of these signals are high the output of gate 807 will be high causing transistor 809 to conduct thus placing a 0 20 25 30 35 40 45 55 65 14 logic 0 on line 811 and setting flip flop 813 The Q output of flip flop 813 on line 833 goes high thus provid ing the alarm enable signal The disarm signal is gen erated by two input AND gate 815 having the alarm control signal coupled to one input by line 803 and line A2 coupled to the other by line 805 When both the a larm control signal and the signal on line A2 are high the output of gate 815 will be high causing transistor 817 to conduct placing a logic 0 on line 819 and reset ting flip flop 813 The alarm enable signal on line 833 will become a logic 0 and the alarm will become dis abled In the armed state the alarm will be triggered when any of the normally open alarm switches 823 are closed either by tilting the computer system or by attempting to loosen the screws which enable access to the interior of the computer hardware These switches 823 connect one of the inputs of gate 827 to ground via line 825 This causes its output to go low The low signal on line 829 provides a set to flip flop 831 which causes the Q output of the flip flop 831 to go h
16. by the simultaneously holding down of the control alternate and delete keys on many computer systems as is well known to those skilled in the art The chart enters the operating system Level 1 via path 201 to a start initiation routine block 202 The computer system is hard wired to transfer program execution to the BOOTSTRAP code contained in the computer system boot ROM The specific routines utilized in this process are described in the above referenced technical reference manual under the heading of BIOS which stands for Basic Input and Output System The initial ization routines check the working part of the computer to be sure that it is completely functional before turning control over to the operator During this process the control sequence passes via path 203 to block 204 in which the operating system scans for a user ROM Such ROMs may be installed the computer system in area having a hexadecimal address range of from C8000 through F4000 If a ROM is installed in this address range and contains the characters AASS in the first two bytes of the ROM the operating system will transfer control of the computer system to the program con tained in the user ROM the present invention the user ROM is installed on the security system circuit board which is plugged into one of the expansion slots in the computer systern Con trol of the computer system proceeds via path 205 to 4 951 249 5 block 206 which contains ins
17. d DOS function call routines a routine for blocking access to said operating system unless said valid user is pre authorized for said operating system 13 The method of claim 8 wherein said computer system further comprises a non keyboard entry device and wherein said step f comprises requiring all opera tors to identify themselves via said non keyboard de vice 14 The method according to claim 13 wherein said non keyboard data entry device reads a magnetically encoded card in step f 15 A security device for a computer system having a keyboard entry device comprising a means for transferring control of said computer system to a security system interposed between an operating system and all peripheral devices and application programs and data stored in said com puter system b means under control of said security system for changing the computer system s keyboard address to an address in the security system 4 951 249 17 c means at said address in said security system for blocking any keyboard input to the computer sys tem which would place the operation of the com puter system outside the control of said security system d identifying means for identifying all operators of said computer system e means for validating the operator s identification f means responsive to validation by said validation means for restoring the address for said keyboard to said computer system s keyboard address g mea
18. en passes to block 709 in which a timeout counter is started Control passes to block 711 in which the data at BS FF1 is read and bit 1 is checked for a logic 1 which means that the clock signal is high If the clock signal is not high bit 1 is not a logic 1 control passes to block 713 in which the timeout timer is checked If the prede termined period of time has not elapsed control passes back to block 711 and the process is repeated If the predetermine period of time has elapsed control passes to block 723 If the clock is high bit 1 equals a logic 1 control passes to block 715 and bit 2 the data bit is stored Control then passes to block 717 in which the timeout counter is restarted after which control is passed to block 719 In block 719 the data at BS FF1 is read and bit 1 is checked for logic 0 which means the clock is low If bit 1 is equal to a logic 0 control passes back to block 709 and this portion of the process is repeated If bit 1 is not a logic 0 control passes to block 721 which checks the timeout counter If the amount of time allowed for this operation has not occurred con trol will pass via the not timeout branch back to block 719 and the process will be repeated If the amount of time has elapsed control will pass to block 723 In block 723 the program searches for the data bit stream stored in the random access memory for the start sentinal bit which contains the bit pattern 01011 If that bit pattern is
19. er detail These circuits are utilized to decode the address lines and develop the chip select signals for the ROM and RAM the card reader and the alarm devices and to buffer the data lines inter 65 facing the security system circuit board with the com puter data bus Before describing the circuit shown in FIG 5 it will be helpful to describe the use of the ad The inverted board select signal at the output of in verter 505 is applied via line 506 to one input of two input AND gate 509 The other input to gate 509 503 The output on line 531 will be high whenever the active low board select is low and line A11 is high As dis cussed above line A11 will be high with addresses starting at hexadecimal 800 The signal on line 531 is applied to one input of two input NAND gate 533 The seven lines 10 through A4 of internal data bus 503 are applied to seven of the eight inputs of eight input NAND gate 515 The other input is tied to the positive logic level of plus 5 volts via line 513 As long as all of 4 951 249 11 these lines A10 through A4 are not simultaneously high the output of gate 515 on line 539 will be high This output is applied to the other input of two input NAND gate 533 In this way the signal on line 539 will be high as long as the address on lines A10 through A4 do not reach hexadecimal FF This will therefore produce an active low signal on line 535 to select the RAM when the addresses on lines A10 through A4 a
20. er et al 364 900 4 685 055 8 1987 Thomas 340 825 31 X 4 713 753 12 1987 Boebert et al 364 200 4 757 533 7 1988 Allen et al 380 23 X Primary Examiner David L Clark Attorney Agent or Firm Schechter Brucker amp Pavane 57 ABSTRACT A computer security system protects the computer software from unauthorized access and the computer hardware from unauthorized intrusion At the start up of the computer system the computer s keyboard and diskette drive are disabled The user is required to iden tify himself through the use of a non keyboard device such as a magnetic card reader As a means of further validation the user enters a PIN via the keyboard which has now been restored to function A valid user will be allowed access to those programs for which he has been preauthorized Attempts to gain access to the operating system or to programs for which the user is not authorized will be filtered by the security system to prevent unauthorized access to certain programs or to preclude efforts to thwart the security system An alarm circuit provides security to the computer hardware 27 Claims 8 Drawing Sheets REQUIRE INSERT OF PREVIOUSLY AUTHORIZED IDENTIFICATION CARO ANO PIN VALID 229 Aug 21 1990 Sheet 1 of 8 4 051 249 U S Patent 9 3 11231 wav T 201 I sng E viva M3LndWOO i i KINO
21. erence to FIG 8 In addition the signal on line 545 is applied to one input of two input NAND gate 547 The other input to gate 547 is line 0 of internal data buss 503 When both of these lines are high an active low signal will appear on line 551 and act as the chip select to enable the card reader and alarm status signal buffer 553 The signals on lines 555 through 561 will be de scribed in more detail below in connection with FIGS 6 and 8 data read from and written to the circuit board are buffered from the computer data bus 567 by an octal data tranceiver 581 having three state outputs The outputs of the tranceiver 581 are placed on the com puter data bus whenever the board select signal is active low via a CS signal on line 502 The direction of the tranceiver signals is controlled by the computer MEMR signal on line 569 which is low for a memory read cycle and high otherwise The inputs to the tranceiver are from the data lines of the ROM integrated circuit 527 the data lines from the RAM integrated circuit 529 the card reader via lines 555 557 and 559 and the alarm status signal via line 561 Lines 555 through 561 are buffered by buffer 553 The ROM and RAM integrated circuits have three state outputs and can therefore be bussed in common to the board side of the data tranceiver The direction of the RAM data lines is controlled by the MEMW line 571 and is low for a memory write cycle and high other wise This line is bu
22. ess buffers 105 and board address decoder 103 Buffer 105 buffers the lower order address bits so that the security system circuit board only presents one TTL load to the computer bus drivers The board address decoder 103 decodes address bits A19 A12 to generate a board select signal and a CS signal on bus 107 A board select signal is coupled via bus 107 to chip address de coder 111 and the CS signal is coupled via bus 107 to the address buffer 105 The output of address buffer 105 on bus 109 is buffered bits A11 A0 which are coupled via bus 109 to the chip address decoder 111 to a read only memory ROM 115 a random access memory RAM 117 and to alarm circuit 119 Chip address decoder 111 10 20 25 30 35 40 45 55 60 65 4 produces CS signals on lines 113 One CS signal which is coupled to the ROM another is coupled to the RAM a third coupled to the alarm circuits Data bus 121 con nects the output of interface circuit 123 the output of ROM 115 the output of alarm circuit 119 and the input output of data buffer 125 to the input output of RAM 117 The signals on bus 121 are buffered by data buffer 125 and appear on computer data bus 127 or the signals on computer bus 127 may be buffered by buffer 125 and appear on bus 121 As is well known to those skilled in the art computer systems operate under the control of an operating sys tem The most common operating system for per sonal computers is the disk
23. exas Instruments 74154 which generates sixteen outputs each which is low for one and only one of the sixteen different bit patterns applied to its four inputs These inputs are address lines A17 4 951 249 9 through A14 Table 2 indicates the bit values for the possible combinations of address lines A14 through A17 on bus 409 which is decoded by decoder 425 One of the Sixteen outputs of the decoder are chosen to limit the board s response to that particular address simply by placing a jumper 454 between that output 453 and the input 455 to inverter 457 Inverter 457 inverts the active low signal at the output of decoder 425 selected by the placement of jumper 455 to generate an active high signal on line 459 TABLE 2 GENERAL BOARD ADDRESS OPTIONS Al9 Al8 AI Al6 AIS 14 A13 12 c8 1 1 0 0 0 0 0 CA Not Used 1 1 0 1 0 0 0 0 D4 1 1 0 0 1 0 0 D 1 0 1 0 0 0 DA Not Used EO 1 1 1 0 0 0 0 0 4 1 1 0 0 1 0 0 E8 1 1 1 0 1 0 0 0 EA Not Used FO 1 1 1 1 0 0 0 0 F4 1 l 1 0 1 0 0 10 10 dress range of the security system circuit board The board address range spans a total of 4K bytes The lower 2K bytes is devoted to the ROM integrated cir cuit 527 All but the last 16 bytes of the top 2K bytes is devoted to the RAM integrated circuit 529 The last 16 bytes of the top 2K bytes is used to address the card reader data and to control the alarm arm and disarm circuits The bit patterns which divide the address range
24. ffered by two inverters 553 and 557 in series to avoid more then a single TTL load on the computer line driver The card reader and alarm status signals are not three state and must therefore be buff ered before placing them on the internal data bus 503 20 25 30 35 40 45 50 60 65 12 This is accomplished by utilizing one half of an octal three state buffer 553 Referring now to FIG 6 the interface circuits for two commercially available magnetic card readers are shown FIG 6A shows the interface circuit for a reader made by American Magnetics Corporation and FIG 6B shows the interface for a card reader made by Ver tex Corporation Both readers conform to American National Standard X4 16 1976 which is incorporated herein by reference The purpose of the interface circuit is to convert the output of the commercially available magnetic card readers to a common format for the computer security system software Both of the com mercially available units illustrated in FIG 6 provide data true output signals on the rising edge of a clock pulse derived from the flux transitions inbedded in the magnetic stripe on the card The system software looks for the positive clock pulses data bit 0 at address 0 1 The clock pulses from the card reader circuit last only a few microseconds so they must be stretched to approximately 500 microseconds in order to ensure that the software will detect them The software w
25. i cal removal of the computer hardware difficult A still further object of the present invention com prises a method for securing a computer system having a keyboard and a non keyboard data entry device Con trol of the computer system is transferred to a security program The operability of the keyboard is disabled All requests which would place the operation of the computer outside of the security program are filtered operators are required to identify themselves via non keyboard device The operators identification is validated and operability of the keyboard is restored Valid users are allowed access only to programs for which they have been preauthorized Yet another object of the invention comprises a secu rity device where a computer system having a keyboard and a non keyboard data entry device Means transfers control of the computer system to a security program Means disables operability of the keyboard Means fil ters all requests which would place the operation of the computer outside of the control of the computer pro gram Means identifies all operators via a non keyboard device Means validates the operators identification and means restores the operability of the keyboard Means allows a valid user access only to programs for which the user has been preauthorized A still further object comprises an alarm for a com puter system enclosed in a housing Tilt detection means detects a tilting of the computer system
26. igh thus providing an alarm on signal on line 841 This signal is ANDed with the enable signal on line 833 by gate 843 If both signals are high a high signal appears on line 845 which causes transistor 847 to conduct thus providing power to oscillator 851 via line 849 Oscillator 851 drives a speaker or buzzer 853 to provide an audible warning Flip flop 831 is reset by the signal on line 811 The alarm status signal on line 839 is provided by buffer amplifier 837 and resistor 835 which is coupled to line 833 This signal is provided to line 561 in FIG 5 The alarm system is powered by a nine volt battery so that the alarm enable and trigger states are not changed by turning the computer on or off In addition this separate source of power provides an audible alert sig nal even when the computer is in the off state While a particular embodiment of the present inven tion has been disclosed herein certain changes and modifications will readily occur for those skilled in the art For example a voice imprinter electronic thumb print scanner or optical bar code scanner can be substi tuted for the magnetic card reader used the non key board entry device which identifies the user All such changes and modifications can be made without depart ing from the invention as defined by the appended claims We claim 1 A security device for a computer system having a keyboard entry device and a floppy disc drive compris i
27. ill be described below in greater detail in connection with FIG 7 FIG 6A shows the interface hardware for an Ameri can Magnetics Corporation magnetic card reader The clock pulses provided on line 603 are applied to the trigger input of a monostable multivibrator 609 The output on line 611 is applied to the clock line out put which goes to the data buffer This line corresponds to line 555 in FIG 5 The data level signal on line 605 is applied to one input of two input AND gate 613 The other input of this gate is tied to line 611 The output of this gate is the data line 615 which is applied to the data buffer This line corresponds to line 557 in FIG 5 The card seat switch is connected via line 607 to the card in status line which is applied to the data buffer This line corresponds to line 559 in FIG 5 The monostable multivibrator 609 stretches the clock pulses in a manner well known to those skilled in the art The circuit of FIG 6B is very similar to the circuit of FIG 6A except that the data true signal from the Ver tex card reader lasts only a few microseconds and there fore must also be stretched A second monostable multi vibrator 633 is triggered by the clock pulses on line 623 The data pulses on line 625 are applied to the clear input to the monostable multivibrator which only al lows the circuit to change states to a high signal at the output when the signal on line 625 is high The ou
28. imulate execution of these routines but do not actually perform them Once this has been accomplished the operation of the computer system procedes via path 207 back to block 204 returning control to the operating system Control passes viz line 209 to block 210 which contin ues with the initiation routines for the operating system One of these routines checks the operational status of the diskette drive and attempts to read additional boot code from any diskette in the drive However the ad dresss stored in the interrupt table Table 1 captures the interrupt routine 13 for the diskette drive and trans fers it to a routine in the security system ROM via line 211 The program in the ROM at that address will indi cate to the operating system that the diskette is not operative and will then return control via line 213 to the operating system at block 210 Control passes via line 215 to block 216 in which the operating system contin ues the initialization process utilizing the boot code stored on the hard disk of the system TABLE 1 SOFTWARE INTERRUPT LISTING INT ADDRESS IN RAM FUNCTION PERFORMED 0 0 3 Divide by zero 1 4 7 Single step 2 8 B Nonmaskable 3 C F Breakpoint 4 10 13 Overflow 5 14 17 Print Screen 6 18 1B Reserved 7 1D 1F Reserved 8 20 23 Time of Day 9 24 27 Keyboard A 28 2B Reserved B 2C 2F Communications 30 33 Communications D 34 37 Disk E 38 3B Diskette F 3C 3F Printer 10 40 43 Video 11
29. ing at said security system address for said DOS function call routines a routine for blocking access to said operating system unless said valid user is pre authorized for said operating system 26 The method of claim 21 wherein said computer system further comprises a non keyboard entry device wherein said step d comprises requiring all operators to identify themselves via said non keyboard device 27 The method according to claim 26 wherein said non keyboard data entry device reads a magnetically encoded card in step d
30. mber in the file of authorized users control will pass via line 229 and line 231 back to block 230 If after two more tries the user does not enter the correct PIN control will pass via 229 and line 233 to passes via line 235 back to block 224 which restarts the SMP If the PIN is correct control will pass via line 227 and line 239 to block 240 In block 240 the SMP will display a list of programs and functions preauthorized by the manager of the security system for this particular user and allow the user to select one of these functions to be executed by the system If the user selects one of these programs of functions control passes via line 241 to block 242 in which the name of the program is stored by the SMP in the data area of the PLP using the desti nation address received by the SMP when it was initi ated At this time the SMP will also store in this area a code indicating to the PLP whether or not the user has been authorized to initiate DOS tasks and or second level programs In normal exit from the SMP will cause control to pass along lines 243 and 245 to point B in FIG 3 This causes the operating system to return control to the instruction in the PLP which immediately follows the one which initiated executed of the SMP Any abnor mal exit from the SMP will be directed to PLP routine for interrupt 24 at block 236 which will cause control to pass via lines 237 and 235 to block 234 and cause the SMP to be reinitiated Refer
31. ng a means for transferring control of said computer system to a security system interposed between an operating system and all peripheral devices and application programs and data stored in said com puter system b means under control of said security system for changing the computer system s keyboard address to an address in the security system c means under control of said security system for changing the computer systern s floppy disc drive address to an address in the security system d means at said address in said security system for said floppy disc drive for blocking any input to the computer system from said floppy disc drive which would place the operation of the computer system outside the control of said security system e means at said address in said security system for blocking any keyboard input to the computer sys 4 951 249 15 tem which would place the operation of the com puter system outside the control of said security system f identifying means for identifying all operators of said computer system g means for validating the operator s identification h means responsive to validation by said validation means for restoring the address for said keyboard to said computer system s keyboard address 1 means responsive to validation by said validation means for restoring the address for said floppy disc drive to said computer system s floppy disc drive address and j means for allowing
32. not found control passes to block 729 and an error message is displayed and the program passes to its exit at block 731 If the start sentinal is found control passes to block 725 and the next five bits are converted into ASCII code using a binary coded decimal four bit character configuration shown in Table 1 of the above referenced American National Standard The program continues in this loop until the end of the bit stream is reached at which time the program exits at block 731 The resulting ASCII stream is used as a key to the authorization file stored on the disk to determine if the person placing the card through the reader is an autho rized user of the system Referring to FIG 8 the alarm circuit for the com puter security system is generally shown as 800 This circuit utilizes CMOS integrated circuits to provide a low quiessent current drain because the entire alarm circuit is powered by a nine volt DC battery The audio alarm 853 is a commercially available buzzer driven by oscillator 851 which is powered by the same nine volt battery The alarm is activated by switching transistor 847 which is controlled by AND gate 843 which has a nine volt output whenever the alarm enable signal 833 and the alarm on signal 841 are both in the logic 1 state The alarm system is armed by software instructions in the menu program which addresses location BS 0FFF2 and disarmed by addressing location BS OFF4 where BS represents the general
33. ns for allowing said validated operator access to only one or more of said programs and data and operating system for which said validated operator has been pre authorized h means under control of said security system for changing the computer system s address for the critical error routine to an address in the security system and i means at said address in said security system for said critical errors for blocking access to the oper ating system 16 The security device according to claim 15 wherein said system includes a display and wherein said means for allowing includes means for displaying on said display a menu of programs and functions which the user is authorized to use 17 The security device according to claim 15 wherein said means for transferring includes a read only memory ROM read by said operating system and which contains instructions transferring control of the computer system to the security program 18 The security device according to claim 17 further comprising means under control of said security system for changing the computer system s address for DOS function call routines to an address in the security system and means at said address in said security system for said DOS function call routines for blocking execution of DOS commands unless said validated operator is pre authorized for said operating system 19 The security device of claim 15 further compris ing a non keyboard data entry device
34. ns has risen dramatically Many firms have thousands of these computers throughout their organization In contrast with the high security traditionally afforded computer equipment and data in the past personal computers are not generally located in high security areas or operated by a relatively small number of highly trained and highly trusted personnel Personal computers are often left on desks where any one a operating system boot diskette can access any of the data stored within the computer with the potential for theft of proprietary information and or the tamper ing with it In addition the location of such computers in unsecured areas and its relatively small physical size leads to theft of the equipment itself This theft may either be of the entire computer or of valuable parts which are easily concealed so that they may taken past the security guard Present security measures have been little more than superficial Passwords and user identification numbers that are entered via the keyboard are vulnerable to hackers and employee laxity in maintaining password secrecy Because the input is via the keyboard any person can attempt to guess a user s password by trying different character sequences at random In addition users in groups sharing machines often find it conve nient to tell others their password in order to facilitate the second individual s access to some function which was intended by management to be available
35. only to the first individual The access control programs in general use to not restrict authorized users from gaining access to the Operating system from which they can thwart the in tended security controls The signon and menu pro grams which require the entry of the password before proceeding to load the user s program selection must be initiated by the user or by the automatic computer start up procedure In the former case the user has access to all of the operating system functions prior to initiating the program requiring the input of the pass word In the latter case the signon menu program can be exited to gain access to the operating system by causing an abnormal program exit such as depressing the control break keys on many computer systems Once access to the operating system is obtained the user can run his programs without the security program in place or possibly change the security program Many of the user programs which authorized users of the system may legitimately execute are designed with out regard to the control over access to the operating system and provide exits to the operating system them selves This too can provide the user access to the 0 20 25 45 55 60 65 2 operating system and thus the ability to bypass the secu rity program It is also possible for a user to insert a diskette into the disk drive found in most computer systems which will enable him to gain access to
36. operating system DOS In order to avoid the problems of the prior art it is neces sary for the security system to act as an intermediary between the user s application program and the com puter operating system FIGS 2 and 3 contain a flow diagram of the operation of the computer security sys tem These figures are divided into five levels Level 1 shows the functions performed by the operating system such as DOS For clarity details of functions performed for programs at other levels are omitted except where they are critical for the understanding of the operating fundamentals of the present invention Level 2 shows the functions performed by the security system during the initial start up procedure by instructions stored in a ROM the security system circuit board Level 3 shows the security system program loader program PLP which loads a signon menu program SMP and all user applications which detects all unauthorized attempts of a user to return to the operating system level Level 4 shows the SMP which authenticates users and presents them with a list of program options and operating system functions which they have been au thorized to execute and passes authorized requests back to the PLP in order to initiate execution Level 5 shows the execution of user programs and the treatment of exits from those programs FIG 2 shows the start of the flow diagram at the turning on of the computer or the performance of a soft start
37. prising a non keyboard data entry device and wherein said means for identifying all operators of said computer system comprises means for identifying all operators of said computer system via said non keyboard device 7 The security device according to claim 6 wherein said non keyboard data entry device is a magnetic card reader 8 A method f r securing a computer system having a keyboard entry device and a floppy disc drive compris ing the steps of a transferring control of said computer system to a security system interposed between an operating system and all peripheral devices and application programs and data stored in said computer system said security system performing the following Steps b changing the computer system s keyboard address to an address in the security system c providing at said security system address a routine for blocking any keyboard input which would 30 45 55 60 65 16 place the operation of the computer outside the control of said security system d changing the computer systems address for said floppy disc drive to an address in the security sys tem e providing at said security system address for said floppy disc drive a routine for blocking any input from said floppy disc drive which would place the computer outside the control of said security sys tem and f requiring all operators to identify themselves g validating the operator s identification h in re
38. re in the range of hexadecimal 800 through FEO Referring again to Table 3 it can be seen that the alarm set reset and card read functions require that all lines in the range A11 through A4 be high simulta neously This condition is detected by inverting the output of eight input NAND gate 515 via inverter 541 having an input connected to line 539 The output of inverter 541 is coupled via line 540 to one input of two input AND gate 543 The other input to gate 543 is the output of gate 509 on line 531 coupled to gate 543 by line 537 The signal on line 531 is high when both board select signal is active and line A11 is high The signal on line 540 will be high when all of the lines A10 through A4 are high These two signals are combined by AND gate 543 to yield a high signal on line 545 whenever both signals at the input of gate 543 are high In view of the fact that the address lines from the computer are in a undefined state during the power on operation it is possible for them to inadvertently disarm the alarm circuits In order to avoid this possibility the signal on line 545 is ANDed with the inverted MEMW signal on line 571 This requires that the MEMW line be low indicating writing to the address in addition to having a high signal on line 545 to produce the alarm control signal at the output of gate 549 This signal is used to gate the arm and disarm alarm signals into the alarm circuits as will be described hereinbelow with ref
39. ring now to FIG 3 the flow diagram 200 for the security system program is continued Line 226 enters FIG 3 at point B and continues to block 244 At block 244 the PLP initiates the execution of the pro gram requested by the user by jumping to the interrupt 21 routine in the BIOS with the AX register set to hexa decimal 4 and with the pointers to the program name in a stated area set up by the SMP Control passes via line 247 to the start input 249 to block 250 in which the program is executed The user program will execute normally as if the security system were not present Any exit from the user program will pass control via exit line 251 and hence via line 253 to block 254 In block 254 the statement in the PLP that immediately follows the statement initiating the user program analyzes the exit 5 20 25 30 35 40 45 50 55 60 65 8 vector set by the user program If the exit is the result of a fatal error or the user depressing the control break keys control passes via line 258 to point A in FIG 2 at which the PLP reinitiates the SMP If the exit is a nor mal request control passes via line 257 to block 260 where a check is made to see if there is an attempt to initiate a DOS function or a second program The PLP will check the authority indicator by the SMP at block 242 FIG 2 If the user is authorized the PLP will pass control to the operating system via line 265 to block 266 In block
40. sponse to validation restoring the address for said keyboard to said computer system s keyboard address i in response to validation restoring the address for said floppy disc drive to said computer system s address for said floppy disc drive and j allowing a valid user access only to one or more of said programs and data and operating system for which the user has been pre authorized 9 The method according to claim 8 wherein said system includes a display and wherein said step j includes displaying on said display a menu of programs and functions for which the user is pre authorized 10 The method according to claim 9 further com prising the following steps prior to step a initiating operation of said computer system via the operating system s startup routine and reading a read only memory containing in structions for the operating system to transfer con trol to said security system 11 The method according to claim 10 and further comprising changing the computer system s address for the criti cal error routine to an address in the security sys tem and providing at said security system address for said critical errors a routine for blocking access to said operating system 12 The method according to claim 10 and further comprising changing the computer system s address for DOS function call routines to an address in the security system and providing at said security system address for sai
41. the operating system and bypass the security functions Physical security of the computer system is often provided by wire cable padlocked to the computer and the desk it sits on However this presents little deterrent to a professional thief who can easily cut the cables or pick the locks In addition if a master key is used for all of the locks to make it easy for authorized personnel to move or repair the equipment lax handling of this mas ter key can render the use of padlocks and cables worth less The computer system itself does not have any means to alert security personnel that a theft is in progress thus allowing the thief to procede without interruption Furthermore the cables and locks make it cumbersome for authorized users to move or repair the equipment or make changes in the installed hardware options SUMMARY OF THE INVENTION It is the general object of the present invention to provide a computer security system that protects both the computer hardware and the computer software Another object of the invention is to restrict autho rized users to a subset of data files and or programs and computer system functions for which they have been preauthorized A further object of the present invention is to allow certain authorized users complete access to all data and all capabilities of the system and to allow them to deter mine the access for other users of the system Yet another object of the invention is to make phys
42. the security system can not be applied to other computer systems The detailed operation of the inter nal parts of these computer systems is described in the IBM PC Technical Manual and in the IBM PC Macro Assembler Language Manual and the Intel IAPX 86 88 User s Manual which are well known to those skilled in the art and which are incorporated herein by reference Referring to FIG 1 an overall block diagram of the computer security system in accordance with the pres ent invention is generally shown as 100 The system comprises a printed circuit board 102 which fits into one of the expansion slots in the computer system and a magnetic card reader 129 which is coupled to the printed circuit board via bus 130 The printed circuit board comprises four blocks of circuitry Block 123 is the interface circuit between the magnetic card reader and the security system which is described in detail in connection with FIG 6 Block 131 contains a circuit necessary for generating the board select BS signal and for buffering the lower address lines A11 A0 which is described in detail in connection with FIG 4 Block 133 contains the circuits necessary for the chip level address decoding circuits and the interface with the computer data bus and is described in greater detail in connection with FIG 5 Block 119 is an alarm circuit which is described in greater detail in connection with FIG 8 In FIG 1 the computer address bus 101 is coupled to addr
43. tput of the first monostable multivibrator 629 is trig gered by the clock pulses on line 623 to provide the stretched clock pulses on line 631 The stretched data pulses are provided on line 635 and the card in status signal is provided on line 627 These lines correspond to lines 555 557 and 559 respectively of FIG 5 The card reader shown in both FIGS 6A and 6B provide a signal indicating that the card has been in serted and a transition in that signal indicates that a withdrawal of the card has begun This indicates that the clock and data signals will represent valid informa tion from the card This card in signal is provided on line 607 in FIG 6A and line 627 in FIG 6B and cor reponds to line 559 in FIG 5 FIG 7 shows a flow diagram for the program used by the computer to process the bit stream from the card reader At block 701 the computer displays the prompt for the user to insert his card Control passes to block 703 where the data at location BS FF1 is read and bit 3 4 951 249 13 is checked for a logic 1 which means that the card has been inserted If bit 3 does not equal a logic 1 the cycle is repeated until it does equal a logic 1 If bit 3 does equal a logic 1 control passes to block 705 where the computer displays a prompt for the user to remove his card Control then passes to block 707 where the data at BS FF1 is read and bit 3 is checked for a logic 0 which means that the card is being removed Control th
44. tructions which will pre vent operator input via the keyboard until the security system is in place between the user and the operating system and which will prevent booting the system from a diskette The instructions in the ROM saves the ad dresses of the operating system keyboard and diskette service routines in the RAM which is on the security system circuit board The above referenced technical manual and the IBM PC Macro Assembler Language Manual contain a detailed description of the way in which service request routines are handled by an opera tion system Basically the addresses of all service rou tines are stored in a table in the RAM of the computer This table is shown in Table 1 The first column of Table 1 shows the interrupt number in hexadecimal notation of the interrupt routine The second column indicates the address in the computer RAM of the rou tine which performs the function which is listed in the third column The interrupt routines of interest for the present invention are the diskette disk routine at hexa decimal 13 and the keyboard service requests at hexa decimal 9 and 16 The program stored in the ROM changes the addresses shown in column 2 of Table 1 for that routine In this manner the computer security sys tem can capture these service requests and provide special treatment for them The program in the ROM replaces the address of these 3 routines with addresses of routines contained in the ROM itself which s
45. wo devices Control then passes via line 221 to block 222 In block 222 the PLP saves and replaces the addresses for the critical error routines interrupt 24 and the DOS function call routine interrupt 21 and substitutes addresses routing the calls to routines in the PLP itself Thus these two routines from Table 1 have been captured and other routines are substituted therefore Control passes via line 223 to block 224 in which the PLP intiates execution of the SMP by returning control to the operating system with pointers equal to the PLP data area to be used by the SMP to transfer the name of the programs to be loaded by the PLP as the result of user input to the SMP As described in the description of interrupt 4B in the above referenced technical man ual the pointers for this function are loaded into regis ters ES BX The execution of the SMP via the interrupt 21 4B instruction to the operating system will cause the operating system to return control to the subsequent statements in the PLP when the SMP program termi nates This is indicated by the dotted line 226 in FIG 2 which goes to point B in FIG 3 The SMP saves the address of the PLP data area received in its program prefix segment This is the result of the interrupt 21 4B call by the PLP as described in the above referenced technical manual in the descrip tion of the DOS control blocks and work areas Control passes via line 225 to block 230 in which the SMP dis plays
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