Importance

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Abstract

A security system for a personal computer, in which hardware and software are combined to provide a tamper-proof manner of protecting user-access and file-access. The hardware component of the system is an expansion board for insertion into an expansion slot of the PC, and has a first EPROM chip containing four portions of machine code for initializing system function calls and for establishing the proper boot-processing of the PC; a second RAM chip serving as scratch pad memory; a third EEPROM chip storing passwords, audit trail log, protection and encryption system flags, and user-access rights; a fourth automatic encryption and decryption chip for files of the PC; and a fifth clock chip for the audit trail. The software component includes a batch file that runs a program in conjunction with the machine code on the EPROM of the expansion board ensuring access is gained only for valid users. The code on the EPROM monitors all DOS 21H file handling function calls, and initializes the 7CH interrupt vector for allowing the security system to access DOS and the files thereof. During boot processing, the 10H video interrupt handler is monitored to prevent circumventing the security system. Hard-disc format-protection is also provided by monitoring of the 13H interrupt function calls. Files may also be created that may not be copied.

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First Claim