Abstract: According to the invention, the keyboard consists of a matrix of keys and variable visible indicia. Each of the variable visible indicia is associated with a key. Upon each keystroke on the keyboard, the system randomly changes the positions of all of the indicia on the matrix. Because the true value of any particular key is independent of the value displayed on the variable visible indicia, a casual observer can not learn the keystrokes being entered into the keyboard. If the code entered at the keyboard matches a stored value, the user is granted access.

Abstract: An apparatus and method having elements and steps selected and arranged to require a timed, coded input for authenticating a code of characters in a set sequence for authorizing user access and having means for emitting a signal or alarm, wherein the system is initialized so as to require matching of representative signals at inhibiting control circuits having an on-state and an off-state so that characters entered sequentially in timed cycles are authenticated as a correct member of a code set in a correct time cycle or disqualified as an unauthentic character.An authentic character is a certain designated character entered in the selected time cycle.

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.

Abstract: A frequency analyzing circuit for converting multifrequencies representing characters into selected signals for writing data into a plurality of channels adapted to effect enabling and disabling signals to a counter having an output code in binary form. Each of the channels is connected to a corresponding selected signal output of the frequency analyzing circuit from which the channel records a signal corresponding to a selected character.A plurality of gates is provided in each channel. The selected data signal read by a channel produces a logic in the gates which activate an enabling output voltage from the channel circuitry which is responsive to the enabling voltage to generate the selected character in binary code and to latch when the binary code character is generated.