Abstract: A personal authentication system provides at least two levels of security for an authentication process, in addition to numerous other security features. The system operates across many different software and hardware platforms, in a client/server fashion, employing a challenge/response process that does not require users to transmit their passwords across a network. An application running on a client computer is coupled with an application running on a server computer. The client generates a response to a challenge, which is provided by the server. The response is a combined function of the server's challenge, a serial number assigned to the client, and a password provided by the user.

Abstract: A clock signal generator within an electronic device locally generates a reference clock signal having a reference frequency from a base clock signal having a base frequency. The base clock signal is from a base signal source that is external to the electronic device, and the base frequency of the base clock signal may vary depending on the base signal source. The present invention includes a plurality of frequency dividers which are coupled to the base signal source. Each of the frequency dividers outputs a divided clock signal having a respective frequency that is the base frequency divided by a respective factor. A multiplexer accepts the value of the base frequency of the base clock signal as stored within a storage device that is external to the electronic device. The multiplexer then selects as the reference clock signal a divided clock signal having a respective frequency that is closest to the reference frequency depending on the value of the base frequency.

Abstract: The present invention provides a method of reducing the amount of memory required to scan a given data string for the presence of computer viruses or other data traits of interest including the steps of 1) loading into a memory of a computer a set of generic features that are functionally similar to standard computer virus signatures, but tend to be less specific to particular viruses, 2) locating occurrences of the generic features within the data string, 3) applying a first mapping from the occurrences located during step 2) to obtain a subset of standard signatures, 4) loading the subset of standard signatures into a memory of said computer, 5) locating occurrences within the data string of all signatures from the subset of standard signatures, and 6) applying a second mapping from the occurrences located during step 5) to identify a set of computer viruses that are likely to be present in the data string.

Abstract: An improved full subtracter is disclosed which receives a minuend signal A having a weight of +1, a subtrahend signal B having a weight of -1 and a borrow input signal Xi having a weight of -1 and provides a difference output: signal D having a weight of +1 and a borrow output signal Xo having a weight of -2. The full subtracter is composed of CMOS transistors such that both the signal D delay time and the signal Xo delay time are decreased by reducing the number of logic gate stages.