Importance

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Abstract

Encryption and authentication techniques which can be implemented on inexpensive, e.g., 8-bit, microprocessors and micro-controllers, using very little of the microprocessor's memory, are described. While the described techniques require little system resources to implement they still provide a good degree of security. In accordance with the present invention, in order to avoid having to specifically dedicate a portion of the microprocessor's limited memory for use as a substitution box, a portion of the code stored in the microprocessor's memory, dedicated to performing another function, is selected to serve as an S-box. This memory saving technique is used to implement a block cipher. The block cipher is used in combination with a series of other data manipulation operations, including XOR operations and rotate operations, to provide a good degree of system security. The operations used to implement the techniques of the present invention are capable of being implemented using 8 bit instructions making the techniques of the present invention well suited for implementation on 8 bit systems such as those used in home and auto control applications. The message protocol and encryption scheme of the present invention involves the subtracting of current message payloads from previously received message payloads to distinguish between new messages and repeated messages which have already been acted upon. Messages are acted upon only once thereby rendering the recording and playing back of previous messages ineffective at defeating system security.

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First Claim