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Abstract

A block-cipher cryptographic device that processes plaintext/encrypted input data with a key signal to provide encrypted/decrypoted output data. Such device includes a shift register for receiving input data; and data processing means for executing the following data processing routine a selected number of cycles to provide output data: processing the contents of said shift register with a key signal to provide initially processed data; initializing a pseudorandom nonlinear sequence generator with the initially processed data; running the pseudorandom nonlinear sequence generator to generate a keystream; segregating portions of the keystream; processing said segregated portions of said keystream with a portion of the data in the shift register to provide a block of processed data; and shifting said block of processed data into the shift register. To further increase the randomness of the pseudorandom keystream generator, and hence the encryption security, the processing means segretates the keystream in accordance with a routine wherein the beginning of said segregated portion is provided at a time related to the beginning of the keystream in response to a duration indication; segregates every nth bit of the keystream from said beginning of said segregated portion for a selected number of segregated bits in response to a frequency indication; and provides said initially processed data by first processing said shift register contents and said key signal and then rotating data produced by said first processing in response to a rotation indication. The duration indication, the frequency indication and the rotation indication are each separately provided for each of the cycles and may be different for each of the cycles.

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First Claim