Importance

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Abstract

Synchronization information for synchronizing encrypting and decrypting key generators (12 and 16) in a secure communications link (10) is transmitted without exacting a bandwidth penalty. Pointer comparators (17 and 18) at the transmission and reception ends of the link monitor the cipher text transmitted between the generators to determine whether it includes a predetermined naturally occurring sequence of bits, referred to as a 'pointer' sequence. Upon the occurrence of the pointer sequence, the pointer comparators (17 and 18) trigger synchronization circuits (20 and 22) to read a sequence in the cipher text that occurs a predetermined period of time after the occurrence of the pointer. Accordingly, both synchronization circuits (20 and 22) read the same cipher-text sequence, which is a naturally occurring part of the cipher text. In response, one of the synchronization circuits (20) places the encrypting key generator (12) into a state designated by the naturally occurring sequence that that synchronization circuit (20) has read, while the other synchronization circuit (22) places the decrypting key generator (16) into the corresponding state. In this way, the encryption and decryption ends of the data link are synchronized without any bandwidth penalty.

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First Claim