Patent ID: 7251326

Claim:
In a cryptographically secured digital communication system, a method of selectively adapting a plurality of block cipher devices having at least a first block cipher device that is computationally a function of a first fixed length selectively variable key to encrypt and decrypt a digital signal for operation with a second block cipher device that is computationally a function of a second fixed length selectively variable key one half the length of the first key to encrypt and decrypt the digital signal the method comprising the steps of: (a) providing a first key generator having two equal sections of symbols, each section a functional replica of a second key generator; (b) replicating the second key in both of sections of the first key; (c) using the symbols provided by one of the two sections to encode and decode the signal in a first stage; and (d) combining the symbols provided by the two sections of the first key generator to cancel the symbols applied to a second stage.