A General Theory for Asynchronous Speech Encryption Techniques

Speech encryption techniques have always been very important for military communications, but most useful techniques require perfect synchronization between the transmitter and the receiver. This not only complicates the implementation, but makes the transmission very sensitive to channel conditions because slight synchronization error might completely break the transmission. Two special techniques were proposed recently in which the synchronization becomes completely unnecessary. This improves the feasibility and reliability tremendously. In this paper, a general theory for such "asynchronous speech encryption techniques" is developed in detail, starting by defining the asynchronous approach and model and ending with a general solution. It will be found that the two techniques proposed earlier become two special cases of the general solution here.