A classification of time element speech scramblers

Abstract

This paper contrasts four methods of time element speech scrambling (t.e.s), which remains an extremely important crytographic technique for narrow band channels, not least because of its robustness in poor transmission conditions such as that experienced on h.f. One method, hopping window t.e.s., although currently widely used, is increasingly being replaced by sliding window t.e.s. systems such as the other three methods described here. The importance of synchronization is emphasied, and three of the four systems described allow continuous synchronization, an overwhelming advantage except in the case when most transmissions are very brief and missing synchronization is not such a disadvantage.