The automated cryptanalysis of analog speech scramblers

Abstract

An automated method of attacking commonly used speech scramblers is presented. The cryptanalysis relies on the availability of the scrambled speech only and makes use of the characteristics of speech. It is shown that some of the currently available time and frequency domain scramblers, based on a fixed permutation can be cryptanalysed. For systems where the permutation is changed with time, methods for partial recovery of the encrypted speech for several existing systems are given. In the case of the frequency domain scramblers a novel method of attack using a codebook is presented.