A secure analog speech scrambler using the discrete cosine transform

Abstract

A secure technique for analog speech encryption is described which uses the Discrete Cosine Transform (DCT). The paper shows how the proposed technique overcomes weaknesses identified in other analog scramblers by using transform domain permutation and the insertion of dummy transform components. It is shown that the DCT scrambler with dummy spectrum insertion offers a similar level of security to a digital scrambler on a bandlimited channel while providing better quality of recovered speech.