Enhancing secrecy by data compression: Theoretical and practical aspects

Abstract

It was recognised by Shannon that data compression increases the strength of secrecy systems when applied prior to encryption. Compression techniques have advanced considerably in recent years. This paper considers the extent to which these techniques can increase security. Estimates are obtained for how far practical compression schemes can increase unicity distance of symmetric ciphers. It is noted that there are other good reasons for using data compression prior to encryption. Comparison is made with homophonic coding and it is suggested that data compression is more worthwhile for practical sources such as natural language.