Reduction of the secret key length in the perfect cipher by data compression and randomisation

TL;DR

This paper proposes a method to reduce the secret key length in perfect ciphers by combining data compression and randomisation, making the key length close to Shannon entropy while maintaining perfect secrecy.

Contribution

It introduces a simple, practical method for key length reduction in perfect ciphers using existing data compressors and randomisation techniques.

Findings

Key length can be reduced close to Shannon entropy.

Method maintains perfect secrecy.

Effective with standard data compression tools.

Abstract

Perfect ciphers have been a very attractive cryptographic tool ever since C. Shannon described them. Note that, by definition, if a perfect cipher is used, no one can get any information about the encrypted message without knowing the secret key. We consider the problem of reducing the key length of perfect ciphers, because in many applications the length of the secret key is a crucial parameter. This paper describes a simple method of key length reduction. This method gives a perfect cipher and is based on the use of data compression and randomisation, and the average key length can be made close to Shannon entropy (which is the key length limit). It should be noted that the method can effectively use readily available data compressors (archivers).