A Method to Ensure the Confidentiality of the Compressed Data

Abstract

The usual way of ensuring the confidentiality of the compressed data is to encrypt it with a standard encryption algorithm such as the AES. However, the cost of encryption not only brings an additional computational complexity, but also lacks the flexibility to perform pattern matching on the compressed data, which is an active research topic in stringology. In this study, we investigate the secure compression solutions, and propose a practical method to keep contents of the compressed data hidden. The method is based on the Burrows -- Wheeler transform ({BWT}) such that a randomly selected permutation of the input symbols are used as the lexicographical ordering during the construction. The motivation is the observation that on BWT of an input data it is not possible to perform a successful search nor construct any part of it without the correct knowledge of the character ordering. %Capturing that secret ordering from the BWT is hard. The proposed method is supposed to be is an elegant alternative to the standard encryption approaches with the advantage of supporting the compressed pattern matching, while still pertaining the confidentiality. When the input data is homophonic such that the frequencies of the symbols are flat and the alphabet is sufficiently large, it is possible to unify compression and security in a single framework with the proposed technique instead of the two -- level compress -- then -- encrypt paradigm.