CRYPTANALYSIS OF HYBRID CRYPTOSYSTEMS

Abstract

An essential issue for the validation of ciphers is cryptanalysis, that is, the study of attacks in order to reveal possible weaknesses. In this paper, we propose a systematic and unified methodology for cryptanalyzing known chaos-based cryptosystems borrowed from the open literature, namely shift keying, discrete parameter modulation, switched message-embedding, time-varying delay-based schemes. It is shown that all of them have a hybrid feature. Based on this consideration, the cryptanalysis leads to a specific parameter identification. The method is extended in straightforward way for hybrid cryptosystems defined over finite fields, involving in particular Boolean functions. The complexity of the cryptanalysis is derived regardless of the exhibited dynamics and provides a new quantitative measure for security assessment, thus allowing to show, by the way, that most of the chaos-based cryptosystems proposed so far in the literature are weak.