A New Approach in Cryptanalysis Through Combinatorial Equivalence of Cryptosystems

TL;DR

This paper introduces a novel cryptanalysis method based on combinatorial equivalence, enabling more effective key discrimination, demonstrated by superior results on secure stream ciphers like Achterbahn.

Contribution

It develops a new cryptanalysis approach using combinatorial equivalence, improving attack effectiveness on modern stream ciphers.

Findings

Outperformed all known cryptanalysis methods on tested ciphers

Successfully applied to Achterbahn cipher with better results

Introduced the Cipherbent6 concept capturing stream cipher complexity

Abstract

We propose a new approach in cryptanalysis based on an evolution of the concept of \textit{Combinatorial Equivalence}. The aim is to rewrite a cryptosystem under a combinatorially equivalent form in order to make appear new properties that are more strongly discriminating the secret key used during encryption. We successfully applied this approach to the most secure stream ciphers category nowadays. We first define a concept cipher called Cipherbent6 that capture most of the difficulty of stream cipher cryptanalysis. We significantly outperformed all known cryptanalysis. We applied this approach to the Achterbahn cipher and we obtained again far better cryptanalysis results.