Cryptanalysis of the SoDark family of cipher algorithms

Abstract

The thesis studies the security of the SoDark family of cipher algorithms through cryptanalysis. The ciphers in question are used to protect messages sent by second- and third-generation automatic link establishment (ALE) systems for high frequency radios. Radios utilizing ALE technology are in use by a multitude of government and non-government organizations worldwide. Structural attacks on up to eight rounds based on differential properties are presented and implemented in practice. An efficient logic circuit representation of the only nonlinear component of the ciphers, the S-box, is generated. That representation, converted to conjunctive normal form (CNF), is used to perform key-recovery attacks on up to four rounds with the use of Boolean satisfiability problem (SAT) solvers. The logic circuit representation is further used to develop an efficient bitslicing CUDA implementation of the cipher. Its efficiency in attacking the cipher is demonstrated. The impact of the attacks on the ALE system is considered. Finally, the thesis includes suggestions regarding a replacement cipher and ideas for further cryptanalysis.