Cihangir Tezcan
Department of Cyber Security, Graduate School of Informatics, Middle East Technical University, Ankara, Türkiye; Department of Computer Science and Engineering, Sabanci University, Istanbul, Türkiye

Gregor Leander
Ruhr University Bochum, Bochum, Germany

Hosein Hadipour
Ruhr University Bochum, Bochum, Germany

Keywords: cryptanalysis, GPU, ASCON, ChaCha, SERPENT

Abstract

Most modern cryptanalysis results are obtained through theoretical analysis, often relying on simplifications and idealized assumptions. In this work, we use the parallel computational power of GPUs to experimentally verify a small portion of the cryptanalysis results published in recent years, focusing on the ciphers Ascon, ChaCha, and Serpent. In none of the attacks we considered did the theoretical estimates fully match the practical values. More precisely, we show that the 4.5-round truncated differential with probability one, the 6-round differential-linear and the 6-round impossible differential distinguishers on Ascon, as well as the best known 7- and 7.5-round differential-linear distinguisher on ChaCha, do not actually work in practice. We also demonstrate that the best known 10-, 11-, and 12-round differential-linear attacks on Serpent perform better in practice than previously estimated, and we provide a new experimentally obtained 9-round differential-linear distinguisher on Serpent that can be used in 10- and 11-round attacks with reduced data complexity. More broadly, we recommend that cryptanalysts experimentally verify reduced versions of theoretically obtained results whenever possible, and we make our optimized code for the studied ciphers available to simplify that process.