Improved Impossible Differential Attack on Reduced Version of Camellia-192/256

As an ISO/IEC international standard, Camellia has been used various cryptographic applications. In this paper, we improve previous attacks on Camellia-192/256 with key-dependent layers FL/FL−1 by using the intrinsic weakness of keyed functions. Specifically, we present the first impossible differential attack on 13-round Camellia with 2121.6 chosen ciphertexts and 2189.9 13-round encryptions, while the analysis for the biggest number of rounds in previous results on Camellia-192 worked on 12 rounds. Furthermore, we successfully attack 14-round Camellia-256 with 2122.1 chosen ciphertexts and 2229.3 14-round encryptions. Compared with the previously best known attack on 14-round Camellia-256, the time complexity of our attack is reduced by 28.9 times and the data complexity is comparable.