## Cryptology ePrint Archive: Report 2012/594

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

Ya Liu and Dawu Gu and Zhiqiang Liu and Wei Li

Abstract: 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 $2^{121.6}$ chosen ciphertexts and $2^{189.9}$ 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 $2^{122.1}$ chosen ciphertexts and $2^{229.3}$ 14-round encryptions. Compared with the previously best known attack on 14-round Camellia-256, the time complexity of our attack is reduced by $2^{8.9}$ times and the data complexity is comparable.

Category / Keywords: Block Cipher, Camellia, Impossible Differential Cryptanalysis

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