Cryptology ePrint Archive: Report 2015/051

Improved Meet-in-the-Middle Distinguisher on Feistel Schemes

Li Lin, Wenling Wu

Abstract: Improved meet-in-the-middle cryptanalysis with efficient tabulation technique has been shown to be a very powerful form of cryptanalysis against SPN block ciphers. However, few literatures show the effectiveness of this cryptanalysis against Balanced-Feistel-Networks (BFN) and Generalized-Feistel-Networks (GFN) ciphers due to the stagger of affected trail and special truncated differential trail. In this paper, we describe a versatile and powerful algorithm for searching the best improved meet-in-the-middle distinguisher with efficient tabulation technique on word-oriented BFN and GFN block ciphers, which is based on recursion and greedy algorithm. To demonstrate the usefulness of our approach, we show key recovery attacks on 14/16-round CLEFIA-192/256 which are the best attacks. We also propose key recovery attacks on 13/15-round Camellia-192/256 (without $FL/FL^{-1}$).

Category / Keywords: Block Ciphers, Improved Meet-in-the-Middle Attack, Efficient Tabulation Technique, Automatic Search Tool, Truncated Differential Trail, CLEFIA, Camellia.

Date: received 21 Jan 2015, last revised 21 Jan 2015

Contact author: linli at tca iscas ac cn

Available format(s): PDF | BibTeX Citation

Version: 20150122:171225 (All versions of this report)

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