Cryptology ePrint Archive: Report 2014/699

Scrutinizing and Improving Impossible Differential Attacks: Applications to CLEFIA, Camellia, LBlock and Simon (Full Version)

Christina Boura and María Naya-Plasencia and Valentin Suder

Abstract: Impossible differential cryptanalysis has shown to be a very powerful form of cryptanalysis against block ciphers. These attacks, even if extensively used, remain not fully understood because of their high technicality. Indeed, numerous are the applications where mistakes have been discovered or where the attacks lack optimality. This paper aims in a first step at formalizing and improving this type of attacks and in a second step at applying our work to block ciphers based on the Feistel construction. In this context, we derive generic complexity analysis formulas for mounting such attacks and develop new ideas for optimizing impossible differential cryptanalysis. These ideas include for example the testing of parts of the internal state for reducing the number of involved key bits. We also develop in a more general way the concept of using multiple differential paths, an idea introduced before in a more restrained context. These advances lead to the improvement of previous attacks against well known ciphers such as CLEFIA-128 and Camellia, while also to new attacks against 23-round LBlock and all members of the Simon family.

Category / Keywords: secret-key cryptography / block ciphers, impossible differential attacks, CLEFIA, Camellia, LBlock, Simon.

Original Publication (with major differences): IACR-ASIACRYPT-2014

Date: received 4 Sep 2014, last revised 9 Sep 2014

Contact author: valentin suder at inria fr

Available format(s): PDF | BibTeX Citation

Version: 20140909:125333 (All versions of this report)

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