Cryptology ePrint Archive: Report 2014/279

Improved Impossible Differential Attacks against Round-Reduced LBlock

Christina Boura and Marine Minier and Marķa Naya-Plasencia and Valentin Suder

Abstract: Impossible differential attacks are among the most powerful forms of cryptanalysis against block ciphers. We present in this paper an in-depth complexity analysis of these attacks. We show an unified way to mount such attacks and provide generic formulas for estimating their time, data and memory complexities. LBlock is a well studied lightweight block cipher with respect to impossible differential attacks. While previous single-key cryptanalysis reached up to 22 rounds, by applying our method we are able to break 23 rounds with time complexity $2^{75.36}$ and data complexity $2^{59}$. Other time/data trade-offs are equally possible. This is to our knowledge the best (non-exhaustive search like) cryptanalysis of this function in the single-key model.

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

Date: received 22 Apr 2014, last revised 9 Sep 2014

Contact author: christina boura at prism uvsq fr

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Version: 20140909:170527 (All versions of this report)

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