Weak Tweak-Keys for the CRAFT Block Cipher

Authors

  • Gregor Leander Ruhr University Bochum, Bochum, Germany
  • Shahram Rasoolzadeh Radboud University, Nijmegen, The Netherlands

DOI:

https://doi.org/10.46586/tosc.v2022.i1.38-63

Keywords:

CRAFT, partial key addition, partial non-linear layer

Abstract

CRAFT is a lightweight tweakable Substitution-Permutation-Network (SPN) block cipher optimized for efficient protection of its implementations against Differential Fault Analysis (DFA) attacks. In this paper, we present an equivalent description of CRAFT up to a simple mapping on the plaintext, ciphertext and round tweakeys. We show that the new representation, for a sub-class of keys, leads to a new structure which is a Feistel network, with non-linear operation and key addition only on half the state. Consequently, it reveals a class of weak keys for which CRAFT is less resistant against differential and linear cryptanalyses. As a result, we present one weak-key single-tweak differential attack on 23 rounds (with time complexity of 294 encryptions and data complexity of 274 chosen plaintext/tweak/ciphertext tuples and works for 2112 weak keys) and one weak-key related-tweak attack on 26 rounds of the cipher (with time complexity of 2105 encryptions and data complexity 273 chosen plaintext/tweak/ciphertext tuples and works for 2108 weak keys). Note that these attacks do not break the security claim of the CRAFT block cipher.

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Published

2022-03-11

Issue

Section

Articles

How to Cite

Weak Tweak-Keys for the CRAFT Block Cipher. (2022). IACR Transactions on Symmetric Cryptology, 2022(1), 38-63. https://doi.org/10.46586/tosc.v2022.i1.38-63