Related-Key Cryptanalysis of Midori

David Gerault (1, 2) , Pascal Lafourcade (2)

1 UCA [2017-2020] - Université Clermont Auvergne [2017-2020]
2 LIMOS - Laboratoire d'Informatique, de Modélisation et d'optimisation des Systèmes

Midori64 and Midori128 [2] are lightweight block ciphers, which respectively cipher 64-bit and 128-bit blocks. While several attack models are discussed by the authors of Midori, the authors made no claims concerning the security of Midori against related-key differential attacks. In this attack model, the attacker uses related-key differential characteristics, i.e., tuples (δP , δK , δC) such that a difference (generally computed as a XOR) of δP in the plaintext coupled with a difference δK in the key yields a difference δC after r rounds with a good probability. In this paper, we propose a constraint programming model to automate the search for optimal (in terms of probability) related-key differential characteristics on Midori. Using it, we build related-key distinguishers on the full-round Midori64 and Midori128, and mount key recovery attacks on both versions of the cipher with practical time complexity, respectively 2 35.8 and 2 43.7 .

Mots clés: Midori; Related-Key Attack; Constraint Programming

Domaines: Cryptographie et sécurité [cs.CR]

David Gerault, Pascal Lafourcade. Related-Key Cryptanalysis of Midori. International Conference on Cryptology in India, Dec 2016, Kolkata, India. ⟨hal-01588566⟩