BBB PRP Security of the Lai-Massey Mode

Ritam Bhaumik, Mohammad Amin Raeisi

Abstract: In spite of being a popular technique for designing block ciphers, Lai-Massey networks have received considerably less attention from a security analysis point of view than Feistel networks and Substitution-Permutation networks. In this paper we study the beyond-birthday-bound (BBB) security of Lai-Massey networks with independent random round functions against chosen-plaintext adversaries. Concretely, we show that five rounds are necessary and sufficient to achieve BBB security.