On the Provable Security of the Tweakable Even-Mansour Cipher Against Multi-Key and Related-Key Attacks

Cogliati et al. introduced the tweakable Even-Mansour cipher constructed from a single permutation and an almost-XORuniversal (AXU) family of hash functions with tweak and key schedule. Most of previous papers considered the security of the (iterated) tweakable Even-Mansour cipher in the single-key setting. In this paper, we focus on the security of the tweakable Even-Mansour cipher in the multi-key and related-key settings. We prove that the tweakable Even-Mansour cipher with related-key-AXU hash functions is secure against multi-key and related-key attacks, and derive a tight bound using H-coefficients technique, respectively. Our work is of high practical relevance because of rekey requirements and the inevitability of related keys in real-world implementations.