Ciphers Secure against Related-Key Attacks

In a related-key attack, the adversary is allowed to transform the secret key and request encryptions of plaintexts under the transformed key. This paper studies the security of PRFand PRP-constructions against related-key attacks. For adversaries who can only transform a part of the key, we propose a construction and prove its security, assuming a conventionally secure block cipher is given. By the terms of concrete security, this is an improvement over a recent result by Bellare and Kohno [2]. Further, based on some technical observations, we present two novel constructions for related-key secure PRFs, and we prove their security under number-theoretical infeasibility assumptions.