On Cipher-Dependent Related-Key Attacks in the Ideal-Cipher Model

Abstract. Bellare and Kohno introduced a formal framework for the study of related-key attacks against blockciphers. They established sufficient conditions (output-unpredictability and collision-resistance) on the set of relatedkey-deriving (RKD) functions under which an ideal cipher is secure against related-key attacks, and suggested this could be used to derive security goals for real blockciphers. However, to do so requires the reinterpretation of results proven in the ideal-cipher model for the standard model (in which a blockcipher is modelled as, say, a pseudorandom permutation family). As we show here, this is a fraught activity. In particular, building on a recent idea of Bernstein, we first demonstrate a related-key attack that applies generically to a large class of blockciphers. The attack exploits the existence of a short description of the blockcipher, and so does not apply in the ideal-cipher model. However, the specific RKD functions used in the attack are provably o...

• Type: Journal
• Year: 2011
• Where: FSE
• Authors: Martin R. Albrecht, Pooya Farshim, Kenny G. Paterson, Gaven J. Watson
• Keywords: Bellare, Cryptology, Formal Framework, FSE 2011, Rkd