Enhancing collision attacks

Abstract

Side Channel Attacks (SCA) have received a huge interest in the last 5 years. These new methods consider non-cryptographic sources of information (like timing or power consumption) in addition to traditional techniques. Consequently block ciphers must now resist a variety of SCAs, among which figures the class of "collision attacks". This recent technique combines side channel information with tools originally developed for block cipher or hash function cryptanalysis, like differential cryptanalysis for instance. In this paper, we propose techniques to enhance collision attacks. First we describe a general framework for collision attacks against Feistel ciphers that extends and improves on previous results specifically obtained against DES. Then, we describe an improved method to attack DES using "almost collisions". Indeed we observed that taking into account internal states which are abnormally similar results in more efficient attacks. Some experimental results obtained against a DES implementation are finally presented. © International Association for Cryptologic Research 2004.