Advanced slide attacks

Abstract

Recently a powerful cryptanalytic tool—the slide attack— was introduced [3]. Slide attacks are very successful in breaking iterative ciphers with a high degree of self-similarity and even more surprisingly are independent of the number of rounds of a cipher. In this paper we extend the applicability of slide attacks to a larger class of ciphers. We find very efficient known- and chosen-text attacks on generic Feistel ciphers with a periodic key-schedule with four independent subkeys, and consequently we are able to break a DES variant proposed in [2] using just 128 chosen texts and negligible time for the analysis (for one out of every 216 keys). We also describe known-plaintext attacks on DESX and Even-Mansour schemes with the same complexity as the best previously known chosen-plaintext attacks on these ciphers. Finally, we provide new insight into the design of GOST by successfully analyzing a 20-round variant (GOST⊕) and demonstrating weak key classes for all 32 rounds.