A related-key attack on block ciphers with weak recurrent key schedules

Abstract

An important component of an iterated block cipher is the key schedule. In this paper, we consider iterated block ciphers with a key schedule algorithm described by a recurrence relation. We present an efficient related-key attack on those ciphers. With regard to similar techniques, such as the slide attack, our proposal considerably reduces the number of necessary plaintexts from O(2 n/4) plaintexts to 2r, where r is the number of recovered round keys. The complexity of our attack is, moreover, almost equal to the complexity of guessing just one round key. © 2012 Springer-Verlag.