Cryptanalysis of MICKEY family of stream ciphers

MICKEY 2.0 is a synchronous hardware-oriented stream cipher designed by Steve Babbage and Matthew Dodd in 2006. It was submitted to eSTREAM and became one of the seven eSTREAM finalists. MICKEY-128 2.0 is a variant version with 128-bit secret key. In this paper, we present a weakness in the initialization of MICKEY family of stream ciphers (i.e., MICKEY 2.0 and MICKEY-128 2.0). With this weakness, we apply a slide resynchronization attack to them, which finds for any K with k0 = d and for any IV with ivn = d, there is a (K′, IV′) pair with probability 2− 1 that generates 1-bit shifted keystream, where d ∈ {0, 1} is a constant. Furthermore, we propose related key attacks on MICKEY family of stream ciphers. Our attacks can break these two ciphers in real time on a PC when 65 and 113 related (K, IV) pairs for MICKEY 2.0 and MICKEY-128 2.0 are obtained, respectively. The success probabilities of our attacks on MICKEY 2.0 and MICKEY-1282.0 are 0.9835 and 0.9714, respectively. This is the first paper presenting a weakness in MICKEY family of stream ciphers, and the results show that MICKEY family of stream ciphers are extremely weak against related key attacks. Copyright © 2012 John Wiley & Sons, Ltd.