Cryptanalysis of EnRUPT

In this paper we present a preimage attack on EnRUPT512. We exploit the fact that the internal state is only a little bit larger than the critical security level: 1152 bits against 1024 bits. The absence of a message expansion and a fairly simple compression function allow us to fix the values for some state words and thus reduce the size of birthday state space in the meet-in-the-middle attack under 1024 bits. Equations that arise through the analysis are solved using look-up tables. The complexity of the attack is around 2 compression function calls and the memory requirement is around 2.