Multicollision Attack on a recently proposed hash function vMDC-۲

In this paper, we describe an attack on a new double block length hash function which was proposed as a variant of MDC-۲ and MDC-۴. The vMDC-۲ compression function is based on two calls to a block cipher that compresses a ۳n-bit string to a ۲n-bit one. This attack is based on the Joux's multicollision attack, where we show that an adversary wins finding collision game by requesting ۲^{۷۰} queries for n=۱۲۸-bit block cipher that is much less than the complexity of birthday attack.