Smashing MASH-1

MASH-1 is modular arithmetic based hash function. It is presented in Part 4 of ISO/IEC 10118 standard for one and a half decade. Cryptographic strength of MASH-1 hash function is based on factorization problem of an RSA modulus along with redundancy in the input blocks of compression functions. Despite of this, we are able to introduce two large classes of moduli which allow practical time collision finding algorithm for MASH-1. In one case even multicollisions of arbitrary length may be constructed.