International Association
for Cryptologic Research

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 can be constructed.