Cryptanalysis of Full RIPEMD-128

In this article we propose a new cryptanalysis method for double-branch hash functions that we apply on the standard

RIPEMD-128

, greatly improving over know results. Namely, we were able to build a very good differential path by placing one non-linear differential part in each computation branch of the

RIPEMD-128

compression function, but not necessarily in the early steps. In order to handle the low differential probability induced by the non-linear part located in later steps, we propose a new method for using the freedom degrees, by attacking each branch separately and then merging them with free message blocks. Overall, we present the first collision attack on the full

RIPEMD-128

compression function as well as the first distinguisher on the full

RIPEMD-128

hash function. Experiments on reduced number of rounds were conducted, confirming our reasoning and complexity analysis. Our results show that 16 years old

RIPEMD-128

, one of the last unbroken primitives belonging to the

MD-SHA

family, might not be as secure as originally thought.