International Association
for Cryptologic Research

RIPEMD-128 is an ISO/IEC standard cryptographic hash function proposed

in 1996 by Dobbertin, Bosselaers and Preneel. There are two

different and independent parallel lines called $line1$ operation and

$line2$ operation, and each operation has 64 steps. The results of two

line operations are combined at the end of every application of the

compression function. In this paper, we present collision

differential characteristics for both $line1$ operation and $line2$ operation by choosing a proper message difference. By using message modification technique seriously, we improve the probabilities of the differential characteristics so that we can give a collision attack on 40-step RIPEMD-128 with a complexity of $2^{35}$ computations.