Preimage attacks on 3-pass HAVAL and step-reduced MD5

Abstract

This paper presents preimage attacks on the hash functions 3-pass HAVAL and step-reduced MD5. Introduced in 1992 and 1991 respectively, these functions underwent severe collision attacks, but no preimage attack. We describe two preimage attacks on the compression function of 3-pass HAVAL. The attacks have a complexity of about 2224 compression function evaluations instead of 2256. We present several preimage attacks on the MD5 compression function that invert up to 47 steps (out of 64) within 296 trials instead of 2128. Although our attacks are not practical, they show that the security margin of 3-pass HAVAL and step-reduced MD5 with respect to preimage attacks is not as high as expected. © 2009 Springer.