Collision Attack on the Full Extended MD4 and Pseudo-Preimage Attack on RIPEMD

摘要

The cryptographic hash functions Extended MD4 and RIPEMD are double-branch hash functions,which consist of two parallel branches.Extended MD4 was proposed by Rivest in 1990,and RIPEMD was devised in the framework of the RIPE project(RACE Integrity Primitives Evaluation,1988～1992).On the basis of differential analysis and meet-in-themiddle attack principle,this paper proposes a collision attack on the full Extended MD4 and a pseudo-preimage attack on the full RIPEMD respectively.The collision attack on Extended MD4 holds with a complexity of 237,and a collision instance is presented.The pseudo-preimage attack on RIPEMD holds with a complexity of 2 125.4,which optimizes the complexity order for brute-force attack.The results in this study will also be beneficial to the analysis of other double-branch hash functions such as RIPEMD-160.