New Techniques for Cryptanalysis of Hash Functions and Improved Attacks on Snefru

Abstract

In 1989–1990, two new hash functions were presented, Snefru and MD4. Snefru was soon broken by the newly introduced differential cryptanalysis, while MD4 remained unbroken for several more years. As a result, newer functions based on MD4, e.g., MD5 and SHA-1, became the de-facto and international standards. Following recent techniques of differential cryptanalysis for hash function, today we know that MD4 is even weaker than Snefru. In this paper we apply recent differential cryptanalysis techniques to Snefru, and devise new techniques that improve the attacks on Snefru further, including using generic attacks with differential cryptanalysis, and using virtual messages with second preimage attacks for finding preimages. Our results reduce the memory requirements of prior attacks to a negligible memory, and present a preimage of 2-pass Snefru. Finally, some observations on the padding schemes of Snefru and MD4 are discussed.