Cryptology ePrint Archive: Report 2008/173

Full Cryptanalysis of LPS and Morgenstern Hash Function

Christophe Petit and Kristin Lauter and Jean-Jacques Quisquater

Abstract: Collisions in the LPS cryptographic hash function of Charles, Goren and Lauter have been found by Zémor and Tillich, but it was not clear whether computing preimages was also easy for this hash function. We present a probabilistic polynomial time algorithm solving this problem. Subsequently, we study the Morgenstern hash, an interesting variant of LPS hash, and break this function as well. Our attacks build upon the ideas of Zémor and Tillich but are not straightforward extensions of it. Finally, we discuss fixes for the Morgenstern hash function and other applications of our results.

Category / Keywords: cryptographic protocols / Hash Functions, Cayley Graphs, Cryptanalysis

Date: received 15 Apr 2008

Contact author: christophe petit at uclouvain be

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Version: 20080421:093426 (All versions of this report)

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