Cryptology ePrint Archive: Report 2006/399

Multi-Property-Preserving Hash Domain Extension and the EMD Transform

Mihir Bellare and Thomas Ristenpart

Abstract: We point out that the seemingly strong pseudorandom oracle preserving (PRO-Pr) property of hash function domain-extension transforms defined and implemented by Coron et. al. [12] can actually weaken our guarantees on the hash function, in particular producing a hash function that fails to be even collision-resistant (CR) even though the compression function to which the transform is applied is CR. Not only is this true in general, but we show that all the transforms presented in [12] have this weakness. We suggest that the appropriate goal of a domain extension transform for the next generation of hash functions is to be multi-property preserving, namely that one should have a single transform that is simultaneously at least collision-resistance preserving, pseudorandom function preserving and PRO-Pr. We present an efficient new transform that is proven to be multi-property preserving in this sense.

Category / Keywords: cryptographic protocols / Hash functions, random oracle, Merkle-Damgard, collision-resistance, psuedorandom function

Publication Info: Preliminary version in Asiacrypt 2006. This is the full version.

Date: received 8 Nov 2006, last revised 18 Oct 2007

Contact author: tristenp at cs ucsd edu

Available format(s): PDF | BibTeX Citation

Note: New update (October 2007) includes fix for an error in the proof of Theorem 5.2. Previously: fixed an error in the proof of Lemma 5.1 (which lead to a too-tight bound).

Version: 20071018:212138 (All versions of this report)

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