Cryptology ePrint Archive: Report 2009/054

On the Security of Tandem-DM

Ewan Fleischmann and Michael Gorski and Stefan Lucks

Abstract: We provide the first proof of security for Tandem-DM one of the oldest and most well-known constructions for turning a blockcipher with n-bit blocklength and 2n-bit keylength into a 2n-bit cryptographic hash function. We prove, that when Tandem-DM is instantiated with AES-256, i.e. blocklength 128 bits and keylength 256 bits, any adversary that asks less than 2^{120.4} queries cannot find a collision with success probability greater than 1/2. We also prove a bound for preimage resistance of Tandem-DM. Interestingly, as there is only one practical construction known (FSE'06, Hirose) turning such an (n,2n)-bit blockcipher into a 2n-bit compression function that has provably birthday-type collision resistance, Tandem-DM is one out of two structures that possess this desirable feature.

Category / Keywords: secret-key cryptography / hash function, blockcipher based, proof of security, double block length, ideal cipher

Publication Info: an extended abstract of this paper will appear at FSE 2009 proceedings, this is the full version

Date: received 3 Feb 2009, last revised 4 Feb 2009

Contact author: ewan fleischmann at uni-weimar de

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Version: 20090204:180546 (All versions of this report)

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