International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: On the Security of Tandem-DM

Ewan Fleischmann
Michael Gorski
Stefan Lucks
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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.
  title={On the Security of Tandem-DM},
  booktitle={IACR Eprint archive},
  keywords={secret-key cryptography / hash function, blockcipher based, proof of security, double block length, ideal cipher},
  note={an extended abstract of this paper will appear at FSE 2009 proceedings, this is the full version 14279 received 3 Feb 2009, last revised 4 Feb 2009},
  author={Ewan Fleischmann and Michael Gorski and Stefan Lucks},