Weimar-DM: a highly secure double-length compression function

  • Authors:
  • Ewan Fleischmann;Christian Forler;Stefan Lucks;Jakob Wenzel

  • Affiliations:
  • Bauhaus-Universität Weimar, Germany;Bauhaus-Universität Weimar, Germany;Bauhaus-Universität Weimar, Germany;Bauhaus-Universität Weimar, Germany

  • Venue:
  • ACISP'12 Proceedings of the 17th Australasian conference on Information Security and Privacy
  • Year:
  • 2012

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Abstract

We present Weimar-DM, a double length compression function using two calls to a block cipher with 2n-bit key and n-bit block size to compress a 3n-bit string to a 2n-bit one. For Weimar-DM, we show that for n=128, no adversary asking less than 2n−1.77=2126.23 queries can find a collision with probability greater than 1/2. This is the highest collision security bound ever shown for such a compression function. Even more important, our security analysis is much simpler than that for comparable functions as, e.g., Tandem-DM, Abreast-DM or Hirose-DM. We also give a preimage security analysis of Weimar-DM showing a near-optimal bound of 22n−5=2251 queries. Our security bounds are asymptotically optimal.