On the Insecurity of the Fiat-Shamir Signatures with Iterative Hash Functions

  • Authors:
  • Eiichiro Fujisaki;Ryo Nishimaki;Keisuke Tanaka

  • Affiliations:
  • NTT, Tokyo, Japan 180-8585;NTT, Tokyo, Japan 180-8585;Department of Mathematical and Computing Sciences, Tokyo Institute of Technology, Tokyo, Japan 152-8552

  • Venue:
  • ProvSec '09 Proceedings of the 3rd International Conference on Provable Security
  • Year:
  • 2009

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Abstract

At FOCS 2003, Goldwasser and Kalai showed the insecurity of the digital signature schemes obtained by the Fiat-Shamir transformation in the standard model. However, the proof of this negative result is complicated. This paper shows a much simpler counter example in the restricted (but realistic) case that the hash functions are designed by iterating an underlying hash function with an a-priori bounded input length, although we slightly extend the Fiat-Shamir paradigm. The result in [19] ruled out the case that the underlying identification schemes are interactive proofs, whereas this result can apply to the case.