International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: On the (In)security of the Fiat-Shamir Paradigm

Shafi Goldwasser
Yael Tauman Kalai
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Abstract: In 1986, Fiat and Shamir suggested a general method for transforming secure 3-round public-coin identification schemes into digital signature schemes. The significant contribution of this method is a means for designing efficient digital signatures, while hopefully achieving security against chosen message attacks. All other known constructions which achieve such security are substantially more inefficient and complicated in design. In 1996, Pointcheval and Stern proved that the signature schemes obtained by the Fiat-Shamir transformation are secure in the so called `Random Oracle Model'. The question is: does the proof of the security of the Fiat-Shamir transformation in the Random Oracle Model, imply that the transformation yields secure signature schemes in the ``real-world"? In this paper we answer this question negatively. We show that there exist secure 3-round public-coin identification schemes for which the Fiat-Shamir methodology produces {\bf insecure} digital signature schemes for {\bf any} implementation of the `Random Oracle Model' in the `real-world' by a function ensemble.
  title={On the (In)security of the Fiat-Shamir Paradigm},
  booktitle={IACR Eprint archive},
  keywords={foundations / Fiat-Shamir},
  note={ 12451 received 18 Feb 2003, last revised 2 Feb 2004},
  author={Shafi Goldwasser and Yael Tauman Kalai},