Weak Verifiable Random Functions

  • Authors:
  • Zvika Brakerski;Shafi Goldwasser;Guy N. Rothblum;Vinod Vaikuntanathan

  • Affiliations:
  • Weizmann Institute of Science,;Weizmann Institute of Science, and CSAIL, MIT,;CSAIL, MIT,;CSAIL, MIT, and IBM Research,

  • Venue:
  • TCC '09 Proceedings of the 6th Theory of Cryptography Conference on Theory of Cryptography
  • Year:
  • 2009

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Abstract

Verifiable random functions (VRFs), introduced by Micali, Rabin and Vadhan, are pseudorandom functions in which the owner of the seed produces a public-key that constitutes a commitment to all values of the function and can then produce, for any input x , a proof that the function has been evaluated correctly on x , preserving pseudorandomness for all other inputs. No public-key (even a falsely generated one) should allow for proving more than one value per input. VRFs are both a natural and a useful primitive, and previous works have suggested a variety of constructions and applications. Still, there are many open questions in the study of VRFs, especially their relation to more widely studied cryptographic primitives and constructing them from a wide variety of cryptographic assumptions. In this work we define a natural relaxation of VRFs that we call weak verifiable random functions, where pseudorandomness is required to hold only for randomly selected inputs. We conduct a study of weak VRFs, focusing on applications, constructions, and their relationship to other cryptographic primitives. We show: Constructions. We present constructions of weak VRFs based on a variety of assumptions, including general assumptions such as (enhanced) trapdoor permutations, as well as constructions based on specific number-theoretic assumptions such as the Diffie-Hellman assumption in bilinear groups. Separations. Verifiable random functions (both weak and standard) cannot be constructed from one-way permutations in a black-box manner. This constitutes the first result separating (standard) VRFs from any cryptographic primitive. Applications. Weak VRFs capture the essence of constructing non-interactive zero-knowledge proofs for all NP languages.