Constrained Pseudorandom Functions for Unconstrained Inputs Revisited: Achieving Verifiability and Key Delegation

  • Pratish DattaEmail author
  • Ratna Dutta
  • Sourav Mukhopadhyay
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 10175)


In EUROCRYPT 2016, Deshpande et al. presented a construction of constrained pseudorandom function (CPRF) supporting inputs of unconstrained polynomial length based on indistinguishability obfuscation and injective pseudorandom generators. Their construction was claimed to be selectively secure. We demonstrate in this paper that their CPRF construction can actually be proven secure not in the selective model, rather in a significantly weaker security model where the adversary is forbidden to query constrained keys adaptively. We also show how to allow adaptive constrained key queries in their construction by innovating new technical ideas. We suitably redesign the security proof. We emphasize that our modification does not involve any additional heavy duty cryptographic tool. Our improved CPRF is further enhanced to present the first constructions of constrained verifiable pseudorandom function (CVPRF) and delegatable constrained pseudorandom function (DCPRF) supporting inputs of unconstrained polynomial length, employing only standard public key encryption (PKE).


Constrained pseudorandom functions Verifiable constrained pseudorandom function Key delegation Indistinguishability obfuscation 


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Copyright information

© International Association for Cryptologic Research 2017

Authors and Affiliations

  • Pratish Datta
    • 1
    Email author
  • Ratna Dutta
    • 1
  • Sourav Mukhopadhyay
    • 1
  1. 1.Department of MathematicsIndian Institute of Technology KharagpurKharagpurIndia

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