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

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• 关键词：Constrained pseudorandom functions ; Verifiable constrained pseudorandom function ; Key delegation ; Indistinguishability obfuscation
• 刊名：Lecture Notes in Computer Science
• 出版年：2017
• 出版时间：2017
• 年：2017
• 卷：10175
• 期：1
• 页码：463-493
• 丛书名：Public-Key Cryptography ?PKC 2017
• ISBN：978-3-662-54388-7
• 卷排序：10175

文摘

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).