Abusalah, Hamza and Fuchsbauer, Georg and Pietrzak, Krzysztof
(2016)
*Constrained PRFs for unbounded inputs.*
In: CT-RSA: Topics in Cryptology, February 29 - March 4, 2016, San Francisco, CA, USA.

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## Abstract

A constrained pseudorandom function F: K × X → Y for a family T ⊆ 2X of subsets of X is a function where for any key k ∈ K and set S ∈ T one can efficiently compute a constrained key kS which allows to evaluate F (k, ·) on all inputs x ∈ S, while even given this key, the outputs on all inputs x ∉ S look random. At Asiacrypt’13 Boneh and Waters gave a construction which supports the most general set family so far. Its keys kc are defined for sets decided by boolean circuits C and enable evaluation of the PRF on any x ∈ X where C(x) = 1. In their construction the PRF input length and the size of the circuits C for which constrained keys can be computed must be fixed beforehand during key generation. We construct a constrained PRF that has an unbounded input length and whose constrained keys can be defined for any set recognized by a Turing machine. The only a priori bound we make is on the description size of the machines. We prove our construction secure assuming publiccoin differing-input obfuscation. As applications of our constrained PRF we build a broadcast encryption scheme where the number of potential receivers need not be fixed at setup (in particular, the length of the keys is independent of the number of parties) and the first identity-based non-interactive key exchange protocol with no bound on the number of parties that can agree on a shared key.

Item Type: | Conference or Workshop Item (Paper) |
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Uncontrolled Keywords: | Constrained PRFs, Broadcast encryption, Identity-based non-interactive key exchange |

Subjects: | 000 Computer science, knowledge & general works > 000 Computer science, knowledge & systems > 005 Computer programming, programs & data 600 Technology > 600 Technology |

Research Group: | Pietrzak Group |

SWORD Depositor: | Sword Import User |

Depositing User: | Sword Import User |

Date Deposited: | 23 Feb 2017 06:37 |

Last Modified: | 30 Aug 2017 08:03 |

URI: | https://repository.ist.ac.at/id/eprint/764 |

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