## Abstract

We revisit the question of Zero-Knowledge PCPs, studied by Kilian, Petrank, and Tardos (STOC '97). A ZK-PCP is defined similarly to a standard PCP, except that the view of any (possibly malicious) verifier can be efficiently simulated up to a small statistical distance. Kilian et al.obtained a ZK-PCP for NEXP in which the proof oracle is in EXP^{NP}. They also obtained a ZK-PCP for NP in which the proof oracle is computable in polynomial-time, but this ZK-PCP is only zero-knowledge against bounded-query verifiers who make at most an a priori fixed polynomial number of queries. The existence of ZK-PCPs for NP with efficient oracles and arbitrary polynomial-time malicious verifiers was left open. This question is motivated by the recent line of work on cryptography using tamper-proof hardware tokens: an efficient ZK-PCP (for any language) is equivalent to a statistical zero-knowledge proof using only a single stateless token sent to the verifier. We obtain the following results regarding efficient ZK-PCPs: Negative Result on Efficient ZK-PCPs. Assuming that the polynomial time hierarchy does not collapse, we settle the above question in the negative for ZK-PCPs in which the verifier is nonadaptive (i.e. the queries only depend on the input and secret randomness but not on the PCP answers). Simplifying Bounded-Query ZK-PCPs. The bounded-query zero-knowledge PCP of Kilian et al. starts from a weakly-sound bounded-query ZK-PCP of Dwork et al. (CRYPTO '92) and amplifies its soundness by introducing and constructing a new primitive called locking scheme - an unconditional oracle-based analogue of a commitment scheme. We simplify the ZK-PCP of Kilian et al. by presenting an elementary new construction of locking schemes. Our locking scheme is purely combinatorial. Black-Box Sublinear ZK Arguments via ZK-PCPs. Kilian used PCPs to construct sublinear-communication zero-knowledge arguments for NP which make a non-black-box use of collision-resistant hash functions (STOC '92). We show that ZK-PCPs can be used to get black-box variants of this result with improved round complexity, as well as an unconditional zero-knowledge variant of Micali's non-interactive CS Proofs (FOCS '94) in the Random Oracle Model.

Original language | English |
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Title of host publication | Theory of Cryptography - 9th Theory of Cryptography Conference, TCC 2012, Proceedings |

Pages | 151-168 |

Number of pages | 18 |

DOIs | |

State | Published - 2012 |

Event | 9th Theory of Cryptography Conference, TCC 2012 - Taormina, Sicily, Italy Duration: 19 Mar 2012 → 21 Mar 2012 |

### Publication series

Name | Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) |
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Volume | 7194 LNCS |

### Conference

Conference | 9th Theory of Cryptography Conference, TCC 2012 |
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Country/Territory | Italy |

City | Taormina, Sicily |

Period | 19/03/12 → 21/03/12 |

## Keywords

- Arthur Merlin Games
- Probabilistically Checkable Proofs
- Sublinear Arguments
- Tamper-Proof Tokens
- Zero-Knowledge

## All Science Journal Classification (ASJC) codes

- Theoretical Computer Science
- Computer Science(all)