In identification protocols with public verifier coins (like Fiat-Shamir), a passive adversary watching the communication gains information intended only for the verifier. On the other hand, private coin protocols with fewer than three rounds cannot be zero-knowledge. In this paper, we introduce the notion of bounded-prover zero-knowledge proofs which require only two rounds and can be considered perfectly zero-knowledge under certain intractibility assumptions. Specifically, we exploit the gap between two computational problems to achieve zero-knowledge in a dishonest verifier scenario.
On the base of home researching the idea of the proxy si gnature a kind of algorithm of the zero knowledge proof is proposed based on proxy signature in this paper. This algorithm has characteristics which are simple and easy to be realized.
Abstract. A shuffle consists of a permutation and re-encryption of a set of input ciphertexts. One application of shuffles is to build mix-nets. We suggest an honest verifier zero-knowledge argument for the correctness of a shuffle of homomorphic encryptions. Our scheme is more efficient than previous schemes both in terms of communication and computation. The honest verifier zero-knowledge argument has a size that is independent of the actual cryptosystem being used and will typically be smaller than the size of the shuffle itself. Moreover, our scheme is well suited for the use of multi-exponentiation and batch-verification techniques. Additionally, we suggest a more efficient honest verifier zero-knowledge argument for a commitment containing a permutation of a set of publicly known messages. We also suggest an honest verifier zero-knowledge argument for the correctness of a combined shuffle-and-decrypt operation that can be used in connection with decrypting mix-nets based on ElGamal encryption. All our honest verifier zero-knowledge arguments can be turned into honest verifier zero-knowledge proofs. We use homomorphic commitments as an essential part of our schemes. When the commitment scheme is statistically hiding we obtain statistical honest verifier zero-knowledge arguments; when the commitment scheme is statistically binding we obtain computational honest verifier zero-knowledge proofs. Key words. Shuffle, Honest verifier zero-knowledge argument, Homomorphic encryption, Mix-net. 1
We present a constant-round protocol for general secure multiparty computation which makes a black-box use of a pseudorandom generator. In particular, the protocol does not require expensive zero-knowledge proofs and its communication complexity does not depend on the computational complexity of the underlying cryptographic primitive. Our protocol withstands an active, adaptive adversary corrupting a minority of the parties. Previous constant-round protocols of this type were only known in the semi-honest model or for restricted classes of functionlities.
In this paper we define a decentralized management mechanism for the dynamic coalition characteristic of virtual organization. We propose an identity-based threshold signature scheme for joint management. We also propose the policy mode for joint management, which uses role-based access control mechanism for authorization policies definition, and voting mechanism for authorization decision-making. Our solution can satisfy the dynamic coalition requirement of virtual organization, and also guarantee the autonomous characteristic of participant organizations and grid entities. Privacy preservation is also provided for grid entities to interact with authorized entities. Authorization revocation mechanism is taken into consideration in this paper. The experimental performance also shows the scalability of the solution.
We introduce the first El Gamal based mix-net in which each mix-server partially decrypts and permutes its input, i.e., no reencryption is necessary. An interesting property of the construction is that a sender can verify non-interactively that its message is processed correctly. We call this sender verifiability. The mix-net is provably UC-secure against static adversaries corrupting any minority of the mix-servers. The result holds under the decision Diffie-Hellman assumption, and assuming an ideal bulletin board and an ideal zero-knowledge proof of knowledge of a correct shuffle. Then we construct the first proof of a decryption-permutation shuffle, and show how this can be transformed into a zero-knowledge proof of knowledge in the UC-framework. The protocol is sound under the strong RSA-assumption and the discrete logarithm assumption. Our proof of a shuffle is not a variation of existing methods. It is based on a novel idea of independent interest, and we argue that it is at least as efficient as previous constructions.
Abstract. Micali, Rabin, and Kilian [9] recently introduced zero-knowledge sets and databases, in which a prover sets up a database by publishing a commitment, and then gives proofs about particular values. While an elegant and useful primitive, zero-knowledge databases do not offer any good way to perform updates. We explore the issue of updating zero-knowledge databases. We define and discuss transparent updates, which (1) allow holders of proofs that are still valid to update their proofs, but (2) otherwise maintain secrecy about the update. We give rigorous definitions for transparently updatable zero-knowledge databases, and give a practical construction based on the Chase et al [2] construction, assuming that verifiable random functions exist and that mercurial commitments exist, in the random oracle model. We also investigate the idea of updatable commitments, an attempt to make simple commitments transparently updatable. We define this new primitive and give a simple secure construction.
Daniele Micciancio, Shien Jin Ong, Amit Sahai, Salil Vadhan
Abstract. We provide unconditional constructions of concurrent statistical zero-knowledge proofs for a variety of non-trivial problems (not known to have probabilistic polynomial-time algorithms). The problems include Graph Isomorphism, Graph Nonisomorphism, Quadratic Residuosity, Quadratic Nonresiduosity, a restricted version of Statistical Difference, and approximate versions of the (coNP forms of the) Shortest Vector Problem and Closest Vector Problem in lattices. For some of the problems, such as Graph Isomorphism and Quadratic Residuosity, the proof systems have provers that can be implemented in polynomial time (given an NP witness) and have ~O(log n) rounds, which is known to be essentially optimal for black-box simulation.
Recently, two generic watermarking protocols were proposed, based on a popular zero-knowledge identification protocol. In this paper, we show that both protocols are flawed and therefore fail to achieve their purpose of allowing a prover to prove to a verifier of his ownership of a watermarked image. We also give some suggestions to fix these flaws.
2 source records
Advanced Steganography and Watermarking Techniques
Mix-nets can be used to shuffle vectors of shared secrets. This operation can be an important building block for solving combinatorial problems where constraints depend on secrets of different participants. A main contribution of this paper is to show how participants in the mix-net can provide Zero-Knowledge proofs to convince each other that they do not tamper with the shuffled secrets, and that inverse permutations are correctly applied at unshu#ing. The approach is related to the proof of knowing an isomorphism between large graphs. We also make a detailed review and comparison with rationales and analysis of Chaum's and Merritt's mix-nets. Another