Abstract not found

The simulation paradigm is central to cryptography. A simulator is an algorithm that tries to simulate the interaction of the adversary with an honest party, without knowing the private input of this honest party. Almost all known simulators use the adversary’s algorithm as a black-box. We present the first constructions of nonblack-box simulators. Using these new non-black-box techniques we obtain several results that were previously proven to be impossible to obtain using black-box simulators. Specifically, assuming the existence of collision resistent hash functions, we construct a new zeroknowledge argument system for NP that satisfies the following properties: 1. This system has a constant number of rounds with negligible soundness error. 2. It remains zero knowledge even when composed concurrently n times, where n is the security parameter. Simultaneously obtaining 1 and 2 has been recently proven to be impossible to achieve using black-box simulators. 3. It is an Arthur-Merlin (public coins) protocol. Simultaneously obtaining 1 and 3 was known to be impossible to achieve with a black-box simulator. 4. It has a simulator that runs in strict polynomial time, rather than in expected polynomial time. All previously known constant-round, negligibleerror zero-knowledge arguments utilized expected polynomial-time simulators.

Sensor networks promise viable solutions to many monitoring problems. However, the practical deployment of sensor networks faces many challenges imposed by real-world demands. Sensor nodes often have limited computation and communication resources and battery power. Moreover, in many applications sensors are deployed in open environments, and hence are vulnerable to physical attacks, potentially compromising the sensor's cryptographic keys. One of the basic and indispensable functionalities of sensor networks is the ability to answer queries over the data acquired by the sensors. The resource constraints and security issues make designing mechanisms for information aggregation in large sensor networks particularly challenging.

Constant-round zero-knowledge proof systems for every language in NP are presented, assuming the existence of a collection of claw-free functions. In particular, it follows that such proof systems exist assuming the intractability of either the Discrete Logarithm Problem or the Factoring Problem for Blum Integers.

The Sanctuary project at UCSD is building a secure infrastructure for mobile agents, and examining

We continue the study of the trade-o between the length of PCPs and their query complexity, establishing the following main results (which refer to proofs of satis ability of circuits of size n): 1. We present PCPs of length exp( ~ O(log log n) ) n that can be veri ed by making o(log log n) Boolean queries.

This paper puts forward a new notion of a proof based on computational complexity and explores its implications for computation at large. Computationally sound proofs provide, in a novel and meaningful framework, answers to old and new questions in complexity theory. In particular, given a random oracle or a new complexity assumption, they enable us to 1. prove that verifying is easier than deciding for all theorems; 2. provide a quite effective way to prove membership in computationally hard languages (such as Co-NP-complete ones); and 3. show that every computation possesses a short certificate vouching its correctness. Finally, if a special type of computationally sound proof exists, we show that Blum’s notion of program checking can be meaningfully broadened so as to prove that NP-complete languages are checkable.

Abstract not found

A secure function evaluation protocol allows two parties to jointly compute a function f(x; y) of their inputs in a manner not leaking more information than necessary. A major result in this field is: "any function f that can be computed using polynomial resources can be computed securely using polynomial resources" (where `resources' refers to communication and computation). This result follows by a general transformation from any circuit for f to a secure protocol that evaluates f . Although the resources used by protocols resulting from this transformation are polynomial in the circuit size, they are much higher (in general) than those required for an insecure computation of f . We propose a new methodology for designing secure protocols, utilizing the communication complexity tree (or branching program) representation of f . We start with an efficient (insecure) protocol for f and transform it into a secure protocol. In other words, "any function f that can be computed using communication complexity c can be can be computed securely using communication complexity that is polynomial in c and a security parameter". We show several simple applications of this new methodology resulting in protocols efficient either in communication or in computation. In particular, we exemplify a protocol for the "millionaires problem ", where two participants want to compare their values but reveal no other information. Our protocol is more efficient than previously known ones in either communication or computation. 1.

. In this paper we present an efficient protocol for "Committed Oblivious Transfer" to perform oblivious transfer on committed bits: suppose Alice is committed to bits a0 and a1 and Bob is committed to b, they both want Bob to learn and commit to a b without Alice learning b nor Bob learning a¯ b . Our protocol, based on the properties of error correcting codes, uses Bit Commitment (bc) and one-out-of-two Oblivious Transfer (ot) as black boxes. Consequently the protocol may be implemented with or without a computational assumption, depending on the kind of bc and ot used by the participants. Assuming a Broadcast Channel is also available, we exploit this result to obtain a protocol for Private Multi-Party Computation, without making assumptions about a specific number or fraction of participants being honest. We analyze the protocol's efficiency in terms of bcs and ots performed. Our approach connects Zero Knowledge proofs on bcs, Oblivious Circuit Evaluation and Private Multi-Party ...