Abstract

. We present a very practical string-commitment scheme which is provably secure based solely on collision-free hashing. Our scheme enables a computationally bounded party to commit strings to an unbounded one, and is optimal (within a small constant factor) in terms of interaction, communication, and computation. Our result also proves that constant round statistical zero-knowledge arguments and constant-round computational zero-knowledge proofs for NP exist based on the existence of collision-free hash functions. 1 Introduction String commitment is a fundamental primitive for cryptographic protocols. A commitment scheme is an electronic way to temporarily hide a value that cannot be changed. Such a scheme emulates by means of a protocol the following twostage process. In Stage 1 (the Commit stage), a party called the Sender locks a message in a box, and sends the locked box to another party called the receiver. In Stage 2 (the De-commit stage), the Sender provides the Receiver with ...

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