Identification Tokens - or: Solving the Chess Grandmaster Problem

Fiat and Shamir have proposed to use zero-knowledge interactive proofs to obtain secure identification mechanisms. Real time attacks in which active eavesdroppers relay questions and answers or in which the prover helps deliberately an impersonator have been described [4j. In this paper a solution against such frauds is given and (based on some physical assumptions) it is proved that the solution protects against the real-time attacks.