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Abstract : |
Abstract. All information-theoretically secure key agreement protocols (e.g. based on quantum cryptography or on noisy channels) described in the literature axe secure only against passive adversaries in the sense that they assume the existence of an authenticated public channel. The goal of this paper is to investigate information-theoretic security even against active adversaries with complete control over the communication channel connecting the two paxties who want to agree on a secret key. Several impossibility results axe proved and some scenarios are characterized in which secret-key agreement secure against active adversaries is possible. In particular, when each of the parties, including the adversary, can ob-serve a sequence of random variables that axe correlated between the paxties, the rate at which key agreement against active adversaries is possible is characterized completely: it is either 0 or equal to the rate achievable against passive adversaries, and the condition for distinguishing between the two cases is given., |
