On the importance of memory resources in the security of key exchange protocols

Abstract

We present a protocol for key exchange which relies on the existence of permutations which are not necessarily trap-door, and which are one-way in a weaker sense than that usually assumed in the literature. Our main result is that, under this assumption, two players can exchange a secret key over an open channel in such a way that an eavesdropper must spend time proportional to TIME · SPACE, where TIME is the time spent by the two players and SPACE is the amount of information which cau be stored and transmitted by the two players. Hence the importance of storage technology for security.