Abstract

: We present a number of attacks, some new, on public key protocols. We also advance a number of principles which may help designers avoid many of the pitfalls, and help attackers spot errors which can be exploited. 1 Introduction Cryptographic protocols are typically used to identify a user to a computer system, to authenticate a transaction, or to set up a key. They typically involve the exchange of about 2--5 messages, and they are very easy to get wrong: bugs have been found in well known protocols years after they were first published. This is quite remarkable; after all, a protocol is a kind of program, and one would expect to get any other program of this size right by staring at it for a while. A number of remedies have been proposed. One approach is formal mathematical proof, and can range from systematic protocol verification techniques such as the BAN logic [BAN89] to the case-by-case reduction of security claims to the intractability of some problem such as factoring. Anot...

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