A cryptographically secure protocol for key exchange

M.Sc. (Computer Science)Since the emergence of electronic communication, scientists have strived to make these communication systems as secure as possible. Classical cryptographical methods provided secrecy, with the proviso that the courier delivering the keys could be trusted. This method of key distribution proved to be too inefficient and costly. 'Cryptographical renaissance' was brought about with the advent of public key cryptography, in which the message key consists of a pair of mathematically complementary keys, instead of the symmetric keys of its forerunner. Classical cryptographical techniques were by no means obsolete, as the idea of using 'hybrid' systems proved to be very effective, by using the tedious public key techniques to allow both parties to share a secret, and the more efficient symmetric algorithms to actually encrypt the message. New technology leads, however, to new difficulties and the problems of key management now arose. Various protocols started emerging as solutions to the key distribution problem, each with their own advantages and disadvantages. The aim of this work is to critically review these protocols, analyse the shortfalls and attempt to design a protocol which will overcome these shortfalls. The class of protocol reviewed are the so-called 'strong authentication' protocols, whereby interaction between the message sender and recipient is required