Abstract
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.