Degree Name

Doctor of Philosophy


School of Information Technology and Computer Science


Message Authentication Codes (MACs) play an important role in today's information communication. Messages which are sent over an insecure channel need to be authenticated to prevent attacks such as message forgery by an intruder who can tamper with the channel. To provide message authenticity, assuming that the transmitter and the receiver share a secret key, a MAC can be used. In a MAC system, the transmitter generates a tag which is a function of the message and the secret key, and appends it to the message before sending it over the channel. The receiver can verify the authenticity of a received message, on the other end of the channel, by recomputing the tag and comparing it with the appended one.

In analysis and design of MACs two different approaches, known as unconditional security and computational security, can be used. The aim of this thesis is to study the existing MAC systems and propose new constructions which are more efficient and meanwhile maintain the required security. We justify the security of our proposed constructions using computational security and unconditional security approaches. We also propose a new definition for keyed hash functions and relate them to MACs. Finally, we cryptanalyze two proposed collisionful hash functions.