Degree Name

Doctor of Philosophy


Faculty of Informatics


One of the main goals of a cryptographic system is to provide authentication, which simply means providing assurance about the content and origin of communicated message. Historically, cryptography began with secret writing and this remained the main area of development until very recently. With the rapid progress in data communication, the need for providing message integrity and authenticity has escalated to the extent that currently authentication is seen as the more urgent goal of cryptographic systems. Traditionally, it was assumed that a secrecy system provides authentication by the virtue of the secret key being only known by the intended communicants; this would prevent an enemy from constructing a fraudulent message. It is a fairly recent realization that secrecy and authenticity are quite distinct goals. In classical or private cryptography these two concepts were closely intertwined. While secrecy depended on the message being unintelligible to any receiver who did not know the secret key, authenticity depended on the inability of anyone without knowledge of the secret key to produce a ciphertext that would decipher to an intelligible message. Simmons argued that the two goals of cryptography are independent. He shows that a system that provides perfect secrecy might not provide any protection against authentication threats. Similarly, a system can provide perfect authentication without concealing the message. This thesis will deal with authentication theory.