| Data communications are susceptible to various security threats and the requirement for secure communication has always been a major momentum in the study of cryptography. In the past twenty years, cryptography has drawn considerable public research in academic field. Together with the advance of computer technology, these researches bear the fruit of modern cryptography which provides indispensable techniques providing privacy and integrity of data and proliferates numerous applications which cannot otherwise be realized in a network environment. However, many incidents, e.g., computer crime, the spread of computer virus, and research results have also shown that current efforts in the development of cryptographic techniques are not enough in preventing services and the network itself from being misused.; In a large network which accommodates many entities and each entity communicates with many others, every entity would have to keep a long list of keys for all its communicating parties. This list gets longer whenever a new application is introduced. As these keys, either public or private, play as the most critical roles for many applications, user authentication and the generation, certification, distribution, and management of these keys become important problems to be solved. In this dissertation, secret sharing which prevents the key from being lost or exposed, key management which controls the growth of the number of keys in a multiservice environment, and software authentication which counteracts the spread of computer viruses are discussed in detail and new solutions are proposed. In the final part of the dissertation, a complete set of authentication protocols for personal communication systems is presented. |
