The objective of this thesis is to study the different authentication methods and the implementation of them to see the shortcommings and powerful aspects of each method. These methods are divided into the following classes:- 1-classical methods 2-subliminal channels 3-digital signatures different authentication techniques. These schemes are based on cryptography which provides a good way to perform the authentication required, either for user authentication or for message authentication, efficientely. Cryptography can be used to provide computer security and give the ability to transmit information in a concealed form. Some authentication methods have been chosen to provide secercy and authenticity and also certain modifications for some of these methods been made to handle certain shortcomings of these methods or to reduce some of the reapeted steps. The implementation of RSA scheme has also been tested on Local Area Network (LAN) to be as an example for other authentication methods that also can applied on LAN. The system is implemented on an IBM personal computer, using Turbo Pascal version 6.0, running under MS-DOS version 3.3.