Two Java packages have been written which contain classes to implement S-expressions and Version 2.0 of the Simple Distributed Security Infrastructure (SDSI) specification. Another package has been written, which contains classes that provide a graphical user interface to the classes and methods in the other packages. Thesis Supervisor: Ronald L. Rivest Title: Edwin Sibley Webster Professor of Computer Science and Engineering 3 Acknowledgements This work is dedicated to my family. Thanks to my advisor Professor Ronald Rivest and to my friends for their encouragement. This research was supported by DARPA Grant DABT63-96-C-0018. 4 Contents Chapter 1 Introduction ...................................................................................................6 1.1 Design of SDSI ....................................................................................................7 1.2 S-expressions .......................................................................................