This book is an introduction to the fundamental concepts in the fields of cryptography and network security. Because cryptography is highly vulnerable to program errors, a simple testing of the cryptosystem will usually uncover a security vulnerability. In this book, the author takes the reader through all of the important design and implementation details of various cryptographic algorithms and network security protocols to enforce network security. The book is divided into four parts: Cryptography, Security Systems, Network Security Applications, and System Security. Numerous diagrams and examples throughout the book are used to explain cryptography and network security concepts.