Cryptography and Computer Network Security

1. Alfred J. Menezes, Paul C. van Oorschot, and Scott A. Vanstone,  Handbook of Applied Cryptography, CRC Press, Inc., Boca Raton, 1996 (all chapters of this book can be downloaded from the book web page).
2. Bruce Schneier, Applied Cryptography - Protocols, Algorithms, and Source Code in C, 2nd ed., John Wiley & Sons, Inc., New York, 1995.

Related mathematical resources

Basics

1. Chapter 8 of
   William Stallings, Cryptography and Network Security: Principles and Practice, 3rd ed., Prentice Hall, Upper Saddle River, 2003.

2. Chapters 2 and 4 of
   Alfred J. Menezes, Paul C. van Oorschot, and Scott A. Vanstone,  Handbook of Applied Cryptography, CRC Press, Inc., Boca Raton, 1996 can be downloaded from the book web page).

Intermediate

1. Song Y. Yan, Number Theory for Computing, 2nd ed., Springer-Verlag, Berlin, 2002.

2. David M. Burton, Elementary Number Theory, International Series in Pure and Applied Mathematics, 3rd. ed., The McGraw-Hill Companies, Inc., 1997.

1. David Kahn, The Codebreakers: The Comprehensive History of Secret Communication from Ancient Times to the Internet, 2nd ed., Scribner, New York, 1996.
2. Simon Singh, The Code Book: The Evolution of Secrecy from Mary, Queen of Scots to Quantum Cryptography, Anchor, 2000.
3. Friedrich L. Bauer, Decrypted Secrets: Methods and Maxims of Cryptology, 2nd ed. Springer, Berlin, 2000.
4. Steven Levy, Crypto: How the Code Rebels Beat the Government Saving Privacy in the Digital Age, Penguin Putnam, 2002.

1. Douglas R. Stinson , Cryptography - Theory and Practice, CRC Press, Inc., Boca Raton, 1995.
2. Charlie Kaufman, Radia Perlman, and Mike Speciner, Network Security: Private Communication in a Public World, PTR Prentice Hall, Englewood Cliffs, 2002.
3. M. Welschenbach, Cryptography in C and C++, Apress, 2001.