For people interested in reading further, there are several good books:
- Singh, Simon (2000). "The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography". ISBN 0-385-49532-3.
- Kahn, D (1973) "The CodeBreakers: The Comprehensive History of Secret Communication". Macmillan
For a look at more modern algorithms, try:
- Schneier, Bruce (1996). "Applied Cryptography", John Wiley & Sons
- Mao, Wenbo (2003). "Modern Cryptography: Theory and Practice", Prentice Hall.
- Menezes, A. van Oorschot, P. Vanstone, S. (1996) "Handbook of Applied Cryptography", Crc Press.
- Stinson, Douglas (2005). "Cryptography: Theory and Practice"
If you're looking for something online that you can access immediately, try: