Cryptography, which translates as "secret writing," refers to the science of concealing the meaning of data so only specified parties understand a transmission's contents. Cryptography has existed for thousands of years; for most of history, however, the users of cryptography were associated with a government or organized group and were working to conceal secret messages from enemies. These days, millions upon millions of secure, encoded transmissions happen online each day -- and cryptographic standards are used to protect banking data, health information, and much more. Without cryptography, e-commerce as we know it would be impossible. Since online security threats evolve so quickly, there are dozens of different schools of thought on how best to use encryption to enhance network security -- not just for governments, but for businesses and end users, too.
Classical Encryption Techniques
Advanced Encryption Standard
Confidentiality Using Symmetric Encryption
Number Theory and Hash Algorithms
Electronic Mail Security
IP Security and Web Security