Cryptography is the study of mathematical techniques related to aspects of information security such as confidentiality, data integrity, entity authentication and data origin authentication.
In data and telecommunications, cryptography is necessary when communicating over any unreliable medium, which includes any network particularly the internet. In cryptographic terminology, the message is called plaintext or clear text.
Encoding the contents of the message in such a way that hides the contents from outsiders is called encryption.
The encrypted message is called cipher text. The process of retrieving the plaintext from the cipher text is called decryption.
Encryption and decryption usually make use of a key and the coding method is such that the decryption can be performed only by knowing the proper key.
Simulation: ModelSim XE III 6.4b.
Synthesis: XiLinx ISE 10.1.