The mathematical methods of protecting and keeping private of shared secrets, usually in a message. Literally means "hidden writing" (greek). For example; ROT13 (a rotation cipher) and Code (word replacement). Modern technoiques include algorythms, hashes and keys. Qantum cryptography allows only a single recipient, as the act of reading alters the contents and so allows detection of a passive eavesdropper - most systems use single photons from a laser. Fibre lasers can provide secure transmissions over long distances. Not to be confused with steganography (the act of hiding the existence of a message, such as in pictures or sounds).

Source: http://identityaccessman.blogspot.com/2006/08/identity-dictionary.html