cryptography

n. [ Cf. F. cryptographie. ] 1. The act or art of writing in code or secret characters; also, secret characters, codes or ciphers, or messages written in a secret code. [ 1913 Webster +PJC ]

2. The science which studies methods for encoding messages so that they can be read only by a person who knows the secret information required for decoding, called the key; it includes cryptanalysis, the science of decoding encrypted messages without possessing the proper key, and has several other branches; see for example steganography. [ PJC ]