If some information is meant to be kept private, the best means
is to keep it well hidden. This is not, of course, always
possible. One way around this is to hide the information or
message in plain sight, that is, encode it in some way so that
even if it is seen, it will be unreadable. The study of such
encoding processes is called Cryptography4.1. The name
``Cryptography'' comes from the Greek words kryptos ( o),
meaning ``hidden'' or secret, and graphia ( ), meaning writing.
Since ancient times, cryptography has been a part of military
and governmental communications. More recently it has become
part of nearly everyone's life because of the Internet,
electronic banking, and so on. The usual jargon is as follows:
the message you want to hide is called the plaintext, and the
act of encoding it is called encryption or enciphering. The
encoded plaintext is called the crypttext or the ciphertext, and
the act of decoding it is called decryption or deciphering (or
``cracking the code'', if the decoder wasn't the