The study of encoding and decoding secret messages is called cryptography. Although secret codes date to the earliest days
of written communication, there has been a recent surge of interest in the subject because of the need to maintain the
privacy of information transmitted over public lines of communication. In the language of cryptography, codes are called
ciphers, uncoded messages are called plaintext, and coded messages are called ciphertext. The process of converting from
plaintext to ciphertext is called enciphering, and the reverse process of converting from ciphertext to plaintext is called
deciphering.