cryptography

n. writing or deciphering of secret codes

Cryptography (or cryptology; derived from Greek κρυπτός kryptós "hidden," and the verb γράφω gráfo "write" or λεγειν legein "to speak") is the practice and study of hiding information. In modern times, cryptography is considered to be a branch of both mathematics and computer science, and is affiliated closely with information theory, computer security, and engineering. Cryptography is used in applications present in technologically advanced societies; examples include the security of ATM cards, computer passwords, and electronic commerce, which all depend on cryptography.
See more at Wikipedia.org...

Noun
1. the science of analyzing and deciphering codes and ciphers and cryptograms
(synonym) cryptanalysis, cryptanalytics, cryptology
(hypernym) science, scientific discipline
2. act of writing in code or cipher
(synonym) coding, secret writing
(hypernym) writing, committal to writing
(hyponym) encoding, encryption

(n.)
The act or art of writing in secret characters; also, secret characters, or cipher.
  

1. [The] principles, means, and methods for rendering plain information unintelligible and for restoring encrypted information to intelligible form. [NIS] 2. The branch of cryptology that treats of the principles, means, and methods of designing and using cryptosystems.