Cryptography

The science of coding and decoding messages so as to keep these messages secure. Coding (see encryption) takes place using a key that ideally is known only by the sender and intended recipient of the message.

Note: Historically used in warfare, cryptography is now used routinely in computer networks. This often pits the desire of individuals and businesses to keep Internet information private against the need of government to investigate crime and terrorism.

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The practise and study of encryption and decryption - encoding data so that it can only be decoded by specific individuals. A system for encrypting and decrypting data is a cryptosystem. These usually involve an algorithm for combining the original data ("plaintext") with one or more "keys" - numbers or strings of characters known only to the sender and/or recipient. The resulting output is known as "ciphertext".
The security of a cryptosystem usually depends on the secrecy of (some of) the keys rather than with the supposed secrecy of the algorithm. A strong cryptosystem has a large range of possible keys so that it is not possible to just try all possible keys (a "brute force" approach). A strong cryptosystem will produce ciphertext which appears random to all standard statistical tests. A strong cryptosystem will resist all known previous methods for breaking codes ("cryptanalysis").
See also cryptology, public-key encryption, RSA.
Usenet newsgroups: sci.crypt, sci.crypt.research.
FAQ MIT.
Cryptography glossary.
RSA cryptography glossary.
Cryptography, PGP, and Your Privacy.
(2000-01-16)