Codeword

Codeword is a term used in several fields with related but distinct meanings. In general, a codeword is a word or short phrase used to represent information in a coded message or to identify a specific item within a code. It can serve as a marker, trigger, or key in a system of rules for encoding and decoding.

In cryptography and intelligence contexts, codewords are often fixed or agreed-upon secrets that authorize access to information, indicate the intended recipient, or prompt a particular interpretation of the surrounding text. They may appear in codebooks or be transmitted as part of secure communications, with the codeword signaling how to process the message.

In coding theory and digital communications, a codeword is a valid encoded vector produced by an encoder from a source message. For a block code, codewords have a fixed length and form a code set with properties such as minimum distance that determine error detection and correction capabilities. For example, in a simple repetition code mapping 0 to 000 and 1 to 111, the codewords are the possible output strings of length three.

In everyday security practice, the term is sometimes used more loosely to mean a password or passphrase used to authenticate or authorize actions. Such codewords are typically expected to be kept secret and may be rotated or revoked as part of security policies, but they differ from formal cryptographic keys or token-based credentials.

See also: codebook, error-correcting code, cryptography, passphrase, authentication.