1 A set of characters used in the encryption of a message. The key is used to vary the algorithm used to transform the message into a form in which it cannot be read by an unauthorized person. For example, a very simple use of a key would be a sequence of character pairs where, when the first character in a pair is encountered in a text, it is replaced by the second character. Once a message has been encrypted it is sent to its recipient who then uses the key for decryption, returning the message to its original form. See also public key, private key, and symmetric key encryption.
2 A unique set of characters that identify a record in a file. For example, in a file containing employee records, each employee is associated with a unique works number which acts as a key.
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