A piece of information that controls the operation of a cryptography algorithm. In encryption, a key specifies the particular transformation of plain text into ciphertext or vice versa during decryption. Keys are also used in other cryptographic algorithms, such as digital signature schemes and keyed-hash functions (also known as MACs), often used for authentication.

A variable value in cryptography that is applied (using an algorithm) to a string or block of unencrypted text to produce encrypted text. A key is also a series of numbers or symbols that are used to encode or decode encrypted data.