The key used in a symmetric algorithm. Since a secret key is used for both encryption and decryption, it must be shared between parties that are transmitting ciphertext to one another but must be kept secret from all unauthorized entities.
The cryptographic key used in a symmetric key algorithm, which results in the secrecy of the encrypted data depending solely upon keeping the key a secret, also known as a symmetric key.
A key known only to authorized parties. It can be used to authenticate the sender or recipient of a message. See secret key cryptography.