This is the oldest and best understood type of cryptography. Its algorithms offer a wide range of security and speed, depending on the algorithm type and variation. Symmetric-key cryptography generally relies on a single, shared key to perform both encryption and decryption on the same piece of data. Thus, the secrecy of the key value is of critical importance to the security of the data. As a result, this type of cryptography is sometimes known as secret-key cryptography. For more information on one mechanism for maintaining the secrecy of symmetric keys, see Asymmetric (public) key cryptography.