The Beale ciphers are another example of a homophonic cipher. Encryption is done by a stream cipher. Early encryption techniques such as the Hill cipher also used matrices. CSS utilizes a proprietary 40-bit stream cipher algorithm. Specifically, ATS requires the use of an encryption cipher that provides forward secrecy. The algorithm used by LTO-4 is AES-GCM, which is an authenticated, symmetric block cipher. Rule 30 was originally suggested as a possible block cipher for use in cryptography. The Romans knew something of cryptography (e.g., the Caesar cipher and its variations). The standard also provides encryption services with the DECT Standard Cipher (DSC). The 340-character cipher has never been decoded. Twofish is related to the earlier block cipher Blowfish. This is termed a binary additive stream cipher. A nonce may be used to ensure security for a stream cipher. To encipher or encode is to convert information into cipher or code. However, Welchman's main contributions were to the process of breaking the German Enigma machine cipher.