Cryptography in payments systems

APACS (Association for Payment Clearing Services) was established in 1985, and is the association of those banks and building societies at the heart of the UK payments industry. It is the umbrella body for the discussion and resolution of matters relating to money transmission in the UK. APACS works to ensure that the development of payment clearing services reflects the needs of its members and their customers, including retailers. During 1994, the APACS clearing companies cleared funds to a total value in excess of £27800 billion. The telecommunications messages supporting these transmissions are all secured-most using cryptographic mechanisms. This paper describes some of the systems that are in place to protect the transmission of electronic payments messages in the UK. While Kerckhoff´s assumption-that the entire mechanism used for encryption, except for the value of the secret key, is known to the enemy cryptanalyst-is still in fundamental use today, no system is absolutely secure, and it is therefore inappropriate to reveal every last detail of the mechanisms used to protect today´s systems from fraudsters. Thus, while the general principles and `architecture´ are discussed, operational details that would be of use to an attacker are omitted