Transaction security system using time variant parameter

An electronic funds transfer (EFT) system in which EFT terminals are connected through a local data processing center to a public switch system, a plurality of card-issuing agencies' data processing centers are also connected to the public switch system and each user of the EFT system has a personal secure intelligent bank card on which is stored a personal account number (PAN) and a personal key (KP), the system including:

• first local data processing center means at each local data processing center to generate session keys (KS) for each of its locally attached terminals, and to transmit an associated session key to a respective terminal;
• at each terminal means to store the session key;
• first card means to generate and store a transaction variable for each transaction initiated at the terminal and to transfer the transaction variable to the terminal;
• first terminal means to encipher sensitive data under the session key whenever a transaction request message is generated;
• second terminal means to generate a transaction variable for each transaction initiated at the terminal and to combine the transaction variable generated at the terminal with the transaction variable received from the card to form a composite transaction variable;
• third terminal means to transfer the transaction variable generated at the terminal and a message request including the terminal-generated composite transaction variable enciphered under KS to the user's card and means on the card to generate a composite transaction variable from the transaction variable generated and stored on the card and the transaction variable received from the terminal and means on the card to generate a message authentication code (MAC) using a time variant key based upon the user's PAN, KP and the card-generated composite transaction variable;
• second card means to return the message request and the MAC to the terminal and subsequently transmit it to local processing center;
• second local data processing center means at each local data processing center to encipher the appropriate session key under a cross-domain key whenever a transaction request message is received and to add the enciphered key to the message;
• first node means at each processing node of the public switch system to translate the enciphered session key from encipherment under a received cross-domain key to a transmission cross-domain key;
• first card-issuing agency's data processing center means at the card-issuing agency's data processing center to decipher the enciphered session key and to use the key to decipher any sensitive data contained in the request message;
• and
• second card-issuing agency's data processing center means to regenerate the message authentication code using the time variant key which is generated from parameters based upon the PAN and KP and the received composite transaction variable for comparison with the message authentication code included in the received message.