Abstract: Each access attempt transmitted to an authentication agency causes the agency to produce a request identifier unique to that request. The request identifier is transmitted back to the authentication code generator of the user initiating the access attempt, and to an authentication code generator in the agency. The agency also retrieves a user identifier from a database and sends it to its authentication code generator. Both the user's authentication code generator and the agency's authentication code generator independently combine, through identical or complementary transformations, the user identifier and the request identifier to form a user authentication code and an agency authentication code. The two authentication codes are presented by a comparator, which issues a permit signal only if the comparison indicates a match between the two authentication codes. The permit signal is transmitted to a transaction control device to permit the transaction to proceed.

Abstract: A verifier for use in a personal identification system of the type in which a generator receives at least a personal account number (PAN) and a secret personal identification number (PIN) and based thereon produces digits A.sub.i 's which are present in a feedback shift register (FSR) A and digits C.sub.i 's present in a feedback shift register (FSR) C respectively. The A.sub.i 's and C.sub.i 's are mapped into D.sub.i 's which represent digits of an Offset Number which together with the PAN are recorded on the magnetic stripe of a card. To use the cards the Offset Number and the PAN are read off therefrom and an intended user enters a secret PIN. In the verifier, the PIN is operated upon to produce C.sub.i 's and the PAN is operated upon to produce A.sub.i 's. The latter together with the D.sub.i 's of the received Offset Number are mapped by a processer (201) to form C.sub.i.sup.c 's. These are compared with the C.sub.

Abstract: A personal identification system comprises a generator which generates an Offset Number which is recorded on the magnetic stripe of a card, together with the account number (PAN) of the person to whom the card is to be issued. The generator stores transformed digits of a sequence of digits (IN) which have been secretly entered by one or more officers of the card-issuing institution. To generate the Offset Number the PAN is entered and transformed before being stored to initialize a first feedback shift register. The person to whom the card is to be issued enters a chosen alphanumeric sequence (PIN) secretly known only to him. The PIN, after undergoing transformation is stored to initialize a second feedback shift register. When both registers have been initialized they are reinitialized by different parts of different digits of the transformed IN.