SCS152

The SCS152 is a third generation token card integrated circuit intended for prepaid applications. Typical appli-cations of the SCS152 include disposable telephone cards, vending machine cards, low value debit cards,access control, and authentication.

The SCS152 incorporates several security features, including an internal signature function and a long transport code. The SCS152 has two modes - issuer mode and user mode. During wafer testing, it is placed in issuer mode for card manufacturing and transporta-tion to the issuer. In issuer mode, the transport code is needed to program the device and, thus, is protectedfrom unauthorized use before personalization by the issuer.

During personalization, a cryptographic key, unique to the card, is programmed into EEPROM. This key can not be read. The system using the card must be able to determine what key was programmed from examining the memory map (i.e., not the token counter) containingthe issuer and serial number information.

The signature function computes an 8-bit value based on a system supplied value (challenge) and the visible memory map. Because of the nature of the signature function and the fact that the key is not known outside the system, it is practically impossible to predict the value which the signature will compute.

A correct signature indicates that the memory contents have not been altered. It can therefore be used to check the serial number, or that changes to the token counter have actually occurred.

Programming the token counter uses a special circuit to ensure that the programming will either be complete or will not happen at all, if the external supply is suddenly removed.* This is called Fail Safe Programming^TM, and, when used in conjunction with the extended writeand erase command, removes the need for special 'tear-out' protection to be performed by the reade