© 1997 Microchip Technology Inc.

Preliminary

DS40150B-page 1

M

SCS152

FEATURES

• ISO 7816-3:1989 “Answer to Reset” compatible

for synchronous cards

• Industry standard 4406 command set compatible

• Extended commands:

- Combined WRITE and

ERASE-WITH-CARRY function

- Cryptographic signature of the EEPROM

contents and challenge

• 40-bit user programmable area with lock bit

• 64-bit cryptographic key

• 64-bit transport code

• Internal protection against token counter value

corruption (anti-tearing)

DESCRIPTION

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 protected

from 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) containing

the 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.

DIE LAYOUT

BLOCK DIAGRAM

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™,

and, when used in conjunction with the extended write

and erase command, removes the need for special

‘tear-out’ protection to be performed by the reader.

Note:

The fail safe feature only works in the token

counter area.

GND

SDIO

SCI

SCK

I/O

SCI

SCK

SDIO

GND

ADDRESS

GENERATION

EEPROM

SIGNATURE

CALCULATOR

CONTROLLER

Token Card Chip

*Patents applied for.