Section J -- Smart Cards and Magnetic Stripe Cards

J-01. What is a Smart Card?

A Smart Card is a plastic card the size of a credit card with an integrated circuit built into it. This integrated circuit may consist only of EEPROM in the case of a memory card, but may also contain ROM, RAM and a CPU.

Smart cards are defined by the ISO 7816 standards.

ISO standard documents are available for purchase from ISO: International Organization for Standardization.

In the U.S., smart cards are utilized in GSM mobile telephones, in DirecTV and EchoStar satellite receivers, and in the American Express Blue card.

Smart cards designed for specific applications may run proprietary operating systems. Smart cards designed with the capability to run multiple applications usually run MULTOS or Java Card.

For more information on Smartcard security, visit Bo Lavare's Smartcard securit information page.

J-02. What are some common Smart Cards?

J-03. What is the layout of data on magnetic stripe cards?

This FAQ answer was written largely with information supplied by wea$el:

Data is laid out on a standard magnetic car in three tracks. A card may have any of these tracks, or a combination of these tracks.

Track 1 was the first track standardized. It was developed by the International Air Transportation Association (IATA) and is still reserved for their use. It is 210bpi with room for 79 7-bit characters.

Track 1 is encoded with a 7-bit scheme (6 data bits plus one parity bit) that's based on ASCII. If your reader does not perform the ASCII conversion, all you have to do is add 0x20 to each byte to turn it into ASCII (there are no "control" characters). The seventh bit is an odd parity bit at the end of each byte.

Track 2 was developed by the American Bankers Association (ABA) for on-line financial transactions. It is 75bpi with room for 40 5-bit numeric characters.

Track 2 is encoded with a 5-bit scheme (4 data bits plus one parity bit.) To convert this data into ASCII, add 0x30 to each byte.

Track 3 is also used for financial transactions. The difference is its read/write ability. It is 210bpi with room for 107 numeric digits. Track 3 is used to store the enciphered PIN, country code, currency units, amount authorized, subsidiary account information, and other account restrictions.

Track 3 has the same properties as track 1 (start and end sentinels and an LRC byte), except that there is no standard for the data content or format. Track 3 is not currently used by any national bank card issuer.

In those rare systems where the PIN is stored on the card, this is the track where it is stored.

For more information of this topic, read the ANSI/ISO 7811/1-5 standard. This document is available from the American Bankers Association.

Other standards documents covering related topics include:

• ANSI X3.92 Data Encryption Algorithm (DEA)
  
• ANSI X3.106 Modems of DEA Operation
  
• ANSI X4.16 American National Standard for financial services, financial transaction cards, magnetic stripe encoding
  
• ANSI X9.8 Personal Identification Number (PIN) Management and Security
  
• ANSI X9.19 Financial Institution Retail Message Authentication (MAC)
  
• ISO 7810
  
• ISO 7811
  
• ISO 7812
  
• ISO 8583 Bank card originated messages; Interchange message specifications; Content for financial transactions.
  
• ISO 8731-1 Banking: Approved algorithms for message authentication
  

  Part 1 - DEA
  Part 2 - Message Authentication algorithms
  

• ISO 7816 Identification cards, Integrated circuit(s) with contacts
  

  Part 1 - Physical Characteristics
  Part 2 - Dimensions and locations of the contacts
  Part 3 - Electronic signals and transmission protocols

J-04. How do I determine if I have a valid credit card number?

Credit cards use the Luhn Check Digit Algorithm. The main purpose of this algorithm is to catch data entry errors, but it does double duty here as a weak security tool.

For a card with an even number of digits, double every odd numbered digit (1st digit, 3rd digit, 5th digit, etc...) and subtract 9 if the product is greater than 9. Add up all the even digits (2nd digit, 4th digit, 6th digit, etc...) as well as the doubled-odd digits, and the result must be a multiple of 10 or it's not a valid card. If the card has an odd number of digits, perform the same addition doubling the even numbered digits instead.

This program, presented in C source code form, will perform this math for you. Feed it all but the last digit of your credit card number, and it will give you the last digit. If it gives you a last digit different from the one you have, you have an invalid credit card number.

#include        <stdio.h>

/*
 * Return last digit of a bank card (e.g. credit card)
 * Receives all the digits, but the last one as input
 * By Diomidis Spinellis <dds@doc.ic.ac.uk>
 */
int bank (u)
char *u;
        {
        register i, s = 0;
        int l, t;

        l = strlen(u);
        for(i = 0; i < l ; i++)
                {
                t = (u[l - i - 1] - '0') * (1 + ((i + 1) % 2));
                s += t < 10 ? t : t - 9;
                }
        return 10 - s % 10;
        }
	
void main (argc, argv)
	
int  argc;
char **argv;
        {
        while (--argc)
                printf ("%d\n", bank (*++argv));
        }