Magnetic stripe on the back of Credit card .. !!

Vaishnavi Chigarapalle

Magnetic Stripe

• A magnetic stripe card is a type of card capable of storing data by modifying the

magnetism of tiny iron-based magnetic particles on the band of magnetic material on

the card.

• The magnetic stripe is sometimes called swipe card or magstripe.

• This is read by swiping past a magnetic reading head.

• This is made up of tiny-iron based magnetic particles in a plastic-like film.

• Each particle is really a very tiny bar magnet about 20 millionths of an inch long.

• The magnetic stripe can be written because the tiny bar magnets can be magnetized.

• This can be done either in a north or south pole direction.

• The magnetic stripe on the back of a credit card is similar to a piece of cassette

tape fastened to the back of a card.

• Instead of motors moving the tape so it can be read, our hand provides the motion

as we swipe a credit card through a reader or insert at the gas station pump.

Magstripe Formats

• There are three tracks on a magstripe.

• Each track is .110-inch wide.

• The ISO/IEC standard 7811, which is used by banks, specifies:

– Track one is 210 bits per inch (bpi), and holds 79 six-bit plus parity bit read-only characters.

– Track two is 75 bpi, and holds 40 four-bit plus parity bit characters.

– Track three is 210 bpi, and holds 107 four-bit plus parity bit characters.

• The credit card typically uses only track one and two.

• Track three is a read-write track.

• The read-write track includes an encrypted PIN, country code, currency units, amount

authorized.

• But the usage of track three is not standardized among banks.

Magstrip Formats

Verification and Authentication System.

Track 1• Track 1 is the only track that may contain alphabetic text, and hence is the only track that

contains the card holder’s name.

• The minimum cardholder account information needed to complete a transaction is

present on both track 1 and track 2.

• Track 1 is written with code known as DEC SIXBIT plus odd bit parity.

• The information on track 1 is contained in several formats:

– A, which is reserved for proprietary use of card issuer.

– B, is as described below.

– C-M, which are reserved for use by ANSI subcommittee X3B10 and

– N-Z, which are available for use by individual card readers.

• Track 1, Format B:

– Start sentinel: 1 character (generally ‘%’)

– Format Code=“B”: 1 character (alpha only)

– Primary account number (PAN): up to 19 characters. Usually, but not always, matches the credit card number

printed on the front of the card.

– Field separator: 1 character (generally ‘^’)

– Country code: 3 characters

– Name: 2-26 characters

– Field separator: 1 character (generally ‘^’)

– Expiration date or separator: 4 characters or 1 character

– Discretionary data: enough characters to fill out maximum record length (79 characters total). May include pin

Verification Key Indicator (PVKI, 1 character), PIN Verification Value (PVV, 4 characters), Card Verification Value

or Card Verification Code (CVV or CVC, 3 characters)

– End sentinel: 1 character (generally ‘?’)

– Longitudinal Redundancy Check (LRC), a form of computed check character; 1 character.

Track 2• Track 2 format was developed by the banking industry (ABA).

• This track is written with a 5-bit scheme (4 data bits + 1 parity), which allows for sixteen

possible characters, which are the numbers 0-9, plus the six characters : ; < = > ?.

• The selection six punctuation may seem odd, but in fact the sixteen codes simply map to

the ASCII range 0x30 through 0x3f, which defines ten digit characters plus those six

symbols.

• Point-of-scale card readers almost always read track 1, or track 2, and sometimes both,

in case one track is unreadable.

• The minimum cardholder account information needed to complete a transaction is

present on both track 1 and track 2.

• Format for Track 2:

– Start sentinel: 1 character (generally ‘;’)

– Primary Account Number (PAN): up to 19 characters. Usually, but not always, matches the credit card number

printed on the front of the card.

– Separator: 1 character (generally ‘=‘)

– Expiration Date or separator: 4 characters or 1 character.

– Service Code: 3 digits. The first digit specifies the interchange rules, the second specifies the authorization

process, and the third specifies the range of services.

– Discretionary data: Enough characters to fill out maximum record length (40 characters total). As in track 1

– End Sentinel: 1 character (generally ‘?’)

– Longitudinal Redundancy Check (LRC): it is 1 character and a validity character calculated from other data on

the track. Most reader devices do not return the value when the card is swiped to the presentation layer, and use It

only to verify the input internally to the reader.

Track 3• Track 3 is a read-write track, but its usage is not standardized among banks.

• This track includes an encrypted PIN, country code, currency units, amount

authorized.

• Track 3 is virtually unused by major worldwide networks.

• This is often isn’t even physically present on the card by virtue of a narrower

magnetic stripe.

Methods to determine what our credit cards will pay for?

• There are three basic methods for determining that out credit card will pay for

what we’re charging:

– Merchants with few transactions each month will do voice authentication, using a touch tone

phone.

– Electronic Data Capture (EDC) magstripe card swipe terminals are becoming more common – so

is having us swipe our own card at the checkout.

– Virtual terminal on the internet.

How it works?• After we or the cashier swipes the credit card through a reader, the EDC software at the

point of sale (POS) terminal dials a stored telephone number via a modem to call an

acquirer.

• An acquirer is an organization that collects credit authentication requests from

merchants and provides a payment guarantee to the merchant.

• When the acquirer company gets the credit card authentication request, it checks the

transaction for validity and the record on the magstripe for:

– Merchant ID

– Valid card number

– Expiration Date

– Credit card limit

– Card usage.

• Single dial-up transactions are processed 1200-2400 bps, while direct internet

attachment uses much higher speeds via this protocol.

• In this system, the cardholder enters a Personal Identification Number (PIN),

using a keypad.

Problems why an ATM doesn’t accept the card

• If the ATM isn’t accepting our card, the problem is probably either:

– Dirty or scratched magstripe.

– Erased magstripe (The most common causes for erased magstripes are exposures to magnets, like

the small ones used to hold notes and pictures on the refrigirator, and a store’s electronic article

surveillance (EAS) tag demagnetizer.

Sources:

• http://money.howstuffworks.com/personal-finance/debt-management/magnetic-stri

pe-credit-card.htm

• http://en.wikipedia.org/wiki/Magnetic_stripe_card

• Images.google.com