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1. What is a magnetic stripe?
2. How does the magnetic stripe
is information encoded on the magnetic stripe?
4. What is coercivity? Is higher coercivity better?
5. Why would I use high
6. Who uses magnetic
7. Are all
magnetic stripes the same?
8. Are there standards for
magnetic stripe use?
9. Do I have to comply with the
have heard that magnetic stripe it is not secure - it is this true?
11. How do security methods
12. My card does not
work in my ATM. What did I do to it?
13. Is there a good
way to protect the stripe on my card
A. A magnetic stripe is the black or brown stripe that you see on your
credit card, or maybe the back of your airline ticket or transit card. The
stripe is made up of tiny magnetic particles in a resin. The particles are
either applied directly to the card or made into a stripe on a plastic backing
which is applied to the card.
The material used to make the particles defines the Coercivity (see below) of
the stripe. Standard low coercivity stripes use iron oxide as the material to
make the particles, high coercivity stripes are made from other materials like
barium ferrite. These materials are mixed with a resin to form a uniform slurry
which is then coated onto a substrate. In the case of a credit card or similar
application the slurry is usually coated onto a wide plastic sheet and dried.
The coating is very thin and the plastic allows the coating to be handled. It is
then sliced into stripe widths and applied to the card during the card
manufacturing process. The methods of application include lamination (where the
stripe and backing is laminated into the card), hot-stamp (where a heated die is
used to transfer the oxide stripe from the backing onto the card after the card
is cut to size), and cold-peel (where the oxide stripe is peeled from the
backing, and then laminated into the card). Each of the methods have their own
advantages and are largely irrelevant to the user of the card.
Another method of putting a stripe on a card is direct coating. In this case,
the oxide slurry is coated onto the card (usually paper or card rather than
plastic) during the manufacturing process for the card. There can be some
manufacturing cost reductions by using this technique, though there may also be
some quality trade off.
Once the slurry is coated onto the substrate (plastic backing or direct to
card stock) the particles in the slurry are aligned to give a good signal to
noise ratio. This is the equivalent of eliminating those pops and bangs you hear
on old tape recordings. The tape with the wet slurry is passed through a
magnetic field to align all the particles. With the iron oxide particles this is
relatively easy for two reasons. The particles are low coercivity so do not need
a large magnetic field to orient them, and the particles are acicular (needle
shaped) with an aspect ratio of approximately six to one. The acicular particles
have an easy axis of magnetization along the length of the particle which makes
the alignment an easy process. This process is not so easy with the high
coercivity materials. The particles used in most of the high coercivity
materials are not acicular, they are platelets. These platelets have an easy
axis of magnetization through the plate, which means the alignment field has to
stand the particles on edge and they have to stay that way to get the best
performance from the stripe. Obviously the particles want to fall over as soon
as the field is removed from the stripe so part of the skill in making a high
quality stripe lies in designing a process that can keep those particles on
their side until the slurry sets.
Unfortunately, the lack of alignment can cause some major problems in the
read and encode process of the magnetic stripe. The waveshape of the read
process can be distorted by the lack of alignment. This distortion can cause
significant problems for some read systems.
In all of the above processes, the final card has the familiar brown or black
stripe on it. The stripe can be encoded because the particles (like iron
filings) can be magnetized in either a north or south pole direction. By
changing the direction of the encoding along the length of the stripe this
allows information to be written on the stripe. This information can be read
back and then changed if required as easily as the first encoding.
|Q. How does the
magnetic stripe work?|
A. The end-user defines the requirements for the magnetic stripe
including the signal amplitude expected, the coercivity of the stripe, the
encoding method and the bit density. The card manufacturer uses the first two
points to select the type of magnetic material to use. The system designer is
concerned with all four of the parameters.
As explained above, the stripe is made from many small particles bound
together in a resin. The density of the particles in the resin is one of the
controlling factors for the signal amplitude. The more particles there are, the
higher the signal amplitude. The density (or loading) combined with the
thickness give a method for controlling the amplitude. Signal amplitude is
important because it defines the design of the readers for the cards. Standards
exist (ISO/IEC 7811) which define the signal amplitude for cards that are used
in the interchange environment (such as banking). By conforming to these
standards, a user ensures that the magnetic stripe can be read in any financial
terminal world wide.
The bit density of the information is selected based on the user requirement.
The ISO/IEC standards (7811) give requirements for bit density for cards used in
the interchange environment. These standards define tracks one and three as 210
bits per inch and track two as 75 bits per inch. The bit density in conjunction
with the data format (see below) dictate how much data is encoded on each
|Q. How is information
encoded on the magnetic stripe?|
A. Each character that is encoded on the stripe is made of a number of
bits. The polarity of the magnetic particles in the stripe are changed to define
each bit. Several schemes exist to determine whether each bit is a one or a
zero, the most commonly used schemes are F2F (or Aiken BiPhase) and MFM
(Modified Frequency Modulation).
The ISO/IEC 7811 standards specify F2F encoding. In this encoding, each bit
has the same physical length on the stripe. The presence or absence of a
polarity change in the middle of the bit dictates whether it is a one or a zero.
The width of a single bit always remains the same but some bits have an extra
polarity change in the middle and these are called ones.
MFM encoding is more complicated. This type of encoding allows twice as much
data to be encoded with the same number of flux reversals (edges). For more
details on MFM the reader is referred to AIM publication "Modified Frequency
Modulation (MFM) for Magnetic Stripes".
The choice of encoding scheme is determined by the application and the user.
If the application is one where conformance with ISO/IEC 7811 is necessary then
F2F encoding is the choice. For applications where large amounts of data must be
encoded, MFM may be a more suitable choice.
Once the encodation scheme is chosen, the format of the data must be
selected. ISO/IEC 7811 specifies two different schemes for use on interchange
cards. These are four bits plus parity and six bits plus parity. The four bits
allow only the encoding of numbers plus some control characters, the use of six
bits allows the full alpha numeric set to be encoded. The parity bit is used to
help determine if an error occurred in the reading of the data. The total number
of "one" bits in a character is added up, in odd parity this must equal an odd
number. If the total is odd, the parity bit is set to a zero, if the total is
even the parity bit is set to a one.
Although the encodation schemes are defined in ISO/IEC 7811, it is only
necessary to follow them if the application requires conformance with 7811. Some
applications depart from this scheme by allowing different bit density/encoding
scheme combinations, others depart significantly by using "proprietary" schemes
down to the bit level. As an example, an identification card may use two bits to
determine eye color (00 = blue, 01 = brown, 10 = green, 11 = other). This is
much more efficient in encoding space, but means the data cannot be read in a
standard interchange terminal. For some applications this is not important and
the extra space available is very important.
|Q. What is coercivity?|
A. Measured in Oersteds, coercivity is the measure of how difficult it
is to encode information on the magnetic stripe. A standard bank card has a
coercivity of approximately 300 Oe (Oersteds) and is considered to be low
coercivity. In Japan there is a second stripe on the credit cards with a
coercivity of 600 Oe. The trend is to move towards higher coercivity with values
of 2100, 2750, 3600 and 4000 Oersteds being common. High coercivity magnetic
stripes bring a new collection of parameters to the magnetic stripe world and
higher is not always better.
Initial coercivity is defined by the type of particles used to manufacture
the stripe. Gamma Ferric Oxide will give you a low coercivity stripe, Barium
Ferrite will give you a high coercivity stripe. The material alone does not
define the final coercivity of the stripe as the manufacturing process will
change the value usually in the downwards direction. It is possible to raise the
coercivity of particles by including other agents in the slurry.
Coercivity is NOT a measure of signal amplitude. Early versions of high
coercivity stripes often had high signal output. This is not a requirement of
high coercivity and is not usually a good thing. Most readers available today
are setup to read signal levels similar to those defined in the ISO/IEC 7811
standard. Keeping the signal output in this range makes the range of available
readers much greater.
Early versions of the high coercivity magnetic stripe were marketed with the
name High Energy. This name suggests high output levels and often causes
confusion amongst users of the technology.
|Q. Why would I use
A. The advantage of high coercivity is that it is harder to encode
information on the stripe. This also means that the it is more difficult to
erase the information and so problems of accidental erasure are diminished. It
is still possible to erase the information, but common household magnets are not
usually powerful enough. This means the person who puts the transit card on the
refrigerator will not usually damage the encoding on the stripe.
The disadvantage is that although the encoding can be read in a standard low
coercivity reader the encoder must be designed to encode high coercivity
|Q. Is higher coercivity
A. Although the coercivity is a factor in erasing a stripe, it is by
no-means the only factor. When a stripe is declared to be a 4000 Oersted(Oe)
stripe, it really means that the nominal value is 4000 Oe. There are also lots
of particles in that stripe with coercivities of other values. The distribution
of the coercivities will typically follow a bell shape curve. The steepness of
the bell shape defines the percentage of particles at the stated value, a sharp
(steep) curve shows that are a large percentage are the nominal value. A flat
curve shows that there are many other coercivities present in the stripe. This
is important because it is used to define something called "squareness" of the
Squareness is a parameter that can be used to help define the susceptibility
of a stripe to erasure. A 2700 Oe magnetic stripe with high squareness (sharp
curve) has a large number of particles at the nominal coercivity. To erase that
stripe, a magnetic force greater than the coercive value will have to be applied
to the stripe. Another stripe with low squareness may have a higher nominal
coercivity but because there may be a large proportion of low coercivity
particles it may be very easy to erase the stripe.
|Q. Who uses magnetic
A. Everyone uses magnetic stripes. The most visible use is your bank
(credit, debit, and ATM) cards, but these are not the only places. Take a look
at your Airline Ticket and Boarding pass (ATB) the next time you travel. Many of
these are now including magnetic stripes on the cards. Other places include your
phone card, your transit (bus or train) ticket, and even your parking lot
|Q. Are all
magnetic stripes the same?|
A. Magnetic stripes are not all the same. On the outside they are all
made of a magnetic material coated in some way on the document. However, as
explained above, there are different ways to coat the material on the document
and different ways to make the magnetic material. These all affect the
performance of the material in some way.
The properties of the magnetic stripe are all defined during the
manufacturing process. These properties define the signal strength of the
encoding, the coercivity of the stripe, the ability to resist erasure, even the
waveshape of the recording. These parameters are not controlled by the user but
they can have a tremendous effect on the performance of the system and should be
defined by the user.
Even the method of coating the magnetic material on the document can
influence the performance of the stripe. A direct coating on a paper ticket may
produce a stripe that is much more abrasive than the stripe on a laminated
plastic card. This abrasiveness will affect the life of the magnetic heads being
Some magnetic stripes have coatings over the stripe to protect the stripe
from abrasion thus prolonging the life of the stripe on the card or ticket. This
coating may affect the performance of the stripe in other ways.
there standards for magnetic stripe use?|
A. Yes there are. The most commonly quoted standards are the ISO/IEC
7810, 11, 12 and 13 series of standards. These standards are written for the
credit and debit card market and so include information on the embossed
characters on the cards as well as the track locations and information on the
magnetic stripe. ISO/IEC 7811 has six parts with parts two and six specifically
about low and high coercivity magnetic stripes. These standards include
information on the magnetic properties that guarantee that the stripe can be
read in a magnetic stripe reader in the U.S.A. as well as in Japan. The
companion to the ISO/IEC 7811 series of standard is ISO/IEC 10 373. This
document details the test methods for the ISO/IEC 7811 series of standards.
AIM released their Technical Specification "Effective Magnetic Parameters of
Magnetic Stripes on Media" in June 1996. This document details a collection of
parameters that can be used to completely define a magnetic stripe and compare
it with another stripe. The parameters include coercivity, amplitude, immunity
to damage, uniformity, resolution, noise, and magnetic alignment. Through the
use of simple tests, anyone can define the required performance of a magnetic
Work is just about to start on three new American National Standards (ANSI)
standards that relate to magnetic stripe performance. These are:
Effective Magnetic Parameters of Magnetic Stripes
Parameter Values for Applications
Magnetic Stripe Readers and Encoders -
The first two of these new standards are related to the AIM published
document, turning it into an ANSI standard. The third item is work that is new
in the magnetic stripe world in that the goal is to create the first standards
that are relevant to the equipment manufacturers.
|Q. Do I have
to comply with the standards?|
A. If you are not intending to use your cards in the banking system
then you can do anything you want. The ISO/IEC 7811 series of standards define
track one as a read only track with 210 bits per inch and 6 bits plus a parity
bit per character. This allows for a full alpha-numeric encoding. Track two and
three both use four bits plus a parity bit (number characters plus A to F) only,
with track two at 75 bits per inch and track three at 210 bits per inch. If you
don't have cards that have to be read in the banking system then you can use any
encoding scheme and bit density on any track you wish. In fact this gives you
some added security, as it makes it more difficult for someone to copy your
have heard that magnetic stripe it is not secure - it is this true?|
A. Magnetic stripes are not inherently secure. The problem with being
easy to manufacture and encode is that it also makes it easy for the crooks to
do the same. Several schemes are available for creating a secure encoding on a
magnetic stripe, Watermark Magnetics, XSec, Holomagnetics, XiShield, Jitter
Enhancement, ValuGard, and MagnaPrint are a few. The contacts for these
technologies are listed at the end of the paper. Each of these technologies
exploits some aspect of the magnetic stripe, the card, and the data on the
stripe to tie everything together to make counterfeiting the card in some
fashion very difficult.
|Q. How do these
security methods work?|
A. The security schemes all work in basically the same way. They focus
on some part of the card/magnetic stripe/encoding and record the information
that makes it different from any other card. This could be the noise in the
magnetic stripe, an intentional permanent signature in or on the stripe, or some
external feature on the card that is permanent.
The advantage to using one of these techniques is that the card and data
become tied together making the duplication of the data very difficult. The
disadvantage to these techniques is that they cost money and are for the most
part, proprietary. Several of the techniques have been used in large
applications where the system demanded some form of extra
|Q. Why do "Eel
Skin Wallets" cause problems for magnetic stripes?|
A. This is a rumor that started during the mid 1980's at a time when
eel skin wallets had become very fashionable. The most common way of providing a
clasp on these wallets was to use a magnet. This magnet was usually powerful
enough to erase a magnetic stripe if the two came into contact. The popular
press picked up the problem and very quickly the rumor that the eel skin was
capable of damaging the magnetic information was spread. In fact the eel skin is
no different from any other kind of leather and was not the problem, the magnet
was the sole cause of the problems.
|Q. My card does not
work in my ATM. What did I do to it?|
A. This is a complicated question to answer that can only be properly
answered after the card has been analyzed by some test equipment. The likely
problems are dirty or scratched stripe, or erased stripe. The stripe on a card
is not delicate but a few simple measures will increase the life of the stripe.
Try to keep the card in a clean place when you are not using it. A gritty
wallet, kept in the back pocket of a pair of pants, will probably end up
scratching the stripe (and probably warping the card). A scratched or dirty card
will eventually not work.
Keep the card away from magnets. The two most likely examples of magnets we
see are the refrigerator magnet and the Electronic Article Surveillance (EAS)
Tag demagnetizer in a store (this is the box that some stores have on the check
out counter that they pass a book or clothes over so that you do not set the
alarms off when you leave the store).
|Q. Is there a good way
to protect the stripe on my card?|
A. The stripe on a card is not delicate but a few simple measures will
increase the life of the stripe. Try to keep the card in a clean place when you
are not using it. A gritty wallet, kept in the back pocket of a pair of pants,
will probably end up scratching the stripe (and probably warping the card). A
scratched card will eventually not work.
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