аааааааааааааааааааааааааааа Magnetic Stripes
ааа Translated from Hack-Tik, #8, #9/10,
available at PO Bos 22953,1100
аааааааааааааааааааа DL Amsterdam, The
Netherlands
ааааааааааааааааааааааа Translation by Dr.
Abuse
аааааа Text/Schematics _copied_ from 2600
Magazine, Summer 1991 by:
аааааааааааааааа
ааааааааааааа *аааааааа ..oooOO Count Zero OOooo..ааааааааааа *
ааааааааааааа *аааааааааааааааааааааааааааааааааааааааааааааа
*
ааааааааааааа *аааа -=Restricted -=Data -=Transmissionsаааааа *
ааааааааааааа *аааааааааааааааааааааааааааааааааааааааааааааа
*
ааааааааааааа *ааа "Truth is cheap, but Information
COSTS!"аа *
(Read _my_
article on Magstripe Technology in Phrack #37 if you want
_detailed_
descriptions of encoding tech, specification, etc.а -c0 )
а People KEEP ASKING me about this article that
appeared in 2600,
and many
people wanted the schematics.а I figured
I might as well
type it up
in order to help spread the info around as efficiently as
possible.а I hand-drew the schematics in 320x200 .GIF
format.а
Enjoy, and
remember to always SHARE the knowledge...
(The
following is a VERBATIM copy of Dr. Abuse's translation.а
Thanks
Doc!)
а "Cash is out.а Plastic is in.а In the nineties, the question is:
who has the
best hand of cards?а We will help you
play the big
magnetic
card game.
аа Everybody has looked at those credit cards
and wondered what
exactly was
on them.а Whoever dared to even ask about
magnetic
readers/writers
was shocked after hearing the price and they went
back to
their daily living.а And this while you
would be very
anxious to
know what the bits and bytes mean.
аа We now give you the opportunity to build
your own credit card
reader/writer.а For the cost of playing around with
electronics plus
a few
dollars, you can build your own magnetic card copier.а This
device
reads from one magnetic card and puts the data out onto the
other
card.а For the advanced electronic
hobbyist, there is the
magnetic
card reader and writer.а Everybody who
knows ehat a TTL is
and can
squeeze something out of his computer and/or hold a
soldering
iron will be able to make this credit card reader/writer
together
with the schematics.
аа Far more interesting than all of the
electronic mumbo-jumbo is to
first see
what's really on the magnetic stripe.а For
that we give
you the
first bit of information in this article.
аа The information on most credit cards is
stored in binary form.а
These ones
and zeros are stored by changing the magnetic field of
the
magnetic head by 180 degrees.а To see
what's really on the card,
you put
some iron filings on the magnetic strip and tap the card
gently onto
the edge of the table (keep paper underneath it because
it probably
would have cost you lots of effort to make the iron
filings)
and behold!а Here's your magnetic
information, plainly
cidible to
the eye.а Some cards have such big bits
that you
theoretically
should be able to change the information on it with a
magnetized
razor blade (Paris Metro cards are a good example).а On
other
cards, the bits are so close to each other that you will only
see a
magnetized solid bar.
аа To store away the information on magnetic
cards, some
international
standars were developed by ISO - the International
Standards
Organization.а To name one: the magnetic
stripe is divided
up into
three tracks.а A lot of manufatcurers use
other coding
methods to
write the cards with and only the iron filing method will
give you
insight as to what's on the card in these instances.
аа The first project as amntioned before is to
copy the information
from
magnetic card to another.а This means
that it doesn't matter
whether the
information is encoded or not since you are just
copying.а The only thing you need to know is the exact
location and
height of
the track with the information that you want to copy.а As
long as the
write head of your copier is bigger than the mangnetic
strip, you
are safe.а See the schematic on this
page. (Schematic #1)
аа
аааааааааааааа The Credit Card Copier
аа At the left of schematic #1 you will see the
read head.а For this
(as well as
the write head) you cannot use any cassette player head
which
happens to be lying around.а You will
need to use a data head
or a card
reader head (you can obtain them from Michigan Magnetics
among
others).а If the head is bigger than the
track you are reading
from, you
will pick up extra noise but if the head is too small, the
signal
might become too weak.а Experimenting
with the gain is
essential.а The write head should be as big as possible
unless you
want to
write more than two narrow tracks next to each other.а
Between
points A and B you can jput a pair of headphones (which you
have put in
series).а If you pass the read head along
the stripe,
you will
hear a sound that might be familiar to you hobbyists who
used to
once work with data cassettes.а Now you
will need to find a
way to make
the read and write head go simultaneously along both
cards.а The trick for this is to take a piece of wood
and mount both
heads on
both ends of it.а Attach the cards (with
scotch tape) to a
solid
surface and gently slide the heads along both cards (making
sure that
the heads go in parallel with the magnetic stripe).
аа There are, however, cards on which the
infomation is not put on
the stripe
at a nintey degree angle.а If you see
something like that
(using the
iron filing method) you will have to adjust the position
on which
the heads are mounted.а A little trick to
adjust the heads
is to
replace the 220 ohms resister in front of the headphones by a
100 nF
capacitor and then listening until you find the angle that
gives you
the highest pitch sound.
аа You can only write to a card which you have
erase previously by,
for
instance, a demagnetizer.а To doublecheck
if your copy is good,
you can
listen to it by passing the read head over it and checking
to see if
the sound of the original and the copy are the same.а We
found ou
that the human ear is a very accurate meter to indicate the
accuracy of
the copy.а One last word about the dual
opamp - pins 4
and 8 of
that chip are used to supply positive and negative voltage
(see
schematic #3).
аааааааааа The Reader/Writer
аа This schematic reads and writes to the same
head.а If you want to
write
something with this schematic, you will have to come up with a
device
which has a very accurate constant speed, like a modified
printer.а The most suitable device, though, would be a
real
reader/writer
mechanism.
аа Most opamps want to have a positive as well
as a negative
voltage.а But by means of an active voltage divider
(see schematics)
we can
supply the whole card reader from one 12 volt power supply.а
The active
voltage dicider is used twice in the reader/writer.а
First of
all to divide the 12 volt down to 6 volts (in order to do
this you
put a 5.8 kohm resistor where the asterisks are in the
schematic).а The second voltage divider you make by
putting a 3.3
kohm at
that spot.а This is done to divide the 5
volts out of your
computer
into 2.5 volts.а The best thing to do is
to plave a relay
on the
write line going to the head.а This is so
as not to introduce
noise while
reading form the card.
ааа Now all you need is an interface that can
control the motor fo
your
read/write unit and which can exchange the bits with the
circuitry
described above.а What you can do then is
make binary
copies of
your card.а The credit card reader/writer
can only be used
on cards
which store their information in binary form, so go and
check first
with iron filings.
ааа In this section, we will describe several
data formats which are
used in
credit cards.а We will only describe the
three tracks as
they were
described by ISO.а On the third track a
large quantity of
formats are
used.а Only two of them are published
here.а The real
formats as
they are used by banks tend to differ from the original
ISO
standards but a little bit of research can do miracles on these
occasions.а You might wonder how the bits as described
later are
encoded
onto the card because the schematic as we described above is
only
capable of putting 180 degree magnetic field changes onto the
card.а To explain that we use track 2 because the
bits are
physically
the largest and this ought to work with homemade
electronics.
аааааааааааааааа Track 2
ааа The bits are encoded as follows: they are
separated by reversing
the
magnetic field.а These reversals make the
output of your reader
go from one
to zero or vice versa.а Beware: the fact
of whether or
not it's a
one or zero is not important, but the change in polarity
is
important.а And now, to make it even more
complicated, not only
is there a
magnetic reversal between tow bits but also in the middle
of a binary
one is a reversal.а So if you have a
constant moving
head over
your card, software should be able to determine whether
they are
reading a zero or a one.а In fact, nobody
is capable of
speeding up
the speed of his reading head twice within the time
period of
one bit.а THerefore, even a constant
speed is not
required.а SO you will get away with cheap, lousy
equipment.
ааа Now you have a whole lot of ones and zeroes
inside your computer
and you
still don't know anything.а The important
thing here is to
know the
bit stream starts at the left side of the card so the strip
is being
read from right ot left and after a couple of zeroes the
data will
start in the following format: P1248P1248 etc.
ааа The P stands for parity bit and the 1,2,4,8
stand for the
decimal
values that they represent (0001 0010 0100 1000).а If you
decode
this, there is your data, which is similar to Track 2
specifications
(ABA).а How the LRC character work (a
checksum) we
don't know
yet.а BUt our mailbox is open to any
suggestions."
---Well,
there is it.а Pretty damn good.а If you want greater
detail, be
sure to check out my article in Phrack #37.а
Happy
hunting!
аааааааааааааа ..oooOO Count Zero OOooo.. *cDc* -=RDT
