Path: utzoo!attcan!uunet!wuarchive!uwm.edu!psuvax1!psuvm!esv
From: ESV@psuvm.psu.edu (ANDREW COLL)
Newsgroups: sci.electronics
Subject: Re: credit-card encoding (was Re: Wiegand wires?)
Message-ID: <90275.180019ESV@psuvm.psu.edu>
Date: 2 Oct 90 22:00:19 GMT
References: <5770030@hpscdc.scd.hp.com> <10960034@hpldola.HP.COM>
 <1990Sep25.153854.2812@zoo.toronto.edu> <wayned.9600@wddami.spoami.com>
 <34388@cup.portal.com>
Organization: Penn State University
Lines: 39

In article <34388@cup.portal.com>, mmm@cup.portal.com (Mark Robert Thorson)
says:
>An even simpler way to duplicate a magnetic card is to place two cards
>together, with the blank on top.  (You make a card blank by wiping a magnet
>across it.)  Then quickly wipe a hot iron across the top card.  This briefly
>heats the magnetic stripe above its Curie point.  When it cools down, it
>picks up the field of the card on the bottom.
>
Along similar lines:
Our university has as system in place where you can obtain
photocopies or laserprinter output via a credit card of sorts.
Its called a "vendacard" and you insert it into little card
readers on either copiers or laserprinters.  You
buy the card by feeding dollar bills into a vending machine
which credits your card with the amount of money minus $0.50
for the card.  The cards are laminated plastic with a magnetic
stripe on the back about 5mm wide.  Occasionally the cards go
bad and are unreadable. (usually due to scratches)  I examined
one of these unreadable cards and found that the magnetic strip
was indeed coded with digital data.  The interesting thing I
found though was that these cards were exceptionally resistant
to erasure by exposure to magnetic fields.  I tried erasing the
stripe using a 20oz permanent magnet:  no luck, the data wasn't
even degraded.  I tried a tape head demagnatizer, same thing.
I then remembered that when you got your card back from the reader,
it was slightly warm.  So I tried immersing the card in hot water
and using the demagnatizer; still nothing.  So I tried the ultimate
torture:  microwaving it in a dish of water.  I microwaved it until
the water boiled, at which point the laminated plastic card was so
soft, it couldn't be picked up.  In this state, I tried the
demagnatizer again; after letting it cool enough so it would go into
the reader, it still had the data intact.  I came to the conclusion
that these cards are extremely resistant to stray or not so stray
magnetic fields, and the only way to damage them is physically.
Therefore, I have extreme confidence in the integrity of my vendacoder
card, and maybe a little more confidence in my credit and ATM cards.

Andrew Coll       ESV@PSUVM.BITNET
                  ESV@PSUVM.PSU.EDU