Path: utzoo!attcan!uunet!mcsun!hp4nl!ooc.uva.nl!ropg
From: ropg@ooc.uva.nl (Rop Gonggrijp)
Newsgroups: sci.electronics
Subject: Re: Credit card encoding
Message-ID: <13619@slice.ooc.uva.nl>
Date: 26 Sep 90 13:09:59 GMT
References: <28174@pasteur.Berkeley.EDU>
Organization: uvabick
Lines: 28

e142-aq@hercules.Berkeley.EDU (Alan Nishioka) writes:

>Does anybody know how information is encoded on the magnetic stripe for
>credit cards, bank cards, my student id, etc.?  Any references?  A trip
>to the library and looking thru the reader 's guide didn't get me anywhere.

Well, there's three tracks (ISO 3554), all 0.110" wide. The top one is
210 BPI and has 7 bits per chr. (incl. parity). Total 79 alpha-num. chrs.
The second track has 75 BPI, 5 bits per chr. (incl. par.) total 40 digits
The third track has agian 210 BPI, 5 bits per chr (yeah incl. par.) total
107 digits.

Data is coded reversing the polarity of the magnetic field once or twice in
the field for that bit. Since you cannot double of half the speed of the card
within the space for 1 bit, it all works.

>I just bought a card reader which had 5 ttl level outputs.  Two for each
>of 2 head tracks and a 5th that goes low when a card is being run thru.
>The chips don't seem to be identifiable.

Well, the bad news is that you'll have to write the decoding software yourself.
Not much to it, I did it on a Commodore-64. Our magazine ("Hack-Tic") printed
the full specs on all this in the last issue.
-- 
Rop Gonggrijp (ropg@ooc.uva.nl) is also editor of  Hack-Tic (hack/phreak mag.)
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