🚀 go-pugleaf

In article <012191.223817BRBOYER@MTUS5.BITNET> BRBOYER@MTUS5.BITNET (Bradley R. Boyer) writes:
>
>   I have a few questions regarding copy cards or other identification cards
>that have magnetic strip memory segments:
>
>   1. What is the memory capacity of the card?

There can be as many as three tracks on the stripe.  Tracks 1 and 2 are read-
only, while track 3 is read/write.  All three tracks include a parity bit
per character, and an LRC character per track.

Track one stores alphanumeric data using a six-bit code.  A maximum of
79 characters can be stored, including overhead such as start/end sentinels,
LRC, etc.

Track two stores numeric data only, using a four-bit code.  Maximum here is 40
characters, including overhead.

Track three stores numeric data only, using the same four-bit code as track 2.
Maximum capacity is 107 characters, including overhead.
>   2. What type of format is used for data storage?

Track one uses a character set which maps into ASCII.  Tracks two and three
use ordinary hexadecimal.

>   3. How volitile is the data contained on the magnetic strip?

It depends on the strength of the field used to record the stripe.  Tracks 1
and 2 are usually pretty firmly implanted, urban folklore aside.  I have had
to "damage" some stripes for test purposes, and it's not as simple as you
might think.  Not that it's difficult.  The stripes will _not_ be damaged by:
     - eelskin wallets.  (something about using the skin of an electric eel)
     - storing several cards stacked on top of each other.
     - airport Xrays and metal screening equipment.
     - flourescent lights. (unless you store your cards ON the ballast)
     - most other things people have _assured_ me will damage the data.

You will need a strong magnetic field.  The recording heads on card-writing
equipment heat up quite a bit from the amount of current used.  The small
units I have worked with have warnings about allowing a certain amount of
"cooling-off" time between cards or after a batch.  Some larger machines are
water-cooled.

Obviously, track three will be the easiest to alter, since that's what it's
designed for.  But the exact data format will depend on the application.  In
general, without expensive equipment you'll be able to erase a card so that
it's unusable, but it will be tough to write new data on it.


For details, see the ISO standards:
     - 7810   (card physical specs)
     - 7811/2 (stripe recording techniques/format)
     - 7811/4 (location of tracks)
     - 7812   (numbering system)


-- 
-----------------------------------------------------
Gordon S. Hlavenka            cgordon@vpnet.chi.il.us
Disclaimer:                Yeah, I said it.  So what?