BRBOYER@MTUS5.BITNET (Bradley R. Boyer) (01/22/91)
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? 2. What type of format is used for data storage? 3. How volitile is the data contained on the magnetic strip? Thanks in advance, Brad. ------------------------ |Bradley R. Boyer | ----------------------------- |BRBOYER @ MTUS5.BITNET| |"How could it have been me?| |Rucell @ MTU1.MERIT | | I wasn't even there!" | ------------------------ -----------------------------
cgordon@vpnet.chi.il.us (gordon hlavenka) (01/23/91)
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?
mcovingt@athena.cs.uga.edu (Michael A. Covington) (01/26/91)
Is it true that the urban legend (eelskin wallets erase mag cards) originated when there was a popular line of eelskin wallets with magnets for clasps? Or is this just a rationalistic counter-legend?