Billy Hoffman wondered what was encoded in the mag stripe inside his various cards. A friend had a reader, that he got from Germany for about $300. He discovered that some encoded his social security number for no apparent reason.

a mag stripe is PVC, magnetic particles and glue. The particles are arranged in magnetized vertical strips. There are 3-4 tracks on each. Stripe 1 can have 100 characters, stripe 2 can have 40, and stripe 3 is journalized. (I’m not sure why journalizing it is useful.)

There’s nothing available for reading cards except expensive, proprietary models. So Billy wrote stripesnoop that displays the contents of a magstripe. You can build a reader for $10-15. They’re developing a writer that will write to all three tracks, for about $75, instead of the $900+ you’ll pay for a proprietary model.

It was an informative talk. Billy’s going to set up his reader and let us see what’s encoded on our cards. (The stripesnoop site has most of the information if you want to get more than this sketch.)

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