22C3 - 2.2

22nd Chaos Communication Congress
Private Investigations

Joseph Battaglia
Day 1
Room Saal 4
Start time 22:00
Duration 01:00
ID 765
Event type Lecture
Track Hacking
Language English

Magnetic Stripe Technology

Find out how magnetic stripe technology works, how it can be hacked, how to build a card reader with parts you can find in your 'junk drawer', and how this reader design can be used to reverse engineer proprietary formats.

Here in New York, I wanted to investigate the content of the MetroCard's magnetic stripe (the fare control card used in the subway system). Because the card format is completely proprietary, I had to design a reader capable of dumping the content, which lead me to the design described here:


I designed the reader hardware to be as simple as possible while having all of the demodulation of the signals done in software (through a sound card interface). I originally wrote the reader software to conform to the standard track formats (ISO 7811, 7813, 4909, etc.) and tweaked it to become capable of reading the MetroCard format as well. I then proceeded to reverse engineer the content of the MetroCard, and as of last Spring, have published (in 2600 Magazine) the most complete description of the MetroCard system that I know to exist.

The lecture will basically describe the theory of magnetic stripes, how the reader design works, how to build one yourself, how the decoding software functions, and how to use it to possibly reverse-engineer other proprietary formats (by using the MetroCard as a recent practical example) -- and of course, read all the standard cards floating around in your wallet ;-).