December 1, 2009 AT 4:29 pm

Square – sound to mag stripe reader…

Pt 2357
Square will allow phones to easily take credit cards, looks like a cool little sound to mag stripe hack/dongle. We’ll try and get one to take apart soon.



  1. Are they expecting people to type their PIN into somebody else’s random phone?

  2. Just like you would with any merchant, you have to put trust in the person you’re giving your information out to. It’s exactly the same information you enter on, only this time in iPhone-form. Also, it’s not the 4 digit PIN, rather it’s the card number (16 digits, if I recall).

  3. “We will try and get one to take apart soon.”

    Yay! I can not wait…

    (please delete the previous comment

  4. Similar to this, which I found interesting:

  5. @peedekk

    Thanks for posting that link! I’ve been wanting to do something like that for a long time. Now I can finally get back at Julia for… …just kidding!

  6. I’m not sure you’re going to find much in there other than the mag stripe reader head itself. I built something like this back in the early 90′s by connecting a mag stripe reader head directly to the microphone input on a sound card. After recording a swipe I was able to see that the zero-crossings of the resulting wave form matched the magnetic pole reversals on the stripe well enough to read the data. I wrote a little program in C to decode the magnetic stripe data and display it. The only tricky bit was compensating for the fact that, no matter how hard you try, the end of the swipe is always faster than the beginning, so your bit times get shorter and shorter over the course of the swipe.

    If anyone’s wondering where I got the mag stripe data format specs, it was in an issue of Phrack magazine. God bless old-school hacker zines!

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