How Apple’s Lightning-Plug Guru Reinvented Square’s Card Reader

The magnetic stripe on your credit card stores data in two separate bands. The old Reader grabbed from just one. With their new custom read head, Square can grab both, which makes every swipe more accurate, and more likely to work on one try.

There are three tracks on a magnetic stripe (IATA, ABA and THRIFT), the first two are used in banking. The first track stores alphanumeric data such as your name; the second track stores numerical data, namely the card number. Reading both tracks doesn't make the swipe "more accurate" at all, since there is no redundancy there.

On one level, developing a custom chip gave Square total control over the processes at the heart of the product: Decoding the magnetic signal from the credit card, encoding the electrical signal being sent to the smartphone, and all the encryption that happens in between.

First, the decoding of the swipe does not happen on the reader. The first version of Square sent the entire audio clip to their servers for decoding; this new version may do it on the phone. Secondly, there is absolutely no encryption between the reader and the phone, any encryption is between the phone and their servers.

The old version relied on a coin cell, which added around two millimeters to the overall thickness of the device. With their own chip, though, Square was able to be much more efficient in their use of power, to the point that they could draw all they needed from the smartphone via the audio jack.

An audio jack provides no power. The signal is created by electromagnetic induction. The previous version of Square used a battery to amplify that signal.

Edit: Square claims their new readers do some sort of "encryption." I am skeptical, but I had only tested the first version of the reader.

The perpetual auto-loop is not quite perfect, but I can't think of a better alternative. I wonder it's hardware accelerated on most phones or if its sucking battery. I assume the browser is definitely smart enough not to render it when it's off screen, but the loop is too tight to try to 'test' that by timing it while scrolling.

I'm not at home but I'm curious what the bitrate is, what tools are used to produce it. I know anigif is popular on reddit and tumblr, nice to see it getting used in this way.

> You have to make the swipe feel satisfying; you have to make it ready [sic] accurately enough that it works the first, every time.

I don't think you have to do this. I've used a number of card readers that didn't read my card the first time (or the second, or the third), and that didn't feel good at all. They still collected my money successfully :)