Square allows you to turn your phone into a payment card terminal.
Cool. For a mere 2.75% overhead, a merchant can accept credit cards using a free magnetic card reader attached to your phone headset jack. Your customers swipe their card and scribble their signature on your iSplat’s screen, your bank account gets a credit.
The obvious questions: How do you secure a mobile application such that it can safely handle payments? Is your Square enabled phone now covered under some sort of compliance regime?
Square says they are secure, but they’ve loaded lots of weasel language into their User Agreement and Commercial Entity Agreement. (I don’t make a habit of reading merchant agreements though, so their language may be typical for the trade, but the part where they exempt themselves from any liability or damages caused by 3rd party trojans would concern me.)
VeriFone disagrees, claiming that the Square system is vulnerable to rogue mobile apps, and claiming to have (in an hour) written an app to exploit Square. But VeriFone is a competitor and FUD works, so we have to ask – is VeriFone any different? From what I read on their FAQ they encrypt in hardware and only use the phone for transmission of encrypted data, so they might be different. As expected, Square disagrees with VeriFone, but in their CEO’s carefully worded letter, makes no assertion as to the security of their application.
I’d compare Square’s solution to running a card swipe terminal on the USB port of an ordinary desktop operating system & reading the card data with an Internet-downloadable application. The operating system must be presumed insecure (we have no evidence that any general purpose operating system has ever been invulnerable to exploitation), the payment card application hosted on the operating system can not (by definition) be more secure than the operating system, and unless the terminal performed some sort of encryption prior to sending the stream to the application, any compromise of the host OS would result in compromise of the card data.
But it is so convenient.
Update 08/05/2011: And insecure.