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Square & VeriFone, My phone accepts payment cards

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.


  1. Seems fairly clear cut to me, though IANAL and IANAQSA.

    If you are a Square customer who agrees to the Commercial Entity Agreement, clause 1.(e.) pretty clearly obligates you to comply with PCI DSS.

    Which means you must only use PA-DSS validated applications.

    The list of Validated Payment Applications

    doesn't list Square as a company making any validated payment applications.

    And, though I can't dig up a citation, I'm pretty sure I've read that the PCI Council had decided they were not going to be accepting any mobile apps for PA DSS validation until they said otherwise.

    I wouldn't recommend Square to anyone who had to accept the CEA, at minimum. I'm not clear whether the general UA ends up obligating one to PCI DSS compliance.

  2. If either the VeriFone or Square solution encrypts in hardware, and the software only transmits to the processing server (which has the decryption key) then the solutions might go a long way to increasing the level of security in a mobile payment environment. That's not to say either solution wouldn't still be vulnerable to the right mobile malware--which hasn't been written yet--but it'd be better than some of what's going on now in this space.

    As for compliance requirements, quoting the PCI stance on mobile payment applications:

    > Until such time that it has completed a comprehensive examination of the mobile communications device
    and mobile payment application landscape, the Council will not approve or list mobile payment
    applications used by merchants to accept and process payment for goods and services as validated PA-
    DSS applications unless all requirements can be satisfied as stated.

    Both VeriFone and Square are subject to PCI's "PA-DSS", or Payment Application Data Security Standards. Neither can be PA-DSS certified, however, because of their mobile nature. So those applications--and any merchants using them--are not compliant with their PCI-DSS requirements. Which probably means if they get breached, it's on them, regardless of contract language in either application.

    (I'm not a lawyer and I'm not a PCI expert, thankfully.)

  3. Verifone claims end to end encryption, but if they permit manual card entry...

  4. It looks like the PCI folks are taking notice of the issue:,289142,sid14_gci1528926,00.htm

  5. Allowing you to turn your phone into a payment card terminal is such a very convenient method for every consumer. This is indeed a very good application. However, it is safer to use if it's PCI compliant. This will give every user the confidence to pay their bills using this method without any hesitations.

    Vulnerability Assessment


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