Visa's contactless payment cards will approve very large transactions in currencies other than the British pound due to a flaw in a protocol, U.K. researchers contend.
They concluded it would be possible for criminals to turn a mobile phone into a point-of-sale terminal and pre-set a large amount of money to be transferred from a payment card even if it was in someone's pocket.
The type of card, known as EMV after its developers Europay, MasterCard and Visa, uses a microchip to facilitate transactions rather than a magnetic stripe. EMV will soon be used widely across the U.S.
Some types of EMV cards are configured for "contactless" payments, where a customer doesn't have to enter a PIN for smaller transactions that in the U.K. are limited to £20 (US$32).
Researchers with Newcastle University found that Visa's contactless card would authorize a transaction up to 999,999.99 without a PIN if it was in a currency other than the pound.
If an improvised point-of-sale device gets close enough to someone's card in a wallet, the contactless card would approve an offline transaction in less than a second.
The researchers cautioned, however, that they did not test the back-end system of banks, so it is unclear if the transaction cleared by the card would be be fully processed. It wasn't clear from the payment protocol's documentation how banks would deal with the inconsistencies the research uncovered.
Still, they wrote in a news release that "the fact that we can bypass the £20 makes this new hack potentially very scalable and lucrative. All a criminal would need to do is set up somewhere like an airport or the London underground where the use of different currencies would appear legitimate." It isn't clear whether the researchers tried to contact Visa or the banks about the flaw.
EMV cards have been used for many years in Europe and other parts of the world. The microchips that contain account information and authorize transactions are not easy to forge unlike the magnetic stripe data on cards today, which can be easily copied.
But the researchers predicted that as the magnetic stripe is phased out, contactless payments may become interesting to criminals.
Visa officials could not be immediately reached for comment.
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