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There is a company out there that developed a product which looks like a simple card ( format of a credit card or so ) and claims to block rfid-signals in a distance of 10mm. It is not a case to protect a card but rather card which you put over the card/cards you want to protect. Is this actually possible or is that a fraud?

I am not talking about two cards blocking rfid signals like in this example but one card that can block anything in a distance of 10mm. Is this possible and if it is can you provide me a trusted source for this?

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    Maybe instead of being a passive device that just blocks signals, it's an active device that gets power from the reader and generates garbage signals to jam any communication, thus preventing any communication with other nearby cards. – André Borie Dec 21 '15 at 8:54
  • That's a cool thought, but I need evidence :D! – user61441 Dec 21 '15 at 9:00
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    Given that just carrying 2 cards next to each other is quite likely to cause contactless payments to fail, it wouldn't be surprising if it did work. 2 cards next to each other isn't a solution in its own right as demonstrated by TFL: '*You may have touched more than one contactless card on the reader at the same time and payment was taken from a card you did not intent to pay with. *' – Chris H Dec 21 '15 at 12:58
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    @ChrisH there seems to be anticollision features built into some NFC cards (Mifare cards for example, not sure about others) and I've personally been able to use LibNFC to talk to multiple cards on the same reader. – André Borie Dec 23 '15 at 12:32
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Are you wondering if such technology exist, or are you wondering if the speech of a company you know but for some reason do not mention is realistic from a technical point of view?

No matter what, such company exist, an example would be Amourcard. I do not know if there are other, they claim to be the first to offer such service.

This company targets more specially the NFC world, which is subset of RFID used mainly for credit card and passport:

Armourcard electronically jams the frequency these credit cards & epassports communicate over (13.56MHz)

NFC technology does not cope with noisy environment. I mean that if the communication frequency is full of garbage information, the communication between the NFC reader and the tag will not be possible.

This card goal is therefore to produce such garbage information. Internally it is most probably exactly the same kind of circuit you may find in NFC enabled credit card, but instead of implementing the NFC communication standard it just endlessly send garbage as soon as an NFC reader tries to communicate (by the way, on their OOperating Instruction page, section 'Tap & Go' payment gateways, they acknowledge that this behavior may lead several readers to crash and reboot).

  • At least in principle, this should effectively work for the designed purpose, which is protecting NFC enabled credit cards and passports, as long as this jammer card is stored together with them,
  • It may be less efficient with other kind of RFID tags, even if they operate on the same frequency, due to protocol or technical differences,
  • It will not be effective at all with RFID tags operating on different frequencies than 13.56MHz.

Quick addendum: while browsing the site of the aforementioned company, I see that they made the choice for their jammer card to embed its own battery instead of relying on the NFC reader signal like classical NFC tags. They announce a battery life within 18-24 month. Be sure to check the battery status regularly (a green led lightning up when you temporarily disable the jamming feature by holding your finger on a small "button" on the card), since when the battery deplates you will not be protected anymore maybe without noticing it (the card needs to be replaced by new one, no way to replace it).

  • In another, totally different scenario, i observed that even a very thin layer oft metal (metal-ink in 400g paper in this case) can block weak/cheap NFC tags. – marstato Dec 21 '15 at 10:11
  • @marstato: this thread focuses on active blockers in credit card shapes, but I know this. Aluminum sleeves are, IMO, the best price/protection level when you have just a few cards (there also RFID blocking wallets, some even providing a per card shield, but I didn't test). There is a video showing this experiment anyone can do of wrapping up a cellphone in an aluminum foil and notice that it cannot be joined anymore. While looking cheap for some people, this shows how it can still be effective. – WhiteWinterWolf Dec 21 '15 at 10:22
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    @WhiteWinterWolf a not-very-scientific test I did just by putting foil in a zipped note compartment of a wallet showed that RFID door keys and NFC payment cards were incompletely blocked. Some signal gets out the edges, but it took many tries on different angles to even get the readers to recognise that a card was nearby. This would probably stop the pocket-bumping type of attacks without being visible/looking cheap. I say probably because a significantly higher-powered reader (as might be used by someone trying to steal card details) would tend to pick up multiple cards and so not work. – Chris H Dec 21 '15 at 12:55
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    readers to crash and reboot Nice! I have to get one of those and try it next time I do the groceries. – njzk2 Dec 21 '15 at 15:45

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