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Question: How could I build an electronic device which disabled the remote interaction functionality of contactless payment cards while not affecting the functions which are accessed via the on-card contacts or magnetic stripe (where equipped)? I am looking for a DIY technological solution that I could implement myself or suggestions about how I may be able to design and build such a system.

NB: The device would be used by me or other owners of such cards to control access to the card's facilities and to prevent fraudulent access. The desired system has no known fraudulent or illegal aspects.

Background:

New chip-and-pin cards come with an antenna which is a coil made of five or so turns of wire (fractions of millimeter thick) located typically along the card perimeter. The antenna is connected to the chip which also has the contact pad used for connecting the card to the terminal when not using the wireless technology.

One important design aspect is that all the turns belong to the same imaginary plane - they are "parallel" (no intersections) to each other and the gap between adjacent turns is more or less constant and is roughly the same as wire diameter. See this and this for pictures of the antenna layout.

There's a bit of paranoia about payWave/PayPass contactless payment features (see this, this and this questions on Money SE). People want to keep all the card features (the card body itself, the stripe and the chip) but disable the payWave/PayPass feature.

Once their banks refuse to disable the feature cardholders proceed to mechanical card alterations - they locate the antenna and either drill through it or slightly cut it with a knife. Typically they succeed but I'd be curious to see the eyes of a cashier who sees this card with two ugly holes one of them through the magnetic stripe. Clearly this may raise a lot of concerns and perhaps even cause an arrest in some cases.

Is there a way to go without notable damage?

Basically we have a small chip which we want to stay intact connected to a coil of very thin wires located in the same imaginary plane (no intersections) all embedded into a thin layer of hard plastic and we only want the coil disconnected in any one point so that it no longer forms a closed circuit.

How can this be done without drilling/cutting/punching a visible hole in the card body?

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    \$\begingroup\$ +1. This probably explains the spate of "how do I get longer range with 13.56MHz RFID reader" questions lately... I returned my shiny new card last summer and [down|up]graded to Maestro. Bank was a bit snooty about it but complied. \$\endgroup\$ Dec 26, 2014 at 11:12

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Electronically: Produce a series tuned circuit tuned resonant at the frequency of the card system - this acts as a "suck out trap. This could be conductive ink printed on paper or similar and stuck on the card surface. The trap need not occupy the whole card area but mechanically overlapping part of the loop conductors may help.

I have not investigated the technology. I assume that this is NFC rather than RF technology - but such loops are almost always still resonant and the same key principles apply.

A similar device tapped to a TV antenna ribbon cable feeder of yore could remove a selected station from the spectrum.

Keeping the card in a shielded sleeve when not in use would be easy enough. This IS an electronic solution.


Related:

Changing banks to one which is receptive (and which will provide cards which are not) is liable to be most effective overall. I'm not exceptionally paranoid (just more than some) but I would not happily have one of these cards if I could not enable and disable it readily at will. The opportunities for abuse are vast.

Adding a 'shield' on the outer surface of a card over the antenna area would be liable to work. A piece of soft iron tape may work. A strip of wide magnetic recording tape (off old half inch tape or ...) may. A mumetal strip may also work for the opposite reason. As all these could effectively present as or under a thin sticker thay may alter the cards cosmesis but not its internal integrity. They MAY make it too thick to work in a magnetic stripe reader depending on how implemented, but this will often not be an issue.

A part sleeve would still allow the card to be used in most ways while screening the antenna. This has the advantage of being removable as required.

A method similar to the one you cite but far less defacing would be to drill one only small diameter hole to break one only track anywhere in the loop. This is not certain to work but probably would. Drilling this from one side only and not penetrating the other surface improves cosmetic effect. The obvious location in in the magnetic stripe, with the hole then being black filled in some manner. The end result could be near invisible and all the cards functions except one would still operate correctly.

The image below has an ~= 1mm dia hole through a track in the antenna loop under the mag stripe at upper right.

enter image description here

Another option may be to impact the card with a sharpish edge of appropriate width at relevant locations one or more times in order to fracture the internal loop. This may or may not be able to be done without visibly severe damage to the card.

A commenter here suggested a slit in from the edge. They suggested it as the mag stripe edge but it could be also from either end - with the left end as seen in XRay possibly being closest. The slit can be essentially zero width - eg a shearing action which rips the card in to the required depth from the edge but has no actual width would sever the tracks and then allow the card to re-align. This MAY be very low visibility and "healing" with superglue or another adhesive may work.

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  • \$\begingroup\$ I like the non-through hole idea. I guess a pin vise featured here diy.stackexchange.com/a/41908/807 with a suitable diameter drill bit would be nearly perfect for this. Filling the hole would isolate the wire ends from each and so prevent their hypothetical accidental connection and also keep the card circuitry insulated from the outer world which is good too. Which compound would be appropriate in your opinion? \$\endgroup\$
    – sharptooth
    Dec 26, 2014 at 10:22
  • \$\begingroup\$ @sharptooth see additions. Any filler that works would work :-). I'd try either an epoxy resin with misc filler to add colour or a silicone rubber. Epoxy has more chance or working I suspect. No filler at all may still look ok. A 1mm hole (0.8mm may do) is not vast and may not usually attract attention - especially if one sided. \$\endgroup\$
    – Russell McMahon
    Dec 26, 2014 at 10:36
  • \$\begingroup\$ I see. I'd be suspicious of not using a filler because then the wires might somehow get reconnected (some dirt perhaps). Filling feels more reliable. \$\endgroup\$
    – sharptooth
    Dec 26, 2014 at 10:44
  • \$\begingroup\$ An external shield should be a full-size short-circuited turn of copper or aluminium, in parallel with the internal coil. You'd need a lot of iron to affect this frequency signal, and magnetic tape has no bulk magnetic properties. It could be a thin sheet of aluminium foil glued on (looks strange), or even a very thin wire wrapped around the edge (won't last long). A partial shield will reduce range a bit. For any shield you invent, you can test its performance using a phone with NFC - A Nexus from 2011 onwards, or an iPhone from 2014 :-P - they can usually read the basics from a card. \$\endgroup\$
    – tomnexus
    Dec 26, 2014 at 12:45
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There is certainly no need to punch 3mm holes through the card as in the image you referenced. All you need to do is cut one of the antenna coil wires and the RFID function is dead. What this looks like after the fact depends on your tools and skills.

You will first need to know where the wires are. You can x-ray a card but that sounds rather expensive unless you happen to have a machine handy. The other method involves just dissecting a card (and a creative story to the bank to get a new one), find out where and how deep the wires are, then use a dremel tool with a fine point bit to cut through them. Careful work should result in a mark less than half a millimeter wide that looks much like a simple scratch. Some model paint and the cut becomes nearly invisible.

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Answering because I get traffic from this question.

Overcooking an answer to this issue is unwarranted. Designing an electronic something to make the modification invisible seems also overkill (even though I love making electronic somethings).

IMHO, the minimum viable solution consists of what is within hands-reach when I'm opening my letters. Being, a smart phone with "torch" function to identify where the antenna traces lie, and a paper hole punch to sever them. Eyeball the card, punch the card. Job done in 30 Seconds. No need to make it any harder than that.

Talk about smaller special invisible holes, and discrete knife cuts etc are all too complicated, and risk making the solution to the problem seem more onerous than it really is.

These days, my frequent flyer card, my supermarket buyer card, and any number of other store cards have started to include RFID, which is capable of being used to track your location within store, for example.

Best answer is simply to end their pleasure today, with the most simple tools at hand. A Faraday case for a temporary solution, or hole punch for the permanent outcome.

YMMV, but I've never had push back from cashiers from using perforated cards. Only interest, and an expression that they must do same.

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  • \$\begingroup\$ Has any store or bank clerk ever questioned the damaged card? \$\endgroup\$
    – sharptooth
    Jan 13, 2015 at 12:18
  • \$\begingroup\$ Yes, happens occasionally. I explain my choices, and often (say 50% of the time), they suggest they'll consider doing the same. No one has ever rejected the card(s), because it works perfectly fine in the machine. \$\endgroup\$
    – feilipu
    Jan 13, 2015 at 13:27

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