Design of an electronic device to disable remote access ability of contactless payment cards without visible alterations and damage to the card

Question

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?

Answer 1

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.

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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.

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.

Answer 2

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.

Answer 3

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.