where is the rfid-antennae in contactless-cards? (q to "adjust" sleeves)


#1

Hi Community,

I’m using RFID-protection-sleeves made of cryptalloy for my contactless-cards; they shield good against unwanted scanning, but they also make it hard to take the cards out (yeah I’m a bit clumsy)

I bought myself some cheap RFID-shieldcases from “overseas” (probably simple alluminium, but also shielding). Of course, those things have a very small “grip-area” for the cards, too.

I now had the idea of “cutting the sleeves out a bit”, so i can easily grab the cards. But I don’t know how much i can cut out without negating the shielding, as I have no idea where the RFID-Antennae in the cards are…

Is there a certain area that should be covered? Or do the antennae (not only revolut cards) go over the whole area of the cards?

BTW: it would be great if Revolut would ship the cards with RFID-shielding sleeves - the Chaos Computer Club demonstrated over a decade ago how easy those things can be spoofed and “sniffed out”… And those sleeves aren’t THAT expensive :wink:

Edit: typos. I fixed as many I could.


#2

I am pretty sure it is part of the chip that you can visible see on the card.


#3

most cards have antenna all around the plastic area so i doubt it would be that small as you may think


#4

yeah i think JoyM is right, i just checked several cards with my (nfc enabled) cellphone by covering up spaces. some cards are close to the chip, others have a wider area…

question’s now “how much exposure is needed to negate the shielding” - eventough the oversea-sleeves were/are cheap, i don’t wanna risk them all by “testcutting” too much out…

anyone has an idea?


#5

I have transparent card, and everything is visible.
See this:


#6

@redi

thanks for the screenshot - interesting layout (and the transparent card is looking cool, too :wink:

seems there’s no way to cut on one of the sides without exposing the antennae…
does anybody know how much of the antennae-length’s needed to induce enough current for the chip to start working? (and making a good signal)


#7

AFAIK this is not antenna, but just coil… So when you cut wire, this will stop working…


#8

I want to adjust the sleeves (i bought), not the card (i like the contactless payments, just not “out of the pocket”, so to speak) :wink: - but yeah, with RFID it’s more a coil then an antennae… The question remains the same though, “how much can be exposed without the chip “starts working”?”


#9

From my observation about 0,7 to 1 cm should be enough


#10

Hi again

I did it - and cut one of the sleeves (hope the img-upload works the way i hope); I just cut the frontside so I can give my thumb a good “grip”, while my finger grabs the opening (front and back are symetrical, refer to the sleeve with the green card in it). So I now have an approx 2cm-opening in the front, and the “old” cut in the back - it’s much easier to get the cards out now… (Edit: and the sleeves still shield form reading the card with cellphone**)

(** BTW - these sleeves from “overseas” (china :wink: are made of a thicker paper (my guess 140g/m² - just a bit thinner than the old “photopapers” for inkjet-printers) and some alluminum-coating on the inside, not very thick. They shield the signal when using a cellphone, not sure how well they work with some “shop-grade” hardware - will test and report results. (at least the cryptalloy-sleeves are completly made of that “alloy”, the protection sure is bigger than those cheap ones)


#11

If you’re on Android you can check by yourself.
Just use this app:
https://play.google.com/store/apps/details?id=com.github.devnied.emvnfccard


#12

ehem @redi …that’s what I did, pal… :wink: (other app, but same principle)