3 ms·

One workaround (instead of buying an rf shielded wallet) I've heard of in the past is to put two cards next to each other because it causes signal interference.

One workaround (instead of buying an rf shielded wallet) I've heard of in the past is to put two cards next to each other because it causes signal interference. I have no idea if it works (I use an iphone) so ymmv.

praseodym 12y ago
Actually some RFID card standards (Mifare for example) have card selection and anti collision built in, so it would still be possible to read the correct card without interference.
ikari_pl 12y ago
It works perfectly with my cards. I can't open the office door if my paypass is too close. My city card (basically a fancy name for a long-term bus ticket) also interferes with both of these two.
- abritishguy 12y ago
  That just means your office doors aren't configured properly and don't know which card to talk to and choose to do nothing in this case. The reader could very well talk to one card (or both) without interference.
abritishguy 12y ago
Having two cards next to each other may well make the illusion of preventing the cards from working as quite a lot of readers will refuse to communicate with a card if there is more than one in range (sensible for some applications). This does not mean, however, that they are not capable of doing so - the first thing a reader does is get all the cards in range to broadcast their UID - it then uses this UID to select a card to talk to. When I was cracking mifare cards (used as authentication in many buildings) I found that it was significantly quicker to crack several cards at the same time than to crack them individually - this is because the attack that I was using required demagnetising the card hundreds of times which takes a lot longer than any communication with the card. I could crack a single mifare card in 5 seconds, I could crack 5 in 6 seconds (and for most applications cracking one card is all you need - all cards use the same encryption key).

praseodym 12y ago

Actually some RFID card standards (Mifare for example) have card selection and anti collision built in, so it would still be possible to read the correct card without interference.

ikari_pl 12y ago

It works perfectly with my cards. I can't open the office door if my paypass is too close. My city card (basically a fancy name for a long-term bus ticket) also interferes with both of these two.

abritishguy 12y ago
That just means your office doors aren't configured properly and don't know which card to talk to and choose to do nothing in this case. The reader could very well talk to one card (or both) without interference.

abritishguy 12y ago

Having two cards next to each other may well make the illusion of preventing the cards from working as quite a lot of readers will refuse to communicate with a card if there is more than one in range (sensible for some applications). This does not mean, however, that they are not capable of doing so - the first thing a reader does is get all the cards in range to broadcast their UID - it then uses this UID to select a card to talk to. When I was cracking mifare cards (used as authentication in many buildings) I found that it was significantly quicker to crack several cards at the same time than to crack them individually - this is because the attack that I was using required demagnetising the card hundreds of times which takes a lot longer than any communication with the card. I could crack a single mifare card in 5 seconds, I could crack 5 in 6 seconds (and for most applications cracking one card is all you need - all cards use the same encryption key).