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Credit Card, Bank Card NFC. The most useless function every invented
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ve7xen:

--- Quote from: edtyler on March 05, 2022, 03:49:07 am ---Relay attacks are demonstrated in some of the Defcon talks. But, there were others with focused RF energy that allowed reading from greater distances.

One can trade convenience for security. I choose more security. Others choose convenience. The only thing that is important is to recognize there is a trade-off and to be able to properly asses one's risk and decide if mitigation is needed.

I'm not claiming that everyone should drill their cards, just that people should be able to make an informed choice.  When banks claim "NFC is super secure", I beg to differ.

--- End quote ---

What you seem to be claiming, though, is that it is possible to clone a card remotely via NFC. In other words, that having temporary access to your card could be used by an attacker to make arbitrary transactions in the future. Barring some major undisclosed problem with the technology, that is not the case, it's a challenge-response system and the nonce is provided by the transaction processor, so you basically have a few seconds to execute the attack before the transaction times out. Any attack would need active access to your card while the transactions are being completed...the relay attack. With fancy antennas and so on maybe you can make this happen at some significant distance, but you still need to be doing this in sight of both the card and the terminal simultaneously. The activity at the terminal would also look pretty suspicious, not to mention someone waving a yagi around pointing at restaurant patrons or whatever. So maybe you can manage to pull off a couple of low-value transactions before you need to tear down your setup and move on. It's a far, far less valuable and higher risk attack than card skimming, and I think pretty impractical. The actual risk seems low, and it's certainly much more secure than the old magstripe or America's chip+sign system.
twospoons:
Don't forget the carrier is 13.5MHz, so any antenna with decent gain is going to be huge.
tom66:
Also, since it's powered for passive NFC cards... NFC has peak power of 1W for distance of ~2-3cm max.  How much power do you need to get NFC to work at say 2-3m?    The card is only going to be chirping at a few milliwatts, so how well will you receive the response at your attack distance?
 
Rough calculation: inverse square law, assuming the antenna is omnidirectional, you're going to be looking at 100W+ transmitter powers.  I think you might notice someone walking around with a 100W radio-transmitter.  You might even just about feel it! Sure the attacker could use a very directional antenna but now the attack has to become a lot more careful - where is the card positioned in the wallet, pocket, etc.?
edtyler:
I often see 2mW (+3dBm) transmitters in the HF band with a range of 20M, using an Omni type antenna. High power transmitters to power the NFC device are easy to conceal, but an efficient antenna would not be. The demos I saw used a somewhat directional magnetic loop, which had a 2M diameter - not too easy to conceal. But, there are wire antennas that could be concealed, especially if one wanted to work at a fixed location for a while.
Marco:

--- Quote from: tom66 on March 15, 2022, 03:25:20 pm ---Rough calculation: inverse square law

--- End quote ---
Up to 20 meters, radiation is an unwanted byproduct, not a mode of operation. For inductive coupling, size and ferrite can substitute for power.
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