6 ms·

How difficult is it to clone MIFARE Ultralight EV1 chips? You mention the UID is signed, can you simply copy this signature? Do you just need to buy one of the

How difficult is it to clone MIFARE Ultralight EV1 chips? You mention the UID is signed, can you simply copy this signature? Do you just need to buy one of the magical chips of the same design, that allow uid/serials to be written? What is the actual mechanism behind the DESFire and other secure NFC chips that prevents cloning?

kens 2y ago
I haven't really looked into the security aspects. I think that you could clone one of the Ultralight chips, but it wouldn't gain you anything because the security is in the backend. It's a lot like a printed concert ticket or boarding pass. You could print as many as you want, but the ticket is still good for just one admission. The DESFire and other secure chips contain a cryptographic key that you can't access. Without the key, you can't make a clone of the chip. The cryptography provides authentication and encryption that you don't get with the cheap Ultralight chip. I think this is all market segmentation; they don't put more security into the Ultralight chip because they don't want to cannibalize their higher-end sales.
- lxgr 2y ago
  Ultralight supports password authentication, and you can diversify the password from the serial number, meaning that until that password is revealed by a legitimate reader as part of a validation transaction (at which time the ticket is invalidated anyway), you can't clone it. Ultralight C does support actual cryptographic authentication.
  - kens 2y ago
    I don't think the password authentication helps against cloning. You could start a transaction and stop after you get the password. Then you could clone the card. (The system could invalidate the ticket as soon as they get the UID, but that would be a reliability nightmare since a failure during the read would invalidate someone's ticket.)
    - lxgr 2y ago
      You could do that, but it still greatly raises the cost for an attacker, since they need to hang around a ticket validator for every ticket they want to clone, as opposed to e.g. a QR code ticket, which can be trivially copied by a simple screenshot. Also, many of these transit systems are eventually consistent (they're usually offline-capable for resilience, but usually manage to send all validation transactions to a backoffice system within at most a day, and often minutes). This allows detecting duplicate usage fairly quickly. In systems where you need to tap out as well as tap in to leave the turnstile, that's where ticket inspectors might take a sudden interest in you if you tap out with a cloned ticket. In the end, as with most security systems, the goal is not to make fraud absolutely impossible, but to make it economically non-viable.
      - szundi 2y ago
        You have to hang out to get the id of a simple 125khz tag too - this is what cloning means
- amluto 2y ago
  In general, the card emulation devices (e.g. the chips in phones) try to avoid letting any arbitrary UID be set. This makes cloning these cards more difficult than it would otherwise be. It’s not terribly difficult to find devices (USB-connected things and battery-less cards) that do allow arbitrary UIDs to be set, though.
  - josephcsible 2y ago
    > the card emulation devices (e.g. the chips in phones) try to avoid letting any arbitrary UID be set. I can't think of a much worse way to do security. That feels like trying to flood the market with lockpicks that don't work instead of making a more pick-resistant lock.
    - amluto 2y ago
      I imagine this is because the locks contain chips from NXP (PN532 chips), the name-brand MIFARE chips are made by NXP, and the lock picks (also PN532 chips!) are made by NXP.

kens 2y ago

I haven't really looked into the security aspects. I think that you could clone one of the Ultralight chips, but it wouldn't gain you anything because the security is in the backend. It's a lot like a printed concert ticket or boarding pass. You could print as many as you want, but the ticket is still good for just one admission. The DESFire and other secure chips contain a cryptographic key that you can't access. Without the key, you can't make a clone of the chip. The cryptography provides authentication and encryption that you don't get with the cheap Ultralight chip. I think this is all market segmentation; they don't put more security into the Ultralight chip because they don't want to cannibalize their higher-end sales.

lxgr 2y ago
Ultralight supports password authentication, and you can diversify the password from the serial number, meaning that until that password is revealed by a legitimate reader as part of a validation transaction (at which time the ticket is invalidated anyway), you can't clone it. Ultralight C does support actual cryptographic authentication.
- kens 2y ago
  I don't think the password authentication helps against cloning. You could start a transaction and stop after you get the password. Then you could clone the card. (The system could invalidate the ticket as soon as they get the UID, but that would be a reliability nightmare since a failure during the read would invalidate someone's ticket.)
  - lxgr 2y ago
    You could do that, but it still greatly raises the cost for an attacker, since they need to hang around a ticket validator for every ticket they want to clone, as opposed to e.g. a QR code ticket, which can be trivially copied by a simple screenshot. Also, many of these transit systems are eventually consistent (they're usually offline-capable for resilience, but usually manage to send all validation transactions to a backoffice system within at most a day, and often minutes). This allows detecting duplicate usage fairly quickly. In systems where you need to tap out as well as tap in to leave the turnstile, that's where ticket inspectors might take a sudden interest in you if you tap out with a cloned ticket. In the end, as with most security systems, the goal is not to make fraud absolutely impossible, but to make it economically non-viable.
    - szundi 2y ago
      You have to hang out to get the id of a simple 125khz tag too - this is what cloning means
amluto 2y ago
In general, the card emulation devices (e.g. the chips in phones) try to avoid letting any arbitrary UID be set. This makes cloning these cards more difficult than it would otherwise be. It’s not terribly difficult to find devices (USB-connected things and battery-less cards) that do allow arbitrary UIDs to be set, though.
- josephcsible 2y ago
  > the card emulation devices (e.g. the chips in phones) try to avoid letting any arbitrary UID be set. I can't think of a much worse way to do security. That feels like trying to flood the market with lockpicks that don't work instead of making a more pick-resistant lock.
  - amluto 2y ago
    I imagine this is because the locks contain chips from NXP (PN532 chips), the name-brand MIFARE chips are made by NXP, and the lock picks (also PN532 chips!) are made by NXP.