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> The Ultralight chip has a few features beyond a printed ticket, though. The chips are manufactured with a unique 7-byte identification code (UID). Moreover, t

> The Ultralight chip has a few features beyond a printed ticket, though. The chips are manufactured with a unique 7-byte identification code (UID). Moreover, the UID is signed, ensuring that fake UIDs cannot be generated. The problem is, they can be just as easily cloned. Your average Flipper Zero can do that. If you want actual security, you have to go for a challenge-response scheme - i.e. every card is provisioned at the factory with a unique private / public key pair, and the public key gets signed by the factory. Then, to verify authenticity, the terminal gives some random nonce, the card signs it using its private key, and the terminal verifies that against the factory's public key. > Even so, there were a couple of times that I lost track of the chip and had to check some specks under the microscope to determine which was the chip and which were dirt. That is the really amazing part for me. We as humans have difficulty handling them, but how on earth does a machine even manufacture these, much less orient them consistently for the bond process to work?!

lxgr 2y ago
> The problem is, they can be just as easily cloned. Not if the validation system uses the password feature of MIFARE Ultralight. For single-use tickets, which are invalidated immediately after being read, this can be good enough and is much more lightweight on the IC side.
chx 2y ago
It's utterly not worth it. Your time to get it working, the equipment... but even if you have all of those if you get caught they will throw the book on you to scare away others. You can be charged by Unauthorized use of computer, Fraud and who knows what else. All of that to save four dollars on a ticket? When every station has cameras?
- mschuster91 2y ago
  The thing is, you have to do it only once, and then the clones and knockoffs come. Like what, there's Tiktoks advising young dumbasses precisely what they need to steal and joyride cars.
  - ForHackernews 2y ago
    > Like what, there's Tiktoks advising young dumbasses precisely what they need to steal and joyride cars. Yeah, because cars are valuable and joyriding a stolen car is impressive and cool to lots of teens. Getting a free ride on the bus is like negative street cred.
GuB-42 2y ago
> If you want actual security, you have to go for a challenge-response scheme Another option is to just store used UIDs in a database. In fact, you could do a system with only UIDs. For a single use ticket, validate the UID signature and mark it as spent the first time it is used, then every use after that will be denied. A card can be cloned, and it will work, once, it means one could steal a ticket by walking by and using appropriate equipment (not just a Flipper Zero as it is too short ranged) and use it before the legitimate owner does. I don't think it is something to worry about for a single use subway ticket. To improve security for multi-use tickets, one could use rolling codes: every time a ticket is scanned and its UID validated, some code is read from the NFC memory and it has to match a sequence, the next code is then written back to memory and has to be provided next time, invalidating any clone. Tickets can still be stolen, but you can't beat the system unless you crack the server-side encryption. More valuable tickets like commuter passes can use a different system with a challenge-response scheme.
- lxgr 2y ago
  This scheme implies a low-latency, high-availability connection to a backend database. That's not easy to achieve in many transit system environments, hence the relative popularity of systems with some level of distribution. Practical systems often are online these days, but only use that connection for eventual consistency style reconciliation. > A card can be cloned, and it will work, once, it means one could steal a ticket by walking by and using appropriate equipment (not just a Flipper Zero as it is too short ranged) and use it before the legitimate owner does. Even MIFARE Ultralight supports a basic password authentication scheme, where only legitimate readers know (or can derive) that password, so there a bit better protected against cloning than pure passive storage cards.
akira2501 2y ago
> If you want actual security, you have to go for a challenge-response scheme Sure you just have to accept that you're now vulnerable to Denial of Service attacks, or just DoS due to unrelated service infrastructure outages caused by things like backhoes. > much less orient them consistently for the bond process to work?! It's not all that consistent. They have a 3% failure rate. And you have to accept a unique map of "broken chips" with every single order you receive.
kevincox 2y ago
> The problem is, they can be just as easily cloned But you can only clone a ticket who's ID you use. So you can buy a ticket and clone it, but what have you achieved? It is still validated "on the backend" once you use either the first time. So the only real risk is that you clone a random person's ticket between them buying it and using it which is a security flaw, but probably a very minor issue in real-world use. Maybe there could be slight issue with day passes? You could buy a single day pass then issue clones at a lower price. However it is likely not an issue worth paying for more expensive chips to avoid.

lxgr 2y ago

> The problem is, they can be just as easily cloned. Not if the validation system uses the password feature of MIFARE Ultralight. For single-use tickets, which are invalidated immediately after being read, this can be good enough and is much more lightweight on the IC side.

chx 2y ago

It's utterly not worth it. Your time to get it working, the equipment... but even if you have all of those if you get caught they will throw the book on you to scare away others. You can be charged by Unauthorized use of computer, Fraud and who knows what else. All of that to save four dollars on a ticket? When every station has cameras?

mschuster91 2y ago
The thing is, you have to do it only once, and then the clones and knockoffs come. Like what, there's Tiktoks advising young dumbasses precisely what they need to steal and joyride cars.
- ForHackernews 2y ago
  > Like what, there's Tiktoks advising young dumbasses precisely what they need to steal and joyride cars. Yeah, because cars are valuable and joyriding a stolen car is impressive and cool to lots of teens. Getting a free ride on the bus is like negative street cred.

GuB-42 2y ago

> If you want actual security, you have to go for a challenge-response scheme Another option is to just store used UIDs in a database. In fact, you could do a system with only UIDs. For a single use ticket, validate the UID signature and mark it as spent the first time it is used, then every use after that will be denied. A card can be cloned, and it will work, once, it means one could steal a ticket by walking by and using appropriate equipment (not just a Flipper Zero as it is too short ranged) and use it before the legitimate owner does. I don't think it is something to worry about for a single use subway ticket. To improve security for multi-use tickets, one could use rolling codes: every time a ticket is scanned and its UID validated, some code is read from the NFC memory and it has to match a sequence, the next code is then written back to memory and has to be provided next time, invalidating any clone. Tickets can still be stolen, but you can't beat the system unless you crack the server-side encryption. More valuable tickets like commuter passes can use a different system with a challenge-response scheme.

lxgr 2y ago
This scheme implies a low-latency, high-availability connection to a backend database. That's not easy to achieve in many transit system environments, hence the relative popularity of systems with some level of distribution. Practical systems often are online these days, but only use that connection for eventual consistency style reconciliation. > A card can be cloned, and it will work, once, it means one could steal a ticket by walking by and using appropriate equipment (not just a Flipper Zero as it is too short ranged) and use it before the legitimate owner does. Even MIFARE Ultralight supports a basic password authentication scheme, where only legitimate readers know (or can derive) that password, so there a bit better protected against cloning than pure passive storage cards.

akira2501 2y ago

> If you want actual security, you have to go for a challenge-response scheme Sure you just have to accept that you're now vulnerable to Denial of Service attacks, or just DoS due to unrelated service infrastructure outages caused by things like backhoes. > much less orient them consistently for the bond process to work?! It's not all that consistent. They have a 3% failure rate. And you have to accept a unique map of "broken chips" with every single order you receive.

kevincox 2y ago

> The problem is, they can be just as easily cloned But you can only clone a ticket who's ID you use. So you can buy a ticket and clone it, but what have you achieved? It is still validated "on the backend" once you use either the first time. So the only real risk is that you clone a random person's ticket between them buying it and using it which is a security flaw, but probably a very minor issue in real-world use. Maybe there could be slight issue with day passes? You could buy a single day pass then issue clones at a lower price. However it is likely not an issue worth paying for more expensive chips to avoid.