4 ms·

I wonder why the Chinese transit card uses an unsecure method. Sounds like that is a lone outlier case so presumably intentional for some reason?

by Havoc 2y ago

atonse 2y ago
Given the UID is the same every time, I can assume it’s to make surveillance easier?
- simondotau 2y ago
  A more secure card doesn't make surveillance any harder. If anything, it's the opposite. An easily copyable UID makes bad data more plausible. Bad data makes surveillance harder.
  - lxgr 2y ago
    The fact that license plates can quite easily be forged by anyone willing to put some effort into it doesn't make them not uniquely capable of tracking where you go in your car.
    - simondotau 2y ago
      I don't disagree with that at all. I never said that insecure unique identifiers weren't useful for tracking. What I said is that a cryptographically system is superior to an insecure system for the purposes of surveillance, because the ability to track is the same, and the quality of data is higher. From this I concluded that surveillance doesn't make sense as a motive for this particular transit market sticking with an older, insecure system. Your analogy is poor for at least two reasons: 1. Transit cards are generally hidden inside a pocket and can only be read when read by specific machines in close proximity. Whereas number plates are designed to be on display and readable by human eyes from medium distances, or from publicly (or privately) owned cameras over long distances. 2. Your unspoken but implied alternative to the highly trackable number plate is no number plate. Whereas this discussion is discussing a cryptographically insecure transit card as an alternative to a cryptographically secure transit card.
      - lxgr 2y ago
        Cryptography is a means to an end. You can achieve both better privacy (e.g. by not revealing the UID to unauthenticated readers, and never in plaintext) and better tracking (by cryptographically authenticating cards to unauthenticated readers), depending on how you structure the system, so I don't think it's possible to intrinsically say one is more private than the other.
- lxgr 2y ago
  Even if it weren't, then there would just be another form of ID at the application layer (e.g. the card number for credit/debit cards used for some other transit systems via Apple Pay).
- gruez 2y ago
  It's China. They can just tell the transit agency to pull up transaction records, no backfired system required.
kormax 2y ago
My guess is that there's some city or transit system which needs the UID to be static for one reason or another, like in order to avoid double charging the same user if they accidentally scan their card multiple times. The T-Union card definitely has other means of doing that, like by checking the card serial, which is stored in one of the files, or by getting the same static UID value as it is also reported in RATS. But in the end, seems like one of the important transit partners did not want to even bother fixing it, so Apple was forced to allow the static UID. It really shows how big companies like Apple, who like to talk about "privacy" and "security", are willing to bend over backwards, if this means getting access to the revenue stream. AFAIK they get a percentage cut of transit card top ups, and Chinese market is obviously massive. For comparison, from what I've heard, when it comes to implementing the same transit feature in the US or in the EU, Apple is extremely strict with their partners. They may even tell their partners that they're unwilling to work with them unless they fully re-implement their transit card standard stack using other technology, or to format their cards differently, even if they are fully secure. The reasoning is, depending on how big the project is, is that Apple may not want to bother with porting the Applet implementation (in case of niche card standards), or writing a new card state parser (for existing card types like Mifare, which can be 'formatted' and store data differently, even if they use the same protocol).
- lxgr 2y ago
  Most stored-value transit systems require to be able to read some form of ID from the card for key diversification (otherwise you'd have to use the same key for all cards in the system, which is obviously pretty insecure). That can be the ISO 14443 level UID (which is what TFA is talking about) or some application-level ID, potentially only accessible once the reader has authenticated itself using a system-wide "ID privacy" key, but unfortunately I'm not aware of any system that does that. In other words, most, if not all, other cards usable in Express Transit mode are just as identifiable. For example, when you enable your credit/debit card for Express Transit in NYC, London or other open-loop systems, anyone (and I really mean anyone, not just any transit system reader, as readers are unauthenticated in the payment scheme protocols based on EMV!) can just read your card number (fortunately Apple Pay masks that and it's not directly usable for payments, but it's definitely a static identifier). That said, you do have to be very close to somebody's device or wallet to be able to read the card.

I wonder why the Chinese transit card uses an unsecure method. Sounds like that is a lone outlier case so presumably intentional for some reason?

by Havoc 2y ago

I wonder why the Chinese transit card uses an unsecure method. Sounds like that is a lone outlier case so presumably intentional for some reason?

atonse 2y ago

Given the UID is the same every time, I can assume it’s to make surveillance easier?

simondotau 2y ago
A more secure card doesn't make surveillance any harder. If anything, it's the opposite. An easily copyable UID makes bad data more plausible. Bad data makes surveillance harder.
- lxgr 2y ago
  The fact that license plates can quite easily be forged by anyone willing to put some effort into it doesn't make them not uniquely capable of tracking where you go in your car.
  - simondotau 2y ago
    I don't disagree with that at all. I never said that insecure unique identifiers weren't useful for tracking. What I said is that a cryptographically system is superior to an insecure system for the purposes of surveillance, because the ability to track is the same, and the quality of data is higher. From this I concluded that surveillance doesn't make sense as a motive for this particular transit market sticking with an older, insecure system. Your analogy is poor for at least two reasons: 1. Transit cards are generally hidden inside a pocket and can only be read when read by specific machines in close proximity. Whereas number plates are designed to be on display and readable by human eyes from medium distances, or from publicly (or privately) owned cameras over long distances. 2. Your unspoken but implied alternative to the highly trackable number plate is no number plate. Whereas this discussion is discussing a cryptographically insecure transit card as an alternative to a cryptographically secure transit card.
    - lxgr 2y ago
      Cryptography is a means to an end. You can achieve both better privacy (e.g. by not revealing the UID to unauthenticated readers, and never in plaintext) and better tracking (by cryptographically authenticating cards to unauthenticated readers), depending on how you structure the system, so I don't think it's possible to intrinsically say one is more private than the other.
lxgr 2y ago
Even if it weren't, then there would just be another form of ID at the application layer (e.g. the card number for credit/debit cards used for some other transit systems via Apple Pay).
gruez 2y ago
It's China. They can just tell the transit agency to pull up transaction records, no backfired system required.

kormax 2y ago

My guess is that there's some city or transit system which needs the UID to be static for one reason or another, like in order to avoid double charging the same user if they accidentally scan their card multiple times. The T-Union card definitely has other means of doing that, like by checking the card serial, which is stored in one of the files, or by getting the same static UID value as it is also reported in RATS. But in the end, seems like one of the important transit partners did not want to even bother fixing it, so Apple was forced to allow the static UID. It really shows how big companies like Apple, who like to talk about "privacy" and "security", are willing to bend over backwards, if this means getting access to the revenue stream. AFAIK they get a percentage cut of transit card top ups, and Chinese market is obviously massive. For comparison, from what I've heard, when it comes to implementing the same transit feature in the US or in the EU, Apple is extremely strict with their partners. They may even tell their partners that they're unwilling to work with them unless they fully re-implement their transit card standard stack using other technology, or to format their cards differently, even if they are fully secure. The reasoning is, depending on how big the project is, is that Apple may not want to bother with porting the Applet implementation (in case of niche card standards), or writing a new card state parser (for existing card types like Mifare, which can be 'formatted' and store data differently, even if they use the same protocol).

lxgr 2y ago
Most stored-value transit systems require to be able to read some form of ID from the card for key diversification (otherwise you'd have to use the same key for all cards in the system, which is obviously pretty insecure). That can be the ISO 14443 level UID (which is what TFA is talking about) or some application-level ID, potentially only accessible once the reader has authenticated itself using a system-wide "ID privacy" key, but unfortunately I'm not aware of any system that does that. In other words, most, if not all, other cards usable in Express Transit mode are just as identifiable. For example, when you enable your credit/debit card for Express Transit in NYC, London or other open-loop systems, anyone (and I really mean anyone, not just any transit system reader, as readers are unauthenticated in the payment scheme protocols based on EMV!) can just read your card number (fortunately Apple Pay masks that and it's not directly usable for payments, but it's definitely a static identifier). That said, you do have to be very close to somebody's device or wallet to be able to read the card.