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The tiny chip that powers Montreal subway tickets

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Re: The tiny chip that powers Montreal subway tickets

#41

Post by lxgr »

politelemon wrote: post #39
kens wrote: post #2

Author here for all your NFC chip questions :-)

Could someone just use an nfc enabled phone to get it to act as a ticket?

For MIFARE Ultralight, yes – it's essentially just a bearer token with no encryption/authentication. I believe there's a password mechanism, though, which might just be good enough for single-use tickets. That password can be derived/diversified from the card's serial number, making such a scheme still significantly better than e.g. simple QR codes.

MIFARE Ultralight C and larger/more expensive chips allow challenge-response authentication, making them pratically uncloneable. These are usually used for reloadable and monthly passes.

Re: The tiny chip that powers Montreal subway tickets

#42

Post by mschuster91 »

> 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?!

Re: The tiny chip that powers Montreal subway tickets

#43

Post by lxgr »

kens wrote: post #30
Waterluvian wrote: post #16

On the topic of NFC: my iPhone ApplePay thing taps so much more reliably than any of my credit or debit cards. Is this because it has its own power supply and doesn’t have to first be powered up by the machine?

NFC supports passive mode (where one side is powered and the card is not) and active mode (where both sides are powered). So, yes, your phone is probably more reliable because it provides a powered data transmission. An NFC card doesn't actively transmit data. Instead, it sends data using "load modulation", where it switches a load across the antenna to change how much power it absorbs. The transmitter can detect thi…

The iPhone doesn't actually use NFC's peer-to-peer/"active" mode (since contactless payments aren't an NFC application; see my other comments on that), but it does specifically include an NFC "field amplifier" IC (shown in some iFixit teardowns), which most other smartphones and of course all physical cards/tags lack.

This does mean that iPhones can't do cool tricks like booting up the secure element purely from the field with a completely dead battery though that some earlier Android and Windows Phones could do (or at least Apple has intentionally deactivated that capability for a more consistent/secure experience) :)

Re: The tiny chip that powers Montreal subway tickets

#44

Post by cbhl »

hammock wrote: post #28
justusthane wrote: post #21

This is fascinating. We were just in Europe where we experienced these tickets for the first time. I had trouble with them; I was trying to figure out how to scan them because it never occurred to me that they might contain an NFC chip. My wife, on the other hand, who is not at all technical, took it for granted that you would tap them and immediately figured it out intuitively.

Where do you live? Chicago has had these contactless paper tickets since 2013

Atlanta has been using a form of these contactless paper tickets since 2006.

Re: The tiny chip that powers Montreal subway tickets

#46

Post by lxgr »

kens wrote: post #19
cypherpunks01 wrote: post #4

Earlier quoted context omitted.

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?

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. Wi…

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.

Re: The tiny chip that powers Montreal subway tickets

#47

Post by lxgr »

BOOSTERHIDROGEN wrote: post #9

I would like a comprehensive analysis of FeliCa.

Same here! It seems like a fascinating system, especially in the federated way in which it's being used by various Japanese transit agencies and issuers. Compared to MIFARE, it was definitely ahead of its time.

Unfortunately, most things I could find are in Japanese, as expected; I suspect that the really interesting parts aren't public, as usual in this industry (there's still a lot of belief in security by obscurity, even if the systems actually don't need it).

Singapore's CEPAS seems very similar conceptually to Felica (at least in application, in that there's multiple issuers of stored-value cards with interoperability), and the specifications for that seem to be available for purchase, but I'm not curious enough to bite that bullet yet :)

Re: The tiny chip that powers Montreal subway tickets

#48

Post by ximus »

gruez wrote: post #31
bboygravity wrote: post #29

Earlier quoted context omitted.

The chip is the size of a grain of salt, but there's a relatively huge antenna inside made of conducting material (metal?) and glue and all that.

all of that is probably negligible compared to how much disposable foil is used for cooking or packaging.

I don't know about justifying or rationalising waste by pointing to a greater source of waste.

Re: The tiny chip that powers Montreal subway tickets

#49

Post by lxgr »

mschuster91 wrote: post #42

> 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 provision…

> 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.

Re: The tiny chip that powers Montreal subway tickets

#50

Post by thriftwy »

devl547 wrote: post #22

All Moscow public transport powered by these chips (actually it was, nowadays the chips we use are clones, made in Russia itself) - trains, metro and buses.

For a few years now, you may usually do a contactless card payment - just tap your bank (debit or credit) card. The fare is often higher but so is convenience.

Back around 2010 I remember reading these accusations that significant part of revenue went directly to Mifare for the massive number of chips.

And for single rides, some of Metro systems still use these steampunk brass tokens. Sometimes, less authentic plastic.

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