Looking at New Haven Line Commuters Will Soon be able to Purchase Rail Tickets with Smartphone App:

When a conductor walks through the train to ask for tickets, the commuter should have their activated digital ticket displayed and show their smartphone screen to the conductor. The conductor will visually inspect the mobile ticket, which incorporates digital anti-counterfeiting features.

how can you do this? I am surprised by the visual part, if it had a QR code or similar then it's trivial crypto but visual? Say, it shows an animation, well, just capture it as a movie. If it shows an animation over your photo, then take the original photo and substract it and add back another photo. I just can't even imagine how this could work. Where could I read more?

Edit: after reading the first answer, sorry, the motivation behind this question is the botched up launch of the Budapest online pass sales system so expect the financial motivation to definitely be there. We are talking of something with a value of like 10% of the average net monthly salary. I only used the New Haven tickets as an explanation of the problem, as the press release describes the system real nicely.

  • "Visually inspect" imho might include barcode scanning. And how exactly does this relate to the Budapest system? – Elias Jul 25 '17 at 9:30
  • Well, they had a very easy to counterfeit version and I am wondering what could be better. – chx Jul 25 '17 at 9:43
  • Could you provide some more background on this system? From what I heard it uses QR codes. – Elias Jul 25 '17 at 10:02
  • Impossible to tell how the counterfeit is done without seeing the e-ticket screenshot. All mobile phone capable of doing screen capture, so any screen base image is NOT a good idea for validation. There must be some interactive stuff. Nevertheless, if I am the policy maker, I will spend more resource to improve the people income and improve mentality, the switch to the merit system that instills in Germany/Switzerland train system. – mootmoot Jul 25 '17 at 10:02
  • @Elias scanning QR codes is way too slow... and I was mostly curious about whether some clever trick exists to make visual anti counterfeiting possible. In another field, at first Diffie–Hellman key exchange sounds impossible at first so I am thinking I might have missed some great trick. – chx Jul 25 '17 at 10:23

I'm not sure about this particular system but one thing I have seen is a simple code (could be a little more sophisticated, like a movie) which changes every few minutes. The conductor just hast to watch the most recent one and then compare.


  1. the low cost of a ticket for a single ride and
  2. the hassle of taking a nice enough picture or video to not get caught combined with
  3. fines for getting caught

this can be sufficient protection.

In practice at least codes are dubious. The conductors don't actually seem to check mine, ever.

  • But doesn't that require the system to be constantly online? Obviously(?) you can't expect that especially not on a train. Again, obviously(?) if you put the code client side someone will break it out. – chx Jul 25 '17 at 9:04
  • For the system described tickets can only be purchased with a validity of one hour starting at the current time. So connectivity is required to buy the ticket in the first place. – Elias Jul 25 '17 at 9:29
  • Note that connectivity is often used as an argument against specific solutions in this context but in many areas it is just not an issue and except for simplicity not every solution has to work on all lines and in all areas. – Elias Jul 25 '17 at 10:19

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