Comment by dmurray
6 hours ago
This is a great investigation but I have two small nits:
> the ZNB field is not empty and not garbage: it contains a well-formed 71-byte DER ECDSA signature, correctly Ascii85-encoded, with the right prefix and a plausible length. But it fails the cryptographic check instantly, because it was signed with somebody else's key.
Seems doubtful! I expect the forgers used a real signature from another card instead, so it has the right key but the wrong data. Reverse engineering the process as the author did and making up their own key wouldn't be of any value to the forgers.
> I built a little demo to check the signatures across California, New York, and Virginia: take a picture of the barcode and check it here.
This is not wrong, but should come with a little warning. A real verifier needs to additionally check the encoded data matches the human-readable data on the front of the card.
> Seems doubtful! I expect the forgers used a real signature from another card instead, so it has the right key but the wrong data. Reverse engineering the process as the author did and making up their own key wouldn't be of any value to the forgers.
This was just bad wording. I meant to say "someone else's key" in the context that it was a key generated by the forgers rather than the state DMV, will update to make it more clear!
> This is not wrong, but should come with a little warning. A real verifier needs to additionally check the encoded data matches the human-readable data on the front of the card.
Correct, but simply checking that it matches the front is likely not enough to deter fraud. You could extract the barcode data from a real ID and put it on a physically different (fake) ID with a different photo and it would still return as valid. To detect this you generally would need a higher end solution (IDScan.net/VeriScan's ID authentication solution (yes... the one that just leaked everyone's data), TokenWorks' IdentiFake, IDScience, amongst others) that does the same high resolution UV/IR checks TSA does. But the forgers are good enough now to be able to sometimes pass those scanners too.
This is why chip-based IDs are superior, esp. with phones and NFC being ubiquitous.
ID chips can't be cloned, so you don't even need photo auth (unless you want to protect against stolen but real IDs).
> A real verifier needs to additionally check the encoded data matches the human-readable data on the front of the card.
I mean, not really? Only the machine-readable part is signed, so it should be treated as the sole source of truth. Besides, only an idiot forger would put different data in the human-readable part - it would be the easiest way to get caught!
It depends entirely on the purpose of the forgery. Some grocery stores do ID checks by looking at the front of the ID. Others just run the ID across a scanner and the employees are so rushed they don't read it or check the picture. Similar things happen e.g. at bars or casinos. Incomplete forgeries can get you far enough under the right circumstances.
But if the forger claims his name is John Smith (or his date of birth is xx/xx/2004) he will edit the human-readable part.
If he pairs the edited human-readable part with a real barcode copied from a real license in someone else's name, then anyone inspecting the license will see the documentation matches his claim, and if they also use this site to check for fake barcodes it will confirm the barcode was really issued by the California DMV.