Thread

1. dmurray · 1789628355 · focus · HN ↗

   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.

   1. crote · 1789630767 · focus · HN ↗

      > 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!

      1. gmueckl · 1789638343 · focus · HN ↗

         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.

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