recovering the signing keys for US driver's license barcodes
Anyway. I only see claims that the public key can be determined from license barcodes, not that a signing key can be determined. What am I missing or misunderstanding?
To head off one potential retort: While it's true that one can use a public key to encrypt data for the recipient that has the private half of that key or verify that data has been signed by the possessor of the private half of that key, I'm almost 100% certain that it's not possible to use that public key to sign data would validate to other folks as being signed by the private half of that key. It has been more than a decade since I've thought about any of this, but isn't the entire point of public-key cryptography that the public part can be distributed to your worst enemy without causing you any trouble at all?
NFC and a challenge-response protocol could work, though, like e.g. the one used in biometric passports.
A fake photo plus a valid barcode will pass any current check right? Unless you still do a secondary proprietary photo lookup that I don’t think exists.
Cryptographic NFC chips are basically free these days, and any modern smartphone can read them. The photo issue is solved by having the chip contain a copy of the photo, as a few extra kilobytes of data isn't an issue when you aren't using barcodes. The copy issue is solved by having the chip sign a verifier-provided nonce together with the data, and having the government sign the chip's public key instead.
Having the photo there just encourages sloppy ID checks by human eye, and it's much easier to mislead the human eye than it is to forge an NFC chip.
If the photo was in the chip only, we'd force ID verifiers to do their job properly, and make forgeries structurally impossible. With basically everybody having an NFC-enabled phone now, you wouldn't even need people to get extra hardware for this.
Of course passports are expensive and not everyone has them, but if you do, next time you renew, opt for the book+card option.
> These are public keys, which are meant to be published - recovering one lets anyone check a signature, not forge one.
It's not like non-technical people understand asymmetric cryptography. Or even technical people, for that matter.
Maybe we should refer to the public key as an address, and the private key is just a password again. You can send stuff, securely, to an address. And you can verify the sender when you have their address (ie check the signature).
The public counterpart is tricky to name but I think attaching "public" to it makes the intended usage plenty clear. There isn't really a physical counterpart unless you consider maybe those machines that check for counterfeit cash but even that's not a great fit because the pubkey is simultaneously analogous to a lock box.
It is true that publishing your private key is bad but you'd hope the name makes that pretty clear. Despite the way I remember (U2's "The Fly" lyrics, "A secret is something that you tell one other person, so I'm telling you, child") people generally do not understand that the whole point of secrets is that at least two parties know, which means you might always be betrayed by somebody you think is keeping your secret. For a private key it's easy, don't tell anybody, nobody knows, you can't be betrayed, done.
For example Hacker News learns my password to this web site every single time I sign in because that's just a secret. We've known how to do better for decades but only a handful of systems I use (e.g. Google) do so and all of them have a "traditional" password option which is like discovering your aeroplane still has a smoking section in 2026.
The inability to betray is a sharp observation but I think the analogy still holds flawlessly. It's a physical lock that you haven't handed out the key for so you're the only one with access to it. However the public counterpart still defies easy explanation.
Why did you put "symmetric keys" in scare quotes? Is that not the common term in your neck of the woods when speaking about symmetric crypto?
I don’t think there’s any process or entity in the physical world that is reasonably familiar to most people that is even remotely suitable as an analogy to public key cryptography.
These are not analogs to things ordinary people had already seen. For Computation we just got used to it being everywhere and so we don't need to explain it so much.
I think the reason we (the HN crowd) don’t like it is that the analogy starts to break down when you start thinking through all of the operations you can do with public keys. But this does not matter much for somebody learning to use them for the first time. I’ve had to grow comfortable with the idea of giving people imperfect explanations so that they can build an intuition. Once that happens I can return with the mathematics so that they can really understand what is going on.
- If you install such keys to a host, and an attacker (with access to said host) has catalogued your ssh keys, they can see that you have access to said host (if they can correlate your method of publishing the keys to your identity)
On the other hand, if you go to the other extreme (?), you can have a different public ssh key per host. This way the server owner/attacker is not able to correlate that ssh key with other keys to recover your identity. (You need to take care that ssh won't offer too many public keys in that case.) Example case of a service that might get offered many ssh keys: github.
Personally I don't bother. But I wouldn't be too bothered about just putting my public keys to some "secret" URL in the internet either, so I can easily enable myself ssh access to a host with a single curl.. Maybe I should indeed do that.
A single Security Key can authenticate to Facebook as WeedLover420 and then be used to sign into the Google account of the Secretary of the US Marijuana Task Force and even if both Facebook and Google were co-operating in the work there's no way to connect these authentications. Obviously WeedLover420 is more likely to get caught because they used the same IP address to do both things and they stink of weed and they look stoned all the time, but none of those are because of the Security Key, that was locked down good.
I hate shit like this. Do not let your crypto layer know about the structure of what it's signing. Keep security stupid.
When you look at the details underneath more crypto, there is a lot of ah hah - and ‘doh’ - moments due to implementation realities.
Digital verification is going to matter a lot more for objects we own rather than the objects that proxy for that (currently the main function of an ID). Identity fraud is only problematic because ownership is tied to a loose record of SIN/DL.
Having a physical medium represent ownership just shifts the burden to the state and allows for social engineering and fraud to persist.
[1]: https://www.dailystar.co.uk/news/latest-news/digital-id-upda...
> 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.
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!
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.
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.
ID chips can't be cloned, so you don't even need photo auth (unless you want to protect against stolen but real IDs).
1. The bank emails/SMSes the customer a link
2. The customer takes out their iPhone, opens whatever email/messaging software & taps the link
3. The link takes the customer to a specially crafted page owned by the bank that triggers a native OS process for opening Apple Wallet and gathering requested ID details with consent.
https://developer.apple.com/videos/play/wwdc2025/232 https://www.w3.org/TR/digital-credentials
This is potentially a superior arrangement because it could eventually establish a strong cryptographic chain of trust all the way to the issuer (e.g. the State of Alabama). Right now there are some gaps in that chain but I see no reason they couldn't be closed over time.
for example, a reliance on apple wallet, instead of an open standard.
With that quibble aside, I do like the basic structure of your solution.
Time for a federal law banning the DMVs from outsourcing this stuff (or selling the bulk data like they do to insurers).
..
When discussing asymmetric cryptography with less technical folk, a lock analogy breaks down quickly as locks are conceptualized as being symmetric. Hence, "key" is a poor word that came from symmetric cryptography; one really needs to discuss the signature or authentication code.
A better analogy may be a transparent display case, where only authorized people can put things into the case. To check a copy outside the case is true, one would want to go to the official display case and compare. This isn't a great analogy because there's no analog to the digital signature, but it gets the asymmetry across.
Perhaps we might do a bit better? Suppose your friend gave you a poster copy of a famous painting from the Metropolitan Museum. On the poster is the curatorial accession number. You could go to the MET and check if your poster matches the painting, which should have matching accession number on the label. This analogy fails since the accession number isn't a signature of a hash.
So far our analogy covers asymmetry but is still centralized. The museum also distributes a catalog of its posters/paintings. Catalog entries have a thumb print of the painting and its accession number. So, if you could find a trusted copy of that catalog, say at your local library, you might also use this to check the painting's authenticity without having to travel to the museum.
Alas, this is an involved process, and for the interested policy maker or their trusted advisors, it's probably much better if we teach the real process with worked examples.
But rather than identifying forgeries by inspecting the handwriting details and ink pigments or whatever, we have math.