this post was submitted on 14 Mar 2025
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How would you make an arbitrary QR code have a verifiable signature?
If you're running a public service, you should have a key that's trusted by a CA anyway. So why couldn't you, especially for qr codes that link to an https site, embed a signature in that qr code that verifies that the person that owns parkyourcar.com's private key also created the code you just scanned? Just like signed pdfs?
Okay and what happens when I overwrite that qr code with one that points to downloadvirus.com? How is a client supposed to know that the qr code isn't supposed to be here?
Well, because it won't be signed by a trusted CA for that task. Like if CAs had a category of certificate issuance that applied here (the standardisation issue) then it would be easy to spot a fake (which wouldn't be correctly signed). Alternatively, you could take the European approach of having everything government related (like public street parking, though Europe mostly uses apps for that, not signed QR codes) rely on government entities and those in turn on a national set of government CAs.
That doesn't make any sense. How would you know if something should or should not be signed? You wouldn't.
If it becomes standard for public parking to be signed, everyone would know. If payment QR codes in general start being signed, your payment app might even know. Lastly there could even be signage by the code to help novices.
The point of a code is to not have an app in the first place. Thus there's no way to validate it.
It wouldn't need a separate app if, for instance, a standard QR payment format way created. If you just want a link to a website to pay, then naturally that would be less secure, but you could always put the URL below the QR code for redundancy (QR would only save time typing then).
Very cool. Why would anyone use qr codes then? When you can just write a url and that's free
QR codes are mostly meant to let you get an amount of info (they're mostly text-based) without having to type or enter it manually when you might make mistakes or when the process is just faster for the amount of text involved.