Caedarai

Because you can make it so that the required certificate/signature has to meet certain criteria to work. For instance, imagine there was a PayPal equivalent type app for paying QR codes, and they required all codes to be signed by one of their business customers (who they have on file). Or with a certificate they themselves issue their customers.

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).

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.

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.

Plenty of people I know have gotten the little echo dots or the bigger alternative with larger speakers for Christmas or birthdays. Technically they didn’t spend money, but their friends and family did.

This seems to be a gross misunderstanding of public key cryptography. Public keys allow you to verify an existing signature is valid and made by the correct entity, but they absolutely don’t allow you to forge a signature: that’s actually what they are designed to prevent.

You pay CAs for certificate issuance, not for signing. You could sign all the QR codes in a city with a single CA-issued certificate as long as the standards for it were all accepted.

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.