Earlier quoted context omitted.
> A given relying party can choose to use or not use attestation and, if they choose to use it, which certificates to trust. True, and a website could decide to issue its own certificates rather than get one from a CA trusted by browsers, but in practice (and potentially one day by law) most sites will defer to the FIDO Alliance to determine which devices are "sufficiently secure". > the FIDO Alliance--which is just…
> True, and a website could decide to issue its own certificates rather than get one from a CA trusted by browsers… That’s quite different. In your example, if a website does so unilaterally, client user agents break. In the FIDO case, nobody else knows or cares which authenticators an RP trusts. More broadly, I don’t get this conspiracy theory. You’re worried…the FIDO alliance will abuse their very limited power to……
I think this is the crux of where our disagreement lies. I grudgingly accept that FIDO makes it easier for companies to check that their employees are storing their keys on company-approved devices, but I don't think that arbitrary websites should be given the power to make demands about the hardware that visitors must use to create accounts. That seems like a worse position for user freedom than we have today with passwords.
You might say that websites already have this power, in some convoluted way. They could say "Enter your credit card details and postal address here and we'll send you a custom device you can use to log in to our website", but in practice no company does that. (Banks and governments are maybe special cases, and less concerning given that: their authenticators are managed out of band; they are highly regulated; they usually have actual branches that you can go to in person to sort things out; and people generally choose to interact with banks/governments that are based in their own country).
Attestation changes the market dynamics here. Suddenly it becomes acceptable for sites to bully users into buying certain types of devices, and for governments to start demanding that these devices be used as online IDs (at least for age verification, to start with). Even if companies don't abuse this power to keep people in their ecosystem (e.g. Apple sites giving you special features if you log in with an Apple device), the first casualties are going to be open source hardware and software implementations, which will be deemed insecure, and further normalise the idea that users can't go online without running proprietary code.