Maybe that could be kept under control by making the keys valuable — hard to replace and maybe even the same keypair that's used for age verifying your mastodon login also used for more important things. But key management is probably going to be a nightmare. Just ask the cryptocurrency guys.

I'm not imagining a friendly adult signing in for their child, I'm thinking a completely automated service that instantly gets past age verification for anyone who signs up for it by sharing a pool of stolen, purchased, fraudulently obtained, or willingly shared IDs.

The ID server knows who its response is about, but it does not know if they're the person using the website.

Okay, there is a nonce. Presumably it is negotiated somehow to prevent the Website from hiding any info in it. But then the question for the ID server is simply "Does a user who knows this nonce have access to a keypair indicating the right age range?" The user (i.e. the "trusted app" that is in their control) can then simply send that question off to Charlie or whoever and get the desired answer to relay to the Website without revealing to anyone any secrets of their own. The ID server has no way to know it was proving the age of the wrong person, the Website doesn't know who it actually got an age for, and neither can identify the actual user.

I think the people implementing these age verification schemes do want to try and defend against that sort of thing, because both the ones I've seen so far in reality (the one from Spain and some other thing a couple years ago that was closer to your idea) seem to have willingly sacrificed any semblance of privacy in their efforts to prevent it.

One particular way in which the story makes no sense to me: The website wants to ask a question about "the visitor." How does it identify the visitor in its message to the central authority? If nothing prevents it, said visitor could simply pass the question on to Charlie's Web Age Verifier Bypass Service down the road which is in posession of an age-appropriate keypair, and relay the response in an automated fashion. How does one prevent that?

I mean it's not as if people wouldn't do it. Borrowing an older kid's ID to buy beer was commonplace when I was younger. Imagine if it could be done automatically, instantly, on a large scale. Shutting down The Pirate Bay is already nigh-impossible for the powers of law and order, it seems. Imagine if everyone under the age of 31 had to use it if they wanted to connect to Instagram.

That protocol is simplified to the point where it makes no sense and thus we cannot really evaluate its security, but yeah, I was glad to see that you do get around to semi-acknowledging that a scheme like that would need to rely on some kind of service like Tor to begin to provide any semblance of privacy. Even then the central authority would have a record of it every time each of us hit an age gate, which is valuable metadata to be giving away whether or not it's probably just pornography.

Lots of people seem eager to claim that it can feasibly be done in a privacy-safe way but I still have yet to be convinced of it.

And it's all just to set up a new system of oppression with the other problems you mention. It seems utterly ridiculous.

@thenewoil Dear @mailbox_org, @Tutanota, and @protonprivacy,

If you want to collectively take a lot of business from Google and Microsoft:
0. Create, for each of your companies, one or more APIs for SMTP, IMAP, CalDAV, and CardDAV bridges, running on customers' hardware. (Yes, some of you already have some of this done, but see step 1.)
1. Create a non-profit trade association to pay developers to create a single, shared, cross-compatible set of turn-key open-source bridges for all of your services, supporting each major desktop and mobile OS, requiring no user technical knowledge, and supporting all the APIs mentioned in step 0.
2. Create video tutorials, and written guides with screenshots, for installing setting up the bridge software in step 1, requiring nothing more complex than setting up a Google account in Apple's software on an iPhone.

Do this, and I can access my Mailbox, Tuta, and/or Proton accounts in the same GUI app as my work email, contacts, and calendars; as my university email, contacts, and calendars; and as my Gmail I use as a bin for promotional content (from "download our free whitepaper" or "use our guest WiFi" pages and the like).

More importantly, do this, and I can set up every non-technical client, and classes of workshop attendees, with an equally convenient and familiar way to use one or more of your European privacy-centric services without any disadvantage relative to their current Google and Microsoft accounts.