If you're a web person who understands SSL, privacy-preserving age verification can be explained by analogy. It's a system which requires a central agency, pro

If you're a web person who understands SSL, privacy-preserving age verification can be explained by analogy. It's a system which requires a central agency, probably a government agency, analogous to a certificate authority. You are authenticated with that agency; it has personal info about you. But you are externally identified by some impersonal identifier, not your name. The agency issues you a certificate binding this identifier to an assertion like "is over 18 years old". When you interact with a site that wants to know whether you are over 18 years old, you present the certificate. The site can see that it's signed by the authority and that it has the assertion that you are over 18. You can't just give that site someone else's certificate because it has to be the one tied to the abstract identity you are presenting (which contains no personal info; it's some kind of UUID or whatever). Plus the cert can be bound to a specific device and such. The cert has a private keys with which you can prove that you own that cert; or at least that you are the authenticated operator of a device to which that cert was issued. It's something like that. I may have some key details wrong. The main idea is that some brokerage that does have info about you can attest that you are over 18 without revealing any of the personal info via certificate-like objects. It sounds like, in theory, the system can achieve good privacy in age verification. But not perfect age verification; people will find ways around it. A grown up can certify themselves to be over 18 and then hand the device to a teenager; and such an operation can likely be scaled to some extent. And of course no cryptographic system can eliminate the possibility that minors are looking at the screen of a device operated by an adult, who may even step out of the way to let them operate it.