[Cryptography] Anonymous age verification

[Kristian Gjøsteen]

16. juli 2026 kl. 04:29 skrev Steven M. Bellovin <smb at cs.columbia.edu>:
> On 15 Jul 2026, at 9:23, zeb--- via cryptography wrote:
> 
>> 
>> The EU has implemented an anonymous age verification app (in minutes, using Claude, I'm led to believe).
>> The current implementation can be bypassed (even en masse using a browser add-on).
>> Disregarding motives and current implementations: is anonymous age verification possible, even in principle?
>> 
> 
> It's possible using zero-knowledge proofs—*if* you can provide suitable evidence to what I call an "identity provider". This is not necessarily easy, though in some places it will be easier than others. See https://www.cs.columbia.edu/~smb/papers/age-verify.pdf for details. (Also see that paper's reference 41, for a much more detailed look at how such a system could work—though that's a law paper, with a lot of US legal analysis, and has features that are not wanted here, e.g., a "deanonymization agent".)

There is an ongoing EU effort to deploy attribute-based identification (EU Digital Identity Wallet), where a web site can ask the user to show certain attributes. The relevant legal requirements then mandates some form of unlinkability, see point 16 of Article 5a at:

	https://eur-lex.europa.eu/eli/reg/2024/1183/oj

There’s a sort of useful web site at:

	https://github.com/eu-digital-identity-wallet

There’s a nice technical critique at:

	https://github.com/eu-digital-identity-wallet/eudi-doc-architecture-and-reference-framework/issues/200

We know how to do the cryptography classically, mostly, and we sort of know how to do it quantum-safe, but honestly, it’s a bit unclear how to do this practically, in particular including usable security, and the EU wants to make implementations interoperable across the EU, making the problem somewhat more challenging.

It’s all very interesting.

Personally, I think it could be a good thing if the EU approach succeeds.

-- 
Kristian Gjøsteen