Verifying your age in a privacy preserving manner

Selective Disclosure JWT (SD-JWT) offers a privacy-preserving approach to age verification. Instead of sharing full identity documents, a government or trusted issuer signs a JWT containing only hashes of individual claims (e.g., age_over_18, birthdate, country). When a website asks if a user is old enough, the user reveals only the specific disclosure — the salt, claim name, and value — for that one claim. The verifier reconstructs the hash and checks it against the JWT, confirming the claim without learning anything else. Drawbacks include potential cross-site correlation if the same credential is reused, and the inability to answer questions not pre-baked into the credential (e.g., 'is user over 25?'), which would require zero-knowledge proofs.