Neither of those ways works in ZKP systems like the EU is in the process of doing or the one Google recently released open source libraries for. The way these

Neither of those ways works in ZKP systems like the EU is in the process of doing or the one Google recently released open source libraries for. The way these work is that the IDP issues a signed digital ID that is stored in a hardware security module tied to you. Typically this would be in your smartphone but could be something else like a smart card. Let's go with a smartphone for the rest of this comment. Later, when you want to prove to a porn site that you are 18+ your smartphone can use a zero knowledge proof (ZKP) protocol to prove the porn site that your phone contains a signed ID from your IDP that shows your age is 18+. The ZKP proof reveals nothing else from your digital ID other than that the date of birth field is at least 18 years in the past. All the porn site finds out is that someone who has an ID from your IDP that says they are 18+ is trying to use the porn site. The IDP doesn't learn anything because they aren't involved in the age verification.