Interesting - did anyone write up how it worked anywhere? I also worked on a similar system in 2015, which provided anonymity and unlinkability in almost all

Interesting - did anyone write up how it worked anywhere? I also worked on a similar system in 2015, which provided anonymity and unlinkability in almost all interactions (you don't know who it is, and you don't know whether the anonymous user is the same one you saw last time). You did have to pay for the service of course, but it issued blind signature tokens for access (similar to what is described in the article). So the service did not know who actually did what. It could also provide anonymous attestation of some attribute (like age). This was a bit more efficient and secure in that you did not need to store a bunch of tokens. It could transform the proof to be unique each time (thus giving unlinkability). It would only work if you had access to your private keys (so you could not just give your age proof token to a kid - you would have to give them your entire account and keys).