Comment by fvirdia
1 year ago
Implementor here. During the Privacy Pass "issuance" protocol, the client will generate a "message" that the server will process. The output from the server is returned to the client, that further modifies this output to produce the final tokens. The last client modification randomises these tokens in such a way that the server will be unable to identify to what issuance they belong.
The very cool thing is that this is the case even if the server tries to misbehave during their phase. This means that users only need to trust the client software, which we open sourced: https://github.com/kagisearch/privacypass-extension
Some posters are mentioning blind signatures, and indeed Privacy Pass can utilise these as a building block. To be precise, however, I should mention that for Kagi we use "Privately Verifiable Tokens" (https://www.rfc-editor.org/rfc/rfc9578.html#name-issuance-pr...) based on "oblivious pseudorandom functions" (OPRFs), which in my personal view are even cooler than blind signatures
If you can get Kagi to agree to it, definitely write a blog post on their behalf, please.
FWIW, the person you're replying to did write most of the blog post. We work together at Kagi on Privacy Pass.
Oh, interesting. Maybe it's just on mobile, but no authors are rendering on the article for me.
Anywho, the person I replied to seemed to be willing and able to go a technical level deeper than the article, and that's something I'm also interested in reading. It sounds like they'd be allowed :)