alt Hacker News> The other is that because it's not possible to link an attestation to a particular device the only mitigation to abuse that is feasible is rate limiting
I still don't see how you can keep something anonymous and still rate limit it. If a service can tell that two requests came from the same party in order to count them then two services can tell that two requests came from the same party (by both pretending to be the same service) and therefore correlate them.
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Just to give an example to prime your intuition: define your "usage token" as H(private_key|service_domain_name|date|4-bit_counter). Make your scheme provably reveal the usage token when you authenticate. Now you can use the service 16 times a day on a particular domain and no more simply by blocking token reuse. And yet the service has no ability to link different tokens to each other or to a specific person because they don't have anyone elses private keys.
You can make variations on this for a wide spectrum of rate limiting behaviors.
But also I agree with xinayder's comment-- the anticompetative, anti-privacy, invasive surveillance is unacceptable. There is a lot of risks with ZKP's that we just make the poison a little less bitter with the end result being more harm to humanity.
I think ZKP systems are intellectually interesting and their lack of use helps make it more clear that the surveillance is really the point of these schemes, not security because most of the security (or more of it) could be achieved without most of the surveillance.
But allowing the apple google duoopoly to control who can read online is wrong even if they did it in a way that better preserved privacy.
And because I can't believe no one else in the thread has linked to it: https://www.gnu.org/philosophy/right-to-read.html
The way it would work with blind signatures is that the server will know the device that comes to it to request a blinded signature and will be able to rate limit how often that device asks it.
But once you get the response you can unblind the signed signature and obtain the token (which is just the unblinded signature). This token can then be used once either because its blacklisted after use (and it expires before the next day starts for example).
The desired property of blind signatures is that given a token it's information theoretically impossible to determine which blinded signature it came from (because it could have come from any of them) even if the cryptographic primitive is broken by a mathematical breakthrough or a quantum computer. There is technically the danger that if the anonymity set is too small and all the other participants collude you can be singled out.
Correlating times is a threat vector that needs to be managed either by delaying actions (not tolerable by normal users) or by acquiring tokens automatically and storing them in expectation. Or something other I haven't thought of probably. There is also a networking aspect to this, you will need a decentralized relay server network that masks origin of requests.