RISC Zero is useful for crypto use-cases: Other people need to verify an exact program was run.
The identity use case is about connecting sources of trust (document issuers) with consumers of that trust ("this is a real person") in ways that don't release more than the minimum information required ("the passport office has signed that this is a real person so we can trust that").
Single purpose circuits make a lot of sense for this - there is just no need to a full ZK RISC-V VM for this use case.
> Single purpose circuits make a lot of sense for this
No, they don't. They lock your system into a single set of trade-offs without an advantage to offset it. They're premature optimization. How do you think ZK systems can be made resilient to cloning attacks without hardware locking if your ZK vocabulary is limited to stupid BBS-style selective disclosure and nothing else?
I don't understand what "BBS-style" means in this context, but selective disclosure is exactly what the requirement is.
For example, age verification: I can run a program that takes a signed time-stamp and an officially-signed birth certificate and produces a yes/no "over 18" boolean, then prove to you I actually ran this program, not just "return true", but WITHOUT revealing the birth certificate.
It's a really neat facility that too few people are thinking about. We've had zero knowledge systems for a few decades now, but until now, each one has been a special bespoke mathematical object that would take years to develop. Over the past year or two, we've 1) made the things 1000x faster, and 2) made it possible to write arbitrary code under zero knowledge instead of having to make each ZK system a PHD thesis.
Others say that zkVMs are pointless because they're less efficient than these bespoke mathematical objects. Yes, they are. So what? The flexibility is worth it. Others say that zkVMs came out of Etherium, so they're only good for "crypto" stuff. False. Sure, it's the Etherium people who did a lot of foundational research into efficient zkVMs. We owe them a debt of gratitude, because they made a new kind of CS object that's going to be useful for tons of things not tied to Etherium or web3 in any way.
Anyway, if you want to get a feel for fully programmable ZK systems, check out https://noir-lang.org/, a programming language for ZK programs (not a zkVM, but same UX). Or https://github.com/a16z/jolt, which lets you run normal Rust under zero knowledge.
Today, you can write normal-looking code and have it execute under zero knowledge, and, importantly, efficiently. You literally couldn't do this two years ago, and it changes everything.
ID verification is not enough, you also need some way to prevent one malicious user from re-selling the same ID to millions of others. Without ZKPs, you know what document the user is trying to sign up with, so you can rate-limit that document. With ZKPs, however, you need those rate limits to exist somewhere else.