> Alice sends out

It relies on trusting that Alice’s request is valid. If Alice sends another proof, she will have a different balance. Alice decides what to send. The server blindly accepts it.

You actually don’t want that for a lot of security and that’s why nobody uses ZKP for passwords or really anywhere outside theory - dumb theory that doesn’t understand basic web dev. We already have hashing and databases. There is a narrow use case for trusting clients - like receiving updates from intranet or p2p devices - maybe you use ZKP to omit unnecessary pii. But that’s it. It’s not what you think it is.