We haven't discussed this one yet, but 254: Hashed claims discovery is a proposal from Justin (and Sarah, I believe) for communicating to a client enough information about the desired claim value(s) so that it can supply the right claim(s) the AS is looking for, without exposing too much of the RO's policies, and without the client pushing too many of the RqP's claims to the AS. So the idea is for it to be mutually (well-roundedly?) privacy protective in the context of a hinted pushed-claims scenario. The issue thread includes a use case.