Between user and RP - The RP is an entity the user may or may not have a direct relationship with, depending on the service in question. Some services may only be offered to those users where such a direct relationship exists (for particularly sensitive services, for example), while some may not require this and would instead be satisfied with basic federation trust guarantees between themselves and the IdP. This may well include the option that the user stays anonymous with respect to the RP (though, obviously, never anonymous to the IdP). If attempting to preserve privacy via data minimization (Section 1), then the only attribute information about Individuals exposed to the RP should be attribute information that is strictly necessary for the operation of the service.