Abstract: In an infrastructure in which some of a plurality of entities provide cryptographically supported services, a method of registering a subscriber entity of a plurality of entities at a principal entity of a plurality of entities, the method comprising the subscriber entity requesting service from the principal entity by sending a request message to a registrar entity of the plurality of entities; the registrar entity verifying the subscriber entity and forwarding the request for service to the principal entity; the principal entity storing the forwarded request and transmitting an acknowledgement message to the registrar entity, the acknowledgement stating acceptance and authentication/authorization information that the subscriber entity requires for the requested service; and the registrar entity verifying the authenticity of the received acknowledgement message, and, if correct, forwarding the acknowledgement message to the subscriber entity.