A first computing entity provides evidence to a second computing entity to demonstrate that the first computing entity has a trusted configuration specification that is one of a set of such specifications agreed between the computing entities. This evidence comprises a computed commitment, made using (but not revealing) the configuration specification of the first computing entity, and a ring signature generated using a plurality of keys where each such key is generated using the commitment and one of the trusted configuration specifications. The second computing entity verifies the ring signature in order to convince itself that the configuration specification of the first computing entity is in the set.