US Patent 7664828 Invalid policy detection

Implementations are described and claimed herein to detect an invalid policy that may reside in a cache at a client. An expired policy is removed from cache and a current policy is requested. Otherwise the cached policy may be used. The client indicates which policy it is using by generating a policy digest, including, in compressed form, one or more assertions. If the host determines the policy digest is invalid, the host issues an invalid digest fault. If the policy digest is valid, but the assertions included in the policy digest are invalid, the host issues an invalid policy fault. In either case, the client is notified that the cached policy is no longer valid and that a current policy should be requested.