Policy-directed certificate retrieval

Any large scale security architecture that uses certificates to provide security in a distributed system will need some automated support for moving certificates around in the network. We believe that for efficiency, this automated support should be tied closely to the consumer of the certificates: the policy verifier. As a proof of concept, we have built QCM, a prototype policy language and verifier that can direct a retrieval mechanism to obtain certificates from the network. Like previous verifiers, QCM takes a policy and certificates supplied by a requester and determines whether the policy is satisfied. Unlike previous verifiers, QCM can take further action if the policy is not satisfied: QCM can examine the policy to decide what certificates might help satisfy it and obtain them from remote servers on behalf of the requester. This takes place automatically, without intervention by the requester; there is no additional burden placed on the requester or the policy writer for the retrieval service we provide. We present examples that show how our technique greatly simplifies certificate-based secure applications ranging from key distribution to ratings systems, and that QCM policies are simple to write. We describe our implementation, and illustrate the operation of the prototype. Comments University of Pennsylvania Department of Computer and Information Science Technical Report No. MSCIS-99-07. This technical report is available at ScholarlyCommons: http://repository.upenn.edu/cis_reports/140 Policy-Directed Certificate Retrieval Technical Report MS-CIS-99-07 Carl A. Gunter and Trevor Jim University of Pennsylvania