What is QCM ?

QCM stands for `Query Certi cate Manager'; it is a software system that has been developed at the University of Pennsylvania as part of the SwitchWare project on active networks. QCM is a Public Key Infrastructure (PKI) intended to support secure maintenance of distributed data sets like Access Control Lists (ACL's) or public key certi cate repositories. An ACL is a list of `principals', identi ed by public keys; such lists can be used to describe who is permitted to access resources such as the ability to read and modify a le, or run a program. A public key certi cate is an association between a public key and an individual or entity. QCM allows policies, such as the ACL of principals allowed to access a resource, to be described in a special-purpose langauge (the language is also called QCM). The system provides two services. First, it veri es whether a policy is satis ed by a request, and, second, it uses the policy veri cation to assist in retrieving the certi cates (digitally signed documents) that are relevant to the veri cation. This integrated veri cation and retrieval mechanism is known as policy directed certi cate retrieval and is the primary novel contribution of the QCM system.