An Algebra for Assessing Trust in Certification Chains

Open networks allow users to communicate without any prior arrangements such as contractual agreement or organisation membership. However, the very nature of open networks makes authenticity difficult to verify. We show tha t authentication can not be based on public key certificates alone, but also needs to include the binding between the key used for certification and it’s owner, as well as the trust relationships between users. We develop a simple algebra around these elements and describe how it can be used to compute measures of authenticity.