An efficient algorithm for establishing trust In strangers

The Internet enables connectivity between many entities that don't know each other, but to enable e-business between them, the parties need to establish some level of trust in each other. The trust can be established through the presentation of 3 party credentials where a credential is a statement made by an issuer about a subject. We describe a Trust Policy Language (TPL) which allows a party to assign different trust levels to potential partners based on credentials they present and based on the level of trust assigned to their credentials’ issuers, to their issuers’ issuers and so on. We then describe an efficient incremental algorithm for an e-commerce application that uses such Trust policies. The algorithm is designed to assign trust levels to millions of users each having several credentials and to cope with a dynamic environment in which new credentials are introduced and existing credentials may expire or be revoked. We first present an algorithm for a monotonic policy where new credentials can only result in new trust level assignments. We then extend the language and we get a non monotonic policy where new credentials can result in invalidating some of the previously trust assignments.