Computer-Aided Decision-Making with Trust Relations and Trust Domains (Cryptographic Applications)

We propose generic declarative definitions of individual and collective trust relations between interacting agents and agent collections, and trust domains of trust-related agents in distributed systems. Our definitions yield (1) (in)compatibility, implicational and transitivity results for trust relationships, including a Datalog-implementability result for their logical structure; (2) computational complexity results for deciding potential and actual trust relationships and membership in trust domains; (3) a positive (negative) compositionality result for strong (weak) trust domains; (4) a computational design pattern for building up strong trust domains; and (5) a negative scalability result for trust domains in general. We instantiate our generic trust concepts in five major cryptographic applications of trust, namely: Access Control, Trusted Third Parties, the Web of Trust, Public-Key Infrastructures and Identity-Based Cryptography. We also show that accountability induces trust. Our defining principle for weak and strong trust (domains) is (common) belief in and (common) knowledge of agent correctness, respectively.