Automated trust negotiation (ATN) is a promising approach to establishing trust between two entities without any prior knowledge of each other. However, real-world authorization processes often involve online input from third parties, which ATN does not support. In this paper, we introduce
multiparty trust negotiation
(MTN) as a new approach to distributed authorization. We define a Datalog-based policy language, Distributed Authorization and Release Control Logic (DARCL), to specify both authorization and release control policies. DARCL suits the needs of MTN and can also serve as a powerful general-purpose policy language for authorization. To orchestrate the negotiation process among multiple parties without a centralized moderator, we propose the
diffusion negotiation protocol
, a set of message-passing conventions that allows parties to carry out a negotiation in a distributed fashion. Building on top of the diffusion negotiation protocol, we propose two negotiation strategies, both safe and complete, to drive MTN with different tradeoffs between privacy and negotiation speed.