|Abstract:||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 to drive MTN with different tradeoffs between privacy and negotiation speed. We also show that these strategies are safe and complete.