Efficient failure discovery with limited authentication

Solutions for agreement problems in distributed systems can generally be divided into two classes: authenticated protocols and non-authenticated protocols. Authenticated protocols make use of authenticated messages, i.e., the messages can be signed in a way that a signed message can be assigned unambiguously to the signer. Little has been said about how to achieve this kind of authentication; in some settings this is impossible without a trusted dealer or other mechanisms outside the system. In this paper, we introduce and investigate a weaker kind of authentication, local authentication. It can be achieved within a distributed system with an arbitrary number of arbitrary faults. We then show that Failure Discovery, a problem introduced by Hadzilacos and Halpern, can be solved with authenticated protocols even if only local authentication is available. Since authenticated protocols for this problem have linear message complexity, as opposed to quadratic complexity in the non-authenticated case, the effort of establishing local authentication once results in a substantial reduction of messages in subsequent failure-discovery protocols.