cient Failure Discovery with Limited Authentication

Solutions for agreement problems in distributed sys tems can generally be divided into two classes authen ticated protocols and non authenticated protocols Au thenticated protocols make use of authenticated mes sages i e the messages can be signed in a way that a signed message can be assigned unambiguously to the signer Few has been said about how to achieve this kind of authentication in some settings this is im possible 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 arbi trary 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 au thenticated protocols for this problem have linear mes sage complexity as opposed to quadratic complexity in the non authenticated case the e ort of establish ing local authentication once results in a substantial reduction of messages in subsequent failure discovery protocols