The Failure Discovery problem

We define a simple variant of the Byzantine agreement (BA) problem, called the Failure Discovery (FD) problem, that roughly speaking, amounts to reaching BA provided that no failures are discovered. We show how a protocol for FD can be extended to one for BA, with no message overhead in the failure-free runs. We also show that, for so-calledbenign failures, if the FD protocol satisfies an additional property, the message-preserving extension to a BA protocol can be accomplished with minimal time overhead in the failure-free runs. Our results show that FD is a useful building block for BA; indeed, it has been used in this way in a companion paper (Hadzilacos and Halpern, 1993).The work of V. Hadzilacos was supported, in part, by a grant from the Natural Sciences and Engineering Research Council of Canada.