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This paper is on the Consensus problem in asynchronous distributed systems where (up to f) processes (among n) can exhibit a Byzantine behavior, i.e., can deviate arbitrarily from their specification. One way to solve the Consensus problem in such a context consists of enriching the system with additional oracles that are powerful enough to cope with the uncertainty and unpredictability created by the combined effect of Byzantine behavior and asynchrony. This paper presents two kinds of Byzantine asynchronous Consensus protocols using two types of oracles, namely, a common coin that provides processes with random values and a failure detector oracle. Both allow the processes to decide in one communication step in favorable circumstances. The first is a randomized protocol for an oblivious scheduler model that assumes n>5f. The second one is a failure detector-based protocol that assumes n>6f. These protocols are designed to be particularly simple and efficient in terms of communication steps, the number of messages they generate in each step, and the size of messages. So, although they are not optimal in the number of Byzantine processes that can be tolerated, they are particularly efficient when we consider the number of communication steps they require to decide and the number and size of the messages they use. In that sense, they are practically appealing.
Asynchronous distributed system, Byzantine process, distributed algorithm, fault tolerance, random oracle, randomized protocol, unreliable failure detector.

R. Friedman, A. Mostefaoui and M. Raynal, "Simple and Efficient Oracle-Based Consensus Protocols for Asynchronous Byzantine Systems," in IEEE Transactions on Dependable and Secure Computing, vol. 2, no. , pp. 46-56, 2005.
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