Formal Verification of Hybrid Byzantine Agreement Under Link Faults

We describe an extended fault model for Byzantine Agreement due to Schmid and Weiss. The new fault model extends the previous “hybrid” fault model of Thambidurai and Park by the addition of omission-faulty nodes, and by the introduction of link faults. We formally verify the Hybrid Oral Messages Algorithm (OMH) under this new fault model. Our formal verification improves the analysis of Schmid and Weiss a little by increasing the independence of node and link faults, and by making explicit the exact assumptions required in final rounds and in the case OMH(0). We also refute a conjecture of Schmid and Weiss that the analysis can be extended to omission-faulty receivers and introduce a symmetric version of the algorithm that does handle these cases correctly.