Reliable Broadcast despite Mobile Byzantine Faults

We investigate the solvability of the Byzantine Reliable Broadcast and Byzantine Broadcast Channel problems in distributed systems affected by Mobile Byzantine Faults. We show that both problems are not solvable even in one of the most constrained system models for mobile Byzantine faults defined so far. By endowing processes with an additional local failure oracle, we provide a solution to the Byzantine Broadcast Channel problem

Optimal self-stabilizing mobile byzantine-tolerant regular register with bounded timestamps

This paper proposes the first implementation of a self-stabilizing regular register emulated by n servers that is tolerant to both Mobile Byzantine Agents and transient failures in a round-free synchronous model. Differently from existing Mobile Byzantine Tolerant register implementations, this paper considers a weaker model where: (i) the computation of the servers is decoupled from the movements of the Byzantine agents, i.e., movements may happen before, concurrently, or after the generation or the delivery of a message, and (ii) servers are not aware of their failure state i.e., they do not know if and when they have been corrupted by a Mobile Byzantine agent. The proposed protocol tolerates (i) any finite number of transient failures, and (ii) up to f Mobile Byzantine agents. In addition, our implementation uses bounded timestamps from the Z13 domain and it is optimal with respect to the number of servers needed to tolerate f Mobile Byzantine agents in the given model (i.e., n>6f when Δ=2δ, and n>8f when Δ=δ, where Δ represents the period at which the Byzantine agents move and δ is the upper bound on the communication latency)

Tight self-stabilizing mobile byzantine-tolerant atomic register

This paper proposes the first implementation of a self-stabilizing atomic register that is tolerant to both Mobile Byzantine Agents and transient failures. The register is maintained by n servers and our algorithm tolerates (i) any number of transient failures and (ii) up to f Mobile Byzantine Failures. In the Mobile Byzantine Failure model, faulty agents move from one server to another and when they are affecting a server, it behaves arbitrarily. Our implementation is designed for the round-based synchronous model where agents are moved from round to round. The paper considers four Mobile Byzantine Failure models differing for the diagnosis capabilities at server side i.e., when servers can diagnose their failure state (that is, be aware that the mobile Byzantine agent has left the server), and when servers cannot self-diagnose. We first prove lower bounds on the number of servers n necessary to construct a register tolerant to the presence of f Mobile Byzantine Failures for each of the Mobile Byzantine Failure models considered and then we propose a parametric algorithm working in all the models and matching the lower bounds