Federated Byzantine Agreement Protocol Robustness to Targeted Network Attacks.

Federated Byzantine Agreement protocols applied in the XRP Ledger and Stellar use voting to reach a consensus. Participants of these protocols select whom to trust in the network and effectively communicate with the trustees to reach an agreement on transactions. Most trustees, for example 80% in the XRP Ledger, must agree on the same transactions for them to appear in the blockchain. However, disruptions to the communication between the trustees can prevent the trustees from reaching an agreement. Thus, halting the blockchain. In this paper, we propose a novel robustness metric to measure the Federated Byzantine Agreement protocol tolerance to node failures. We show that the XRP Ledger Consensus Protocol is vulnerable to targeted attacks. An attacker has to disconnect only 9% of the highest-degree nodes to halt the blockchain. We propose a mitigation strategy which maintains critical XRP Ledger network topology properties whilst increasing the robustness up to 45%.