Robust and Low-degree Overlay for Secure Flooding Against Resource-bounded Adversaries

The security of large-scale blockchains relies on successful message flooding among the honest parties, on an overlay topology. The crux of doing such flooding successfully is to have a robust and low-degree overlay topology: Robust means that even if the malicious parties all refuse to relay messages, the remaining honest parties should still constitute a connected component in the overlay network. Low-degree means that the nodes in the overlay network should have relatively small node degrees. The central challenge of designing such robust and low-degree topology is that in permissionless blockchain context, the adversary is often bounded by resource (such as computation power or stake), rather than by the total number of malicious parties. We show that existing works of designing robust overlay against such resource-bounded adversaries all require excessively large node degrees (e.g., 25000 or more under real-world settings). As our main contribution, we propose a novel LoR overlay topology that is robust against such resource-bounded adversaries. Our design is the very first such design with practically-feasible node degrees (e.g., 200 to 400 under real-world settings with up to 100000 nodes).