Greedy Networking in Cryptocurrency Blockchain

Proof of work (PoW) is a widely adopted distributed consensus protocol which enables cryptocurrency transaction processing without a trusted third party. The miners are financially incentivized to participate in the PoW consensus protocol, and PoW relies on the underlying peer-to-peer (P2P) networking for receiving and transmitting the transactions and the up-to-date blocks (which are the inputs for the PoW consensus protocol). We study the rational miner strategy but control an orthogonal parameter from those in the previous blockchain research, which has studied the control of the mining power or the timing of the block submissions (e.g., selfish mining or block withholding). More specifically, we study greedy networking, in which a miner node increases its connectivity beyond the default protocol to expedite the deliveries of blocks and transactions for an unfair mining advantage. While greedy networking has been actively studied in the general P2P networking, it has not been systematically studied in cryptocurrency and blockchain despite the alleged real-world instances by the Bitcoin community. We build an analytical framework for greedy networking and study how the networking control impacts the cryptocurrency application to quantify the benefits and costs of the networking control. To demonstrate the use of our framework, we implement a greedy networking prototype based on an active Bitcoin node connected to the Mainnet while simulating different miner capabilities by varying the computing backend of the miner. In contrast to the previous belief in blockchain and cryptocurrency, we discover that the optimal number of connections is bounded (limiting the greedy behavior) and depends on the hash computing capability of the miner.