The Bitcoin network relies on peer-to-peer broadcast to distribute pending transactions and confirmed blocks. The topology over which this broadcast is distributed af- fects which nodes have advantages and whether some at- tacks are feasible. As such, it is particularly important to understand not just which nodes participate in the
Bit- coin network, but how they are connected.
In this paper, we introduce AddressProbe, a technique that discovers peer-to-peer links in Bitcoin, and apply this to the live topology. To support AddressProbe and other tools, we develop CoinScope, an infrastructure to manage short, but large-scale experiments in Bitcoin. We analyze the measured topology to discover both high- degree nodes and a well connected giant component. Yet, efficient propagation over the Bitcoin backbone does not necessarily result in a transaction being accepted into the block chain. We introduce a “decloaking” method to find influential nodes in the topology that are well connected to a mining pool. Our results find that in contrast to Bit- coin’s idealized vision of spreading mining responsibil- ity to each node, mining pools are prevalent and hidden: roughly 2% of the (influential) nodes represent three- quarters of the mining power.