Taking Another Look at the Use of Bloom Filters in Bitcoin

Abstract

Lightweight nodes in the Bitcoin network do not have the capability to synchronize the entire contents of the blockchain. In order to receive information that is relevant to them, they use the Simplified Payment Verification (SPV) protocol to communicate with full nodes, that hold the entire blockchain. Bloom filters are used by the SPV protocol to mitigate known privacy issues. Still, the effectiveness of using Bloom filters comes into question. In this paper, we analyze the behaviour of Bloom filter requests with respect to their target False Positive Rate (FPR) values. Our findings show that small FPR values have very limited bandwidth requirements, while higher values are not suitable for use with bandwidth restricted devices. At the same time, we confirm that privacy implications of Bloom filters are still valid today, when an increasing number of new addresses appears in the Bitcoin blockchain every day. We also study the effect that multiple concurrent requests made by Bloom filter enabled lightweight clients have on the disk and CPU utilization, as well as RAM consumption of full node clients.