This is a revision of #609 that is intended as a replacement due to the number of substantial changes. Test vectors will be added once the BIP has been reviewed by the community and the reference implementation is updated.
Abstract
This BIP describes a new light client protocol in Bitcoin that improves upon currently available options. The standard light client protocol in use today, defined in BIP 37, has known flaws that weaken the security and privacy of clients and allow denial-of-service attack vectors on full nodes. The new protocol overcomes these issues by allowing light clients to obtain compact probabilistic filters of block content from full nodes and download full blocks if the filter matches relevant data.
New P2P messages empower light clients to securely sync the blockchain without relying on a trusted source. This BIP also defines a filter header, which serves as a commitment to all filters for previous blocks and provides the ability to efficiently detect malicious or faulty peers serving invalid filters. The resulting protocol guarantees that light clients with at least one honest peer are able to identify the correct block filters.
State of Implementation
We've tested the implementation of both a light client implementing this BIP, as well as the serving full-node on Bitcoin's testnet over the past several months. Additionally, this new operating mode also serves as the basis for our light weight Lightning node. These implementations are based on an earlier version of the spec, and require some updates.
