BIP 157 Client-Side Block Filtering

Overview

BIP 157 defines how Bitcoin nodes provide compact block filters and related peer-to-peer messages. Instead of a lightweight wallet sending a list of its addresses or scripts to a remote node, the wallet downloads a small filter for each block and checks the filter locally. If the filter indicates a possible match, the client requests the full block or other necessary data and verifies the transaction. False positives are possible, but false negatives should not occur when filters are constructed correctly for the specified filter type. This model improves privacy compared with server-side filtering because peers do not receive the wallet’s exact search criteria. It also supports verification across multiple peers and makes the filter chain independently checkable through filter headers.

BIP 157 defines the protocol for obtaining and validating the filters, while BIP 158 specifies the construction of the basic filter itself. The two standards are commonly discussed together but describe different parts of the system. The protocol lets clients request filters for blocks, compare filter-header chains, and obtain the relevant block when a local match occurs. Because the client does not send an address list or script set, the server learns less about the wallet than it would under server-side Bloom filtering. BIP 157 does not define which elements belong in the basic filter or how those elements are encoded; that is the role of BIP 158. The distinction matters: BIP 157 is primarily the network service and client protocol, while BIP 158 is the filter construction standard. Clients still need to validate block headers and inspect matching blocks. A filter match can be a false positive, so it indicates that further verification is required rather than proving that a wallet received a payment.