CHIPs · CHIP-2026-02 · draft
Simplified Header Verification (SHV)
Proposes a Merkle Mountain Range commitment over block headers so light wallets can verify header history with a small, fixed-size state instead of downloading every header.
Summary
SHV applies the idea behind SPV to block headers. A server keeps a Merkle Mountain Range (MMR), an append-only accumulator over all headers, and can prove any past header against the latest root. A light wallet holds only the latest accumulator state, O(log n) hashes, and can extend it itself as new headers arrive.
Motivation
The author found the data structure while working on Faster Blocks, which would grow the header chain 10×, from about 4.2 to about 42 MB per year. SHV makes the header data a light wallet must keep fixed-size, whatever the block rate. It is useful even if block times never change.
The author cites prior art: the “History Tree” (Crosby and Wallach, 2009), later called a Merkle Mountain Range (Todd, 2012), and work describing it as the optimal accumulator for append-only data.
What it specifies
- A header-chain MMR that nodes can compute and serve.
- A P2P protocol extension for header roots and Merkle proofs.
- A client specification, revised in March 2026 to guard against CVE-2012-2459 (duplicate sub-tree issue in Bitcoin’s Merkle tree construction), which could otherwise let a server lie about a header’s height.
The Faster Blocks CHIP lists SHV work, including a Bitcoin Cash Node merge request and Electron Cash pull requests, as related actions that can be done “at any time, ahead or after changing consensus rules.”
Current status
Draft, posted 25 February 2026. No formal stakeholder statements were found.