Overview

BIP 341, “Taproot: SegWit version 1 spending rules”, is a Bitcoin Improvement Proposal authored by Pieter Wuille, Jonas Nick, and Anthony Towns, assigned in January 2020. It specifies the consensus rules for spending SegWit version 1 outputs, the core of the Taproot soft-fork upgrade. Taproot combines Schnorr signatures (defined in the companion BIP 340) with a Merkle-tree script commitment (MAST) so that an output can be spent either by a single key or by revealing one of several committed scripts. The proposal was activated on Bitcoin mainnet at block 709,632.

Key points

• Defines SegWit version 1 outputs (Taproot outputs), where the witness program is a 32-byte tweaked public key.
• Key-path spending authorizes the output with a single Schnorr signature over the tweaked key, indistinguishable on-chain from any other Taproot spend.
• Script-path spending commits alternative spending conditions in a Merkle tree of tapleaves (MAST), revealing only the executed script plus its Merkle branch.
• The output key Q is derived by tweaking the internal key P with the Merkle root: Q = P + hash(P || merkle_root) * G, binding scripts to the key without disclosing them unless used.
• Script-path spends supply a control block (length 33 + 32m bytes) carrying the internal key, leaf version, and Merkle proof needed to verify inclusion.
• Requires BIP 340 (Schnorr signatures) and is paired with BIP 342 (Tapscript) for the associated script semantics.

Relevance to Truestamp

Bitcoin is one of the public blockchains Truestamp commits its block hashes to, so the Taproot spending rules govern the modern outputs used in those transactions. This source is cited in the Truestamp whitepaper. See Bitcoin and block commitment for how external commitments record Truestamp blocks on Bitcoin.

Citations

1. Taproot: SegWit version 1 spending rules (BIP 341). Pieter Wuille, Jonas Nick, and Anthony Towns. Bitcoin Improvement Proposal 341, January 2020.