* [bitcoindev] [taproot][script] 4-leaf Taproot Merkle Tree in Python: testnet implementation + control block analysis
@ 2025-07-08 14:45 aaron.recompile
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From: aaron.recompile @ 2025-07-08 14:45 UTC (permalink / raw)
To: Bitcoin Development Mailing List
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Hi all,
I'm Aaron Zhang, an independent developer focused on Bitcoin script
engineering and Taproot experimentation.
I’d like to share a hands-on project involving a fully constructed 4-leaf
Taproot Merkle tree in Python, with testnet-validated spending transactions
and in-depth analysis of control block internals.
This work features:
- Construction of a *Taproot address with 4 distinct script leaves*:
1. `OP_SHA256` + `OP_EQUAL` hashlock
2. 2-of-2 `OP_CHECKMULTISIG`
3. `OP_CSV` + `OP_CHECKSIG`
4. `OP_CHECKSIG`
- A total of *five spending paths*, including four script path spends and
one key path spend, all confirmed through on-chain transactions on Bitcoin
testnet.
- Merkle tree construction and Taproot output key tweaking (internal key +
script tree root), followed by a **byte-by-byte breakdown of the control
blocks**, including:
- Control byte (leaf version + parity)
- Internal public key
- Ordered Merkle sibling hashes
- *Code-level analysis and experimental validation of how these control
blocks* are constructed and verified against the Taproot output, based on
actual testnet spends.
- *Witness stack inspection and visualization of script execution*, showing
the actual runtime behavior for each script path.
Resources:
*- Part 1: 4-leaf tree construction and testnet validation *
https://medium.com/@aaron.recompile/building-a-4-leaf-taproot-tree-in-python-the-first-complete-implementation-on-bitcoin-testnet-c8b66c331f29
*- Part 2: Control block structure and stack visualization *
https://medium.com/@aaron.recompile/taproot-control-block-deep-analysis-stack-execution-visualization-5ff10f98032c
- GitHub repo with code, testnet transactions, and diagrams
https://github.com/btcstudy/btcstudy.github.io/tree/main/Not-Just-Hodling:bitcoin-script-Engineering/demo3_taproot_4leaf
This project aims to provide a fully verifiable and pedagogical example of
non-trivial Taproot path spends, helping developers better understand
script trees, control blocks, and Tapscript execution through practical
experimentation.
I’d be happy to receive any feedback or discussion around:
- Control block design and merkle path optimization
- Spend path visibility and privacy tradeoffs
- Tooling for visualizing script-path execution and verification
Thanks and best regards,
Aaron Zhang
[@aaron.recompile](https://medium.com/@aaron.recompile)
GitHub: https://github.com/btcstudy
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