H4: Use BIP-341 NUMS point as unspendable Taproot internal key for V3+#914
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Add CreateUnspendableInternalKeyV2() using the well-known BIP-341 NUMS point (0x50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0) which is provably unspendable because no one knows its discrete log. BuildTaprootSpendInfo now accepts a projectVersion parameter: - V3+: uses the NUMS point (cryptographically guaranteed unspendable) - V1/V2: uses the legacy derived internal key (backward compatible) This prevents any possibility of spending via the key path in Taproot outputs, ensuring funds can only be spent via the script path as intended.
dangershony
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Jul 4, 2026
dangershony
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Jul 7, 2026
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We need to make sure the version is used in later upgrade right?
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Summary
Use the well-known BIP-341 NUMS (Nothing Up My Sleeve) point as the Taproot internal key for V3+ projects, making the key path provably unspendable.
Problem
The current implementation derives the internal key from project data. While it was intended to be unspendable, there's no cryptographic guarantee — a flaw in the derivation logic or a future refactor could accidentally make it spendable, allowing funds to bypass the script path.
Solution
For V3+ projects, use the standard NUMS point from BIP-341:
0x50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0This point is the SHA-256 hash of the Generator point G interpreted as a public key. No one can know its discrete logarithm, so the key path is cryptographically guaranteed to be unspendable.
Changes
CreateUnspendableInternalKeyV2()returning the NUMSTaprootInternalPubKeyBuildTaprootSpendInfonow acceptsprojectVersionparameterTesting
All 154 shared tests pass.