contractcourt: implement production taproot witness selection
What the developer wrote
Authored by Olaoluwa Osuntokun
contractcourt: implement production taproot witness selection
This commit implements the core logic for selecting appropriate witness types
based on channel type in the contract resolution system. The commit sweep
resolver, HTLC timeout resolver, and HTLC success resolver have been updated
to use production taproot witness types when handling final taproot channels.
For each resolver, the witness type selection follows a consistent three-way
pattern: production taproot channels use Final witness types, staging taproot
channels use the existing taproot witness types, and legacy channels continue
to use their established witness types. This ensures that each channel type
uses the appropriate script structure and witness generation logic.
The HTLC success resolver required the addition of a new production input
constructor to properly handle direct HTLC sweeps on remote commitments with
production taproot channels. The HTLC timeout resolver was updated to handle
both second-level timeout transactions and direct timeout sweeps with the
correct production witness types.
These changes ensure that production taproot channels benefit from the
optimized script structure using OP_CHECKSIGVERIFY while maintaining full
backward compatibility with staging taproot and legacy channel types.
What changed, and why it matters
This commit updates part of LND's on-chain dispute-resolution code so that a new 'final' taproot channel type uses its own dedicated witness types when spending commitment outputs. It is a feature-completion change that adds the correct script/witness selection for production taproot channels while keeping older channel types on their existing paths. There is no direct evidence in the commit that this fixes an active security vulnerability; it appears to be correctness and compatibility work for a new channel type.
Treat as a normal feature/correctness commit. Review the related HTLC resolver and input constructor changes mentioned in the commit message to confirm the full witness-selection matrix is consistent. Run or verify taproot channel sweep tests, especially for final vs. staging channel types, before deploying in production.
Security signals we found
Witness-type selection logic for commitment output sweeps
New channel feature flag (IsTaprootFinal) introduced in selection path
Maintains backward-compatible fall-through for staging taproot and legacy channels
Commit message frames change as production taproot correctness, not a vulnerability fix
Evidence from the diff
The change is confined to contractcourt/commit_sweep_resolver.go. It extends decideWitnessType() to branch on c.chanType.IsTaprootFinal() before the existing IsTaproot() check. For local commitment sweeps it now selects TaprootLocalCommitSpendFinal for final taproot channels and keeps TaprootLocalCommitSpend for staging taproot channels. For remote commitment sweeps it selects TaprootRemoteCommitSpendFinal for final taproot channels and keeps TaprootRemoteCommitSpend for staging. Legacy channels are unaffected. The commit message also mentions corresponding updates to HTLC timeout/success resolvers and a new production input constructor, but those changes are not present in the supplied diff.
Changed components
contractcourt/commit_sweep_resolver.godecideWitnessType() methodTaproot channel commitment sweep pathInspect captured patch +10 / −2
diff --git a/contractcourt/commit_sweep_resolver.go b/contractcourt/commit_sweep_resolver.go
index d8c8c39..dd02e84 100644
--- a/contractcourt/commit_sweep_resolver.go
+++ b/contractcourt/commit_sweep_resolver.go
@@ -470,11 +470,19 @@ func (c *commitSweepResolver) decideWitnessType() (input.WitnessType, error) {
// commitment tweak to discern which type of commitment this is.
var witnessType input.WitnessType
switch {
- // The local delayed output for a taproot channel.
+ // The local delayed output for a final taproot channel.
+ case isLocalCommitTx && c.chanType.IsTaprootFinal():
+ witnessType = input.TaprootLocalCommitSpendFinal
+
+ // The local delayed output for a staging taproot channel.
case isLocalCommitTx && c.chanType.IsTaproot():
witnessType = input.TaprootLocalCommitSpend
- // The CSV 1 delayed output for a taproot channel.
+ // The CSV 1 delayed output for a final taproot channel.
+ case !isLocalCommitTx && c.chanType.IsTaprootFinal():
+ witnessType = input.TaprootRemoteCommitSpendFinal
+
+ // The CSV 1 delayed output for a staging taproot channel.
case !isLocalCommitTx && c.chanType.IsTaproot():
witnessType = input.TaprootRemoteCommitSpend
Why this scored 32/100
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