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input: update CommitSpendNoDelay to be aware of tweakless commits, add new witness type

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In this commit, we update the `CommitSpendNoDelay` method to be aware of
the alternate spending mechanism for commitments that don't have a tweak
for the remote party's non-delay output. We also add a new witness type
so callers can convey their expected signing path.
This commit is contained in:
Olaoluwa Osuntokun
2019-07-31 20:02:52 -07:00
parent a9541b8f6a
commit bee777ab5f
3 changed files with 42 additions and 9 deletions
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29
input/script_utils.go
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@@ -902,13 +902,15 @@ func CommitSpendRevoke(signer Signer, signDesc *SignDescriptor,
}
// CommitSpendNoDelay constructs a valid witness allowing a node to spend their
// settled no-delay output on the counterparty's commitment transaction.
// settled no-delay output on the counterparty's commitment transaction. If the
// tweakless field is true, then we'll omit the set where we tweak the pubkey
// with a random set of bytes, and use it directly in the witness stack.
//
// NOTE: The passed SignDescriptor should include the raw (untweaked) public
// key of the receiver and also the proper single tweak value based on the
// current commitment point.
func CommitSpendNoDelay(signer Signer, signDesc *SignDescriptor,
sweepTx *wire.MsgTx) (wire.TxWitness, error) {
sweepTx *wire.MsgTx, tweakless bool) (wire.TxWitness, error) {
if signDesc.KeyDesc.PubKey == nil {
return nil, fmt.Errorf("cannot generate witness with nil " +
@@ -923,14 +925,25 @@ func CommitSpendNoDelay(signer Signer, signDesc *SignDescriptor,
}
// Finally, we'll manually craft the witness. The witness here is the
// exact same as a regular p2wkh witness, but we'll need to ensure that
// we use the tweaked public key as the last item in the witness stack
// which was originally used to created the pkScript we're spending.
// exact same as a regular p2wkh witness, depending on the value of the
// tweakless bool.
witness := make([][]byte, 2)
witness[0] = append(sweepSig, byte(signDesc.HashType))
witness[1] = TweakPubKeyWithTweak(
signDesc.KeyDesc.PubKey, signDesc.SingleTweak,
).SerializeCompressed()
switch tweakless {
// If we're tweaking the key, then we use the tweaked public key as the
// last item in the witness stack which was originally used to created
// the pkScript we're spending.
case false:
witness[1] = TweakPubKeyWithTweak(
signDesc.KeyDesc.PubKey, signDesc.SingleTweak,
).SerializeCompressed()
// Otherwise, we can just use the raw pubkey, since there's no random
// value to be combined.
case true:
witness[1] = signDesc.KeyDesc.PubKey.SerializeCompressed()
}
return witness, nil
}