lnwallet+contractcourt: publicly export DeriveCommitmentKeys use in chain watcher

In this commit, we consolidate the number of areas where we derive our
commitment keys. Before this commit, the `isOurCommitment` function in
the chain watcher used a custom routine to derive the expected
scripts/keys for our commitment at that height. With the recent changes,
we now have additional logic in `DeriveCommitmentKeys` that wasn't
copied over to this area. As a result, the prior logic would erroneously
detect if it was our commitment that had hit the chain or not.

In this commit, we remove the old custom code, and use
`DeriveCommitmentKeys` wihtin the chain watcher as well. This ensures
that we only need to maintain the key derivation code in a single place,
preventing future bugs of this nature.

lnwallet/channel.go

@@ -876,13 +876,13 @@ func (lc *LightningChannel) diskCommitToMemCommit(isLocal bool,
 	// haven't yet received a responding commitment from the remote party.
 	var localCommitKeys, remoteCommitKeys *CommitmentKeyRing
 	if localCommitPoint != nil {
-		localCommitKeys = deriveCommitmentKeys(
+		localCommitKeys = DeriveCommitmentKeys(
 			localCommitPoint, true, tweaklessCommit,
 			lc.localChanCfg, lc.remoteChanCfg,
 		)
 	}
 	if remoteCommitPoint != nil {
-		remoteCommitKeys = deriveCommitmentKeys(
+		remoteCommitKeys = DeriveCommitmentKeys(
 			remoteCommitPoint, false, tweaklessCommit,
 			lc.localChanCfg, lc.remoteChanCfg,
 		)
@@ -981,10 +981,10 @@ type CommitmentKeyRing struct {
 	RevocationKey *btcec.PublicKey
 }
 
-// deriveCommitmentKey generates a new commitment key set using the base points
+// DeriveCommitmentKey generates a new commitment key set using the base points
 // and commitment point. The keys are derived differently depending whether the
 // commitment transaction is ours or the remote peer's.
-func deriveCommitmentKeys(commitPoint *btcec.PublicKey,
+func DeriveCommitmentKeys(commitPoint *btcec.PublicKey,
 	isOurCommit, tweaklessCommit bool,
 	localChanCfg, remoteChanCfg *channeldb.ChannelConfig) *CommitmentKeyRing {
 
@@ -1711,9 +1711,8 @@ func (lc *LightningChannel) restoreCommitState(
 
 		// We'll also re-create the set of commitment keys needed to
 		// fully re-derive the state.
-		tweaklessCommit := (lc.channelState.ChanType ==
-			channeldb.SingleFunderTweakless)
-		pendingRemoteKeyChain = deriveCommitmentKeys(
+		tweaklessCommit := lc.channelState.ChanType.IsTweakless()
+		pendingRemoteKeyChain = DeriveCommitmentKeys(
 			pendingCommitPoint, false, tweaklessCommit,
 			lc.localChanCfg, lc.remoteChanCfg,
 		)
@@ -1999,8 +1998,8 @@ func NewBreachRetribution(chanState *channeldb.OpenChannel, stateNum uint64,
 
 	// With the commitment point generated, we can now generate the four
 	// keys we'll need to reconstruct the commitment state,
-	tweaklessCommit := chanState.ChanType == channeldb.SingleFunderTweakless
-	keyRing := deriveCommitmentKeys(
+	tweaklessCommit := chanState.ChanType.IsTweakless()
+	keyRing := DeriveCommitmentKeys(
 		commitmentPoint, false, tweaklessCommit,
 		&chanState.LocalChanCfg, &chanState.RemoteChanCfg,
 	)
@@ -3258,11 +3257,9 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig, []ch
 	// Grab the next commitment point for the remote party. This will be
 	// used within fetchCommitmentView to derive all the keys necessary to
 	// construct the commitment state.
-	tweaklessCommit := (lc.channelState.ChanType ==
-		channeldb.SingleFunderTweakless)
-	keyRing := deriveCommitmentKeys(
-		commitPoint, false, tweaklessCommit, lc.localChanCfg,
-		lc.remoteChanCfg,
+	keyRing := DeriveCommitmentKeys(
+		commitPoint, false, lc.channelState.ChanType.IsTweakless(),
+		lc.localChanCfg, lc.remoteChanCfg,
 	)
 
 	// Create a new commitment view which will calculate the evaluated
@@ -4017,11 +4014,9 @@ func (lc *LightningChannel) ReceiveNewCommitment(commitSig lnwire.Sig,
 		return err
 	}
 	commitPoint := input.ComputeCommitmentPoint(commitSecret[:])
-	tweaklessCommit := (lc.channelState.ChanType ==
-		channeldb.SingleFunderTweakless)
-	keyRing := deriveCommitmentKeys(
-		commitPoint, true, tweaklessCommit, lc.localChanCfg,
-		lc.remoteChanCfg,
+	keyRing := DeriveCommitmentKeys(
+		commitPoint, true, lc.channelState.ChanType.IsTweakless(),
+		lc.localChanCfg, lc.remoteChanCfg,
 	)
 
 	// With the current commitment point re-calculated, construct the new
@@ -5050,8 +5045,8 @@ func NewUnilateralCloseSummary(chanState *channeldb.OpenChannel, signer input.Si
 
 	// First, we'll generate the commitment point and the revocation point
 	// so we can re-construct the HTLC state and also our payment key.
-	tweaklessCommit := chanState.ChanType == channeldb.SingleFunderTweakless
-	keyRing := deriveCommitmentKeys(
+	tweaklessCommit := chanState.ChanType.IsTweakless()
+	keyRing := DeriveCommitmentKeys(
 		commitPoint, false, tweaklessCommit, &chanState.LocalChanCfg,
 		&chanState.RemoteChanCfg,
 	)
@@ -5706,10 +5701,9 @@ func NewLocalForceCloseSummary(chanState *channeldb.OpenChannel, signer input.Si
 		return nil, err
 	}
 	commitPoint := input.ComputeCommitmentPoint(revocation[:])
-	tweaklessCommit := chanState.ChanType == channeldb.SingleFunderTweakless
-	keyRing := deriveCommitmentKeys(
-		commitPoint, true, tweaklessCommit, &chanState.LocalChanCfg,
-		&chanState.RemoteChanCfg,
+	keyRing := DeriveCommitmentKeys(
+		commitPoint, true, chanState.ChanType.IsTweakless(),
+		&chanState.LocalChanCfg, &chanState.RemoteChanCfg,
 	)
 	selfScript, err := input.CommitScriptToSelf(csvTimeout, keyRing.DelayKey,
 		keyRing.RevocationKey)

lnwallet/wallet.go

@@ -663,11 +663,11 @@ func CreateCommitmentTxns(localBalance, remoteBalance btcutil.Amount,
 	fundingTxIn wire.TxIn,
 	tweaklessCommit bool) (*wire.MsgTx, *wire.MsgTx, error) {
 
-	localCommitmentKeys := deriveCommitmentKeys(
+	localCommitmentKeys := DeriveCommitmentKeys(
 		localCommitPoint, true, tweaklessCommit, ourChanCfg,
 		theirChanCfg,
 	)
-	remoteCommitmentKeys := deriveCommitmentKeys(
+	remoteCommitmentKeys := DeriveCommitmentKeys(
 		remoteCommitPoint, false, tweaklessCommit, ourChanCfg,
 		theirChanCfg,
 	)