lnwallet: move latest SignDescriptor + serialization

lnwallet/interface.go

@@ -224,66 +224,6 @@ type BlockChainIO interface {
 	GetBlock(blockHash *chainhash.Hash) (*wire.MsgBlock, error)
 }
 
-// SignDescriptor houses the necessary information required to successfully sign
-// a given output. This struct is used by the Signer interface in order to gain
-// access to critical data needed to generate a valid signature.
-type SignDescriptor struct {
-	// Pubkey is the public key to which the signature should be generated
-	// over. The Signer should then generate a signature with the private
-	// key corresponding to this public key.
-	PubKey *btcec.PublicKey
-
-	// SingleTweak is a scalar value that will be added to the private key
-	// corresponding to the above public key to obtain the private key to
-	// be used to sign this input. This value is typically derived via the
-	// following computation:
-	//
-	//  * derivedKey = privkey + sha256(perCommitmentPoint || pubKey) mod N
-	//
-	// NOTE: If this value is nil, then the input can be signed using only
-	// the above public key. Either a SingleTweak should be set or a
-	// DoubleTweak, not both.
-	SingleTweak []byte
-
-	// DoubleTweak is a private key that will be used in combination with
-	// its corresponding private key to derive the private key that is to
-	// be used to sign the target input. Within the Lightning protocol,
-	// this value is typically the commitment secret from a previously
-	// revoked commitment transaction. This value is in combination with
-	// two hash values, and the original private key to derive the private
-	// key to be used when signing.
-	//
-	//  * k = (privKey*sha256(pubKey || tweakPub) +
-	//        tweakPriv*sha256(tweakPub || pubKey)) mod N
-	//
-	// NOTE: If this value is nil, then the input can be signed using only
-	// the above public key. Either a SingleTweak should be set or a
-	// DoubleTweak, not both.
-	DoubleTweak *btcec.PrivateKey
-
-	// WitnessScript is the full script required to properly redeem the
-	// output. This field will only be populated if a p2wsh or a p2sh
-	// output is being signed.
-	WitnessScript []byte
-
-	// Output is the target output which should be signed. The PkScript and
-	// Value fields within the output should be properly populated,
-	// otherwise an invalid signature may be generated.
-	Output *wire.TxOut
-
-	// HashType is the target sighash type that should be used when
-	// generating the final sighash, and signature.
-	HashType txscript.SigHashType
-
-	// SigHashes is the pre-computed sighash midstate to be used when
-	// generating the final sighash for signing.
-	SigHashes *txscript.TxSigHashes
-
-	// InputIndex is the target input within the transaction that should be
-	// signed.
-	InputIndex int
-}
-
 // Signer represents an abstract object capable of generating raw signatures as
 // well as full complete input scripts given a valid SignDescriptor and
 // transaction. This interface fully abstracts away signing paving the way for

lnwallet/signdescriptor.go

@@ -2,6 +2,7 @@ package lnwallet
 
 import (
 	"encoding/binary"
+	"errors"
 	"io"
 
 	"github.com/lightningnetwork/lnd/lnwire"
@@ -10,6 +11,12 @@ import (
 	"github.com/roasbeef/btcd/wire"
 )
 
+var (
+	// ErrTweakOverdose signals a SignDescriptor is invalid because both of its
+	// SingleTweak and DoubleTweak are non-nil.
+	ErrTweakOverdose = errors.New("sign descriptor should only have one tweak")
+)
+
 // SignDescriptor houses the necessary information required to successfully sign
 // a given output. This struct is used by the Signer interface in order to gain
 // access to critical data needed to generate a valid signature.
@@ -19,14 +26,33 @@ type SignDescriptor struct {
 	// key corresponding to this public key.
 	PubKey *btcec.PublicKey
 
-	// PrivateTweak is a scalar value that should be added to the private
+	// SingleTweak is a scalar value that will be added to the private key
-	// key corresponding to the above public key to obtain the private key
+	// corresponding to the above public key to obtain the private key to
-	// to be used to sign this input. This value is typically a leaf node
+	// be used to sign this input. This value is typically derived via the
-	// from the revocation tree.
+	// following computation:
+	//
+	//  * derivedKey = privkey + sha256(perCommitmentPoint || pubKey) mod N
 	//
 	// NOTE: If this value is nil, then the input can be signed using only
-	// the above public key.
+	// the above public key. Either a SingleTweak should be set or a
-	PrivateTweak []byte
+	// DoubleTweak, not both.
+	SingleTweak []byte
+
+	// DoubleTweak is a private key that will be used in combination with
+	// its corresponding private key to derive the private key that is to
+	// be used to sign the target input. Within the Lightning protocol,
+	// this value is typically the commitment secret from a previously
+	// revoked commitment transaction. This value is in combination with
+	// two hash values, and the original private key to derive the private
+	// key to be used when signing.
+	//
+	//  * k = (privKey*sha256(pubKey || tweakPub) +
+	//        tweakPriv*sha256(tweakPub || pubKey)) mod N
+	//
+	// NOTE: If this value is nil, then the input can be signed using only
+	// the above public key. Either a SingleTweak should be set or a
+	// DoubleTweak, not both.
+	DoubleTweak *btcec.PrivateKey
 
 	// WitnessScript is the full script required to properly redeem the
 	// output. This field will only be populated if a p2wsh or a p2sh
@@ -62,7 +88,15 @@ func WriteSignDescriptor(w io.Writer, sd *SignDescriptor) error {
 		return err
 	}
 
-	if err := wire.WriteVarBytes(w, 0, sd.PrivateTweak); err != nil {
+	if err := wire.WriteVarBytes(w, 0, sd.SingleTweak); err != nil {
+		return err
+	}
+
+	var doubleTweakBytes []byte
+	if sd.DoubleTweak != nil {
+		doubleTweakBytes = sd.DoubleTweak.Serialize()
+	}
+	if err := wire.WriteVarBytes(w, 0, doubleTweakBytes); err != nil {
 		return err
 	}
 
@@ -96,20 +130,41 @@ func ReadSignDescriptor(r io.Reader, sd *SignDescriptor) error {
 		return err
 	}
 
-	privateTweak, err := wire.ReadVarBytes(r, 0, 32, "privateTweak")
+	singleTweak, err := wire.ReadVarBytes(r, 0, 32, "singleTweak")
 	if err != nil {
 		return err
 	}
 
-	// Serializing a SignDescriptor with a nil-valued PrivateTweak results in
+	// Serializing a SignDescriptor with a nil-valued SingleTweak results in
-	// deserializing a zero-length slice. Since a nil-valued PrivateTweak has
+	// deserializing a zero-length slice. Since a nil-valued SingleTweak has
-	// special meaning and a zero-length slice for a PrivateTweak is invalid,
+	// special meaning and a zero-length slice for a SingleTweak is invalid,
 	// we can use the zero-length slice as the flag for a nil-valued
-	// PrivateTweak.
+	// SingleTweak.
-	if len(privateTweak) == 0 {
+	if len(singleTweak) == 0 {
-		sd.PrivateTweak = nil
+		sd.SingleTweak = nil
 	} else {
-		sd.PrivateTweak = privateTweak
+		sd.SingleTweak = singleTweak
+	}
+
+	doubleTweakBytes, err := wire.ReadVarBytes(r, 0, 32, "doubleTweak")
+	if err != nil {
+		return err
+	}
+
+	// Serializing a SignDescriptor with a nil-valued DoubleTweak results in
+	// deserializing a zero-length slice. Since a nil-valued DoubleTweak has
+	// special meaning and a zero-length slice for a DoubleTweak is invalid,
+	// we can use the zero-length slice as the flag for a nil-valued
+	// DoubleTweak.
+	if len(doubleTweakBytes) == 0 {
+		sd.DoubleTweak = nil
+	} else {
+		sd.DoubleTweak, _ = btcec.PrivKeyFromBytes(btcec.S256(), doubleTweakBytes)
+	}
+
+	// Only one tweak should ever be set, fail if both are present.
+	if sd.SingleTweak != nil && sd.DoubleTweak != nil {
+		return ErrTweakOverdose
 	}
 
 	witnessScript, err := wire.ReadVarBytes(r, 0, 100, "witnessScript")

lnwallet/signdescriptor_test.go

@@ -34,7 +34,7 @@ func TestSignDescriptorSerialization(t *testing.T) {
 
 	signDescriptors := []SignDescriptor{
 		{
-			PrivateTweak: []byte{
+			SingleTweak: []byte{
 				0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02,
 				0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02,
 				0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02,
@@ -66,7 +66,7 @@ func TestSignDescriptorSerialization(t *testing.T) {
 
 		// Test serializing a SignDescriptor with a nil-valued PrivateTweak
 		{
-			PrivateTweak: nil,
+			SingleTweak: nil,
 			WitnessScript: []byte{
 				0x00, 0x14, 0xee, 0x91, 0x41, 0x7e, 0x85, 0x6c, 0xde,
 				0x10, 0xa2, 0x91, 0x1e, 0xdc, 0xbd, 0xbd, 0x69, 0xe2,