netann/node_signer: copy and export NodeSigner from main

netann/node_signer.go

@@ -0,0 +1,82 @@
+package netann
+
+import (
+	"fmt"
+
+	"github.com/btcsuite/btcd/btcec"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/lightningnetwork/lnd/lnwallet"
+)
+
+// NodeSigner is an implementation of the MessageSigner interface backed by the
+// identity private key of running lnd node.
+type NodeSigner struct {
+	privKey *btcec.PrivateKey
+}
+
+// NewNodeSigner creates a new instance of the NodeSigner backed by the target
+// private key.
+func NewNodeSigner(key *btcec.PrivateKey) *NodeSigner {
+	priv := &btcec.PrivateKey{}
+	priv.Curve = btcec.S256()
+	priv.PublicKey.X = key.X
+	priv.PublicKey.Y = key.Y
+	priv.D = key.D
+	return &NodeSigner{
+		privKey: priv,
+	}
+}
+
+// SignMessage signs a double-sha256 digest of the passed msg under the
+// resident node's private key. If the target public key is _not_ the node's
+// private key, then an error will be returned.
+func (n *NodeSigner) SignMessage(pubKey *btcec.PublicKey,
+	msg []byte) (*btcec.Signature, error) {
+
+	// If this isn't our identity public key, then we'll exit early with an
+	// error as we can't sign with this key.
+	if !pubKey.IsEqual(n.privKey.PubKey()) {
+		return nil, fmt.Errorf("unknown public key")
+	}
+
+	// Otherwise, we'll sign the dsha256 of the target message.
+	digest := chainhash.DoubleHashB(msg)
+	sign, err := n.privKey.Sign(digest)
+	if err != nil {
+		return nil, fmt.Errorf("can't sign the message: %v", err)
+	}
+
+	return sign, nil
+}
+
+// SignCompact signs a double-sha256 digest of the msg parameter under the
+// resident node's private key. The returned signature is a pubkey-recoverable
+// signature.
+func (n *NodeSigner) SignCompact(msg []byte) ([]byte, error) {
+	// We'll sign the dsha256 of the target message.
+	digest := chainhash.DoubleHashB(msg)
+
+	return n.SignDigestCompact(digest)
+}
+
+// SignDigestCompact signs the provided message digest under the resident
+// node's private key. The returned signature is a pubkey-recoverable signature.
+func (n *NodeSigner) SignDigestCompact(hash []byte) ([]byte, error) {
+
+	// Should the signature reference a compressed public key or not.
+	isCompressedKey := true
+
+	// btcec.SignCompact returns a pubkey-recoverable signature
+	sig, err := btcec.SignCompact(
+		btcec.S256(), n.privKey, hash, isCompressedKey,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("can't sign the hash: %v", err)
+	}
+
+	return sig, nil
+}
+
+// A compile time check to ensure that NodeSigner implements the MessageSigner
+// interface.
+var _ lnwallet.MessageSigner = (*NodeSigner)(nil)