lnd: add a daemon-level implementation of the MessageSigner interface

nodesigner.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/roasbeef/btcd/btcec"
+	"github.com/roasbeef/btcd/chaincfg/chainhash"
+)
+
+// 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 {
+	return &nodeSigner{
+		privKey: key,
+	}
+}
+
+// SignMessage signs a double-sha256 digest of the passed msg under the
+// resident node 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
+}
+
+// A compile time check to ensure that nodeSigner implements the MessageSigner
+// interface.
+var _ lnwallet.MessageSigner = (*nodeSigner)(nil)