watchtower: extend and rename SecretKeyRing

watchtower/wtclient/client.go

@@ -132,7 +132,7 @@ type Config struct {
 	// SecretKeyRing is used to derive the session keys used to communicate
 	// with the tower. The client only stores the KeyLocators internally so
 	// that we never store private keys on disk.
-	SecretKeyRing SecretKeyRing
+	SecretKeyRing ECDHKeyRing
 
 	// Dial connects to an addr using the specified net and returns the
 	// connection object.

watchtower/wtclient/derivation.go

@@ -12,7 +12,7 @@ import (
 // derivation path of:
 //
 //  * m/1017'/coinType'/8/0/index
-func DeriveSessionKey(keyRing SecretKeyRing,
+func DeriveSessionKey(keyRing ECDHKeyRing,
 	index uint32) (*btcec.PrivateKey, error) {
 
 	return keyRing.DerivePrivKey(keychain.KeyDescriptor{

watchtower/wtclient/interface.go

@@ -112,10 +112,18 @@ func AuthDial(localPriv *btcec.PrivateKey, netAddr *lnwire.NetAddress,
 	return brontide.Dial(localPriv, netAddr, dialer)
 }
 
-// SecretKeyRing abstracts the ability to derive HD private keys given a
-// description of the derivation path.
-type SecretKeyRing interface {
+// ECDHKeyRing abstracts the ability to derive shared ECDH keys given a
+// description of the derivation path of a private key.
+type ECDHKeyRing interface {
+	keychain.ECDHRing
+
 	// DerivePrivKey derives the private key from the root seed using a
 	// key descriptor specifying the key's derivation path.
 	DerivePrivKey(loc keychain.KeyDescriptor) (*btcec.PrivateKey, error)
+
+	// DeriveKey attempts to derive an arbitrary key specified by the
+	// passed KeyLocator. This may be used in several recovery scenarios,
+	// or when manually rotating something like our current default node
+	// key.
+	DeriveKey(keyLoc keychain.KeyLocator) (keychain.KeyDescriptor, error)
 }

watchtower/wtclient/session_negotiator.go

@@ -44,7 +44,7 @@ type NegotiatorConfig struct {
 
 	// SecretKeyRing allows the client to derive new session private keys
 	// when attempting to negotiate session with a tower.
-	SecretKeyRing SecretKeyRing
+	SecretKeyRing ECDHKeyRing
 
 	// Candidates is an abstract set of tower candidates that the negotiator
 	// will traverse serially when attempting to negotiate a new session.