Allow to sign and verify arbitrary messages

* Node / KeysManager: add feature to sign any msg and verify signature

* Test coverage: sign & verify node methods

* Fix cargo fmt errors

* New Error for message signing and rename error for wallet signing

* Better docs for sign and verify methods.
Also we expose them via bindings.

* Node: corrections in sign/verify msg docs,
verify_signature now accepts public key as a parameter

Author: telelvis

bindings/ldk_node.udl

@@ -60,6 +60,9 @@ interface Node {
 	boolean remove_payment([ByRef]PaymentHash payment_hash);
 	sequence<PeerDetails> list_peers();
 	sequence<ChannelDetails> list_channels();
+	[Throws=NodeError]
+	string sign_message([ByRef]sequence<u8> msg);
+	boolean verify_signature([ByRef]sequence<u8> msg, [ByRef]string sig, [ByRef]PublicKey pkey);
 };
 
 [Error]
@@ -75,7 +78,8 @@ enum NodeError {
 	"ChannelClosingFailed",
 	"PersistenceFailed",
 	"WalletOperationFailed",
-	"WalletSigningFailed",
+	"OnchainTxSigningFailed",
+	"MessageSigningFailed",
 	"TxSyncFailed",
 	"GossipUpdateFailed",
 	"InvalidAddress",

src/error.rs

@@ -25,8 +25,10 @@ pub enum Error {
 	PersistenceFailed,
 	/// A wallet operation failed.
 	WalletOperationFailed,
-	/// A siging operation failed.
-	WalletSigningFailed,
+	/// A signing operation for transaction failed.
+	OnchainTxSigningFailed,
+	/// A signing operation for message failed.
+	MessageSigningFailed,
 	/// A transaction sync operation failed.
 	TxSyncFailed,
 	/// A gossip updating operation failed.
@@ -71,7 +73,8 @@ impl fmt::Display for Error {
 			Self::ChannelClosingFailed => write!(f, "Failed to close channel."),
 			Self::PersistenceFailed => write!(f, "Failed to persist data."),
 			Self::WalletOperationFailed => write!(f, "Failed to conduct wallet operation."),
-			Self::WalletSigningFailed => write!(f, "Failed to sign given transaction."),
+			Self::OnchainTxSigningFailed => write!(f, "Failed to sign given transaction."),
+			Self::MessageSigningFailed => write!(f, "Failed to sign given message."),
 			Self::TxSyncFailed => write!(f, "Failed to sync transactions."),
 			Self::GossipUpdateFailed => write!(f, "Failed to update gossip data."),
 			Self::InvalidAddress => write!(f, "The given address is invalid."),
@@ -96,7 +99,7 @@ impl std::error::Error for Error {}
 impl From<bdk::Error> for Error {
 	fn from(e: bdk::Error) -> Self {
 		match e {
-			bdk::Error::Signer(_) => Self::WalletSigningFailed,
+			bdk::Error::Signer(_) => Self::OnchainTxSigningFailed,
 			_ => Self::WalletOperationFailed,
 		}
 	}

src/lib.rs

@@ -1556,6 +1556,22 @@ impl Node {
 			})
 			.collect()
 	}
+
+	/// Creates a digital ECDSA signature of a message with the node's secret key.
+	///
+	/// A receiver knowing the corresponding `PublicKey` (e.g. the node’s id) and the message
+	/// can be sure that the signature was generated by the caller.
+	/// Signatures are EC recoverable, meaning that given the message and the
+	/// signature the PublicKey of the signer can be extracted.
+	pub fn sign_message(&self, msg: &[u8]) -> Result<String, Error> {
+		self.keys_manager.sign_message(msg)
+	}
+
+	/// Verifies that the given ECDSA signature was created for the given message with the
+	/// secret key corresponding to the given public key.
+	pub fn verify_signature(&self, msg: &[u8], sig: &str, pkey: &PublicKey) -> bool {
+		self.keys_manager.verify_signature(msg, sig, pkey)
+	}
 }
 
 impl Drop for Node {

src/test/functional_tests.rs

@@ -363,3 +363,18 @@ fn onchain_spend_receive() {
 	assert!(node_b.onchain_balance().unwrap().get_spendable() > 99000);
 	assert!(node_b.onchain_balance().unwrap().get_spendable() < 100000);
 }
+
+#[test]
+fn sign_verify_msg() {
+	let (_, electrsd) = setup_bitcoind_and_electrsd();
+	let esplora_url = electrsd.esplora_url.as_ref().unwrap();
+	let node = Builder::from_config(random_config(esplora_url)).build();
+
+	node.start().unwrap();
+
+	// Tests arbitrary message signing and later verification
+	let msg = "OK computer".as_bytes();
+	let sig = node.sign_message(msg).unwrap();
+	let pkey = node.node_id();
+	assert!(node.verify_signature(msg, sig.as_str(), &pkey));
+}

src/wallet.rs

@@ -13,6 +13,8 @@ use lightning::chain::keysinterface::{
 use lightning::ln::msgs::{DecodeError, UnsignedGossipMessage};
 use lightning::ln::script::ShutdownScript;
 
+use lightning::util::message_signing;
+
 use bdk::blockchain::{Blockchain, EsploraBlockchain};
 use bdk::database::BatchDatabase;
 use bdk::wallet::AddressIndex;
@@ -373,6 +375,15 @@ where
 			secp_ctx,
 		)
 	}
+
+	pub fn sign_message(&self, msg: &[u8]) -> Result<String, Error> {
+		message_signing::sign(msg, &self.inner.get_node_secret_key())
+			.or(Err(Error::MessageSigningFailed))
+	}
+
+	pub fn verify_signature(&self, msg: &[u8], sig: &str, pkey: &PublicKey) -> bool {
+		message_signing::verify(msg, sig, pkey)
+	}
 }
 
 impl<D> NodeSigner for WalletKeysManager<D>