Add helper functions to verify node and channel annoucements

Right now the only real way to verify the node and channel
announcements is to call `update_node_from_announcement`/
`update_channel_from_announcement`. If you want to do some
processing before you add to your network graph then you need to
manually verify the signature. This adds some nice helper functions
to make it easier.

I tried to do the same for channel update but it did not seem as
easy so figured that is fine to punt on since I don't see many
people doing manual things with channel updates.

Author: benthecarman

lightning/src/routing/gossip.rs

@@ -10,7 +10,7 @@
 //! The [`NetworkGraph`] stores the network gossip and [`P2PGossipSync`] fetches it from peers
 
 use bitcoin::secp256k1::constants::PUBLIC_KEY_SIZE;
-use bitcoin::secp256k1::PublicKey;
+use bitcoin::secp256k1::{PublicKey, Verification};
 use bitcoin::secp256k1::Secp256k1;
 use bitcoin::secp256k1;
 
@@ -404,6 +404,29 @@ macro_rules! get_pubkey_from_node_id {
 	}
 }
 
+/// Verifies the signature of a [`NodeAnnouncement`].
+///
+/// Returns an error if it is invalid.
+pub fn verify_node_announcement<C: Verification>(msg: &NodeAnnouncement, secp_ctx: &Secp256k1<C>) -> Result<(), LightningError> {
+	let msg_hash = hash_to_message!(&Sha256dHash::hash(&msg.contents.encode()[..])[..]);
+	secp_verify_sig!(secp_ctx, &msg_hash, &msg.signature, &get_pubkey_from_node_id!(msg.contents.node_id, "node_announcement"), "node_announcement");
+
+	Ok(())
+}
+
+/// Verifies all signatures included in a [`ChannelAnnouncement`].
+///
+/// Returns an error if one of the signatures is invalid.
+pub fn verify_channel_announcement<C: Verification>(msg: &ChannelAnnouncement, secp_ctx: &Secp256k1<C>) -> Result<(), LightningError> {
+	let msg_hash = hash_to_message!(&Sha256dHash::hash(&msg.contents.encode()[..])[..]);
+	secp_verify_sig!(secp_ctx, &msg_hash, &msg.node_signature_1, &get_pubkey_from_node_id!(msg.contents.node_id_1, "channel_announcement"), "channel_announcement");
+	secp_verify_sig!(secp_ctx, &msg_hash, &msg.node_signature_2, &get_pubkey_from_node_id!(msg.contents.node_id_2, "channel_announcement"), "channel_announcement");
+	secp_verify_sig!(secp_ctx, &msg_hash, &msg.bitcoin_signature_1, &get_pubkey_from_node_id!(msg.contents.bitcoin_key_1, "channel_announcement"), "channel_announcement");
+	secp_verify_sig!(secp_ctx, &msg_hash, &msg.bitcoin_signature_2, &get_pubkey_from_node_id!(msg.contents.bitcoin_key_2, "channel_announcement"), "channel_announcement");
+
+	Ok(())
+}
+
 impl<G: Deref<Target=NetworkGraph<L>>, U: Deref, L: Deref> RoutingMessageHandler for P2PGossipSync<G, U, L>
 where U::Target: UtxoLookup, L::Target: Logger
 {
@@ -1387,8 +1410,7 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
 	/// RoutingMessageHandler implementation to call it indirectly. This may be useful to accept
 	/// routing messages from a source using a protocol other than the lightning P2P protocol.
 	pub fn update_node_from_announcement(&self, msg: &msgs::NodeAnnouncement) -> Result<(), LightningError> {
-		let msg_hash = hash_to_message!(&Sha256dHash::hash(&msg.contents.encode()[..])[..]);
-		secp_verify_sig!(self.secp_ctx, &msg_hash, &msg.signature, &get_pubkey_from_node_id!(msg.contents.node_id, "node_announcement"), "node_announcement");
+		verify_node_announcement(msg, &self.secp_ctx)?;
 		self.update_node_from_announcement_intern(&msg.contents, Some(&msg))
 	}
 
@@ -1451,11 +1473,7 @@ impl<L: Deref> NetworkGraph<L> where L::Target: Logger {
 	where
 		U::Target: UtxoLookup,
 	{
-		let msg_hash = hash_to_message!(&Sha256dHash::hash(&msg.contents.encode()[..])[..]);
-		secp_verify_sig!(self.secp_ctx, &msg_hash, &msg.node_signature_1, &get_pubkey_from_node_id!(msg.contents.node_id_1, "channel_announcement"), "channel_announcement");
-		secp_verify_sig!(self.secp_ctx, &msg_hash, &msg.node_signature_2, &get_pubkey_from_node_id!(msg.contents.node_id_2, "channel_announcement"), "channel_announcement");
-		secp_verify_sig!(self.secp_ctx, &msg_hash, &msg.bitcoin_signature_1, &get_pubkey_from_node_id!(msg.contents.bitcoin_key_1, "channel_announcement"), "channel_announcement");
-		secp_verify_sig!(self.secp_ctx, &msg_hash, &msg.bitcoin_signature_2, &get_pubkey_from_node_id!(msg.contents.bitcoin_key_2, "channel_announcement"), "channel_announcement");
+		verify_channel_announcement(msg, &self.secp_ctx)?;
 		self.update_channel_from_unsigned_announcement_intern(&msg.contents, Some(msg), utxo_lookup)
 	}