Add ShutdownScript for BOLT 2 acceptable scripts

BOLT 2 enumerates the script formats that may be used for a shutdown
script. KeysInterface::get_shutdown_pubkey returns a PublicKey used to
form one of the acceptable formats (P2WPKH). Add a ShutdownScript
abstraction to encapsulate all accept formats and be backwards
compatible with P2WPKH scripts serialized as the corresponding
PublicKey.

Author: jkczyz

lightning/src/ln/mod.rs

@@ -27,6 +27,7 @@ pub mod msgs;
 pub mod peer_handler;
 pub mod chan_utils;
 pub mod features;
+pub mod script;
 
 #[cfg(feature = "fuzztarget")]
 pub mod peer_channel_encryptor;

lightning/src/ln/script.rs

@@ -0,0 +1,185 @@
+//! Abstractions for scripts used in the Lightning Network.
+
+use bitcoin::bech32::u5;
+use bitcoin::blockdata::opcodes::all::OP_PUSHBYTES_0 as SEGWIT_V0;
+use bitcoin::blockdata::script::Script;
+use bitcoin::hashes::Hash;
+use bitcoin::hash_types::{PubkeyHash, ScriptHash, WPubkeyHash, WScriptHash};
+use bitcoin::secp256k1::key::PublicKey;
+use std::convert::From;
+use std::convert::TryFrom;
+
+/// A script pubkey for shutting down a channel as defined by [BOLT #2].
+///
+/// [BOLT #2]: https://github.com/lightningnetwork/lightning-rfc/blob/master/02-peer-protocol.md
+pub struct ShutdownScript(ShutdownScriptImpl);
+
+/// An error occurring when converting from [`Script`] to [`ShutdownScript`].
+#[derive(Debug)]
+pub struct InvalidShutdownScript(Script);
+
+enum ShutdownScriptImpl {
+	/// [`PublicKey`] used to form a P2WPKH script pubkey. Used to support backward-compatible
+	/// serialization.
+	Legacy(PublicKey),
+
+	/// [`Script`] adhering to a script pubkey format specified in BOLT #2.
+	Bolt2(Script),
+}
+
+impl ShutdownScript {
+	/// Generates a P2PKH script pubkey from the given [`PubkeyHash`].
+	pub fn new_p2pkh(pubkey_hash: &PubkeyHash) -> Self {
+		Self(ShutdownScriptImpl::Bolt2(Script::new_p2pkh(pubkey_hash)))
+	}
+
+	/// Generates a P2SH script pubkey from the given [`ScriptHash`].
+	pub fn new_p2sh(script_hash: &ScriptHash) -> Self {
+		Self(ShutdownScriptImpl::Bolt2(Script::new_p2sh(script_hash)))
+	}
+
+	/// Generates a P2WPKH script pubkey from the given [`WPubkeyHash`].
+	pub fn new_p2wpkh(pubkey_hash: &WPubkeyHash) -> Self {
+		Self(ShutdownScriptImpl::Bolt2(Script::new_v0_wpkh(pubkey_hash)))
+	}
+
+	/// Generates a P2WSH script pubkey from the given [`WScriptHash`].
+	pub fn new_p2wsh(script_hash: &WScriptHash) -> Self {
+		Self(ShutdownScriptImpl::Bolt2(Script::new_v0_wsh(script_hash)))
+	}
+
+	/// Generates a P2WSH script pubkey from the given segwit version and program.
+	///
+	/// # Panics
+	///
+	/// This function may panic if given a segwit program with an invalid length.
+	pub fn new_witness_program(version: u5, program: &[u8]) -> Self {
+		let script = Script::new_witness_program(version, program);
+		Self::try_from(script).expect("Invalid segwit program")
+	}
+
+	/// Converts the shutdown script into the underlying [`Script`].
+	pub fn into_inner(self) -> Script {
+		self.into()
+	}
+}
+
+impl From<PublicKey> for ShutdownScript {
+	fn from(pubkey: PublicKey) -> Self {
+		Self(ShutdownScriptImpl::Legacy(pubkey))
+	}
+}
+
+impl TryFrom<Script> for ShutdownScript {
+	type Error = InvalidShutdownScript;
+
+	fn try_from(script: Script) -> Result<Self, Self::Error> {
+		if script.is_p2pkh() || script.is_p2sh() || script.is_v0_p2wpkh() || script.is_v0_p2wsh() {
+			Ok(Self(ShutdownScriptImpl::Bolt2(script)))
+		} else if script.is_witness_program() && script.as_bytes()[0] != SEGWIT_V0.into_u8() {
+			Ok(Self(ShutdownScriptImpl::Bolt2(script)))  // option_shutdown_anysegwit
+		} else {
+			Err(InvalidShutdownScript(script))
+		}
+	}
+}
+
+impl Into<Script> for ShutdownScript {
+	fn into(self) -> Script {
+		match self.0 {
+			ShutdownScriptImpl::Legacy(pubkey) =>
+				Script::new_v0_wpkh(&WPubkeyHash::hash(&pubkey.serialize())),
+			ShutdownScriptImpl::Bolt2(script_pubkey) => script_pubkey,
+		}
+	}
+}
+
+#[cfg(test)]
+mod shutdown_script_tests {
+	use super::ShutdownScript;
+	use bitcoin::bech32::u5;
+	use bitcoin::blockdata::opcodes;
+	use bitcoin::blockdata::script::{Builder, Script};
+	use bitcoin::secp256k1::Secp256k1;
+	use bitcoin::secp256k1::key::{PublicKey, SecretKey};
+	use std::convert::TryFrom;
+
+	fn pubkey() -> bitcoin::util::ecdsa::PublicKey {
+		let secp_ctx = Secp256k1::signing_only();
+		let secret_key = SecretKey::from_slice(&[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]).unwrap();
+		bitcoin::util::ecdsa::PublicKey::new(PublicKey::from_secret_key(&secp_ctx, &secret_key))
+	}
+
+	fn redeem_script() -> Script {
+		let pubkey = pubkey();
+		Builder::new()
+			.push_opcode(opcodes::all::OP_PUSHNUM_2)
+			.push_key(&pubkey)
+			.push_key(&pubkey)
+			.push_opcode(opcodes::all::OP_PUSHNUM_2)
+			.push_opcode(opcodes::all::OP_CHECKMULTISIG)
+			.into_script()
+	}
+
+	#[test]
+	fn generates_p2wpkh_from_pubkey() {
+		let pubkey = pubkey();
+		let pubkey_hash = pubkey.wpubkey_hash().unwrap();
+		let p2wpkh_script = Script::new_v0_wpkh(&pubkey_hash);
+
+		let shutdown_script = ShutdownScript::from(pubkey.key);
+		assert_eq!(shutdown_script.into_inner(), p2wpkh_script);
+	}
+
+	#[test]
+	fn generates_p2pkh_from_pubkey_hash() {
+		let pubkey_hash = pubkey().pubkey_hash();
+		let p2pkh_script = Script::new_p2pkh(&pubkey_hash);
+
+		let shutdown_script = ShutdownScript::new_p2pkh(&pubkey_hash);
+		assert_eq!(shutdown_script.into_inner(), p2pkh_script);
+		assert!(ShutdownScript::try_from(p2pkh_script).is_ok());
+	}
+
+	#[test]
+	fn generates_p2sh_from_script_hash() {
+		let script_hash = redeem_script().script_hash();
+		let p2sh_script = Script::new_p2sh(&script_hash);
+
+		let shutdown_script = ShutdownScript::new_p2sh(&script_hash);
+		assert_eq!(shutdown_script.into_inner(), p2sh_script);
+		assert!(ShutdownScript::try_from(p2sh_script).is_ok());
+	}
+
+	#[test]
+	fn generates_p2wpkh_from_pubkey_hash() {
+		let pubkey_hash = pubkey().wpubkey_hash().unwrap();
+		let p2wpkh_script = Script::new_v0_wpkh(&pubkey_hash);
+
+		let shutdown_script = ShutdownScript::new_p2wpkh(&pubkey_hash);
+		assert_eq!(shutdown_script.into_inner(), p2wpkh_script);
+		assert!(ShutdownScript::try_from(p2wpkh_script).is_ok());
+	}
+
+	#[test]
+	fn generates_p2wsh_from_script_hash() {
+		let script_hash = redeem_script().wscript_hash();
+		let p2wsh_script = Script::new_v0_wsh(&script_hash);
+
+		let shutdown_script = ShutdownScript::new_p2wsh(&script_hash);
+		assert_eq!(shutdown_script.into_inner(), p2wsh_script);
+		assert!(ShutdownScript::try_from(p2wsh_script).is_ok());
+	}
+
+	#[test]
+	fn fails_from_unsupported_script() {
+		let op_return = Script::new_op_return(&[0; 42]);
+		assert!(ShutdownScript::try_from(op_return).is_err());
+	}
+
+	#[test]
+	fn fails_from_invalid_segwit_v0_program() {
+		let witness_program = Script::new_witness_program(u5::try_from_u8(0).unwrap(), &[0; 2]);
+		assert!(ShutdownScript::try_from(witness_program).is_err());
+	}
+}