From 29199fae4634425eb4307651b3b21d93580c8f42 Mon Sep 17 00:00:00 2001 From: Matt Corallo Date: Thu, 23 Apr 2020 15:43:21 -0400 Subject: [PATCH] Don't modify LocalCommitmemntTransaction after construction Instead of adding signatures to LocalCommitmentTransactions, we instead leave them unsigned and use them to construct signed Transactions when we want them. This cleans up the guts of LocalCommitmentTransaction enough that we can, and do, expose its state to the world, allowing external signers to have a basic awareness of what they're signing. --- lightning/src/ln/chan_utils.rs | 123 +++++++++++++++-------------- lightning/src/ln/channel.rs | 11 ++- lightning/src/ln/channelmonitor.rs | 8 +- lightning/src/ln/onchaintx.rs | 17 ++-- 4 files changed, 78 insertions(+), 81 deletions(-) diff --git a/lightning/src/ln/chan_utils.rs b/lightning/src/ln/chan_utils.rs index f6cbdc23..d576fd33 100644 --- a/lightning/src/ln/chan_utils.rs +++ b/lightning/src/ln/chan_utils.rs @@ -484,10 +484,30 @@ pub fn build_htlc_transaction(prev_hash: &Sha256dHash, feerate_per_kw: u64, to_s /// to broadcast. Eventually this will require a signer which is possibly external, but for now we /// just pass in the SecretKeys required. pub struct LocalCommitmentTransaction { - tx: Transaction, - pub(crate) local_keys: TxCreationKeys, - pub(crate) feerate_per_kw: u64, - pub(crate) per_htlc: Vec<(HTLCOutputInCommitment, Option)>, + // TODO: We should migrate away from providing the transaction, instead providing enough to + // allow the ChannelKeys to construct it from scratch. Luckily we already have HTLC data here, + // so we're probably most of the way there. + /// The commitment transaction itself, in unsigned form. + pub unsigned_tx: Transaction, + /// Our counterparty's signature for the transaction, above. + pub their_sig: Signature, + // Which order the signatures should go in when constructing the final commitment tx witness. + // The user should be able to reconstruc this themselves, so we don't bother to expose it. + our_sig_first: bool, + /// The key derivation parameters for this commitment transaction + pub local_keys: TxCreationKeys, + /// The feerate paid per 1000-weight-unit in this commitment transaction. This value is + /// controlled by the channel initiator. + pub feerate_per_kw: u64, + /// The HTLCs and remote htlc signatures which were included in this commitment transaction. + /// + /// Note that this includes all HTLCs, including ones which were considered dust and not + /// actually included in the transaction as it appears on-chain, but who's value is burned as + /// fees and not included in the to_local or to_remote outputs. + /// + /// The remote HTLC signatures in the second element will always be set for non-dust HTLCs, ie + /// those for which transaction_output_index.is_some(). + pub per_htlc: Vec<(HTLCOutputInCommitment, Option)>, } impl LocalCommitmentTransaction { #[cfg(test)] @@ -499,16 +519,19 @@ impl LocalCommitmentTransaction { }, script_sig: Default::default(), sequence: 0, - witness: vec![vec![], vec![], vec![]] + witness: vec![] }; let dummy_key = PublicKey::from_secret_key(&Secp256k1::new(), &SecretKey::from_slice(&[42; 32]).unwrap()); + let dummy_sig = Secp256k1::new().sign(&secp256k1::Message::from_slice(&[42; 32]).unwrap(), &SecretKey::from_slice(&[42; 32]).unwrap()); Self { - tx: Transaction { + unsigned_tx: Transaction { version: 2, input: vec![dummy_input], output: Vec::new(), lock_time: 0, }, + their_sig: dummy_sig, + our_sig_first: false, local_keys: TxCreationKeys { per_commitment_point: dummy_key.clone(), revocation_key: dummy_key.clone(), @@ -524,23 +547,14 @@ impl LocalCommitmentTransaction { /// Generate a new LocalCommitmentTransaction based on a raw commitment transaction, /// remote signature and both parties keys - pub(crate) fn new_missing_local_sig(mut tx: Transaction, their_sig: &Signature, our_funding_key: &PublicKey, their_funding_key: &PublicKey, local_keys: TxCreationKeys, feerate_per_kw: u64, htlc_data: Vec<(HTLCOutputInCommitment, Option)>) -> LocalCommitmentTransaction { - if tx.input.len() != 1 { panic!("Tried to store a commitment transaction that had input count != 1!"); } - if tx.input[0].witness.len() != 0 { panic!("Tried to store a signed commitment transaction?"); } - - tx.input[0].witness.push(Vec::new()); // First is the multisig dummy - - if our_funding_key.serialize()[..] < their_funding_key.serialize()[..] { - tx.input[0].witness.push(Vec::new()); - tx.input[0].witness.push(their_sig.serialize_der().to_vec()); - tx.input[0].witness[2].push(SigHashType::All as u8); - } else { - tx.input[0].witness.push(their_sig.serialize_der().to_vec()); - tx.input[0].witness[1].push(SigHashType::All as u8); - tx.input[0].witness.push(Vec::new()); - } + pub(crate) fn new_missing_local_sig(unsigned_tx: Transaction, their_sig: Signature, our_funding_key: &PublicKey, their_funding_key: &PublicKey, local_keys: TxCreationKeys, feerate_per_kw: u64, htlc_data: Vec<(HTLCOutputInCommitment, Option)>) -> LocalCommitmentTransaction { + if unsigned_tx.input.len() != 1 { panic!("Tried to store a commitment transaction that had input count != 1!"); } + if unsigned_tx.input[0].witness.len() != 0 { panic!("Tried to store a signed commitment transaction?"); } - Self { tx, + Self { + unsigned_tx, + their_sig, + our_sig_first: our_funding_key.serialize()[..] < their_funding_key.serialize()[..], local_keys, feerate_per_kw, per_htlc: htlc_data, @@ -550,22 +564,7 @@ impl LocalCommitmentTransaction { /// Get the txid of the local commitment transaction contained in this /// LocalCommitmentTransaction pub fn txid(&self) -> Sha256dHash { - self.tx.txid() - } - - /// Check if LocalCommitmentTransaction has already been signed by us - pub(crate) fn has_local_sig(&self) -> bool { - if self.tx.input.len() != 1 { panic!("Commitment transactions must have input count == 1!"); } - if self.tx.input[0].witness.len() == 4 { - assert!(!self.tx.input[0].witness[1].is_empty()); - assert!(!self.tx.input[0].witness[2].is_empty()); - true - } else { - assert_eq!(self.tx.input[0].witness.len(), 3); - assert!(self.tx.input[0].witness[0].is_empty()); - assert!(self.tx.input[0].witness[1].is_empty() || self.tx.input[0].witness[2].is_empty()); - false - } + self.unsigned_tx.txid() } /// Gets our signature for the contained commitment transaction given our funding private key. @@ -577,32 +576,28 @@ impl LocalCommitmentTransaction { /// ChannelKeys::sign_local_commitment() calls directly. /// Channel value is amount locked in funding_outpoint. pub fn get_local_sig(&self, funding_key: &SecretKey, funding_redeemscript: &Script, channel_value_satoshis: u64, secp_ctx: &Secp256k1) -> Signature { - let sighash = hash_to_message!(&bip143::SighashComponents::new(&self.tx) - .sighash_all(&self.tx.input[0], funding_redeemscript, channel_value_satoshis)[..]); + let sighash = hash_to_message!(&bip143::SighashComponents::new(&self.unsigned_tx) + .sighash_all(&self.unsigned_tx.input[0], funding_redeemscript, channel_value_satoshis)[..]); secp_ctx.sign(&sighash, funding_key) } + pub(crate) fn add_local_sig(&self, funding_redeemscript: &Script, our_sig: Signature) -> Transaction { + let mut tx = self.unsigned_tx.clone(); + // First push the multisig dummy, note that due to BIP147 (NULLDUMMY) it must be a zero-length element. + tx.input[0].witness.push(Vec::new()); - pub(crate) fn add_local_sig(&mut self, funding_redeemscript: &Script, our_sig: Signature) { - if self.has_local_sig() { return; } - - if self.tx.input[0].witness[1].is_empty() { - self.tx.input[0].witness[1] = our_sig.serialize_der().to_vec(); - self.tx.input[0].witness[1].push(SigHashType::All as u8); + if self.our_sig_first { + tx.input[0].witness.push(our_sig.serialize_der().to_vec()); + tx.input[0].witness.push(self.their_sig.serialize_der().to_vec()); } else { - self.tx.input[0].witness[2] = our_sig.serialize_der().to_vec(); - self.tx.input[0].witness[2].push(SigHashType::All as u8); + tx.input[0].witness.push(self.their_sig.serialize_der().to_vec()); + tx.input[0].witness.push(our_sig.serialize_der().to_vec()); } + tx.input[0].witness[1].push(SigHashType::All as u8); + tx.input[0].witness[2].push(SigHashType::All as u8); - self.tx.input[0].witness.push(funding_redeemscript.as_bytes().to_vec()); - } - - /// Get raw transaction without asserting if witness is complete - pub(crate) fn without_valid_witness(&self) -> &Transaction { &self.tx } - /// Get raw transaction with panics if witness is incomplete - pub(crate) fn with_valid_witness(&self) -> &Transaction { - assert!(self.has_local_sig()); - &self.tx + tx.input[0].witness.push(funding_redeemscript.as_bytes().to_vec()); + tx } /// Get a signature for each HTLC which was included in the commitment transaction (ie for @@ -679,12 +674,14 @@ impl PartialEq for LocalCommitmentTransaction { } impl Writeable for LocalCommitmentTransaction { fn write(&self, writer: &mut W) -> Result<(), ::std::io::Error> { - if let Err(e) = self.tx.consensus_encode(&mut WriterWriteAdaptor(writer)) { + if let Err(e) = self.unsigned_tx.consensus_encode(&mut WriterWriteAdaptor(writer)) { match e { encode::Error::Io(e) => return Err(e), _ => panic!("local tx must have been well-formed!"), } } + self.their_sig.write(writer)?; + self.our_sig_first.write(writer)?; self.local_keys.write(writer)?; self.feerate_per_kw.write(writer)?; writer.write_all(&byte_utils::be64_to_array(self.per_htlc.len() as u64))?; @@ -697,13 +694,15 @@ impl Writeable for LocalCommitmentTransaction { } impl Readable for LocalCommitmentTransaction { fn read(reader: &mut R) -> Result { - let tx = match Transaction::consensus_decode(reader.by_ref()) { + let unsigned_tx = match Transaction::consensus_decode(reader.by_ref()) { Ok(tx) => tx, Err(e) => match e { encode::Error::Io(ioe) => return Err(DecodeError::Io(ioe)), _ => return Err(DecodeError::InvalidValue), }, }; + let their_sig = Readable::read(reader)?; + let our_sig_first = Readable::read(reader)?; let local_keys = Readable::read(reader)?; let feerate_per_kw = Readable::read(reader)?; let htlcs_count: u64 = Readable::read(reader)?; @@ -714,12 +713,14 @@ impl Readable for LocalCommitmentTransaction { per_htlc.push((htlc, sigs)); } - if tx.input.len() != 1 { + if unsigned_tx.input.len() != 1 { // Ensure tx didn't hit the 0-input ambiguity case. return Err(DecodeError::InvalidValue); } Ok(Self { - tx, + unsigned_tx, + their_sig, + our_sig_first, local_keys, feerate_per_kw, per_htlc, diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs index c5908906..35e688a0 100644 --- a/lightning/src/ln/channel.rs +++ b/lightning/src/ln/channel.rs @@ -1460,7 +1460,7 @@ impl Channel { // They sign the "local" commitment transaction... secp_check!(self.secp_ctx.verify(&local_sighash, &sig, self.their_funding_pubkey()), "Invalid funding_created signature from peer"); - let localtx = LocalCommitmentTransaction::new_missing_local_sig(local_initial_commitment_tx, sig, &PublicKey::from_secret_key(&self.secp_ctx, self.local_keys.funding_key()), self.their_funding_pubkey(), local_keys, self.feerate_per_kw, Vec::new()); + let localtx = LocalCommitmentTransaction::new_missing_local_sig(local_initial_commitment_tx, sig.clone(), &PublicKey::from_secret_key(&self.secp_ctx, self.local_keys.funding_key()), self.their_funding_pubkey(), local_keys, self.feerate_per_kw, Vec::new()); let remote_keys = self.build_remote_transaction_keys()?; let remote_initial_commitment_tx = self.build_commitment_transaction(self.cur_remote_commitment_transaction_number, &remote_keys, false, false, self.feerate_per_kw).0; @@ -1574,7 +1574,7 @@ impl Channel { let funding_txo_script = funding_redeemscript.to_v0_p2wsh(); macro_rules! create_monitor { () => { { - let local_commitment_tx = LocalCommitmentTransaction::new_missing_local_sig(local_initial_commitment_tx.clone(), &msg.signature, &PublicKey::from_secret_key(&self.secp_ctx, self.local_keys.funding_key()), their_funding_pubkey, local_keys.clone(), self.feerate_per_kw, Vec::new()); + let local_commitment_tx = LocalCommitmentTransaction::new_missing_local_sig(local_initial_commitment_tx.clone(), msg.signature.clone(), &PublicKey::from_secret_key(&self.secp_ctx, self.local_keys.funding_key()), their_funding_pubkey, local_keys.clone(), self.feerate_per_kw, Vec::new()); let mut channel_monitor = ChannelMonitor::new(self.local_keys.clone(), &self.shutdown_pubkey, self.our_to_self_delay, &self.destination_script, (funding_txo.clone(), funding_txo_script.clone()), @@ -1902,7 +1902,7 @@ impl Channel { let mut monitor_update = ChannelMonitorUpdate { update_id: self.latest_monitor_update_id, updates: vec![ChannelMonitorUpdateStep::LatestLocalCommitmentTXInfo { - commitment_tx: LocalCommitmentTransaction::new_missing_local_sig(local_commitment_tx.0, &msg.signature, &PublicKey::from_secret_key(&self.secp_ctx, self.local_keys.funding_key()), &their_funding_pubkey, local_keys, self.feerate_per_kw, htlcs_without_source), + commitment_tx: LocalCommitmentTransaction::new_missing_local_sig(local_commitment_tx.0, msg.signature.clone(), &PublicKey::from_secret_key(&self.secp_ctx, self.local_keys.funding_key()), &their_funding_pubkey, local_keys, self.feerate_per_kw, htlcs_without_source), htlc_outputs: htlcs_and_sigs }] }; @@ -4516,11 +4516,10 @@ mod tests { })* assert_eq!(unsigned_tx.1.len(), per_htlc.len()); - localtx = LocalCommitmentTransaction::new_missing_local_sig(unsigned_tx.0.clone(), &their_signature, &PublicKey::from_secret_key(&secp_ctx, chan.local_keys.funding_key()), chan.their_funding_pubkey(), keys.clone(), chan.feerate_per_kw, per_htlc); + localtx = LocalCommitmentTransaction::new_missing_local_sig(unsigned_tx.0.clone(), their_signature.clone(), &PublicKey::from_secret_key(&secp_ctx, chan.local_keys.funding_key()), chan.their_funding_pubkey(), keys.clone(), chan.feerate_per_kw, per_htlc); let local_sig = chan_keys.sign_local_commitment(&localtx, &chan.secp_ctx).unwrap(); - localtx.add_local_sig(&redeemscript, local_sig); - assert_eq!(serialize(localtx.with_valid_witness())[..], + assert_eq!(serialize(&localtx.add_local_sig(&redeemscript, local_sig))[..], hex::decode($tx_hex).unwrap()[..]); let htlc_sigs = chan_keys.sign_local_commitment_htlc_transactions(&localtx, chan.their_to_self_delay, &chan.secp_ctx).unwrap(); diff --git a/lightning/src/ln/channelmonitor.rs b/lightning/src/ln/channelmonitor.rs index 0dbf98c7..c417671e 100644 --- a/lightning/src/ln/channelmonitor.rs +++ b/lightning/src/ln/channelmonitor.rs @@ -1066,8 +1066,8 @@ impl ChannelMonitor { let mut onchain_tx_handler = OnchainTxHandler::new(destination_script.clone(), keys.clone(), their_to_self_delay, logger.clone()); - let local_tx_sequence = initial_local_commitment_tx.without_valid_witness().input[0].sequence as u64; - let local_tx_locktime = initial_local_commitment_tx.without_valid_witness().lock_time as u64; + let local_tx_sequence = initial_local_commitment_tx.unsigned_tx.input[0].sequence as u64; + let local_tx_locktime = initial_local_commitment_tx.unsigned_tx.lock_time as u64; let local_commitment_tx = LocalSignedTx { txid: initial_local_commitment_tx.txid(), revocation_key: initial_local_commitment_tx.local_keys.revocation_key, @@ -1249,8 +1249,8 @@ impl ChannelMonitor { return Err(MonitorUpdateError("A local commitment tx has already been signed, no new local commitment txn can be sent to our counterparty")); } let txid = commitment_tx.txid(); - let sequence = commitment_tx.without_valid_witness().input[0].sequence as u64; - let locktime = commitment_tx.without_valid_witness().lock_time as u64; + let sequence = commitment_tx.unsigned_tx.input[0].sequence as u64; + let locktime = commitment_tx.unsigned_tx.lock_time as u64; let mut new_local_commitment_tx = LocalSignedTx { txid, revocation_key: commitment_tx.local_keys.revocation_key, diff --git a/lightning/src/ln/onchaintx.rs b/lightning/src/ln/onchaintx.rs index 6b5da67c..49572f2c 100644 --- a/lightning/src/ln/onchaintx.rs +++ b/lightning/src/ln/onchaintx.rs @@ -814,9 +814,6 @@ impl OnchainTxHandler { // HTLC-timeout or channel force-closure), don't allow any further update of local // commitment transaction view to avoid delivery of revocation secret to counterparty // for the aformentionned signed transaction. - if let Some(ref local_commitment) = self.local_commitment { - if local_commitment.has_local_sig() { return Err(()) } - } if self.local_htlc_sigs.is_some() || self.prev_local_htlc_sigs.is_some() { return Err(()); } @@ -865,25 +862,25 @@ impl OnchainTxHandler { pub(super) fn get_fully_signed_local_tx(&mut self, funding_redeemscript: &Script) -> Option { if let Some(ref mut local_commitment) = self.local_commitment { match self.key_storage.sign_local_commitment(local_commitment, &self.secp_ctx) { - Ok(sig) => local_commitment.add_local_sig(funding_redeemscript, sig), + Ok(sig) => Some(local_commitment.add_local_sig(funding_redeemscript, sig)), Err(_) => return None, } - return Some(local_commitment.with_valid_witness().clone()); + } else { + None } - None } #[cfg(test)] pub(super) fn get_fully_signed_copy_local_tx(&mut self, funding_redeemscript: &Script) -> Option { if let Some(ref mut local_commitment) = self.local_commitment { - let mut local_commitment = local_commitment.clone(); + let local_commitment = local_commitment.clone(); match self.key_storage.sign_local_commitment(&local_commitment, &self.secp_ctx) { - Ok(sig) => local_commitment.add_local_sig(funding_redeemscript, sig), + Ok(sig) => Some(local_commitment.add_local_sig(funding_redeemscript, sig)), Err(_) => return None, } - return Some(local_commitment.with_valid_witness().clone()); + } else { + None } - None } pub(super) fn get_fully_signed_htlc_tx(&mut self, outp: &::bitcoin::OutPoint, preimage: &Option) -> Option { -- 2.30.2