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Create and Sign PSBTs for spendable outputs #2286

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May 11, 2023
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Create and Sign PSBTs for spendable outputs #2286

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4 changes: 2 additions & 2 deletions lightning/src/ln/functional_tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4263,15 +4263,15 @@ macro_rules! check_spendable_outputs {
match event {
Event::SpendableOutputs { mut outputs } => {
for outp in outputs.drain(..) {
txn.push($keysinterface.backing.spend_spendable_outputs(&[&outp], Vec::new(), Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, &secp_ctx).unwrap());
txn.push($keysinterface.backing.spend_spendable_outputs(&[&outp], Vec::new(), Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, None, &secp_ctx).unwrap());
all_outputs.push(outp);
}
},
_ => panic!("Unexpected event"),
};
}
if all_outputs.len() > 1 {
if let Ok(tx) = $keysinterface.backing.spend_spendable_outputs(&all_outputs.iter().map(|a| a).collect::<Vec<_>>(), Vec::new(), Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, &secp_ctx) {
if let Ok(tx) = $keysinterface.backing.spend_spendable_outputs(&all_outputs.iter().map(|a| a).collect::<Vec<_>>(), Vec::new(), Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, None, &secp_ctx) {
txn.push(tx);
}
}
Expand Down
4 changes: 2 additions & 2 deletions lightning/src/ln/monitor_tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -114,7 +114,7 @@ fn test_spendable_output<'a, 'b, 'c, 'd>(node: &'a Node<'b, 'c, 'd>, spendable_t
if let Event::SpendableOutputs { outputs } = spendable.pop().unwrap() {
assert_eq!(outputs.len(), 1);
let spend_tx = node.keys_manager.backing.spend_spendable_outputs(&[&outputs[0]], Vec::new(),
Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, &Secp256k1::new()).unwrap();
Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, None, &Secp256k1::new()).unwrap();
check_spends!(spend_tx, spendable_tx);
} else { panic!(); }
}
Expand Down Expand Up @@ -2348,7 +2348,7 @@ fn test_anchors_aggregated_revoked_htlc_tx() {
if let Event::SpendableOutputs { outputs } = event {
assert_eq!(outputs.len(), 1);
let spend_tx = nodes[0].keys_manager.backing.spend_spendable_outputs(
&[&outputs[0]], Vec::new(), Script::new_op_return(&[]), 253, &Secp256k1::new(),
&[&outputs[0]], Vec::new(), Script::new_op_return(&[]), 253, None, &Secp256k1::new(),
).unwrap();
check_spends!(spend_tx, revoked_claims[idx]);
} else {
Expand Down
4 changes: 2 additions & 2 deletions lightning/src/ln/reorg_tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -587,7 +587,7 @@ fn do_test_to_remote_after_local_detection(style: ConnectStyle) {
if let Event::SpendableOutputs { outputs } = node_a_spendable.pop().unwrap() {
assert_eq!(outputs.len(), 1);
let spend_tx = nodes[0].keys_manager.backing.spend_spendable_outputs(&[&outputs[0]], Vec::new(),
Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, &Secp256k1::new()).unwrap();
Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, None, &Secp256k1::new()).unwrap();
check_spends!(spend_tx, remote_txn_b[0]);
}

Expand All @@ -607,7 +607,7 @@ fn do_test_to_remote_after_local_detection(style: ConnectStyle) {
if let Event::SpendableOutputs { outputs } = node_b_spendable.pop().unwrap() {
assert_eq!(outputs.len(), 1);
let spend_tx = nodes[1].keys_manager.backing.spend_spendable_outputs(&[&outputs[0]], Vec::new(),
Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, &Secp256k1::new()).unwrap();
Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(), 253, None, &Secp256k1::new()).unwrap();
check_spends!(spend_tx, remote_txn_a[0]);
}
}
Expand Down
241 changes: 165 additions & 76 deletions lightning/src/sign/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ use bitcoin::blockdata::transaction::{Transaction, TxOut, TxIn, EcdsaSighashType
use bitcoin::blockdata::script::{Script, Builder};
use bitcoin::blockdata::opcodes;
use bitcoin::network::constants::Network;
use bitcoin::psbt::PartiallySignedTransaction;
use bitcoin::util::bip32::{ExtendedPrivKey, ExtendedPubKey, ChildNumber};
use bitcoin::util::sighash;

Expand Down Expand Up @@ -218,6 +219,126 @@ impl_writeable_tlv_based_enum!(SpendableOutputDescriptor,
(2, StaticPaymentOutput),
);

impl SpendableOutputDescriptor {
/// Turns this into a [`bitcoin::psbt::Input`] which can be used to create a
/// [`PartiallySignedTransaction`] which spends the given descriptor.
///
/// Note that this does not include any signatures, just the information required to
/// construct the transaction and sign it.
pub fn to_psbt_input(&self) -> bitcoin::psbt::Input {
match self {
SpendableOutputDescriptor::StaticOutput { output, .. } => {
// Is a standard P2WPKH, no need for witness script
bitcoin::psbt::Input {
witness_utxo: Some(output.clone()),
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Oh these don't have outpoints? Ugh, oh well, still probably useful just annoying.

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Yeah PSBTv0 has a lot of weird stuff like that

..Default::default()
}
},
SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
// TODO we could add the witness script as well
bitcoin::psbt::Input {
witness_utxo: Some(descriptor.output.clone()),
..Default::default()
}
},
SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
// TODO we could add the witness script as well
bitcoin::psbt::Input {
witness_utxo: Some(descriptor.output.clone()),
..Default::default()
}
},
}
}

/// Creates an unsigned [`PartiallySignedTransaction`] which spends the given descriptors to
/// the given outputs, plus an output to the given change destination (if sufficient
/// change value remains). The PSBT will have a feerate, at least, of the given value.
///
/// The `locktime` argument is used to set the transaction's locktime. If `None`, the
/// transaction will have a locktime of 0. It it recommended to set this to the current block
/// height to avoid fee sniping, unless you have some specific reason to use a different
/// locktime.
///
/// Returns the PSBT and expected max transaction weight.
///
/// Returns `Err(())` if the output value is greater than the input value minus required fee,
/// if a descriptor was duplicated, or if an output descriptor `script_pubkey`
/// does not match the one we can spend.
Comment on lines +265 to +267
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Would be cool to enumerate these.

///
/// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
pub fn create_spendable_outputs_psbt(descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: Script, feerate_sat_per_1000_weight: u32, locktime: Option<PackedLockTime>) -> Result<(PartiallySignedTransaction, usize), ()> {
let mut input = Vec::with_capacity(descriptors.len());
let mut input_value = 0;
let mut witness_weight = 0;
let mut output_set = HashSet::with_capacity(descriptors.len());
for outp in descriptors {
match outp {
SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
if !output_set.insert(descriptor.outpoint) { return Err(()); }
input.push(TxIn {
previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
script_sig: Script::new(),
sequence: Sequence::ZERO,
witness: Witness::new(),
});
witness_weight += StaticPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
#[cfg(feature = "grind_signatures")]
{ witness_weight -= 1; } // Guarantees a low R signature
input_value += descriptor.output.value;
},
SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
if !output_set.insert(descriptor.outpoint) { return Err(()); }
input.push(TxIn {
previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
script_sig: Script::new(),
sequence: Sequence(descriptor.to_self_delay as u32),
witness: Witness::new(),
});
witness_weight += DelayedPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
#[cfg(feature = "grind_signatures")]
{ witness_weight -= 1; } // Guarantees a low R signature
input_value += descriptor.output.value;
},
SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output } => {
if !output_set.insert(*outpoint) { return Err(()); }
input.push(TxIn {
previous_output: outpoint.into_bitcoin_outpoint(),
script_sig: Script::new(),
sequence: Sequence::ZERO,
witness: Witness::new(),
});
witness_weight += 1 + 73 + 34;
#[cfg(feature = "grind_signatures")]
{ witness_weight -= 1; } // Guarantees a low R signature
input_value += output.value;
}
}
if input_value > MAX_VALUE_MSAT / 1000 { return Err(()); }
}
let mut tx = Transaction {
version: 2,
lock_time: locktime.unwrap_or(PackedLockTime::ZERO),
input,
output: outputs,
};
let expected_max_weight =
transaction_utils::maybe_add_change_output(&mut tx, input_value, witness_weight, feerate_sat_per_1000_weight, change_destination_script)?;

let psbt_inputs = descriptors.iter().map(|d| d.to_psbt_input()).collect::<Vec<_>>();
let psbt = PartiallySignedTransaction {
inputs: psbt_inputs,
outputs: vec![Default::default(); tx.output.len()],
unsigned_tx: tx,
xpub: Default::default(),
version: 0,
proprietary: Default::default(),
unknown: Default::default(),
};
Ok((psbt, expected_max_weight))
}
}

/// A trait to handle Lightning channel key material without concretizing the channel type or
/// the signature mechanism.
pub trait ChannelSigner {
Expand Down Expand Up @@ -1171,97 +1292,40 @@ impl KeysManager {
)
}

/// Creates a [`Transaction`] which spends the given descriptors to the given outputs, plus an
/// output to the given change destination (if sufficient change value remains). The
/// transaction will have a feerate, at least, of the given value.
/// Signs the given [`PartiallySignedTransaction`] which spends the given [`SpendableOutputDescriptor`]s.
/// The resulting inputs will be finalized and the PSBT will be ready for broadcast if there
/// are no other inputs that need signing.
///
/// Returns `Err(())` if the output value is greater than the input value minus required fee,
/// if a descriptor was duplicated, or if an output descriptor `script_pubkey`
/// does not match the one we can spend.
///
/// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
/// Returns `Err(())` if the PSBT is missing a descriptor or if we fail to sign.
///
/// May panic if the [`SpendableOutputDescriptor`]s were not generated by channels which used
/// this [`KeysManager`] or one of the [`InMemorySigner`] created by this [`KeysManager`].
pub fn spend_spendable_outputs<C: Signing>(&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: Script, feerate_sat_per_1000_weight: u32, secp_ctx: &Secp256k1<C>) -> Result<Transaction, ()> {
let mut input = Vec::new();
let mut input_value = 0;
let mut witness_weight = 0;
let mut output_set = HashSet::with_capacity(descriptors.len());
for outp in descriptors {
match outp {
SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
input.push(TxIn {
previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
script_sig: Script::new(),
sequence: Sequence::ZERO,
witness: Witness::new(),
});
witness_weight += StaticPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
#[cfg(feature = "grind_signatures")]
{ witness_weight -= 1; } // Guarantees a low R signature
input_value += descriptor.output.value;
if !output_set.insert(descriptor.outpoint) { return Err(()); }
},
SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
input.push(TxIn {
previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
script_sig: Script::new(),
sequence: Sequence(descriptor.to_self_delay as u32),
witness: Witness::new(),
});
witness_weight += DelayedPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
#[cfg(feature = "grind_signatures")]
{ witness_weight -= 1; } // Guarantees a low R signature
input_value += descriptor.output.value;
if !output_set.insert(descriptor.outpoint) { return Err(()); }
},
SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output } => {
input.push(TxIn {
previous_output: outpoint.into_bitcoin_outpoint(),
script_sig: Script::new(),
sequence: Sequence::ZERO,
witness: Witness::new(),
});
witness_weight += 1 + 73 + 34;
#[cfg(feature = "grind_signatures")]
{ witness_weight -= 1; } // Guarantees a low R signature
input_value += output.value;
if !output_set.insert(*outpoint) { return Err(()); }
}
}
if input_value > MAX_VALUE_MSAT / 1000 { return Err(()); }
}
let mut spend_tx = Transaction {
version: 2,
lock_time: PackedLockTime(0),
input,
output: outputs,
};
let expected_max_weight =
transaction_utils::maybe_add_change_output(&mut spend_tx, input_value, witness_weight, feerate_sat_per_1000_weight, change_destination_script)?;

pub fn sign_spendable_outputs_psbt<C: Signing>(&self, descriptors: &[&SpendableOutputDescriptor], psbt: &mut PartiallySignedTransaction, secp_ctx: &Secp256k1<C>) -> Result<(), ()> {
let mut keys_cache: Option<(InMemorySigner, [u8; 32])> = None;
let mut input_idx = 0;
for outp in descriptors {
match outp {
SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
let input_idx = psbt.unsigned_tx.input.iter().position(|i| i.previous_output == descriptor.outpoint.into_bitcoin_outpoint()).ok_or(())?;
if keys_cache.is_none() || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id {
keys_cache = Some((
self.derive_channel_keys(descriptor.channel_value_satoshis, &descriptor.channel_keys_id),
descriptor.channel_keys_id));
}
spend_tx.input[input_idx].witness = Witness::from_vec(keys_cache.as_ref().unwrap().0.sign_counterparty_payment_input(&spend_tx, input_idx, &descriptor, &secp_ctx)?);
let witness = Witness::from_vec(keys_cache.as_ref().unwrap().0.sign_counterparty_payment_input(&psbt.unsigned_tx, input_idx, &descriptor, &secp_ctx)?);
psbt.inputs[input_idx].final_script_witness = Some(witness);
},
SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
let input_idx = psbt.unsigned_tx.input.iter().position(|i| i.previous_output == descriptor.outpoint.into_bitcoin_outpoint()).ok_or(())?;
if keys_cache.is_none() || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id {
keys_cache = Some((
self.derive_channel_keys(descriptor.channel_value_satoshis, &descriptor.channel_keys_id),
descriptor.channel_keys_id));
}
spend_tx.input[input_idx].witness = Witness::from_vec(keys_cache.as_ref().unwrap().0.sign_dynamic_p2wsh_input(&spend_tx, input_idx, &descriptor, &secp_ctx)?);
let witness = Witness::from_vec(keys_cache.as_ref().unwrap().0.sign_dynamic_p2wsh_input(&psbt.unsigned_tx, input_idx, &descriptor, &secp_ctx)?);
psbt.inputs[input_idx].final_script_witness = Some(witness);
},
SpendableOutputDescriptor::StaticOutput { ref output, .. } => {
SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output } => {
let input_idx = psbt.unsigned_tx.input.iter().position(|i| i.previous_output == outpoint.into_bitcoin_outpoint()).ok_or(())?;
let derivation_idx = if output.script_pubkey == self.destination_script {
1
} else {
Expand All @@ -1288,17 +1352,42 @@ impl KeysManager {

if payment_script != output.script_pubkey { return Err(()); };

let sighash = hash_to_message!(&sighash::SighashCache::new(&spend_tx).segwit_signature_hash(input_idx, &witness_script, output.value, EcdsaSighashType::All).unwrap()[..]);
let sighash = hash_to_message!(&sighash::SighashCache::new(&psbt.unsigned_tx).segwit_signature_hash(input_idx, &witness_script, output.value, EcdsaSighashType::All).unwrap()[..]);
let sig = sign_with_aux_rand(secp_ctx, &sighash, &secret.private_key, &self);
let mut sig_ser = sig.serialize_der().to_vec();
sig_ser.push(EcdsaSighashType::All as u8);
spend_tx.input[input_idx].witness.push(sig_ser);
spend_tx.input[input_idx].witness.push(pubkey.inner.serialize().to_vec());
let witness = Witness::from_vec(vec![sig_ser, pubkey.inner.serialize().to_vec()]);
psbt.inputs[input_idx].final_script_witness = Some(witness);
},
}
input_idx += 1;
}

Ok(())
}

/// Creates a [`Transaction`] which spends the given descriptors to the given outputs, plus an
/// output to the given change destination (if sufficient change value remains). The
/// transaction will have a feerate, at least, of the given value.
///
/// The `locktime` argument is used to set the transaction's locktime. If `None`, the
/// transaction will have a locktime of 0. It it recommended to set this to the current block
/// height to avoid fee sniping, unless you have some specific reason to use a different
/// locktime.
///
/// Returns `Err(())` if the output value is greater than the input value minus required fee,
/// if a descriptor was duplicated, or if an output descriptor `script_pubkey`
/// does not match the one we can spend.
///
/// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
///
/// May panic if the [`SpendableOutputDescriptor`]s were not generated by channels which used
/// this [`KeysManager`] or one of the [`InMemorySigner`] created by this [`KeysManager`].
pub fn spend_spendable_outputs<C: Signing>(&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: Script, feerate_sat_per_1000_weight: u32, locktime: Option<PackedLockTime>, secp_ctx: &Secp256k1<C>) -> Result<Transaction, ()> {
let (mut psbt, expected_max_weight) = SpendableOutputDescriptor::create_spendable_outputs_psbt(descriptors, outputs, change_destination_script, feerate_sat_per_1000_weight, locktime)?;
self.sign_spendable_outputs_psbt(descriptors, &mut psbt, secp_ctx)?;

let spend_tx = psbt.extract_tx();

debug_assert!(expected_max_weight >= spend_tx.weight());
// Note that witnesses with a signature vary somewhat in size, so allow
// `expected_max_weight` to overshoot by up to 3 bytes per input.
Expand Down Expand Up @@ -1512,8 +1601,8 @@ impl PhantomKeysManager {
}

/// See [`KeysManager::spend_spendable_outputs`] for documentation on this method.
pub fn spend_spendable_outputs<C: Signing>(&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: Script, feerate_sat_per_1000_weight: u32, secp_ctx: &Secp256k1<C>) -> Result<Transaction, ()> {
self.inner.spend_spendable_outputs(descriptors, outputs, change_destination_script, feerate_sat_per_1000_weight, secp_ctx)
pub fn spend_spendable_outputs<C: Signing>(&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: Script, feerate_sat_per_1000_weight: u32, locktime: Option<PackedLockTime>, secp_ctx: &Secp256k1<C>) -> Result<Transaction, ()> {
self.inner.spend_spendable_outputs(descriptors, outputs, change_destination_script, feerate_sat_per_1000_weight, locktime, secp_ctx)
}

/// See [`KeysManager::derive_channel_keys`] for documentation on this method.
Expand Down