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ref(signer): Use Psbt::sighash_ecdsa for computing sighashes
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- Change param `hash` to `&Message` in `sign_psbt_ecdsa`
- Remove unused methods `compute_legacy_sighash`,
and `compute_segwitv0_sighash`.
- Match on `self.ctx` when signing for `SignerWrapper<PrivateKey>`
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@ValuedMammal
ValuedMammal committed Jun 20, 2024
1 parent ee56993 commit 0a7ae6c
Showing 1 changed file with 84 additions and 223 deletions.
307 changes: 84 additions & 223 deletions crates/wallet/src/wallet/signer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -91,7 +91,7 @@ use bitcoin::bip32::{ChildNumber, DerivationPath, Fingerprint, Xpriv};
use bitcoin::hashes::hash160;
use bitcoin::secp256k1::Message;
use bitcoin::sighash::{EcdsaSighashType, TapSighash, TapSighashType};
use bitcoin::{ecdsa, psbt, sighash, taproot, transaction};
use bitcoin::{ecdsa, psbt, sighash, taproot};
use bitcoin::{key::TapTweak, key::XOnlyPublicKey, secp256k1};
use bitcoin::{PrivateKey, Psbt, PublicKey};

Expand Down Expand Up @@ -159,12 +159,10 @@ pub enum SignerError {
NonStandardSighash,
/// Invalid SIGHASH for the signing context in use
InvalidSighash,
/// Error while computing the hash to sign a P2WPKH input.
SighashP2wpkh(sighash::P2wpkhError),
/// Error while computing the hash to sign a Taproot input.
SighashTaproot(sighash::TaprootError),
/// Error while computing the hash, out of bounds access on the transaction inputs.
TxInputsIndexError(transaction::InputsIndexError),
/// PSBT sign error.
Psbt(psbt::SignError),
/// Miniscript PSBT error
MiniscriptPsbt(MiniscriptPsbtError),
/// To be used only by external libraries implementing [`InputSigner`] or
Expand All @@ -173,24 +171,6 @@ pub enum SignerError {
External(String),
}

impl From<transaction::InputsIndexError> for SignerError {
fn from(v: transaction::InputsIndexError) -> Self {
Self::TxInputsIndexError(v)
}
}

impl From<sighash::P2wpkhError> for SignerError {
fn from(e: sighash::P2wpkhError) -> Self {
Self::SighashP2wpkh(e)
}
}

impl From<sighash::TaprootError> for SignerError {
fn from(e: sighash::TaprootError) -> Self {
Self::SighashTaproot(e)
}
}

impl fmt::Display for SignerError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Expand All @@ -205,9 +185,8 @@ impl fmt::Display for SignerError {
Self::MissingHdKeypath => write!(f, "Missing fingerprint and derivation path"),
Self::NonStandardSighash => write!(f, "The psbt contains a non standard sighash"),
Self::InvalidSighash => write!(f, "Invalid SIGHASH for the signing context in use"),
Self::SighashP2wpkh(err) => write!(f, "Error while computing the hash to sign a P2WPKH input: {}", err),
Self::SighashTaproot(err) => write!(f, "Error while computing the hash to sign a Taproot input: {}", err),
Self::TxInputsIndexError(err) => write!(f, "Error while computing the hash, out of bounds access on the transaction inputs: {}", err),
Self::Psbt(err) => write!(f, "Error computing the sighash: {}", err),
Self::MiniscriptPsbt(err) => write!(f, "Miniscript PSBT error: {}", err),
Self::External(err) => write!(f, "{}", err),
}
Expand Down Expand Up @@ -472,92 +451,87 @@ impl InputSigner for SignerWrapper<PrivateKey> {
}

let pubkey = PublicKey::from_private_key(secp, self);
let x_only_pubkey = XOnlyPublicKey::from(pubkey.inner);

if let SignerContext::Tap { is_internal_key } = self.ctx {
if let Some(psbt_internal_key) = psbt.inputs[input_index].tap_internal_key {
if is_internal_key
&& psbt.inputs[input_index].tap_key_sig.is_none()
&& sign_options.sign_with_tap_internal_key
&& x_only_pubkey == psbt_internal_key
{
let (hash, hash_ty) = compute_tap_sighash(psbt, input_index, None)?;
sign_psbt_schnorr(
&self.inner,
x_only_pubkey,
None,
&mut psbt.inputs[input_index],
hash,
hash_ty,
secp,
);

match self.ctx {
SignerContext::Tap { is_internal_key } => {
let x_only_pubkey = XOnlyPublicKey::from(pubkey.inner);

if let Some(psbt_internal_key) = psbt.inputs[input_index].tap_internal_key {
if is_internal_key
&& psbt.inputs[input_index].tap_key_sig.is_none()
&& sign_options.sign_with_tap_internal_key
&& x_only_pubkey == psbt_internal_key
{
let (sighash, sighash_type) = compute_tap_sighash(psbt, input_index, None)?;
sign_psbt_schnorr(
&self.inner,
x_only_pubkey,
None,
&mut psbt.inputs[input_index],
sighash,
sighash_type,
secp,
);
}
}
}

if let Some((leaf_hashes, _)) =
psbt.inputs[input_index].tap_key_origins.get(&x_only_pubkey)
{
let leaf_hashes = leaf_hashes
.iter()
.filter(|lh| {
// Removing the leaves we shouldn't sign for
let should_sign = match &sign_options.tap_leaves_options {
TapLeavesOptions::All => true,
TapLeavesOptions::Include(v) => v.contains(lh),
TapLeavesOptions::Exclude(v) => !v.contains(lh),
TapLeavesOptions::None => false,
};
// Filtering out the leaves without our key
should_sign
&& !psbt.inputs[input_index]
.tap_script_sigs
.contains_key(&(x_only_pubkey, **lh))
})
.cloned()
.collect::<Vec<_>>();
for lh in leaf_hashes {
let (hash, hash_ty) = compute_tap_sighash(psbt, input_index, Some(lh))?;
sign_psbt_schnorr(
&self.inner,
x_only_pubkey,
Some(lh),
&mut psbt.inputs[input_index],
hash,
hash_ty,
secp,
);
if let Some((leaf_hashes, _)) =
psbt.inputs[input_index].tap_key_origins.get(&x_only_pubkey)
{
let leaf_hashes = leaf_hashes
.iter()
.filter(|lh| {
// Removing the leaves we shouldn't sign for
let should_sign = match &sign_options.tap_leaves_options {
TapLeavesOptions::All => true,
TapLeavesOptions::Include(v) => v.contains(lh),
TapLeavesOptions::Exclude(v) => !v.contains(lh),
TapLeavesOptions::None => false,
};
// Filtering out the leaves without our key
should_sign
&& !psbt.inputs[input_index]
.tap_script_sigs
.contains_key(&(x_only_pubkey, **lh))
})
.cloned()
.collect::<Vec<_>>();
for lh in leaf_hashes {
let (sighash, sighash_type) =
compute_tap_sighash(psbt, input_index, Some(lh))?;
sign_psbt_schnorr(
&self.inner,
x_only_pubkey,
Some(lh),
&mut psbt.inputs[input_index],
sighash,
sighash_type,
secp,
);
}
}
}
SignerContext::Segwitv0 | SignerContext::Legacy => {
if psbt.inputs[input_index].partial_sigs.contains_key(&pubkey) {
return Ok(());
}

return Ok(());
}

if psbt.inputs[input_index].partial_sigs.contains_key(&pubkey) {
return Ok(());
}
let mut sighasher = sighash::SighashCache::new(psbt.unsigned_tx.clone());
let (msg, sighash_type) = psbt
.sighash_ecdsa(input_index, &mut sighasher)
.map_err(SignerError::Psbt)?;

let (hash, hash_ty) = match self.ctx {
SignerContext::Segwitv0 => {
let (h, t) = compute_segwitv0_sighash(psbt, input_index)?;
let h = h.to_raw_hash();
(h, t)
}
SignerContext::Legacy => {
let (h, t) = compute_legacy_sighash(psbt, input_index)?;
let h = h.to_raw_hash();
(h, t)
sign_psbt_ecdsa(
&self.inner,
pubkey,
&mut psbt.inputs[input_index],
&msg,
sighash_type,
secp,
sign_options.allow_grinding,
);
}
_ => return Ok(()), // handled above
};
sign_psbt_ecdsa(
&self.inner,
pubkey,
&mut psbt.inputs[input_index],
hash,
hash_ty,
secp,
sign_options.allow_grinding,
);
}

Ok(())
}
Expand All @@ -567,12 +541,11 @@ fn sign_psbt_ecdsa(
secret_key: &secp256k1::SecretKey,
pubkey: PublicKey,
psbt_input: &mut psbt::Input,
hash: impl bitcoin::hashes::Hash<Bytes = [u8; 32]>,
msg: &Message,
sighash_type: EcdsaSighashType,
secp: &SecpCtx,
allow_grinding: bool,
) {
let msg = &Message::from_digest(hash.to_byte_array());
let signature = if allow_grinding {
secp.sign_ecdsa_low_r(msg, secret_key)
} else {
Expand All @@ -594,7 +567,7 @@ fn sign_psbt_schnorr(
pubkey: XOnlyPublicKey,
leaf_hash: Option<taproot::TapLeafHash>,
psbt_input: &mut psbt::Input,
hash: TapSighash,
sighash: TapSighash,
sighash_type: TapSighashType,
secp: &SecpCtx,
) {
Expand All @@ -606,7 +579,7 @@ fn sign_psbt_schnorr(
Some(_) => keypair, // no tweak for script spend
};

let msg = &Message::from(hash);
let msg = &Message::from(sighash);
let signature = secp.sign_schnorr(msg, &keypair);
secp.verify_schnorr(&signature, msg, &XOnlyPublicKey::from_keypair(&keypair).0)
.expect("invalid or corrupted schnorr signature");
Expand Down Expand Up @@ -870,120 +843,6 @@ impl Default for SignOptions {
}
}

/// Computes the legacy sighash.
fn compute_legacy_sighash(
psbt: &Psbt,
input_index: usize,
) -> Result<(sighash::LegacySighash, EcdsaSighashType), SignerError> {
if input_index >= psbt.inputs.len() || input_index >= psbt.unsigned_tx.input.len() {
return Err(SignerError::InputIndexOutOfRange);
}

let psbt_input = &psbt.inputs[input_index];
let tx_input = &psbt.unsigned_tx.input[input_index];

let sighash_type = psbt_input
.sighash_type
.unwrap_or_else(|| EcdsaSighashType::All.into())
.ecdsa_hash_ty()
.map_err(|_| SignerError::InvalidSighash)?;

let script = match psbt_input.redeem_script {
Some(ref redeem_script) => redeem_script.clone(),
None => {
let non_witness_utxo = psbt_input
.non_witness_utxo
.as_ref()
.ok_or(SignerError::MissingNonWitnessUtxo)?;
let prev_out = non_witness_utxo
.output
.get(tx_input.previous_output.vout as usize)
.ok_or(SignerError::InvalidNonWitnessUtxo)?;

prev_out.script_pubkey.clone()
}
};

Ok((
sighash::SighashCache::new(&psbt.unsigned_tx).legacy_signature_hash(
input_index,
&script,
sighash_type.to_u32(),
)?,
sighash_type,
))
}

/// Computes the segwitv0 sighash.
fn compute_segwitv0_sighash(
psbt: &Psbt,
input_index: usize,
) -> Result<(sighash::SegwitV0Sighash, EcdsaSighashType), SignerError> {
if input_index >= psbt.inputs.len() || input_index >= psbt.unsigned_tx.input.len() {
return Err(SignerError::InputIndexOutOfRange);
}

let psbt_input = &psbt.inputs[input_index];
let tx_input = &psbt.unsigned_tx.input[input_index];

let sighash_type = psbt_input
.sighash_type
.unwrap_or_else(|| EcdsaSighashType::All.into())
.ecdsa_hash_ty()
.map_err(|_| SignerError::InvalidSighash)?;

// Always try first with the non-witness utxo
let utxo = if let Some(prev_tx) = &psbt_input.non_witness_utxo {
// Check the provided prev-tx
if prev_tx.compute_txid() != tx_input.previous_output.txid {
return Err(SignerError::InvalidNonWitnessUtxo);
}

// The output should be present, if it's missing the `non_witness_utxo` is invalid
prev_tx
.output
.get(tx_input.previous_output.vout as usize)
.ok_or(SignerError::InvalidNonWitnessUtxo)?
} else if let Some(witness_utxo) = &psbt_input.witness_utxo {
// Fallback to the witness_utxo. If we aren't allowed to use it, signing should fail
// before we get to this point
witness_utxo
} else {
// Nothing has been provided
return Err(SignerError::MissingNonWitnessUtxo);
};
let value = utxo.value;

let mut sighasher = sighash::SighashCache::new(&psbt.unsigned_tx);

let sighash = match psbt_input.witness_script {
Some(ref witness_script) => {
sighasher.p2wsh_signature_hash(input_index, witness_script, value, sighash_type)?
}
None => {
if utxo.script_pubkey.is_p2wpkh() {
sighasher.p2wpkh_signature_hash(
input_index,
&utxo.script_pubkey,
value,
sighash_type,
)?
} else if psbt_input
.redeem_script
.as_ref()
.map(|s| s.is_p2wpkh())
.unwrap_or(false)
{
let script_pubkey = psbt_input.redeem_script.as_ref().unwrap();
sighasher.p2wpkh_signature_hash(input_index, script_pubkey, value, sighash_type)?
} else {
return Err(SignerError::MissingWitnessScript);
}
}
};
Ok((sighash, sighash_type))
}

/// Computes the taproot sighash.
fn compute_tap_sighash(
psbt: &Psbt,
Expand Down Expand Up @@ -1026,7 +885,9 @@ fn compute_tap_sighash(
let extra = extra.map(|leaf_hash| (leaf_hash, 0xFFFFFFFF));

Ok((
cache.taproot_signature_hash(input_index, &prevouts, None, extra, sighash_type)?,
cache
.taproot_signature_hash(input_index, &prevouts, None, extra, sighash_type)
.map_err(SignerError::SighashTaproot)?,
sighash_type,
))
}
Expand Down

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