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fuzzamoto-ir: implement BuildPayToBareMulti #129

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75 changes: 75 additions & 0 deletions fuzzamoto-ir/src/compiler.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -178,6 +178,11 @@ enum SigningRequest {
private_key_var: usize,
sighash_var: usize,
},
BareMulti {
required: u8,
private_keys: Vec<[u8; 32]>,
sighash_var: usize,
},
Taproot {
spend_info_var: Option<usize>,
selected_leaf: Option<TaprootLeaf>,
Expand Down Expand Up @@ -410,6 +415,7 @@ impl Compiler {
| Operation::BuildPayToPubKey
| Operation::BuildPayToPubKeyHash
| Operation::BuildPayToWitnessPubKeyHash
| Operation::BuildPayToBareMulti { .. }
| Operation::BuildPayToTaproot => {
self.handle_script_building_operations(instruction)?;
}
Expand Down Expand Up @@ -1061,6 +1067,38 @@ impl Compiler {
requires_signing: None,
});
}
Operation::BuildPayToBareMulti {
required,
private_keys,
} => {
let n = u8::try_from(private_keys.len()).map_err(|_| {
CompilerError::MiscError("too many keys in bare multisig".to_string())
})?;
let required_clamped = (*required).min(n).max(1);

let mut spk_builder = ScriptBuf::builder().push_int(i64::from(required_clamped));
for sk_bytes in private_keys {
let pk = PrivateKey::from_slice(sk_bytes, NetworkKind::Main).map_err(|_| {
CompilerError::MiscError("invalid bare multisig private key".to_string())
})?;
spk_builder = spk_builder.push_key(&pk.public_key(&self.secp_ctx));
}
let script_pubkey = spk_builder
.push_int(i64::from(n))
.push_opcode(bitcoin::opcodes::all::OP_CHECKMULTISIG)
.into_script();

self.append_variable(Scripts {
script_pubkey: script_pubkey.into(),
script_sig: vec![],
witness: Witness { stack: Vec::new() },
requires_signing: Some(SigningRequest::BareMulti {
required: required_clamped,
private_keys: private_keys.clone(),
sighash_var: instruction.inputs[0],
}),
});
}
Operation::BuildPayToScriptHash => {
let script = self.get_input::<Vec<u8>>(&instruction.inputs, 0)?;
let witness_var = self.get_input::<Witness>(&instruction.inputs, 1)?;
Expand Down Expand Up @@ -2128,6 +2166,43 @@ impl Compiler {
_ => {}
}
}
SigningRequest::BareMulti {
required,
private_keys,
sighash_var,
} => {
let sighash_flag = *self.get_variable::<u8>(*sighash_var).unwrap();
let sighash_type =
EcdsaSighashType::from_consensus(u32::from(sighash_flag));

// scriptPubKey is already on the txo; use it for signing
let script_code = Script::from_bytes(&txo_var.scripts.script_pubkey);

// Collect `required` signatures (first `required` keys)
let mut sig_script_builder =
ScriptBuf::builder().push_opcode(bitcoin::opcodes::OP_0);

for sk_bytes in private_keys.iter().take(*required as usize) {
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@dergoegge dergoegge Mar 11, 2026

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Will this ever result in a p2ms that has less signatures than required?

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@brunoerg brunoerg Mar 12, 2026

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No, because of let required_clamped = (*required).min(n).max(1); which is the used required here. So it can never produce fewer signatures than required.

if let Ok(hash) = cache.legacy_signature_hash(
idx,
script_code,
u32::from(sighash_flag),
) {
let signature = ecdsa::Signature {
signature: self.secp_ctx.sign_ecdsa(
&secp256k1::Message::from_digest(*hash.as_byte_array()),
&SecretKey::from_slice(sk_bytes.as_slice()).unwrap(),
),
sighash_type,
};
sig_script_builder = sig_script_builder.push_slice(
PushBytesBuf::try_from(signature.to_vec()).unwrap(),
);
}
}

tx_var.tx.input[idx].script_sig = sig_script_builder.into_script();
}
SigningRequest::Taproot {
spend_info_var,
selected_leaf,
Expand Down
25 changes: 24 additions & 1 deletion fuzzamoto-ir/src/generators/tx.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,18 +21,20 @@ enum OutputType {
PayToPubKeyHash,
PayToWitnessPubKeyHash,
PayToTaproot,
PayToBareMulti,
OpReturn,
}

fn get_random_output_type<R: RngCore>(rng: &mut R) -> OutputType {
match rng.gen_range(0..8) {
match rng.gen_range(0..9) {
0 => OutputType::PayToWitnessScriptHash,
1 => OutputType::PayToAnchor,
2 => OutputType::PayToScriptHash,
3 => OutputType::PayToPubKey,
4 => OutputType::PayToPubKeyHash,
5 => OutputType::PayToWitnessPubKeyHash,
6 => OutputType::PayToTaproot,
7 => OutputType::PayToBareMulti,
_ => OutputType::OpReturn,
}
}
Expand Down Expand Up @@ -114,6 +116,7 @@ fn build_outputs<R: RngCore>(
)
}
OutputType::PayToTaproot => build_taproot_scripts(builder, rng),
OutputType::PayToBareMulti => build_bare_multi_scripts(builder, rng),
};

let amount_var =
Expand Down Expand Up @@ -546,6 +549,26 @@ fn random_merkle_path<R: RngCore>(rng: &mut R) -> Vec<[u8; 32]> {
(0..depth).map(|_| random_node_hash(rng)).collect()
}

fn build_bare_multi_scripts<R: RngCore>(
builder: &mut ProgramBuilder,
rng: &mut R,
) -> IndexedVariable {
let n = rng.gen_range(1u8..=3u8);
let required = rng.gen_range(1u8..=n);
let private_keys: Vec<[u8; 32]> = (0..n).map(|_| gen_secret_key_bytes(rng)).collect();

let sighash_flags_var =
builder.force_append_expect_output(vec![], &Operation::LoadSigHashFlags(0));

builder.force_append_expect_output(
vec![sighash_flags_var.index],
&Operation::BuildPayToBareMulti {
required,
private_keys,
},
)
}

fn gen_secret_key_bytes<R: RngCore>(rng: &mut R) -> [u8; 32] {
loop {
let mut secret = [0u8; 32];
Expand Down
1 change: 1 addition & 0 deletions fuzzamoto-ir/src/instruction.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,7 @@ impl Instruction {
| Operation::TakeCoinbaseTxo
| Operation::TaprootScriptsUseAnnex
| Operation::TaprootTxoUseAnnex
| Operation::BuildPayToBareMulti { .. }
| Operation::TakeTxo => true,

Operation::Nop { .. }
Expand Down
25 changes: 24 additions & 1 deletion fuzzamoto-ir/src/operation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -106,7 +106,7 @@ pub enum Operation {
BuildRawScripts,
BuildPayToWitnessScriptHash,
// TODO: BuildPayToTaproot,
// TODO: BuildPayToBareMulti, BeginMultiSig, EndMultiSig
// TODO: BeginMultiSig, EndMultiSig
BuildPayToPubKey,
BuildPayToPubKeyHash,
BuildPayToWitnessPubKeyHash,
Expand All @@ -115,6 +115,13 @@ pub enum Operation {
BuildPayToAnchor,
BuildPayToTaproot,

BuildPayToBareMulti {
/// m-of-n: number of required signatures (1..=n)
required: u8,
/// Private keys for each pubkey in the script
private_keys: Vec<[u8; 32]>,
},

// cmpctblock building operations
BuildCompactBlock,

Expand Down Expand Up @@ -214,6 +221,17 @@ impl fmt::Display for Operation {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Operation::Nop { .. } => write!(f, "Nop"),
Operation::BuildPayToBareMulti {
required,
private_keys,
} => {
write!(
f,
"BuildPayToBareMulti({}-of-{})",
required,
private_keys.len()
)
}
Operation::LoadBytes(bytes) => write!(
f,
"LoadBytes(\"{}\")",
Expand Down Expand Up @@ -584,6 +602,7 @@ impl Operation {
| Operation::Probe
| Operation::TaprootScriptsUseAnnex
| Operation::TaprootTxoUseAnnex
| Operation::BuildPayToBareMulti { .. }
| Operation::BuildTaprootTree { .. } => false,
}
}
Expand Down Expand Up @@ -743,6 +762,7 @@ impl Operation {
| Operation::BuildCoinbaseTxInput
| Operation::AddCoinbaseTxOutput
| Operation::SendBlockTxn
| Operation::BuildPayToBareMulti { .. }
| Operation::Probe => false,
}
}
Expand Down Expand Up @@ -799,6 +819,7 @@ impl Operation {
Operation::LoadConnectionType(_) => vec![Variable::ConnectionType],
Operation::LoadDuration(_) => vec![Variable::Duration],
Operation::LoadAddr(_) => vec![Variable::AddrRecord],
Operation::BuildPayToBareMulti { .. } => vec![Variable::Scripts],
Operation::LoadBlockHeight(_) => vec![Variable::BlockHeight],
Operation::LoadCompactFilterType(_) => vec![Variable::CompactFilterType],
Operation::SendRawMessage => vec![],
Expand Down Expand Up @@ -980,6 +1001,7 @@ impl Operation {
Variable::Scripts,
Variable::ConstAmount,
],
Operation::BuildPayToBareMulti { .. } => vec![Variable::SigHashFlags],
Operation::TakeTxo => vec![Variable::ConstTx],
Operation::TakeCoinbaseTxo => vec![Variable::ConstCoinbaseTx],
Operation::AddWitness => vec![Variable::MutWitnessStack, Variable::Bytes],
Expand Down Expand Up @@ -1142,6 +1164,7 @@ impl Operation {
| Operation::BuildOpReturnScripts
| Operation::BuildPayToAnchor
| Operation::BuildPayToTaproot
| Operation::BuildPayToBareMulti { .. }
| Operation::BuildPayToPubKey
| Operation::BuildPayToPubKeyHash
| Operation::BuildPayToWitnessPubKeyHash
Expand Down