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Expose SIGHASH_SINGLE bug in `encode_signing_data_to` 

Via `Option` return value

Fix #1015
This commit is contained in:
Dawid Ciężarkiewicz 2022-05-29 20:52:20 -07:00
parent a9365375c1
commit 42a91ab32a
2 changed files with 158 additions and 66 deletions
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196
src/blockdata/transaction.rs
View File

@ -40,18 +40,11 @@ use crate::consensus::{encode, Decodable, Encodable};
use crate::consensus::encode::MAX_VEC_SIZE;
use crate::hash_types::{Sighash, Txid, Wtxid};
use crate::VarInt;
use crate::util::sighash::UINT256_ONE;
#[cfg(doc)]
use crate::util::sighash::SchnorrSighashType;
/// Used for signature hash for invalid use of SIGHASH_SINGLE.
const UINT256_ONE: [u8; 32] = [
1, 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
];
/// A reference to a transaction output.
///
/// ### Bitcoin Core References
@ -262,6 +255,67 @@ impl Default for TxOut {
}
}
/// Result of [`Transaction::encode_signing_data_to`].
///
/// This type forces the caller to handle SIGHASH_SINGLE bug case.
///
/// This corner case can't be expressed using standard `Result`,
/// in a way that is both convenient and not-prone to accidental
/// mistakes (like calling `.expect("writer never fails")`).
#[must_use]
pub enum EncodeSigningDataResult<E> {
/// Input data is an instance of `SIGHASH_SINGLE` bug
SighashSingleBug,
/// Operation performed normally.
WriteResult(Result<(), E>),
}
impl<E> EncodeSigningDataResult<E> {
/// Checks for SIGHASH_SINGLE bug returning error if the writer failed.
///
/// This method is provided for easy and correct handling of the result because
/// SIGHASH_SINGLE bug is a special case that must not be ignored nor cause panicking.
/// Since the data is usually written directly into a hasher which never fails,
/// the recommended pattern to handle this is:
///
/// ```rust
/// # use bitcoin::consensus::deserialize;
/// # use bitcoin::{Transaction, Sighash};
/// # use bitcoin_hashes::{Hash, hex::FromHex};
/// # let mut writer = Sighash::engine();
/// # let input_index = 0;
/// # let script_pubkey = bitcoin::Script::new();
/// # let sighash_u32 = 0u32;
/// # const SOME_TX: &'static str = "0100000001a15d57094aa7a21a28cb20b59aab8fc7d1149a3bdbcddba9c622e4f5f6a99ece010000006c493046022100f93bb0e7d8db7bd46e40132d1f8242026e045f03a0efe71bbb8e3f475e970d790221009337cd7f1f929f00cc6ff01f03729b069a7c21b59b1736ddfee5db5946c5da8c0121033b9b137ee87d5a812d6f506efdd37f0affa7ffc310711c06c7f3e097c9447c52ffffffff0100e1f505000000001976a9140389035a9225b3839e2bbf32d826a1e222031fd888ac00000000";
/// # let raw_tx = Vec::from_hex(SOME_TX).unwrap();
/// # let tx: Transaction = deserialize(&raw_tx).unwrap();
/// if tx.encode_signing_data_to(&mut writer, input_index, &script_pubkey, sighash_u32)
/// .is_sighash_single_bug()
/// .expect("writer can't fail") {
/// // use a hash value of "1", instead of computing the actual hash due to SIGHASH_SINGLE bug
/// }
/// ```
pub fn is_sighash_single_bug(self) -> Result<bool, E> {
match self {
EncodeSigningDataResult::SighashSingleBug => Ok(true),
EncodeSigningDataResult::WriteResult(Ok(())) => Ok(false),
EncodeSigningDataResult::WriteResult(Err(e)) => Err(e),
}
}
/// Maps a `Result<T, E>` to `Result<T, F>` by applying a function to a
/// contained [`Err`] value, leaving an [`Ok`] value untouched.
///
/// Like [`Result::map_err`].
pub fn map_err<E2, F>(self, f: F) -> EncodeSigningDataResult<E2> where F: FnOnce(E) -> E2 {
match self {
EncodeSigningDataResult::SighashSingleBug => EncodeSigningDataResult::SighashSingleBug,
EncodeSigningDataResult::WriteResult(Err(e)) => EncodeSigningDataResult::WriteResult(Err(f(e))),
EncodeSigningDataResult::WriteResult(Ok(o)) => EncodeSigningDataResult::WriteResult(Ok(o)),
}
}
}
/// Bitcoin transaction.
///
/// An authenticated movement of coins.
@ -370,19 +424,23 @@ impl Transaction {
/// - Does NOT attempt to support OP_CODESEPARATOR. In general this would require evaluating
/// `script_pubkey` to determine which separators get evaluated and which don't, which we don't
/// have the information to determine.
/// - Does NOT handle the sighash single bug, you should either handle that manually or use
/// [`Self::signature_hash()`] instead.
/// - Does NOT handle the sighash single bug (see "Return type" section)
///
/// # Return type
///
/// This function can't handle the SIGHASH_SINGLE bug internally, so it returns [`EncodeSigningDataResult`]
/// that must be handled by the caller (see [`EncodeSigningDataResult::is_sighash_single_bug`]).
///
/// # Panics
///
/// If `input_index` is out of bounds (greater than or equal to `self.input.len()`).
pub fn encode_signing_data_to<Write: io::Write, U: Into<u32>>(
&self,
mut writer: Write,
writer: Write,
input_index: usize,
script_pubkey: &Script,
sighash_type: U,
) -> Result<(), encode::Error> {
) -> EncodeSigningDataResult<io::Error> {
let sighash_type: u32 = sighash_type.into();
assert!(input_index < self.input.len()); // Panic on OOB
@ -391,56 +449,73 @@ impl Transaction {
// will result in the data written to the writer being hashed, however the correct
// handling of the SIGHASH_SINGLE bug is to return the 'one array' - either implement
// this behaviour manually or use `signature_hash()`.
writer.write_all(b"[not a transaction] SIGHASH_SINGLE bug")?;
return Ok(())
return EncodeSigningDataResult::SighashSingleBug;
}
let (sighash, anyone_can_pay) = EcdsaSighashType::from_consensus(sighash_type).split_anyonecanpay_flag();
fn encode_signing_data_to_inner<Write: io::Write>(
self_: &Transaction,
mut writer: Write,
input_index: usize,
script_pubkey: &Script,
sighash_type: u32,
) -> Result<(), io::Error> {
let (sighash, anyone_can_pay) = EcdsaSighashType::from_consensus(sighash_type).split_anyonecanpay_flag();
// Build tx to sign
let mut tx = Transaction {
version: self.version,
lock_time: self.lock_time,
input: vec![],
output: vec![],
};
// Add all inputs necessary..
if anyone_can_pay {
tx.input = vec![TxIn {
previous_output: self.input[input_index].previous_output,
script_sig: script_pubkey.clone(),
sequence: self.input[input_index].sequence,
witness: Witness::default(),
}];
} else {
tx.input = Vec::with_capacity(self.input.len());
for (n, input) in self.input.iter().enumerate() {
tx.input.push(TxIn {
previous_output: input.previous_output,
script_sig: if n == input_index { script_pubkey.clone() } else { Script::new() },
sequence: if n != input_index && (sighash == EcdsaSighashType::Single || sighash == EcdsaSighashType::None) { 0 } else { input.sequence },
// Build tx to sign
let mut tx = Transaction {
version: self_.version,
lock_time: self_.lock_time,
input: vec![],
output: vec![],
};
// Add all inputs necessary..
if anyone_can_pay {
tx.input = vec![TxIn {
previous_output: self_.input[input_index].previous_output,
script_sig: script_pubkey.clone(),
sequence: self_.input[input_index].sequence,
witness: Witness::default(),
});
}];
} else {
tx.input = Vec::with_capacity(self_.input.len());
for (n, input) in self_.input.iter().enumerate() {
tx.input.push(TxIn {
previous_output: input.previous_output,
script_sig: if n == input_index { script_pubkey.clone() } else { Script::new() },
sequence: if n != input_index && (sighash == EcdsaSighashType::Single || sighash == EcdsaSighashType::None) { 0 } else { input.sequence },
witness: Witness::default(),
});
}
}
// ..then all outputs
tx.output = match sighash {
EcdsaSighashType::All => self_.output.clone(),
EcdsaSighashType::Single => {
let output_iter = self_.output.iter()
.take(input_index + 1) // sign all outputs up to and including this one, but erase
.enumerate() // all of them except for this one
.map(|(n, out)| if n == input_index { out.clone() } else { TxOut::default() });
output_iter.collect()
}
EcdsaSighashType::None => vec![],
_ => unreachable!()
};
// hash the result
tx.consensus_encode(&mut writer)?;
let sighash_arr = endian::u32_to_array_le(sighash_type);
sighash_arr.consensus_encode(&mut writer)?;
Ok(())
}
// ..then all outputs
tx.output = match sighash {
EcdsaSighashType::All => self.output.clone(),
EcdsaSighashType::Single => {
let output_iter = self.output.iter()
.take(input_index + 1) // sign all outputs up to and including this one, but erase
.enumerate() // all of them except for this one
.map(|(n, out)| if n == input_index { out.clone() } else { TxOut::default() });
output_iter.collect()
}
EcdsaSighashType::None => vec![],
_ => unreachable!()
};
// hash the result
tx.consensus_encode(&mut writer)?;
let sighash_arr = endian::u32_to_array_le(sighash_type);
sighash_arr.consensus_encode(&mut writer)?;
Ok(())
EncodeSigningDataResult::WriteResult(
encode_signing_data_to_inner(
self,
writer,
input_index,
script_pubkey,
sighash_type
)
)
}
/// Computes a signature hash for a given input index with a given sighash flag.
@ -473,12 +548,15 @@ impl Transaction {
sighash_u32: u32
) -> Sighash {
if self.is_invalid_use_of_sighash_single(sighash_u32, input_index) {
return Sighash::from_slice(&UINT256_ONE).expect("const-size array");
return Sighash::from_inner(UINT256_ONE);
}
let mut engine = Sighash::engine();
self.encode_signing_data_to(&mut engine, input_index, script_pubkey, sighash_u32)
.expect("engines don't error");
if self.encode_signing_data_to(&mut engine, input_index, script_pubkey, sighash_u32)
.is_sighash_single_bug()
.expect("engines don't error") {
return Sighash::from_slice(&UINT256_ONE).expect("const-size array");
}
Sighash::from_engine(engine)
}

28
src/util/sighash.rs
View File

@ -20,6 +20,7 @@
//! and legacy (before Bip143).
//!
use crate::blockdata::transaction::EncodeSigningDataResult;
use crate::prelude::*;
pub use crate::blockdata::transaction::{EcdsaSighashType, SighashTypeParseError};
@ -36,6 +37,14 @@ use crate::{Script, Transaction, TxOut};
use super::taproot::LeafVersion;
/// Used for signature hash for invalid use of SIGHASH_SINGLE.
pub(crate) const UINT256_ONE: [u8; 32] = [
1, 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
];
/// Efficiently calculates signature hash message for legacy, segwit and taproot inputs.
#[derive(Debug)]
pub struct SighashCache<T: Deref<Target=Transaction>> {
@ -638,23 +647,24 @@ impl<R: Deref<Target = Transaction>> SighashCache<R> {
/// Encodes the legacy signing data for any flag type into a given object implementing a
/// [`std::io::Write`] trait. Internally calls [`Transaction::encode_signing_data_to`].
#[must_use]
pub fn legacy_encode_signing_data_to<Write: io::Write, U: Into<u32>>(
&self,
mut writer: Write,
input_index: usize,
script_pubkey: &Script,
sighash_type: U,
) -> Result<(), Error> {
) -> EncodeSigningDataResult<Error> {
if input_index >= self.tx.input.len() {
return Err(Error::IndexOutOfInputsBounds {
return EncodeSigningDataResult::WriteResult(Err(Error::IndexOutOfInputsBounds {
index: input_index,
inputs_size: self.tx.input.len(),
});
}));
}
self.tx
.encode_signing_data_to(&mut writer, input_index, script_pubkey, sighash_type.into())
.expect("writers don't error");
Ok(())
.map_err(|e| e.into())
}
/// Computes the legacy sighash for any `sighash_type`.
@ -665,8 +675,12 @@ impl<R: Deref<Target = Transaction>> SighashCache<R> {
sighash_type: u32,
) -> Result<Sighash, Error> {
let mut enc = Sighash::engine();
self.legacy_encode_signing_data_to(&mut enc, input_index, script_pubkey, sighash_type)?;
Ok(Sighash::from_engine(enc))
if self.legacy_encode_signing_data_to(&mut enc, input_index, script_pubkey, sighash_type)
.is_sighash_single_bug()? {
Ok(Sighash::from_inner(UINT256_ONE))
} else {
Ok(Sighash::from_engine(enc))
}
}
#[inline]