From: Ken Sedgwick <ken@bonsai.com>
Date: Wed, 29 Dec 2021 04:37:20 +0000 (-0800)
Subject: Set the SigHashType of remote htlc signatures w/ anchors to SinglePlusAnyoneCanPay
X-Git-Tag: v0.0.105~40^2~9
X-Git-Url: http://git.bitcoin.ninja/?a=commitdiff_plain;h=8f09e5a7ff464109ca1d7de065f56635c17bd0ac;p=rust-lightning

Set the SigHashType of remote htlc signatures w/ anchors to SinglePlusAnyoneCanPay
---

diff --git a/lightning/src/chain/keysinterface.rs b/lightning/src/chain/keysinterface.rs
index 9e0cfb06e..a7965d4f3 100644
--- a/lightning/src/chain/keysinterface.rs
+++ b/lightning/src/chain/keysinterface.rs
@@ -612,7 +612,8 @@ impl BaseSign for InMemorySigner {
 		for htlc in commitment_tx.htlcs() {
 			let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, commitment_tx.feerate_per_kw(), self.holder_selected_contest_delay(), htlc, self.opt_anchors(), &keys.broadcaster_delayed_payment_key, &keys.revocation_key);
 			let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, self.opt_anchors(), &keys);
-			let htlc_sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, SigHashType::All)[..]);
+			let htlc_sighashtype = if self.opt_anchors() { SigHashType::SinglePlusAnyoneCanPay } else { SigHashType::All };
+			let htlc_sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, htlc_sighashtype)[..]);
 			let holder_htlc_key = chan_utils::derive_private_key(&secp_ctx, &keys.per_commitment_point, &self.htlc_base_key).map_err(|_| ())?;
 			htlc_sigs.push(secp_ctx.sign(&htlc_sighash, &holder_htlc_key));
 		}
diff --git a/lightning/src/ln/chan_utils.rs b/lightning/src/ln/chan_utils.rs
index cbafbed67..6e11dc42b 100644
--- a/lightning/src/ln/chan_utils.rs
+++ b/lightning/src/ln/chan_utils.rs
@@ -1394,6 +1394,8 @@ impl<'a> TrustedCommitmentTransaction<'a> {
 	/// which HTLCOutputInCommitment::transaction_output_index.is_some()).
 	///
 	/// The returned Vec has one entry for each HTLC, and in the same order.
+	///
+	/// This function is only valid in the holder commitment context, it always uses SigHashType::All.
 	pub fn get_htlc_sigs<T: secp256k1::Signing>(&self, htlc_base_key: &SecretKey, channel_parameters: &DirectedChannelTransactionParameters, secp_ctx: &Secp256k1<T>) -> Result<Vec<Signature>, ()> {
 		let inner = self.inner;
 		let keys = &inner.keys;
@@ -1429,12 +1431,14 @@ impl<'a> TrustedCommitmentTransaction<'a> {
 
 		let htlc_redeemscript = get_htlc_redeemscript_with_explicit_keys(&this_htlc, self.opt_anchors(), &keys.broadcaster_htlc_key, &keys.countersignatory_htlc_key, &keys.revocation_key);
 
+		let sighashtype = if self.opt_anchors() { SigHashType::SinglePlusAnyoneCanPay } else { SigHashType::All };
+
 		// First push the multisig dummy, note that due to BIP147 (NULLDUMMY) it must be a zero-length element.
 		htlc_tx.input[0].witness.push(Vec::new());
 
 		htlc_tx.input[0].witness.push(counterparty_signature.serialize_der().to_vec());
 		htlc_tx.input[0].witness.push(signature.serialize_der().to_vec());
-		htlc_tx.input[0].witness[1].push(SigHashType::All as u8);
+		htlc_tx.input[0].witness[1].push(sighashtype as u8);
 		htlc_tx.input[0].witness[2].push(SigHashType::All as u8);
 
 		if this_htlc.offered {
diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index ca6c6781f..2f97f9a88 100644
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -2625,7 +2625,8 @@ impl<Signer: Sign> Channel<Signer> {
 					&keys.broadcaster_delayed_payment_key, &keys.revocation_key);
 
 				let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, self.opt_anchors(), &keys);
-				let htlc_sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, SigHashType::All)[..]);
+				let htlc_sighashtype = if self.opt_anchors() { SigHashType::SinglePlusAnyoneCanPay } else { SigHashType::All };
+				let htlc_sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, htlc_sighashtype)[..]);
 				log_trace!(logger, "Checking HTLC tx signature {} by key {} against tx {} (sighash {}) with redeemscript {} in channel {}.",
 					log_bytes!(msg.htlc_signatures[idx].serialize_compact()[..]), log_bytes!(keys.countersignatory_htlc_key.serialize()),
 					encode::serialize_hex(&htlc_tx), log_bytes!(htlc_sighash[..]), encode::serialize_hex(&htlc_redeemscript), log_bytes!(self.channel_id()));
@@ -6288,7 +6289,8 @@ mod tests {
 						chan.get_counterparty_selected_contest_delay().unwrap(),
 						&htlc, opt_anchors, &keys.broadcaster_delayed_payment_key, &keys.revocation_key);
 					let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, opt_anchors, &keys);
-					let htlc_sighash = Message::from_slice(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, SigHashType::All)[..]).unwrap();
+					let htlc_sighashtype = if opt_anchors { SigHashType::SinglePlusAnyoneCanPay } else { SigHashType::All };
+					let htlc_sighash = Message::from_slice(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, htlc_sighashtype)[..]).unwrap();
 					secp_ctx.verify(&htlc_sighash, &remote_signature, &keys.countersignatory_htlc_key).unwrap();
 
 					let mut preimage: Option<PaymentPreimage> = None;