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Avoid unwrap'ing channel_parameters in to_counterparty signing #2634

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merged 3 commits into from
Oct 3, 2023
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Avoid unwrap'ing channel_parameters in to_counterparty signing #2634

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6a55dcc
Avoid unwrap'ing `channel_parameters` in to_counterparty signing
TheBlueMatt Oct 1, 2023
65569ed
Make `InMemorySigner` parameter-fetching utilities return `Option`s
TheBlueMatt Oct 3, 2023
60567da
Note when we're allowed to unwrap channel parameters in docs
TheBlueMatt Oct 3, 2023
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12 changes: 9 additions & 3 deletions lightning/src/sign/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -947,14 +947,20 @@ impl InMemorySigner {
if spend_tx.input[input_idx].previous_output != descriptor.outpoint.into_bitcoin_outpoint() { return Err(()); }

let remotepubkey = bitcoin::PublicKey::new(self.pubkeys().payment_point);
let witness_script = if self.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
// We cannot always assume that `channel_parameters` is set, so can't just call
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// `self.channel_parameters()` or anything that relies on it
let supports_anchors_zero_fee_htlc_tx = self.channel_parameters.as_ref()
.map(|params| params.channel_type_features.supports_anchors_zero_fee_htlc_tx())
.unwrap_or(false);
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Might be worth adding a helper. We do this in create_spendable_outputs_psbt, too, and it looks like we have an unchecked use in sign_counterparty_commitment. Though maybe that is never reached in practice?

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Yeah sign_counterparty_commitment shouldn't happen, we always provide the parameters there before signing commitment transactions.

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Turns out the one in create_spendable_outputs_psbt is not on self but rather on StaticPaymentOutputDescriptor. While we could DRY up that usage and StaticPaymentOutputDescriptor::max_witness_length, it's probably not worth it because we may refactor the former as per #2605 (comment).


let witness_script = if supports_anchors_zero_fee_htlc_tx {
chan_utils::get_to_countersignatory_with_anchors_redeemscript(&remotepubkey.inner)
} else {
Script::new_p2pkh(&remotepubkey.pubkey_hash())
};
let sighash = hash_to_message!(&sighash::SighashCache::new(spend_tx).segwit_signature_hash(input_idx, &witness_script, descriptor.output.value, EcdsaSighashType::All).unwrap()[..]);
let remotesig = sign_with_aux_rand(secp_ctx, &sighash, &self.payment_key, &self);
let payment_script = if self.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
let payment_script = if supports_anchors_zero_fee_htlc_tx {
witness_script.to_v0_p2wsh()
} else {
Script::new_v0_p2wpkh(&remotepubkey.wpubkey_hash().unwrap())
Expand All @@ -965,7 +971,7 @@ impl InMemorySigner {
let mut witness = Vec::with_capacity(2);
witness.push(remotesig.serialize_der().to_vec());
witness[0].push(EcdsaSighashType::All as u8);
if self.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
if supports_anchors_zero_fee_htlc_tx {
witness.push(witness_script.to_bytes());
} else {
witness.push(remotepubkey.to_bytes());
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