Implement signing PSBT taproot key spends

Author: bbrtj

lib/Bitcoin/Crypto/Role/PSBT/Finalizer.pm

@@ -104,7 +104,7 @@ sub _should_finalize_P2TR_keypath
 	return () unless $sig;
 
 	return (
-		{type => 'witness', sigs => [$sig]},
+		{type => 'witness', sigs => [$sig->value]},
 	);
 }
 
@@ -113,6 +113,7 @@ sub _should_finalize_P2TR_scriptpath
 	my ($self, $input, $input_index) = @_;
 
 	# TODO: custom script tree - check public keys and signatures for leaves
+	return ();
 }
 
 sub _should_finalize_P2TR

lib/Bitcoin/Crypto/Role/PSBT/Signer.pm

@@ -6,6 +6,8 @@ use warnings;
 use Mooish::Base -standard, -role;
 use Types::Common -sigs;
 
+use Bitcoin::Crypto qw(btc_script_tree);
+
 sub _add_partial_signature
 {
 	my ($self, $input_index, $key, $signature) = @_;
@@ -57,12 +59,56 @@ sub _do_sign_P2WSH
 	return 0;
 }
 
+sub _do_sign_P2TR_keypath
+{
+	my ($self, $key, $tx, $input, $input_index) = @_;
+
+	my $tree_root = $self->get_all_fields('PSBT_IN_TAP_MERKLE_ROOT', $input_index);
+	my $tree = $tree_root ? btc_script_tree->new(tree => [{hash => $tree_root->value}]) : undef;
+
+	my $output_key = $key->get_public_key->get_taproot_output_key($tree ? $tree->get_merkle_root : ());
+	return 0 unless $output_key->get_xonly_key eq $input->utxo->output->locking_script->get_raw_address;
+
+	my $signer = $tx->sign(
+		signing_index => $input_index,
+		($tree ? (script_tree => $tree) : ()),
+	);
+	my $sighash = $self->get_all_fields('PSBT_IN_SIGHASH_TYPE', $input_index);
+
+	# use transaction signer's ability to give us the signature
+	my $signature = $signer->add_signature($key, sighash => $sighash ? $sighash->value : undef)
+		->signature->[-1];
+
+	$self->add_field(
+		type => 'PSBT_IN_TAP_KEY_SIG',
+		index => $input_index,
+		value => $signature,
+	);
+
+	return 1;
+}
+
+sub _do_sign_P2TR_scriptpath
+{
+	my ($self, $key, $tx, $input, $input_index) = @_;
+
+	my $script = $self->get_all_fields('PSBT_IN_TAP_LEAF_SCRIPT', $input_index);
+	return 0 unless $script;
+
+	# TODO: detect simple P2MS scripts with checksigadd
+
+	return 1;
+}
+
 sub _do_sign_P2TR
 {
 	my ($self, $key, $tx, $input, $input_index) = @_;
 
-	# TODO
-	return 0;
+	my $res = $self->_do_sign_P2TR_scriptpath($key, $tx, $input, $input_index);
+	$res = $self->_do_sign_P2TR_keypath($key, $tx, $input, $input_index)
+		unless $res;
+
+	return $res;
 }
 
 sub _do_sign

t/PSBT/roles.t

@@ -1,5 +1,5 @@
 use Test2::V0;
-use Bitcoin::Crypto qw(btc_transaction btc_prv btc_psbt);
+use Bitcoin::Crypto qw(btc_transaction btc_prv btc_psbt btc_script_tree);
 use Bitcoin::Crypto::Constants qw(:transaction);
 use Bitcoin::Crypto::Util qw(to_format);
 use Bitcoin::Crypto::Transaction::Output;
@@ -86,6 +86,42 @@ subtest 'should sign and set final signatures when finalizing P2WPKH input' => s
 	ok lives { $psbt->get_transaction->verify }, 'verification passed';
 };
 
+subtest 'should sign and set final signatures when finalizing P2TR key input' => sub {
+	my $fake_merkle_root = [hex => "1d358125e4839360ade708a32c64548b0ffde92421bc3348eaf07a55ad775651"];
+	my $tree = btc_script_tree->new(tree => [{hash => $fake_merkle_root}]);
+
+	my $psbt = build_psbt(
+		[[$fake_txid, 0], [$fake_txid, 1]],
+		@fields,
+		{
+			type => 'PSBT_IN_WITNESS_UTXO',
+			index => 0,
+			value => Bitcoin::Crypto::Transaction::Output->new(
+				value => 5000,
+				locking_script => [address => $priv->get_public_key->get_taproot_address],
+			),
+		},
+		{
+			type => 'PSBT_IN_WITNESS_UTXO',
+			index => 1,
+			value => Bitcoin::Crypto::Transaction::Output->new(
+				value => 5000,
+				locking_script => [address => $priv->get_public_key->get_taproot_address($tree)],
+			),
+		},
+		{
+			type => 'PSBT_IN_TAP_MERKLE_ROOT',
+			index => 1,
+			value => $fake_merkle_root,
+		},
+	);
+
+	is $psbt->sign($priv), 2, 'both inputs were signed';
+	$psbt->finalize;
+
+	ok lives { $psbt->get_transaction->verify }, 'verification passed';
+};
+
 done_testing;
 
 sub build_psbt