bip322: add message verification

This commit adds verification functions for the generic message signing
protocol and also adds test cases for all common script types.

Author: guggero

bip322/bip322.go

@@ -5,6 +5,7 @@ go 1.25.0
 require (
 	github.com/btcsuite/btcd/address/v2 v2.0.0
 	github.com/btcsuite/btcd/btcec/v2 v2.5.0
+	github.com/btcsuite/btcd/btcutil/v2 v2.0.0
 	github.com/btcsuite/btcd/chaincfg/v2 v2.0.0
 	github.com/btcsuite/btcd/chainhash/v2 v2.0.0
 	github.com/btcsuite/btcd/psbt/v2 v2.0.0
@@ -14,7 +15,6 @@ require (
 )
 
 require (
-	github.com/btcsuite/btcd/btcutil/v2 v2.0.0 // indirect
 	github.com/btcsuite/btclog v1.0.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/decred/dcrd/crypto/blake256 v1.1.0 // indirect

bip322/bip322_test.go

@@ -118,7 +118,13 @@ func signInputWitness(packet *psbt.Packet, idx int, script []byte,
 		if txIn.PreviousOutPoint.Index >= uint32(len(prevTx.TxOut)) {
 			return fmt.Errorf("input %d has no UTXO", idx)
 		}
-		return fmt.Errorf("input %d has no witness UTXO", idx)
+
+		if prevTx.TxHash() != txIn.PreviousOutPoint.Hash {
+			return fmt.Errorf("non witness utxo does not match " +
+				"input prevout")
+		}
+
+		utxo = prevTx.TxOut[txIn.PreviousOutPoint.Index]
 	}
 
 	prevOutFetcher := PsbtPrevOutputFetcher(packet)

bip322/go.mod

@@ -0,0 +1,108 @@
+package bip322
+
+import (
+	mrand "math/rand/v2"
+	"strings"
+	"testing"
+	"unicode/utf8"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/stretchr/testify/require"
+)
+
+// randomUTF8String returns a string of n randomly-chosen valid UTF-8 runes.
+func randomUTF8String(n int) string {
+	runes := make([]rune, n)
+	for i := range runes {
+		runes[i] = randomRune()
+	}
+	return string(runes)
+}
+
+// randomRune returns a random valid Unicode scalar value. It rejects the
+// surrogate range (U+D800–U+DFFF) and anything above U+10FFFF, both of which
+// cannot be legally encoded as UTF-8.
+func randomRune() rune {
+	for {
+		// Random value in [0, 0x10FFFF].
+		r := rune(mrand.Int64N(utf8.MaxRune + 1))
+		if utf8.ValidRune(r) {
+			return r
+		}
+	}
+}
+
+// TestSign tests that a valid signature can be created for all supported
+// single-key address types.
+func TestSign(t *testing.T) {
+	for range 100 {
+		randString := randomUTF8String(256)
+
+		randPrivateKey, err := btcec.NewPrivateKey()
+		require.NoError(t, err)
+
+		// Sign for a P2TR address.
+		sigP2TR, err := SignP2TR(randString, randPrivateKey)
+		require.NoError(t, err)
+		require.Contains(t, sigP2TR, PrefixSimple)
+		require.True(t, strings.HasPrefix(sigP2TR, PrefixSimple))
+
+		scriptP2TR, err := payToTaprootScript(randPrivateKey)
+		require.NoError(t, err)
+
+		valid, _, err := verifyMessageForChallenge(
+			[]byte(randString), scriptP2TR, sigP2TR,
+		)
+		require.NoError(t, err)
+		require.True(t, valid)
+
+		// Sign for a P2WPKH address.
+		sigP2WPKH, err := SignP2WPKH(randString, randPrivateKey)
+		require.NoError(t, err)
+		require.Contains(t, sigP2WPKH, PrefixSimple)
+		require.True(t, strings.HasPrefix(sigP2WPKH, PrefixSimple))
+
+		scriptP2WPKH, err := payToWitnessPubKeyHashScript(
+			randPrivateKey,
+		)
+		require.NoError(t, err)
+
+		valid, _, err = verifyMessageForChallenge(
+			[]byte(randString), scriptP2WPKH, sigP2WPKH,
+		)
+		require.NoError(t, err)
+		require.True(t, valid)
+
+		// Sign for a NP2WPKH address.
+		sigNP2WPKH, err := SignNestedP2WPKH(randString, randPrivateKey)
+		require.NoError(t, err)
+		require.Contains(t, sigNP2WPKH, PrefixFull)
+		require.True(t, strings.HasPrefix(sigNP2WPKH, PrefixFull))
+
+		scriptNP2WPKH, _, err := payToNestedWitnessPubKeyHashScript(
+			randPrivateKey,
+		)
+		require.NoError(t, err)
+
+		valid, _, err = verifyMessageForChallenge(
+			[]byte(randString), scriptNP2WPKH, sigNP2WPKH,
+		)
+		require.NoError(t, err)
+		require.True(t, valid)
+
+		// Sign for a P2PKH address.
+		sigP2PKH, err := SignP2PKH(randString, randPrivateKey)
+		require.NoError(t, err)
+		require.Contains(t, sigP2PKH, PrefixFull)
+		require.True(t, strings.HasPrefix(sigP2PKH, PrefixFull))
+
+		scriptP2PKH, err := payToPubKeyHashScript(randPrivateKey)
+		require.NoError(t, err)
+
+		valid, _, err = verifyMessageForChallenge(
+			[]byte(randString), scriptP2PKH, sigP2PKH,
+		)
+		require.NoError(t, err)
+		require.True(t, valid)
+	}
+}