From ff8f1371b5d889f129db06c07877799569a4f3db Mon Sep 17 00:00:00 2001
From: Oliver Gugger <gugger@gmail.com>
Date: Fri, 27 Jan 2023 16:13:09 +0100
Subject: [PATCH] itest: add itest for MuSig2 CombineKey

Before we change anything in the MuSig2 API, we first add an integration
test that makes sure the current version of the API combines keys
according to the v0.4.0 test vectors.
---
 lntest/itest/lnd_taproot_test.go | 48 ++++++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 3 deletions(-)

diff --git a/lntest/itest/lnd_taproot_test.go b/lntest/itest/lnd_taproot_test.go
index 1cbb82355..17c619ab4 100644
--- a/lntest/itest/lnd_taproot_test.go
+++ b/lntest/itest/lnd_taproot_test.go
@@ -35,11 +35,14 @@ const (
 )
 
 var (
-	dummyInternalKeyBytes, _ = hex.DecodeString(
+	hexDecode = func(keyStr string) []byte {
+		keyBytes, _ := hex.DecodeString(keyStr)
+		return keyBytes
+	}
+	dummyInternalKey, _ = btcec.ParsePubKey(hexDecode(
 		"03464805f5468e294d88cf15a3f06aef6c89d63ef1bd7b42db2e0c74c1ac" +
 			"eb90fe",
-	)
-	dummyInternalKey, _ = btcec.ParsePubKey(dummyInternalKeyBytes)
+	))
 )
 
 // testTaproot ensures that the daemon can send to and spend from taproot (p2tr)
@@ -61,6 +64,7 @@ func testTaproot(ht *lntemp.HarnessTest) {
 	testTaprootMuSig2KeySpendRootHash(ht, ht.Alice)
 	testTaprootMuSig2ScriptSpend(ht, ht.Alice)
 	testTaprootMuSig2CombinedLeafKeySpend(ht, ht.Alice)
+	testMuSig2CombineKey(ht, ht.Alice)
 
 	testTaprootImportTapscriptFullTree(ht, ht.Alice)
 	testTaprootImportTapscriptPartialReveal(ht, ht.Alice)
@@ -1856,3 +1860,41 @@ func testTaprootCoopClose(ht *lntemp.HarnessTest) {
 	require.False(ht, assertTaprootDeliveryUsed(closingTxid),
 		"taproot addr shouldn't be used!")
 }
+
+// testMuSig2CombineKey makes sure that combining a key with MuSig2 returns the
+// correct result according to the MuSig2 version specified.
+func testMuSig2CombineKey(ht *lntemp.HarnessTest, alice *node.HarnessNode) {
+	testVector040Key1 := hexDecode(
+		"F9308A019258C31049344F85F89D5229B531C845836F99B08601F113BCE0" +
+			"36F9",
+	)
+	testVector040Key2 := hexDecode(
+		"DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502B" +
+			"A659",
+	)
+	testVector040Key3 := hexDecode(
+		"3590A94E768F8E1815C2F24B4D80A8E3149316C3518CE7B7AD338368D038" +
+			"CA66",
+	)
+
+	resp := alice.RPC.MuSig2CombineKeys(&signrpc.MuSig2CombineKeysRequest{
+		AllSignerPubkeys: [][]byte{
+			testVector040Key1, testVector040Key2,
+			testVector040Key3,
+		},
+		TaprootTweak: &signrpc.TaprootTweakDesc{
+			KeySpendOnly: true,
+		},
+	})
+
+	expectedFinalKey := hexDecode(
+		"5b257b4e785d61157ef5303051f45184bd5cb47bc4b4069ed4dd453645" +
+			"9cb83b",
+	)
+	expectedPreTweakKey := hexDecode(
+		"d70cd69a2647f7390973df48cbfa2ccc407b8b2d60b08c5f1641185c79" +
+			"98a290",
+	)
+	require.Equal(ht, expectedFinalKey, resp.CombinedKey)
+	require.Equal(ht, expectedPreTweakKey, resp.TaprootInternalKey)
+}