Merge bitcoin/bitcoin#32724: Musig2 tests

a3c71c7201 [test] Add BIP 328 test vectors for Musig2 (w0xlt)

Pull request description:

  Built on https://github.com/bitcoin/bitcoin/pull/31244

  This PR adds explicit tests for Bitcoin Core's MuSig2 interface.

  Any issues in musig2.{cpp,h} will likely also be caught by the descriptor tests, but having more detailed tests for the MuSig2 class itself improves test reporting/coverage.

  It uses BIP 328 test vectors.

ACKs for top commit:
  achow101:
    ACK a3c71c7201
  rkrux:
    lgtm ACK a3c71c7

Tree-SHA512: fc13beb5445c292cd7c75a47810fb1c4032ee2e3c1800dc44089b95959ccce8330291084bf788457e1d55c02d706ef04be7044badfee134149e004c44b19ec32

src/test/CMakeLists.txt

@@ -62,6 +62,7 @@ add_executable(test_bitcoin
   miniscript_tests.cpp
   minisketch_tests.cpp
   multisig_tests.cpp
+  bip328_tests.cpp
   net_peer_connection_tests.cpp
   net_peer_eviction_tests.cpp
   net_tests.cpp

src/test/bip328_tests.cpp

@@ -0,0 +1,114 @@
+// Copyright (c) 2026-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <boost/test/unit_test.hpp>
+
+#include <key.h>
+#include <key_io.h>
+#include <musig.h>
+#include <test/util/setup_common.h>
+#include <util/strencodings.h>
+#include <crypto/hex_base.h>
+
+#include <string>
+#include <vector>
+
+namespace {
+
+struct BIP328TestVector {
+    std::vector<std::string> pubkeys;
+    std::string expected_aggregate_pubkey;
+    std::string expected_aggregate_xpub;
+};
+
+BOOST_FIXTURE_TEST_SUITE(bip328_tests, BasicTestingSetup)
+
+BOOST_AUTO_TEST_CASE(valid_keys)
+{
+    // BIP 328 test vectors
+    std::vector<BIP328TestVector> test_vectors = {
+        // Test vector 0
+        {
+            .pubkeys = {
+                "03935F972DA013F80AE011890FA89B67A27B7BE6CCB24D3274D18B2D4067F261A9",
+                "02F9308A019258C31049344F85F89D5229B531C845836F99B08601F113BCE036F9"
+            },
+            .expected_aggregate_pubkey = "0354240c76b8f2999143301a99c7f721ee57eee0bce401df3afeaa9ae218c70f23",
+            .expected_aggregate_xpub = "xpub661MyMwAqRbcFt6tk3uaczE1y6EvM1TqXvawXcYmFEWijEM4PDBnuCXwwXEKGEouzXE6QLLRxjatMcLLzJ5LV5Nib1BN7vJg6yp45yHHRbm"
+        },
+        // Test vector 1
+        {
+            .pubkeys = {
+                "02F9308A019258C31049344F85F89D5229B531C845836F99B08601F113BCE036F9",
+                "03DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659",
+                "023590A94E768F8E1815C2F24B4D80A8E3149316C3518CE7B7AD338368D038CA66"
+            },
+            .expected_aggregate_pubkey = "0290539eede565f5d054f32cc0c220126889ed1e5d193baf15aef344fe59d4610c",
+            .expected_aggregate_xpub = "xpub661MyMwAqRbcFt6tk3uaczE1y6EvM1TqXvawXcYmFEWijEM4PDBnuCXwwVk5TFJk8Tw5WAdV3DhrGfbFA216sE9BsQQiSFTdudkETnKdg8k"
+        },
+        // Test vector 2
+        {
+            .pubkeys = {
+                "02DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659",
+                "023590A94E768F8E1815C2F24B4D80A8E3149316C3518CE7B7AD338368D038CA66",
+                "02F9308A019258C31049344F85F89D5229B531C845836F99B08601F113BCE036F9",
+                "03935F972DA013F80AE011890FA89B67A27B7BE6CCB24D3274D18B2D4067F261A9"
+            },
+            .expected_aggregate_pubkey = "022479f134cdb266141dab1a023cbba30a870f8995b95a91fc8464e56a7d41f8ea",
+            .expected_aggregate_xpub = "xpub661MyMwAqRbcFt6tk3uaczE1y6EvM1TqXvawXcYmFEWijEM4PDBnuCXwwUvaZYpysLX4wN59tjwU5pBuDjNrPEJbfxjLwn7ruzbXTcUTHkZ"
+        }
+    };
+
+    // Iterate through all test vectors
+    for (int i = 0; i < (int) test_vectors.size(); ++i) {
+        const auto& test = test_vectors[i];
+
+        // Parse public keys
+        std::vector<CPubKey> pubkeys;
+        for (const auto& hex_pubkey : test.pubkeys) {
+            std::vector<unsigned char> data = ParseHex(hex_pubkey);
+            CPubKey pubkey(data.begin(), data.end());
+            pubkeys.push_back(pubkey);
+        }
+
+        // Aggregate public keys
+        std::optional<CPubKey> m_aggregate_pubkey = MuSig2AggregatePubkeys(pubkeys);
+        BOOST_CHECK_MESSAGE(m_aggregate_pubkey.has_value(), "Test vector " << i << ": Failed to aggregate pubkeys");
+
+        // Check aggregate pubkey
+        std::string combined_keys = HexStr(m_aggregate_pubkey.value());
+        BOOST_CHECK_MESSAGE(combined_keys == test.expected_aggregate_pubkey, "Test vector " << i << ": Aggregate pubkey mismatch");
+
+        // Create extended public key
+        CExtPubKey extpub = CreateMuSig2SyntheticXpub(m_aggregate_pubkey.value());
+
+        // Check xpub
+        std::string xpub = EncodeExtPubKey(extpub);
+        BOOST_CHECK_MESSAGE(xpub == test.expected_aggregate_xpub, "Test vector " << i << ": Synthetic xpub mismatch");
+    }
+}
+
+BOOST_AUTO_TEST_CASE(invalid_key)
+{
+    std::vector<std::string> test_vectors = {
+        "00ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
+        "02DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659"
+    };
+
+    // Parse public keys
+    std::vector<CPubKey> pubkeys;
+    for (const auto& hex_pubkey : test_vectors) {
+        std::vector<unsigned char> data = ParseHex(hex_pubkey);
+        CPubKey pubkey(data.begin(), data.end());
+        pubkeys.push_back(pubkey);
+    }
+
+    // Aggregate public keys
+    std::optional<CPubKey> m_aggregate_pubkey = MuSig2AggregatePubkeys(pubkeys);
+    BOOST_CHECK_MESSAGE(!m_aggregate_pubkey.has_value(), "Aggregate key with an invalid public key is null");
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+
+}