Support for Schnorr signatures and integration in SignatureCheckers (BIP 340)

This enables the schnorrsig module in libsecp256k1, adds the relevant types
and functions to src/pubkey, as well as in higher-level `SignatureChecker`
classes. The (verification side of the) BIP340 test vectors is also added.

1 files changed, 13 insertions, 5 deletions

diff --git a/src/test/fuzz/script_sigcache.cpp b/src/test/fuzz/script_sigcache.cpp
index 0de1617d57..87af71897b 100644
--- a/src/test/fuzz/script_sigcache.cpp
+++ b/src/test/fuzz/script_sigcache.cpp
@@ -35,11 +35,19 @@ void test_one_input(const std::vector<uint8_t>& buffer)
     const bool store = fuzzed_data_provider.ConsumeBool();
     PrecomputedTransactionData tx_data;
     CachingTransactionSignatureChecker caching_transaction_signature_checker{mutable_transaction ? &tx : nullptr, n_in, amount, store, tx_data};
-    const std::optional<CPubKey> pub_key = ConsumeDeserializable<CPubKey>(fuzzed_data_provider);
-    if (pub_key) {
-        const std::vector<uint8_t> random_bytes = ConsumeRandomLengthByteVector(fuzzed_data_provider);
-        if (!random_bytes.empty()) {
-            (void)caching_transaction_signature_checker.VerifyECDSASignature(random_bytes, *pub_key, ConsumeUInt256(fuzzed_data_provider));
+    if (fuzzed_data_provider.ConsumeBool()) {
+        const auto random_bytes = fuzzed_data_provider.ConsumeBytes<unsigned char>(64);
+        const XOnlyPubKey pub_key(ConsumeUInt256(fuzzed_data_provider));
+        if (random_bytes.size() == 64) {
+            (void)caching_transaction_signature_checker.VerifySchnorrSignature(random_bytes, pub_key, ConsumeUInt256(fuzzed_data_provider));
+        }
+    } else {
+        const auto random_bytes = ConsumeRandomLengthByteVector(fuzzed_data_provider);
+        const auto pub_key = ConsumeDeserializable<CPubKey>(fuzzed_data_provider);
+        if (pub_key) {
+            if (!random_bytes.empty()) {
+                (void)caching_transaction_signature_checker.VerifyECDSASignature(random_bytes, *pub_key, ConsumeUInt256(fuzzed_data_provider));
+            }
         }
     }
 }