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, 15 insertions, 0 deletions

diff --git a/src/pubkey.cpp b/src/pubkey.cpp
index fc14f41a0c..69e3d91392 100644
--- a/src/pubkey.cpp
+++ b/src/pubkey.cpp
@@ -7,6 +7,7 @@
 
 #include <secp256k1.h>
 #include <secp256k1_recovery.h>
+#include <secp256k1_schnorrsig.h>
 
 namespace
 {
@@ -166,6 +167,20 @@ int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_
     return 1;
 }
 
+XOnlyPubKey::XOnlyPubKey(Span<const unsigned char> bytes)
+{
+    assert(bytes.size() == 32);
+    std::copy(bytes.begin(), bytes.end(), m_keydata.begin());
+}
+
+bool XOnlyPubKey::VerifySchnorr(const uint256& msg, Span<const unsigned char> sigbytes) const
+{
+    assert(sigbytes.size() == 64);
+    secp256k1_xonly_pubkey pubkey;
+    if (!secp256k1_xonly_pubkey_parse(secp256k1_context_verify, &pubkey, m_keydata.data())) return false;
+    return secp256k1_schnorrsig_verify(secp256k1_context_verify, sigbytes.data(), msg.begin(), &pubkey);
+}
+
 bool CPubKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) const {
     if (!IsValid())
         return false;