1 files changed, 49 insertions, 4 deletions
diff --git a/src/pubkey.cpp b/src/pubkey.cpp
index fc1624af25..51cc826b00 100644
--- a/src/pubkey.cpp
+++ b/src/pubkey.cpp
@@ -5,9 +5,16 @@
 
 #include <pubkey.h>
 
+#include <hash.h>
 #include <secp256k1.h>
+#include <secp256k1_extrakeys.h>
 #include <secp256k1_recovery.h>
 #include <secp256k1_schnorrsig.h>
+#include <span.h>
+#include <uint256.h>
+
+#include <algorithm>
+#include <cassert>
 
 namespace
 {
@@ -173,6 +180,12 @@ XOnlyPubKey::XOnlyPubKey(Span<const unsigned char> bytes)
     std::copy(bytes.begin(), bytes.end(), m_keydata.begin());
 }
 
+bool XOnlyPubKey::IsFullyValid() const
+{
+    secp256k1_xonly_pubkey pubkey;
+    return secp256k1_xonly_pubkey_parse(secp256k1_context_verify, &pubkey, m_keydata.data());
+}
+
 bool XOnlyPubKey::VerifySchnorr(const uint256& msg, Span<const unsigned char> sigbytes) const
 {
     assert(sigbytes.size() == 64);
@@ -181,13 +194,45 @@ bool XOnlyPubKey::VerifySchnorr(const uint256& msg, Span<const unsigned char> si
     return secp256k1_schnorrsig_verify(secp256k1_context_verify, sigbytes.data(), msg.begin(), &pubkey);
 }
 
-bool XOnlyPubKey::CheckPayToContract(const XOnlyPubKey& base, const uint256& hash, bool parity) const
+static const CHashWriter HASHER_TAPTWEAK = TaggedHash("TapTweak");
+
+uint256 XOnlyPubKey::ComputeTapTweakHash(const uint256* merkle_root) const
+{
+    if (merkle_root == nullptr) {
+        // We have no scripts. The actual tweak does not matter, but follow BIP341 here to
+        // allow for reproducible tweaking.
+        return (CHashWriter(HASHER_TAPTWEAK) << m_keydata).GetSHA256();
+    } else {
+        return (CHashWriter(HASHER_TAPTWEAK) << m_keydata << *merkle_root).GetSHA256();
+    }
+}
+
+bool XOnlyPubKey::CheckTapTweak(const XOnlyPubKey& internal, const uint256& merkle_root, bool parity) const
+{
+    secp256k1_xonly_pubkey internal_key;
+    if (!secp256k1_xonly_pubkey_parse(secp256k1_context_verify, &internal_key, internal.data())) return false;
+    uint256 tweak = internal.ComputeTapTweakHash(&merkle_root);
+    return secp256k1_xonly_pubkey_tweak_add_check(secp256k1_context_verify, m_keydata.begin(), parity, &internal_key, tweak.begin());
+}
+
+std::optional<std::pair<XOnlyPubKey, bool>> XOnlyPubKey::CreateTapTweak(const uint256* merkle_root) const
 {
     secp256k1_xonly_pubkey base_point;
-    if (!secp256k1_xonly_pubkey_parse(secp256k1_context_verify, &base_point, base.data())) return false;
-    return secp256k1_xonly_pubkey_tweak_add_check(secp256k1_context_verify, m_keydata.begin(), parity, &base_point, hash.begin());
+    if (!secp256k1_xonly_pubkey_parse(secp256k1_context_verify, &base_point, data())) return std::nullopt;
+    secp256k1_pubkey out;
+    uint256 tweak = ComputeTapTweakHash(merkle_root);
+    if (!secp256k1_xonly_pubkey_tweak_add(secp256k1_context_verify, &out, &base_point, tweak.data())) return std::nullopt;
+    int parity = -1;
+    std::pair<XOnlyPubKey, bool> ret;
+    secp256k1_xonly_pubkey out_xonly;
+    if (!secp256k1_xonly_pubkey_from_pubkey(secp256k1_context_verify, &out_xonly, &parity, &out)) return std::nullopt;
+    secp256k1_xonly_pubkey_serialize(secp256k1_context_verify, ret.first.begin(), &out_xonly);
+    assert(parity == 0 || parity == 1);
+    ret.second = parity;
+    return ret;
 }
 
+
 bool CPubKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) const {
     if (!IsValid())
         return false;
@@ -293,7 +338,7 @@ void CExtPubKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE]) {
 bool CExtPubKey::Derive(CExtPubKey &out, unsigned int _nChild) const {
     out.nDepth = nDepth + 1;
     CKeyID id = pubkey.GetID();
-    memcpy(&out.vchFingerprint[0], &id, 4);
+    memcpy(out.vchFingerprint, &id, 4);
     out.nChild = _nChild;
     return pubkey.Derive(out.pubkey, out.chaincode, _nChild, chaincode);
 }