Switch to libsecp256k1-based validation for ECDSA

src/pubkey.h

@@ -177,6 +177,11 @@ public:
      */
     bool Verify(const uint256& hash, const std::vector<unsigned char>& vchSig) const;
 
+    /**
+     * Check whether a signature is normalized (lower-S).
+     */
+    static bool CheckLowS(const std::vector<unsigned char>& vchSig);
+
     //! Recover a public key from a compact signature.
     bool RecoverCompact(const uint256& hash, const std::vector<unsigned char>& vchSig);
 
@@ -205,4 +210,15 @@ struct CExtPubKey {
     bool Derive(CExtPubKey& out, unsigned int nChild) const;
 };
 
+/** Users of this module must hold an ECCVerifyHandle. The constructor and
+ *  destructor of these are not allowed to run in parallel, though. */
+class ECCVerifyHandle
+{
+    static int refcount;
+
+public:
+    ECCVerifyHandle();
+    ~ECCVerifyHandle();
+};
+
 #endif // BITCOIN_PUBKEY_H