Add CKey::ECDH

Author: stevenroose

src/key.cpp

@@ -12,6 +12,7 @@
 
 #include <secp256k1.h>
 #include <secp256k1_recovery.h>
+#include <secp256k1_ecdh.h>
 
 static secp256k1_context* secp256k1_context_sign = nullptr;
 
@@ -202,6 +203,15 @@ bool SigHasLowR(const secp256k1_ecdsa_signature* sig)
     return compact_sig[0] < 0x80;
 }
 
+uint256 CKey::ECDH(const CPubKey& pubkey) const {
+    assert(fValid);
+    uint256 result;
+    secp256k1_pubkey pkey;
+    assert(secp256k1_ec_pubkey_parse(secp256k1_context_sign, &pkey, pubkey.begin(), pubkey.size()));
+    assert(secp256k1_ecdh(secp256k1_context_sign, result.begin(), &pkey, begin(), NULL, NULL));
+    return result;
+}
+
 bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, bool grind, uint32_t test_case) const {
     if (!fValid)
         return false;

src/key.h

@@ -110,6 +110,11 @@ class CKey
      */
     CPubKey GetPubKey() const;
 
+    /**
+     * Compute the ECDH exchange result using this private key and another public key.
+     */
+    uint256 ECDH(const CPubKey& pubkey) const;
+
     /**
      * Create a DER-serialized signature.
      * The test_case parameter tweaks the deterministic nonce.