rct amount key modified as per luigi1111's recommendations

This allows the key to be not the same for two outputs sent to
the same address (eg, if you pay yourself, and also get change
back). Also remove the key amounts lists and return parameters
since we don't actually generate random ones, so we don't need
to save them as we can recalculate them when needed if we have
the correct keys.

1 files changed, 20 insertions, 8 deletions

diff --git a/src/simplewallet/simplewallet.cpp b/src/simplewallet/simplewallet.cpp
index 9e7341451..7c5e8e541 100644
--- a/src/simplewallet/simplewallet.cpp
+++ b/src/simplewallet/simplewallet.cpp
@@ -3077,15 +3077,27 @@ bool simple_wallet::check_tx_key(const std::vector<std::string> &args_)
           try
           {
             rct::key Ctmp;
-            rct::key amount_key = rct::hash_to_scalar(rct::scalarmultKey(rct::pk2rct(address.m_view_public_key), rct::sk2rct(tx_key)));
-            rct::ecdhTuple ecdh_info = tx.rct_signatures.ecdhInfo[n];
-            rct::ecdhDecodeFromSharedSecret(ecdh_info, amount_key);
-            rct::key C = tx.rct_signatures.outPk[n].mask;
-            rct::addKeys2(Ctmp, ecdh_info.mask, ecdh_info.amount, rct::H);
-            if (rct::equalKeys(C, Ctmp))
-              amount = rct::h2d(ecdh_info.amount);
-            else
+            //rct::key amount_key = rct::hash_to_scalar(rct::scalarmultKey(rct::pk2rct(address.m_view_public_key), rct::sk2rct(tx_key)));
+            crypto::key_derivation derivation;
+            bool r = crypto::generate_key_derivation(address.m_view_public_key, tx_key, derivation);
+            if (!r)
+            {
+              LOG_ERROR("Failed to generate key derivation to decode rct output " << n);
               amount = 0;
+            }
+            else
+            {
+              crypto::secret_key scalar1;
+              crypto::derivation_to_scalar(derivation, n, scalar1);
+              rct::ecdhTuple ecdh_info = tx.rct_signatures.ecdhInfo[n];
+              rct::ecdhDecode(ecdh_info, rct::sk2rct(scalar1));
+              rct::key C = tx.rct_signatures.outPk[n].mask;
+              rct::addKeys2(Ctmp, ecdh_info.mask, ecdh_info.amount, rct::H);
+              if (rct::equalKeys(C, Ctmp))
+                amount = rct::h2d(ecdh_info.amount);
+              else
+                amount = 0;
+            }
           }
           catch (...) { amount = 0; }
         }