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.

4 files changed, 16 insertions, 6 deletions

diff --git a/src/crypto/crypto.cpp b/src/crypto/crypto.cpp
index f0ee3bdc3..250779ac3 100644
--- a/src/crypto/crypto.cpp
+++ b/src/crypto/crypto.cpp
@@ -151,7 +151,7 @@ namespace crypto {
     return true;
   }
 
-  static void derivation_to_scalar(const key_derivation &derivation, size_t output_index, ec_scalar &res) {
+  void crypto_ops::derivation_to_scalar(const key_derivation &derivation, size_t output_index, ec_scalar &res) {
     struct {
       key_derivation derivation;
       char output_index[(sizeof(size_t) * 8 + 6) / 7];
diff --git a/src/crypto/crypto.h b/src/crypto/crypto.h
index aa437d57d..b396fc7db 100644
--- a/src/crypto/crypto.h
+++ b/src/crypto/crypto.h
@@ -113,6 +113,8 @@ namespace crypto {
     friend bool secret_key_to_public_key(const secret_key &, public_key &);
     static bool generate_key_derivation(const public_key &, const secret_key &, key_derivation &);
     friend bool generate_key_derivation(const public_key &, const secret_key &, key_derivation &);
+    static void derivation_to_scalar(const key_derivation &derivation, size_t output_index, ec_scalar &res);
+    friend void derivation_to_scalar(const key_derivation &derivation, size_t output_index, ec_scalar &res);
     static bool derive_public_key(const key_derivation &, std::size_t, const public_key &, public_key &);
     friend bool derive_public_key(const key_derivation &, std::size_t, const public_key &, public_key &);
     static void derive_secret_key(const key_derivation &, std::size_t, const secret_key &, secret_key &);
@@ -181,6 +183,9 @@ namespace crypto {
     const public_key &base, public_key &derived_key) {
     return crypto_ops::derive_public_key(derivation, output_index, base, derived_key);
   }
+  inline void derivation_to_scalar(const key_derivation &derivation, size_t output_index, ec_scalar &res) {
+    return crypto_ops::derivation_to_scalar(derivation, output_index, res);
+  }
   inline void derive_secret_key(const key_derivation &derivation, std::size_t output_index,
     const secret_key &base, secret_key &derived_key) {
     crypto_ops::derive_secret_key(derivation, output_index, base, derived_key);
diff --git a/src/cryptonote_core/cryptonote_format_utils.cpp b/src/cryptonote_core/cryptonote_format_utils.cpp
index 8f4020829..6a3172d4e 100644
--- a/src/cryptonote_core/cryptonote_format_utils.cpp
+++ b/src/cryptonote_core/cryptonote_format_utils.cpp
@@ -458,8 +458,9 @@ namespace cryptonote
     return encrypt_payment_id(payment_id, public_key, secret_key);
   }
   //---------------------------------------------------------------
-  bool construct_tx_and_get_tx_keys(const account_keys& sender_account_keys, const std::vector<tx_source_entry>& sources, const std::vector<tx_destination_entry>& destinations, std::vector<uint8_t> extra, transaction& tx, uint64_t unlock_time, crypto::secret_key &tx_key, std::vector<crypto::secret_key> &amount_keys, bool rct)
+  bool construct_tx_and_get_tx_key(const account_keys& sender_account_keys, const std::vector<tx_source_entry>& sources, const std::vector<tx_destination_entry>& destinations, std::vector<uint8_t> extra, transaction& tx, uint64_t unlock_time, crypto::secret_key &tx_key, bool rct)
   {
+    std::vector<crypto::secret_key> amount_keys;
     tx.vin.clear();
     tx.vout.clear();
     tx.signatures.clear();
@@ -577,6 +578,12 @@ namespace cryptonote
       bool r = crypto::generate_key_derivation(dst_entr.addr.m_view_public_key, txkey.sec, derivation);
       CHECK_AND_ASSERT_MES(r, false, "at creation outs: failed to generate_key_derivation(" << dst_entr.addr.m_view_public_key << ", " << txkey.sec << ")");
 
+      if (tx.version > 1)
+      {
+        crypto::secret_key scalar1;
+        crypto::derivation_to_scalar(derivation, output_index, scalar1);
+        amount_keys.push_back(scalar1);
+      }
       r = crypto::derive_public_key(derivation, output_index, dst_entr.addr.m_spend_public_key, out_eph_public_key);
       CHECK_AND_ASSERT_MES(r, false, "at creation outs: failed to derive_public_key(" << derivation << ", " << output_index << ", "<< dst_entr.addr.m_spend_public_key << ")");
 
@@ -686,7 +693,6 @@ namespace cryptonote
         destinations.push_back(rct::pk2rct(boost::get<txout_to_key>(tx.vout[i].target).key));
         outamounts.push_back(tx.vout[i].amount);
         amount_out += tx.vout[i].amount;
-        amount_keys.push_back(rct::rct2sk(rct::hash_to_scalar(rct::scalarmultKey(rct::pk2rct(shuffled_dsts[i].addr.m_view_public_key), rct::sk2rct(txkey.sec)))));
       }
 
       if (use_simple_rct)
@@ -745,8 +751,7 @@ namespace cryptonote
   bool construct_tx(const account_keys& sender_account_keys, const std::vector<tx_source_entry>& sources, const std::vector<tx_destination_entry>& destinations, std::vector<uint8_t> extra, transaction& tx, uint64_t unlock_time)
   {
      crypto::secret_key tx_key;
-     std::vector<crypto::secret_key> amount_keys;
-     return construct_tx_and_get_tx_keys(sender_account_keys, sources, destinations, extra, tx, unlock_time, tx_key, amount_keys);
+     return construct_tx_and_get_tx_key(sender_account_keys, sources, destinations, extra, tx, unlock_time, tx_key);
   }
   //---------------------------------------------------------------
   bool get_inputs_money_amount(const transaction& tx, uint64_t& money)
diff --git a/src/cryptonote_core/cryptonote_format_utils.h b/src/cryptonote_core/cryptonote_format_utils.h
index f70b22573..5da256921 100644
--- a/src/cryptonote_core/cryptonote_format_utils.h
+++ b/src/cryptonote_core/cryptonote_format_utils.h
@@ -74,7 +74,7 @@ namespace cryptonote
 
   //---------------------------------------------------------------
   bool construct_tx(const account_keys& sender_account_keys, const std::vector<tx_source_entry>& sources, const std::vector<tx_destination_entry>& destinations, std::vector<uint8_t> extra, transaction& tx, uint64_t unlock_time);
-  bool construct_tx_and_get_tx_keys(const account_keys& sender_account_keys, const std::vector<tx_source_entry>& sources, const std::vector<tx_destination_entry>& destinations, std::vector<uint8_t> extra, transaction& tx, uint64_t unlock_time, crypto::secret_key &tx_key, std::vector<crypto::secret_key> &amount_keys, bool rct = false);
+  bool construct_tx_and_get_tx_key(const account_keys& sender_account_keys, const std::vector<tx_source_entry>& sources, const std::vector<tx_destination_entry>& destinations, std::vector<uint8_t> extra, transaction& tx, uint64_t unlock_time, crypto::secret_key &tx_key, bool rct = false);
 
   template<typename T>
   bool find_tx_extra_field_by_type(const std::vector<tx_extra_field>& tx_extra_fields, T& field)