Add view tags to outputs to reduce wallet scanning time

Implements view tags as proposed by @UkoeHB in MRL issue
https://github.com/monero-project/research-lab/issues/73

At tx construction, the sender adds a 1-byte view tag to each
output. The view tag is derived from the sender-receiver
shared secret. When scanning for outputs, the receiver can
check the view tag for a match, in order to reduce scanning
time. When the view tag does not match, the wallet avoids the
more expensive EC operations when deriving the output public
key using the shared secret.

tests/performance_tests/CMakeLists.txt

@@ -43,6 +43,7 @@ set(performance_tests_headers
   generate_keypair.h
   signature.h
   is_out_to_acc.h
+  out_can_be_to_acc.h
   subaddress_expand.h
   range_proof.h
   bulletproof.h

tests/performance_tests/derive_view_tag.h

@@ -0,0 +1,62 @@
+// Copyright (c) 2014-2021, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
+
+#pragma once
+
+#include "crypto/crypto.h"
+#include "cryptonote_basic/cryptonote_basic.h"
+
+#include "single_tx_test_base.h"
+
+class test_derive_view_tag : public single_tx_test_base
+{
+public:
+  static const size_t loop_count = 10000;
+
+  bool init()
+  {
+    if (!single_tx_test_base::init())
+      return false;
+
+    crypto::generate_key_derivation(m_tx_pub_key, m_bob.get_keys().m_view_secret_key, m_key_derivation);
+
+    return true;
+  }
+
+  bool test()
+  {
+    crypto::view_tag view_tag;
+    crypto::derive_view_tag(m_key_derivation, 0, view_tag);
+    return true;
+  }
+
+private:
+  crypto::key_derivation m_key_derivation;
+};

tests/performance_tests/is_out_to_acc.h

@@ -43,8 +43,9 @@ public:
 
   bool test()
   {
-    const cryptonote::txout_to_key& tx_out = boost::get<cryptonote::txout_to_key>(m_tx.vout[0].target);
-    return cryptonote::is_out_to_acc(m_bob.get_keys(), tx_out, m_tx_pub_key, m_additional_tx_pub_keys, 0);
+    crypto::public_key output_public_key;
+    cryptonote::get_output_public_key(m_tx.vout[0], output_public_key);
+    return cryptonote::is_out_to_acc(m_bob.get_keys(), output_public_key, m_tx_pub_key, m_additional_tx_pub_keys, 0);
   }
 };
 

tests/performance_tests/main.cpp

@@ -42,6 +42,7 @@
 #include "cn_slow_hash.h"
 #include "derive_public_key.h"
 #include "derive_secret_key.h"
+#include "derive_view_tag.h"
 #include "ge_frombytes_vartime.h"
 #include "ge_tobytes.h"
 #include "generate_key_derivation.h"
@@ -50,6 +51,7 @@
 #include "generate_keypair.h"
 #include "signature.h"
 #include "is_out_to_acc.h"
+#include "out_can_be_to_acc.h"
 #include "subaddress_expand.h"
 #include "sc_reduce32.h"
 #include "sc_check.h"
@@ -194,6 +196,9 @@ int main(int argc, char** argv)
 
   TEST_PERFORMANCE0(filter, p, test_is_out_to_acc);
   TEST_PERFORMANCE0(filter, p, test_is_out_to_acc_precomp);
+  TEST_PERFORMANCE2(filter, p, test_out_can_be_to_acc, false, true); // no view tag, owned
+  TEST_PERFORMANCE2(filter, p, test_out_can_be_to_acc, true, false); // use view tag, not owned
+  TEST_PERFORMANCE2(filter, p, test_out_can_be_to_acc, true, true); // use view tag, owned
   TEST_PERFORMANCE0(filter, p, test_generate_key_image_helper);
   TEST_PERFORMANCE0(filter, p, test_generate_key_derivation);
   TEST_PERFORMANCE0(filter, p, test_generate_key_image);
@@ -206,6 +211,7 @@ int main(int argc, char** argv)
   TEST_PERFORMANCE0(filter, p, test_sc_check);
   TEST_PERFORMANCE1(filter, p, test_signature, false);
   TEST_PERFORMANCE1(filter, p, test_signature, true);
+  TEST_PERFORMANCE0(filter, p, test_derive_view_tag);
 
   TEST_PERFORMANCE2(filter, p, test_wallet2_expand_subaddresses, 50, 200);
 

tests/performance_tests/out_can_be_to_acc.h

@@ -0,0 +1,103 @@
+// Copyright (c) 2014-2021, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
+
+#pragma once
+
+#include "crypto/crypto.h"
+#include "cryptonote_basic/cryptonote_basic.h"
+
+#include "single_tx_test_base.h"
+
+using namespace crypto;
+
+// use_view_tags: whether to enable view tag checking
+// is_owned: whether the output is owned by us
+template<bool use_view_tags, bool is_owned>
+class test_out_can_be_to_acc : public single_tx_test_base
+{
+  public:
+    static const size_t loop_count = 1000;
+
+    bool init()
+    {
+      if (!single_tx_test_base::init())
+        return false;
+
+      crypto::key_derivation key_derivation;
+      crypto::view_tag vt;
+
+      m_output_index = 0;
+      m_view_secret_key = m_bob.get_keys().m_view_secret_key;
+      m_spend_public_key = m_bob.get_keys().m_account_address.m_spend_public_key;
+
+      cryptonote::get_output_public_key(m_tx.vout[m_output_index], m_output_public_key);
+
+      if (use_view_tags)
+      {
+        crypto::generate_key_derivation(m_tx_pub_key, m_view_secret_key, key_derivation);
+        crypto::derive_view_tag(key_derivation, m_output_index, vt);
+        m_view_tag_opt = vt;
+      }
+      else
+        m_view_tag_opt = boost::optional<crypto::view_tag>();
+
+      return true;
+    }
+
+    bool test()
+    {
+      // include key derivation to demonstrate performance improvement when using view tags
+      crypto::key_derivation key_derivation;
+      crypto::generate_key_derivation(m_tx_pub_key, m_view_secret_key, key_derivation);
+
+      // if using view tags, this ensures we computed the view tag properly
+      if (!cryptonote::out_can_be_to_acc(m_view_tag_opt, key_derivation, m_output_index))
+        return false;
+
+      // if user owns output, this tests the output public key matches the derived
+      if (is_owned)
+      {
+        crypto::public_key output_public_key;
+        crypto::derive_public_key(key_derivation, m_output_index, m_spend_public_key, output_public_key);
+
+        if (m_output_public_key != output_public_key)
+          return false;
+      }
+
+      return true;
+    }
+
+    private:
+      size_t m_output_index;
+      crypto::secret_key m_view_secret_key;
+      crypto::public_key m_spend_public_key;
+      crypto::public_key m_output_public_key;
+      boost::optional<crypto::view_tag> m_view_tag_opt;
+};