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.

3 files changed, 36 insertions, 0 deletions

diff --git a/src/serialization/crypto.h b/src/serialization/crypto.h
index 7be04c910..c2a4846ee 100644
--- a/src/serialization/crypto.h
+++ b/src/serialization/crypto.h
@@ -85,6 +85,7 @@ BLOB_SERIALIZER(crypto::secret_key);
 BLOB_SERIALIZER(crypto::key_derivation);
 BLOB_SERIALIZER(crypto::key_image);
 BLOB_SERIALIZER(crypto::signature);
+BLOB_SERIALIZER(crypto::view_tag);
 VARIANT_TAG(debug_archive, crypto::hash, "hash");
 VARIANT_TAG(debug_archive, crypto::hash8, "hash8");
 VARIANT_TAG(debug_archive, crypto::public_key, "public_key");
@@ -92,4 +93,5 @@ VARIANT_TAG(debug_archive, crypto::secret_key, "secret_key");
 VARIANT_TAG(debug_archive, crypto::key_derivation, "key_derivation");
 VARIANT_TAG(debug_archive, crypto::key_image, "key_image");
 VARIANT_TAG(debug_archive, crypto::signature, "signature");
+VARIANT_TAG(debug_archive, crypto::view_tag, "view_tag");
 
diff --git a/src/serialization/json_object.cpp b/src/serialization/json_object.cpp
index e98e327e5..8de5860f6 100644
--- a/src/serialization/json_object.cpp
+++ b/src/serialization/json_object.cpp
@@ -563,6 +563,27 @@ void fromJsonValue(const rapidjson::Value& val, cryptonote::txout_to_key& txout)
   GET_FROM_JSON_OBJECT(val, txout.key, key);
 }
 
+void toJsonValue(rapidjson::Writer<epee::byte_stream>& dest, const cryptonote::txout_to_tagged_key& txout)
+{
+  dest.StartObject();
+
+  INSERT_INTO_JSON_OBJECT(dest, key, txout.key);
+  INSERT_INTO_JSON_OBJECT(dest, view_tag, txout.view_tag);
+
+  dest.EndObject();
+}
+
+void fromJsonValue(const rapidjson::Value& val, cryptonote::txout_to_tagged_key& txout)
+{
+  if (!val.IsObject())
+  {
+    throw WRONG_TYPE("json object");
+  }
+
+  GET_FROM_JSON_OBJECT(val, txout.key, key);
+  GET_FROM_JSON_OBJECT(val, txout.view_tag, view_tag);
+}
+
 void toJsonValue(rapidjson::Writer<epee::byte_stream>& dest, const cryptonote::tx_out& txout)
 {
   dest.StartObject();
@@ -578,6 +599,10 @@ void toJsonValue(rapidjson::Writer<epee::byte_stream>& dest, const cryptonote::t
     {
       INSERT_INTO_JSON_OBJECT(dest, to_key, output);
     }
+    void operator()(cryptonote::txout_to_tagged_key const& output) const
+    {
+      INSERT_INTO_JSON_OBJECT(dest, to_tagged_key, output);
+    }
     void operator()(cryptonote::txout_to_script const& output) const
     {
       INSERT_INTO_JSON_OBJECT(dest, to_script, output);
@@ -616,6 +641,12 @@ void fromJsonValue(const rapidjson::Value& val, cryptonote::tx_out& txout)
       fromJsonValue(elem.value, tmpVal);
       txout.target = std::move(tmpVal);
     }
+    else if (elem.name == "to_tagged_key")
+    {
+      cryptonote::txout_to_tagged_key tmpVal;
+      fromJsonValue(elem.value, tmpVal);
+      txout.target = std::move(tmpVal);
+    }
     else if (elem.name == "to_script")
     {
       cryptonote::txout_to_script tmpVal;
diff --git a/src/serialization/json_object.h b/src/serialization/json_object.h
index e7caa8377..968707165 100644
--- a/src/serialization/json_object.h
+++ b/src/serialization/json_object.h
@@ -230,6 +230,9 @@ void fromJsonValue(const rapidjson::Value& val, cryptonote::txout_to_scripthash&
 void toJsonValue(rapidjson::Writer<epee::byte_stream>& dest, const cryptonote::txout_to_key& txout);
 void fromJsonValue(const rapidjson::Value& val, cryptonote::txout_to_key& txout);
 
+void toJsonValue(rapidjson::Writer<epee::byte_stream>& dest, const cryptonote::txout_to_tagged_key& txout);
+void fromJsonValue(const rapidjson::Value& val, cryptonote::txout_to_tagged_key& txout);
+
 void toJsonValue(rapidjson::Writer<epee::byte_stream>& dest, const cryptonote::tx_out& txout);
 void fromJsonValue(const rapidjson::Value& val, cryptonote::tx_out& txout);