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.

1 files changed, 18 insertions, 1 deletions

diff --git a/src/cryptonote_basic/cryptonote_basic.h b/src/cryptonote_basic/cryptonote_basic.h
index 4ae29281a..127958796 100644
--- a/src/cryptonote_basic/cryptonote_basic.h
+++ b/src/cryptonote_basic/cryptonote_basic.h
@@ -74,6 +74,7 @@ namespace cryptonote
     crypto::hash hash;
   };
 
+  // outputs <= HF_VERSION_VIEW_TAGS
   struct txout_to_key
   {
     txout_to_key() { }
@@ -81,6 +82,19 @@ namespace cryptonote
     crypto::public_key key;
   };
 
+  // outputs >= HF_VERSION_VIEW_TAGS
+  struct txout_to_tagged_key
+  {
+    txout_to_tagged_key() { }
+    txout_to_tagged_key(const crypto::public_key &_key, const crypto::view_tag &_view_tag) : key(_key), view_tag(_view_tag) { }
+    crypto::public_key key;
+    crypto::view_tag view_tag; // optimization to reduce scanning time
+
+    BEGIN_SERIALIZE_OBJECT()
+      FIELD(key)
+      FIELD(view_tag)
+    END_SERIALIZE()
+  };
 
   /* inputs */
 
@@ -137,7 +151,7 @@ namespace cryptonote
 
   typedef boost::variant<txin_gen, txin_to_script, txin_to_scripthash, txin_to_key> txin_v;
 
-  typedef boost::variant<txout_to_script, txout_to_scripthash, txout_to_key> txout_target_v;
+  typedef boost::variant<txout_to_script, txout_to_scripthash, txout_to_key, txout_to_tagged_key> txout_target_v;
 
   //typedef std::pair<uint64_t, txout> out_t;
   struct tx_out
@@ -562,6 +576,7 @@ VARIANT_TAG(binary_archive, cryptonote::txin_to_key, 0x2);
 VARIANT_TAG(binary_archive, cryptonote::txout_to_script, 0x0);
 VARIANT_TAG(binary_archive, cryptonote::txout_to_scripthash, 0x1);
 VARIANT_TAG(binary_archive, cryptonote::txout_to_key, 0x2);
+VARIANT_TAG(binary_archive, cryptonote::txout_to_tagged_key, 0x3);
 VARIANT_TAG(binary_archive, cryptonote::transaction, 0xcc);
 VARIANT_TAG(binary_archive, cryptonote::block, 0xbb);
 
@@ -572,6 +587,7 @@ VARIANT_TAG(json_archive, cryptonote::txin_to_key, "key");
 VARIANT_TAG(json_archive, cryptonote::txout_to_script, "script");
 VARIANT_TAG(json_archive, cryptonote::txout_to_scripthash, "scripthash");
 VARIANT_TAG(json_archive, cryptonote::txout_to_key, "key");
+VARIANT_TAG(json_archive, cryptonote::txout_to_tagged_key, "tagged_key");
 VARIANT_TAG(json_archive, cryptonote::transaction, "tx");
 VARIANT_TAG(json_archive, cryptonote::block, "block");
 
@@ -582,5 +598,6 @@ VARIANT_TAG(debug_archive, cryptonote::txin_to_key, "key");
 VARIANT_TAG(debug_archive, cryptonote::txout_to_script, "script");
 VARIANT_TAG(debug_archive, cryptonote::txout_to_scripthash, "scripthash");
 VARIANT_TAG(debug_archive, cryptonote::txout_to_key, "key");
+VARIANT_TAG(debug_archive, cryptonote::txout_to_tagged_key, "tagged_key");
 VARIANT_TAG(debug_archive, cryptonote::transaction, "tx");
 VARIANT_TAG(debug_archive, cryptonote::block, "block");