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, 9 insertions, 1 deletions

diff --git a/tests/crypto/main.cpp b/tests/crypto/main.cpp
index 59a2a7d77..045ffc08d 100644
--- a/tests/crypto/main.cpp
+++ b/tests/crypto/main.cpp
@@ -260,7 +260,6 @@ int main(int argc, char *argv[]) {
         goto error;
       }
     } else if (cmd == "check_ge_p3_identity") {
-      cerr << "Testing: " << cmd << endl;
       public_key point;
       bool expected_bad, expected_good, result_badfunc, result_goodfunc;
       get(input, point, expected_bad, expected_good);
@@ -269,6 +268,15 @@ int main(int argc, char *argv[]) {
       if (expected_bad != result_badfunc || expected_good != result_goodfunc) {
         goto error;
       }
+    } else if (cmd == "derive_view_tag") {
+      key_derivation derivation;
+      size_t output_index;
+      view_tag expected, actual;
+      get(input, derivation, output_index, expected);
+      derive_view_tag(derivation, output_index, actual);
+      if (expected != actual) {
+        goto error;
+      }
     } else {
       throw ios_base::failure("Unknown function: " + cmd);
     }