Handles reset on camera (#495)

A reset made on the camera will rewind the GOP counter
which on the validation side will be detected as an
old SEI. If an old SEI is detected, but the GOP hash
is correct return success.

Co-authored-by: bjornvolcker <bjornvolcker@users.noreply.github.com>

Author: bjornvolcker

lib/src/sv_auth.c

@@ -719,10 +719,18 @@ validate_authenticity(signed_video_t *self, bu_list_item_t *sei)
     num_expected = -1;
   } else if (validation_flags->num_lost_seis < 0) {
     DEBUG_LOG("Found an old SEI. Mark (partial) GOP as not authentic.");
-    remove_sei_association(self->bu_list, sei);
-    sei = NULL;
-    verify_success = verify_hashes_without_sei(self, 0);
-    num_expected = -1;
+    // If the number of lost SEIs is negative it either indicates a re-order of SEIs or
+    // if the signing side reset the session. For the latter case, the GOP hash should be
+    // correct, only the link is off.
+    bool gop_hash_ok = verify_gop_hash(self);
+    if (gop_hash_ok) {
+      verify_success = verify_hashes_with_sei(self, sei);
+    } else {
+      remove_sei_association(self->bu_list, sei);
+      sei = NULL;
+      verify_success = verify_hashes_without_sei(self, 0);
+      num_expected = -1;
+    }
   } else {
     verify_success = verify_hashes_with_sei(self, sei);
   }

tests/check/check_signed_video_auth.c

@@ -1093,8 +1093,6 @@ END_TEST
  */
 START_TEST(camera_reset_on_signing_side)
 {
-  // TODO: Enable when solved
-  return;
   // Generate 2 GOPs
   test_stream_t *list = create_signed_stream("IPPIPPIP", settings[_i]);
   test_stream_check_types(list, "IPPISPPISP");