diff --git a/tuf/encoding/targets_asn1_coder.py b/tuf/encoding/targets_asn1_coder.py
index 826ed0ecd0..533dedbc37 100644
--- a/tuf/encoding/targets_asn1_coder.py
+++ b/tuf/encoding/targets_asn1_coder.py
@@ -225,12 +225,10 @@ def set_asn_targets(json_signed, targetsMetadata):
         if customkey == 'ecu_serial':
           # ecu_serial field name currently goes from ecu_serial to ecuIdentifier
           custom['ecuIdentifier'] = filemeta['custom'][customkey]
-        # TODO: Include other cases specific to Uptane here (release counter
-        # and hardware identifier.)
-        # elif customkey == 'release_counter':
-        #   pass
-        # elif customkey == 'hardware_identifier':
-        #   pass
+        elif customkey == 'release_counter':
+          custom['releaseCounter'] = filemeta['custom'][customkey]
+        elif customkey == 'hardware_id':
+          custom['hardwareIdentifier'] = filemeta['custom'][customkey]
         else:
           custom[customkey] = filemeta['custom'][customkey] # Will probably break.
 
@@ -360,9 +358,28 @@ def set_json_targets(json_signed, targetsMetadata):
     # Optional bit.
     custom = targetAndCustom['custom']
     if custom:
-      json_custom = {
-        'ecu_serial': str(custom['ecuIdentifier'])
-      }
+      json_custom = dict()
+      for customkey in custom:
+        if customkey == 'ecuIdentifier':
+          # ecu_serial field name currently goes from ecu_serial to ecuIdentifier
+          # try to get enteries corresponding to the various keys in custom metedata
+          # and if the enteries are empty, ignore and move forward
+          # When there are no enteries corresponding to a certain key,
+          # pyasn1 raises an exception.
+          try:
+            json_custom['ecu_serial'] = str(custom[customkey])
+          except:
+            pass
+        elif customkey == 'releaseCounter':
+          try:
+            json_custom['release_counter'] = str(custom[customkey])
+          except:
+            pass
+        elif customkey == 'hardwareIdentifier':
+          try:
+            json_custom['hardware_id'] = str(custom[customkey])
+          except:
+            pass
       filemeta['custom'] = json_custom
 
     json_targets[filename] = filemeta