Tighten access permissions of the key directory

debian/tang-common.postinst

@@ -35,6 +35,7 @@ configure)
     # assert db directory
     mkdir -p "$DB_DIR"
     chown _tang:_tang "$DB_DIR"
+    chmod 0750 "$DB_DIR"
 
     ;;
 abort-upgrade|abort-remove|abort-deconfigure)