IFF is an acronym for Identification Friend or Foe, a transponder-based system of spacecraft identification, used to distinguish friendly from enemy craft.
Colonial civilian and military ships, such as Vipers and Raptors, also have transponders. The civilian ships likely use civilian transponders used for commercial passenger flight, but are now recognized by Galactica as part of its Fleet. The Blackbird was likely not equipped with a transponder (or the transponder is disabled as part of its function), which almost leads to it being attacked by other Vipers whose pilots mistake its questionable DRADIS signature as a Cylon target after the stealth fighter returns from a reconnaissance mission (Resurrection Ship, Part II).
- Real life IFF systems use an automated and encrypted "question and answer" routine between one aircraft and another. A correct response leads to the questioned aircraft being identified as friendly. In this respect, IFF can be considered a challenge-response authentication system. However, an aircraft not replying is not automatically designated as a foe, since there may be legitimate reasons for that, such as battle damage or outdated encryption keys.
- IFF systems can also be incorporated into missile and or defense systems, preventing them from acquiring friendly and firing on friendly targets and thus prevent friendly fire incidents.