How the NSA turns back the clock on phone taps without choking on data

National Security Agency documents released by The Washington Post gave a glimpse of an NSA program that allows the agency to capture the voice content of virtually every phone call in an unnamed country and perform searches against the stored calls’ metadata to find and listen to conversations for up to a month after they happened.

Just as the NSA and GCHQ have used Xkeyscore to make it possible to search through torrents of Internet traffic captured by its Turmoil monitoring systems scattered around the world, a system called Retrospective (or Retro) allows analysts to search through phone calls that are up to 30 days old based on call metadata.

Originally developed for the NSA’s Mystic international telephone monitoring effort as a “one-off” capability, Retro may now be used in a number of other countries, scooping up calls that undoubtedly include ones that have nothing to do with the NSA’s foreign intelligence goals.

Of course, whether that capture can be considered monitoring comes down to semantics. In the NSA’s reasoning, it’s not “surveillance” until a human listens in. And since most of the calls accessible by Retrospective are flushed from its “cache” after a month without being queried, the NSA could argue that the calls have never been surveilled.