The first trailer for Snowden, the Oliver Stone-directed movie about the NSA leak starring Joseph Gordon-Levitt, has been released online. And like Snowden himself, it appears to play its cards close to its chest.

It is very much a teaser: clocking in at 20 seconds duration, it has no footage of Gordon-Levitt, Shailene Woodley (who plays Snowden’s girlfriend Lindsay Mills) – or in fact anything that resembles a scene from the film itself. Instead we are offered a series of angled shots of the US flag – which reveals itself in the final frames to be upside down. It also features a parody of the pledge of allegiance, written on the white stripes of the flag: “Under surveillance/for liberty/and justice for all.”

Snowden’s story has already been filmed in the Oscar-winning documentary Citizenfour, directed by Laura Poitras. Stone’s film, based on The Snowden Files by Guardian reporter Luke Harding and Time of the Octopus by Anatoly Kucherena, is due for release in the US on Christmas day, 2015.