Disclaimer: I haven’t tried this system personally. I’m not sure that there is anything out there that isn’t “crackable” by our government overlords. The fact that it was used by Greenwald and Snowden for so long lends credence that it did work. Even if they can’t crack it, doesn’t mean that they can’t recognize that you are using it. It might draw attention to you because they can’t read it.
Tails — which is described by its developers as “privacy for anyone anywhere” — has been around since 2009 and has received the Mozilla Open Source Support Award (2016), the Access Innovation Prize (2014), and the OpenITP award (2013). More importantly, it has been used by dissidents in oppressive nations, activists who feel the need to remain anonymous, whistleblowers, and investigative journalists. In fact, the three journalists most involved in the Snowden revelations all used Tails when communicating with him about NSA surveillance. Snowden insisted on it. In April 2014, Freedom of the Press Foundation reported that Laura Poitras, Glenn Greenwald, and Barton Gellman all told the foundation that Tails was instrumental in allowing them to communicate with Snowden about NSA surveillance while avoiding the very surveillance they were preparing to report on. Read more here.