It's almost four years since Edward Snowden leaked U.S. National Security Agency documents revealing the extent of the organization's surveillance of global internet traffic, but he's still making the headlines in Germany. At the Cebit trade show in Hannover, Germany, he'll be looking back at that period in live video interview from Moscow on Tuesday evening. There have been a lot of changes on the internet in those four years, but one of the biggest is the growth in the use of encryption. In 2013, the NSA had free rein and could listen in on almost any communication it wanted. And you don't have to be an enemy of the state to use an end-to-end encrypted messaging system such as WhatsApp simply to chat with friends.