WhatsApp encryption: What is it, how does it work and why is the government so worried about it?

Home Secretary Amber Rudd has criticised WhatsApp's use of encryption to protects its users' communications, in the wake of the Westminster terror attack. It has emerged that the attacker, Khalid Masood, sent a WhatsApp message moments before launching his assault, and Ms Rudd accused the Facebook-owned app of providing terrorists with a place to "hide". In the government's line of fire is end-to-end encryption, a security technique designed to keep users' data private, which Ms Rudd described as "completely unacceptable" while speaking on the BBC's Andrew Marr Show. WhatsApp added end-to-end encryption to all of its messages in April 2016, enabling it by default on all conversations. "From now on when you and your contacts use the latest version of the app, every call you make, and every message, photo, video, file, and voice message you send, is end-to-end encrypted by default, including group chats," it said at the time.