In the four or so years since it launched, end-to-end encrypted messaging app Signal has become the security community's gold standard for surveillance-resistant communications. Its creators have built an encryption protocol that companies from WhatsApp to Facebook Messenger to Skype have all added to their own products to offer truly private conversations to billions of people.

Get in-depth coverage of current and future trends in technology, and how they are shaping business, entertainment, communications, science, politics, and society.