For nearly 10 years, WhatsApp’s chat messages have been end-to-end encrypted, meaning they can’t be read by anyone except the sender and the receiver. Drawing on an open-source encryption system developed by Signal, WhatsApp began the move shortly after it was acquired by Facebook in 2014. For the most part, its encryption has been running quietly in the background ever since. There have been legal challenges, but for the world’s largest source of end-to-end encrypted communications, the past de...