What is End-to-End Encryption?

End-to-end encryption scrambles a message on the sender's device and unscrambles it only on the recipient's, so nobody in between can read it. That includes the company running the service, which carries the message without being able to open it. It protects what you say, not the fact that you said it.

Almost every service already encrypts your messages, so it is worth being precise about what the extra words buy you. With ordinary encryption the company holds a key. That means it can read what you send whenever it chooses to, or whenever a court requires it. End-to-end encryption moves the lock and the key onto the two handsets, the sender's and the recipient's, and the key never leaves them. Everyone in between now carries a sealed package they cannot open, the wifi and the internet provider and the company's own servers alike. What this still does not cover is the outside of the envelope, so who you contacted, when and how often all stay visible. That pattern frequently says more than the words would. It also stops helping the moment a message sits on an unlocked phone, because somebody is then simply reading the screen.

Sending a sealed letter through the post rather than a postcard. The postal service moves both, but it can read the postcard as it goes and cannot read the letter, and that difference is decided when you seal it and not by any promise from the post office. What the post office can always see is the outside: your address, the recipient's, and the date. A stack of envelopes to the same address tells a story even if every letter stays sealed.