The WhatsApp privacy policy states: "We also offer end-to-end encryption for our Services, which is on by default, when you and the people with whom you message use a version of our app released after April 2, 2016. End-to-end encryption means that your messages are encrypted to protect against us and third parties from reading them." The service's technical white paper states: "WhatsApp Messenger allows people to exchange messages (including chats, group chats, images, videos, voice messages and files) and make WhatsApp calls around the world WhatsApp messages, voice and video calls between a sender and receiver that use WhatsApp client software released after March 31, 2016 are end-to-end encrypted. The Signal Protocol, designed by Open Whisper Systems, is the basis for WhatsApp’s end-to-end encryption. This end-to-end encryption protocol is designed to prevent third parties and WhatsApp from having plaintext access to messages or calls. What’s more, even if encryption keys from a user’s device are ever physically compromised, they cannot be used to go back in time to decrypt previously transmitted messages."