Facebook begins rolling out opt-in end-to-end encryption for its Messenger service Secret Conversations. The encryption service is not on by default and is available only on one device at a time. Users will have to designate a preferred device for the service, Facebook said. Facebook also published a white paper that delivers technical details and explains how the service is designed to be a device-based interaction. Messages are encrypted with encryption with AES-CBC and authenticated using HMAC-SHA256.
Source: https://threatpost.com/facebook-messenger-end-to-end-encryption-not-on-by-default/119133/