WhatsApp implemented the encryption by default on Android OS with the collaboration of the Open Whisper company. The company intends to demonstrate the importance it assigns to user security and privacy, it recently added end-to-end encryption for some mobile clients. The encryption implemented in the WhatsApp client is available only for Android OS and only could be used only for direct messages and not group messages. The WhatsApp Android client does not yet support encrypted messaging for group chat or media messages, but well be rolling out support for those next, in addition to support for more client platforms.”]
Source: https://securityaffairs.co/wordpress/30310/security/whatsapp-implements-encryption.html