Users who are using the latest beta release of WhatsApp will have the option of enabling the end-to-end encrypted backups feature inside the app’s settings.
Once enabled, the feature offers users a couple of mechanisms to secure their backups. The first involves setting up a password, and the second uses a 64-digit encryption key.
Irrespective of the method you choose, you’ll need the password or the encryption key in order to restore messages from your cloud backup. Since this is end-to-end encryption, the password/encryption key never leaves your devices and WhatsApp will not be able to restore your messages in case you forget/misplace them.
Note however that the end-to-end encrypted backups feature is not yet generally available. Instead, WhatsApp has begun pushing it out to users who’ve opted in to test unreleased versions of the WhatsApp app. There’s also no word on WhatsApp’s plans to extend the feature to iOS devices and cloud platforms like iCloud.