Google automatically backs up some of your phone's data, such as SMS messages (Nexus / Pixel only) and call history, to the cloud. This way, if you need to erase your device or if it is lost / stolen, you will not miss a chance. Android Pie includes changes in the way these backups are stored so that even Google can not read your data.

In his blog on online security, Google revealed that "devices can take advantage of a new feature that saved application data can only be decrypted by a randomly generated key on the client" . The key is based on the password of the lock screen of the user, which is not known to Google. The data is then stored on a Titan security module on one of Google's servers, which constantly blocks access after too many unsuccessful attempts.

To ensure the security of the new backup method, Google has retained the services of the NCC Group security group to perform a full audit. The agency has discovered some problems, but Google says that these have been quickly resolved. The full report is available here.

It's unclear exactly which phones are using this new backup feature, but Android 9 Pie is one of the requirements. At the very least, it is probably safe to assume that Google's Pixel devices use it.