What is “Android Backup”?
This backup option uses Google’s “Auto Backup for Apps” to periodically create encrypted backups on Google Drive. The following data is saved:
- ID and key pair
- Contacts and verification levels
- Group memberships
- Contact and group images
- All settings
Please note that media files are not saved.
Backups are created about every 24 hours, provided the device is idle and connected to a Wi-Fi network and an external power source. The exact time is determined by the operating system based on various parameters. Threema can’t initiate the backup process. In some cases, it can take several days until a backup is created. There is no way to manually trigger the backup process.
In the “Android Backup” tab, the status is “pending” until the first backup is created; then, date and time of the latest backup will be displayed. To get a list of all backups, open the Google Drive app and navigate to “[side drawer] > Backups > [device name] backup > Apps > Threema”.
Backups are encrypted using NaCl and stored on Google Drive. It’s not possible to store backups in a different location. Since the symmetric key is derived from the password, it’s particularly important to choose a strong password. For more information about encryption, please consult the Cryptography Whitepaper.
If Android’s “Automatic restore” is enabled (in “Settings > Backup & reset”), the latest backup will be automatically restored after the app was installed on a new device (or reinstalled on the current device), provided the same Google account is used. When opening the newly installed app, the user is prompted for the password, and once the correct password is entered, Threema restores the latest backup and restarts.
Differences between “Android Backup” and data backup
When using “Android Backup”, backups will be created on a regular basis without any user interaction, whereas the creation of data backups must be manually triggered by the user. Hence, there is always a current backup available when using “Android Backup”. This is a key advantage of “Android Backup” over data backups. Furthermore, app settings are included in “Android Backups” (but they are not included in data backups). On the other hand, data backups can include media files, while “Android Backups” don’t include media files because Google limits the backup size to 25 MB per app and user.