NullKey 
Before changing phones
On the old phone, unlock NullKey and open Settings, then choose “Create encrypted backup”. Save the file with Android’s document picker. Wait for NullKey’s read-back check to say the backup was saved and checked. Keep the matching passphrase or recovery key separately from the backup. Follow the backup creation and read-back steps first, and read which secret belongs to the backup. NullKey’s encrypted backup workflow is also described here.
Install and choose Restore
Install the current NullKey app from Google Play on the new phone. Open it to the welcome screen and choose Restore. Android’s document picker opens; select the backup file you copied to a destination available on the new device.
Unlock the backup and inspect the vault
Enter the passphrase or recovery key used for that backup. Restore authenticates the archive before installing it and requires that no vault already exists on the new phone. Unlock the restored vault and check several photos, files and notes. Restoring turns off optional biometric, screen-lock and pattern unlock settings; set those up again only after confirming the vault works.
Keep the old phone until you are sure
Do not uninstall NullKey or clear its storage on the old phone. Keep the verified backup and its matching secret until you have checked the new vault and made a fresh backup. After restoring with the passphrase, unlock the vault and save the new recovery key when prompted. It replaces the restored vault’s recovery key once you confirm it. Restoring with the recovery key keeps that key. Older backup files are unchanged; keep their matching secrets separately.
Older package IDs need extra care
This flow describes restoring a backup made by the current NullKey app. Earlier Cellar and NullKey package IDs install separately, and compatibility of their old backups with the current Play app has not been verified. Keep the old app and data; contact support with app versions to confirm a path before changing anything.
