Encrypt data stored in the cloud
Before sending data to an external storage service, encrypt it (using sufficiently robust encryption) so that it cannot be used in the event of an error or violation of access rights. Encryption replaces the concept of access rights and uses decryption keys, which need to be backed up separately.
Storage in the cloud provides a legal - but not technical - guarantee that the access to files is strictly limited to the data owner. Correct encryption overcomes this potential risk, provided that the cloud provider does not have access to the decryption keys for the files concerned.