Hmm, could they use on-the-fly encryption/decryption? That is, use a symmetric cipher to encrypt the stored data on the servers and then do a simple backup of t

Hmm, could they use on-the-fly encryption/decryption? That is, use a symmetric cipher to encrypt the stored data on the servers and then do a simple backup of the data. When you delete your account they would just delete the encryption key. Backing up the encryption key could be done on your side (send you your own encryption key if you need to recover your data).