My understanding is, ignoring implementation details, iOS disk encryption works like this: On boot (and/or every time you unlock your phone) an ephemeral session key is created that can decrypt encrypted files.
My question is, how is it possible to create ephemeral keys, without re-encrypting the files on disk?
The only solution that comes to my mind is use the ephemeral key to decrypt the "real" key that then is used to decrypt the files. And when your session expires and you need to invalidate the ephemeral key basically you delete the encrypted copy of the real key that was encrypted by the ephemeral session key.
Are there any other solutions to this? basically to create ephemeral keys without re-encrypting the data?