Right, but clearly I meant that you can't arrange to delete individual files and lose their derived keys. The reason is that the bits you need to derive the ke

Right, but clearly I meant that you can't arrange to delete individual files and lose their derived keys. The reason is that the bits you need to derive the keys may still be somewhere on disk, and one could -having access to the root keys- find them and "undelete" and re-derive the keys and recover the file contents. Having to wipe an entire filesystem to securely delete a file is not useful.