If *no* applications care whether the filenames are encrypted or not, sure.
But are you absolutely sure that no applications care? How do you know? And what
is the advantage of not encrypting the filenames anyway? It is better to
encrypt by default.
File-name is a kind of File-system semantic and altering based on the on
the user key context does not guarantee the system will be compatible with
all their legacy applications.
In theory we could make it optional whether or not file names are
encrypted. But that means extra complexity, and extra complexity
means potential bugs and vulnerabilities --- both potential
implementation bugs, vulnerabilities caused by users getting confused
by how they configure the system settings. So in general with
security systems it's better to limit the complexity to the bare
minimum.
That's right from the dev perspective. But for every security fix
there is a convenience that is being sacrificed by the user. Providing a
security fix even if there is no threat just adds pain to the
user/solution and nothing else. Of course it all depends on the use case.
BTRFS has an experimental fscrypt implementation[1] which does not
include the file-name encryption part it should be included but as an
optional since not all uses cases saves sensitive information in the
file-name. OR even if the attacker is able to identify a file called
secrete.txt and break it then its still points at the weakness of the
file-data encryption. Can we say that ? apparently from the discussion
here it seems the answer is yes.
[1]
Kernel: https://github.com/asj/linux-btrfs-fscryptv1
The only case which you've come up with in terms of potential
vulnerabilities is backup and restore, and backup and restore is
complicated for a number of numbers, since you need to be able to
backup and restore not just the file name and the encrypted data
blocks, but also the encrypted per-file key.
So getting this right
will almost certainly require that the backup/restore software be
fscrypt aware.
Not necessarily, as below..
Hence, making the encryption of the filenames optional doesn't just to
make life easier for backup/restore isn't a compelling argument, since
the backup/restore program is going to have to have special case
handling for fscrypt protected file systems *anyway*.
fscrypt backup and restore does not work even without file-name
encryption because the Extended Attribute needs special ioctl in the
fscrypt (I did rise this objection before).
But its entirely possible to create a string based encryption metadata
which can be updated/retrieved using the legacy backup tools such as
rsync --xattrs
That will be a design for fscryptv2 probably..
OR I mean to say possible optional file-name encryption is not the
ground reason for the encrypted backup and restore challenge.
Thanks, Anand
Cheers,
- Ted
