Hi Anand,

On Mon, Aug 28, 2017 at 08:18:46PM +0800, Anand Jain wrote:

On 08/23/2017 01:07 AM, Eric Biggers wrote:

quoted

On Tue, Aug 22, 2017 at 11:33:51PM +0800, Anand Jain wrote:

quoted

On 08/22/2017 10:55 AM, Eric Biggers wrote:

quoted

On Tue, Aug 22, 2017 at 10:22:30AM +0800, Anand Jain wrote:

quoted

Hi Eric,

  How about a section on the threat model specific to the file-name ?

  (Sorry if I am missing something).

Thanks, Anand

It's already mentioned that filenames are encrypted: "fscrypt protects the
confidentiality of file contents and filenames in the event of a single
point-in-time permanent offline compromise of the block device content."
There's not much more to it than that; all the other points in the "Threat
model" section (offline manipulations, timing attacks, access control, key
eviction, etc.) are essentially the same between contents and filenames
encryption.

 Do you think if application does not keep the sensitive information
in the file-name, would that remove the file-name from the list of
items that should be protected ?

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.

Eric

 (sorry for the delay in reply due to my vacation).

 It all depends on the use case, Android is one such use case. Some
data center use a known set of application. Again it all depends on
the use case.

 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.

You really need to give more detail about why filename encryption specifically
is a problem.  What "legacy applications" is a problem for, and why?  What do
you mean by a "data center" use case?  Isn't contents encryption a "problem" for
some "legacy applications" as well?  Contents encryption changes filesystem
semantics as well.

 Also a section on backup and restore in this doc will be a good
idea. As I think that will be affected IMO. And needing to have the
user master key to restore encrypted file isn't practical in some
data center multi tenanted solutions. Albeit it may work in some
cases but hard to generalize.

The proposed documentation already mentions that there is no way to backup the
raw ciphertext currently.  I'll try to make this a bit clearer, but in any case
I am documenting the current state of things; the new documentation file is
*not* a plan for things that don't exist yet.  If/when someone proposes a
patchset which adds a backup+restore API they can propose a documentation update
along with it.

Eric