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: > >On Tue, Aug 22, 2017 at 11:33:51PM +0800, Anand Jain wrote: > >> > >> > >>On 08/22/2017 10:55 AM, Eric Biggers wrote: > >>>On Tue, Aug 22, 2017 at 10:22:30AM +0800, Anand Jain wrote: > >>>> > >>>>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
