linux-ext4 - Re: [PATCH] fscrypt: add a documentation file for filesystem-level encryption

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Message-ID: <20170822170720.GA9587@gmail.com>
Date:   Tue, 22 Aug 2017 10:07:20 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     Anand Jain <anand.jain@...cle.com>
Cc:     linux-fscrypt@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Richard Weinberger <richard@....at>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH] fscrypt: add a documentation file for filesystem-level
 encryption

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