[dm-crypt] The future of disk encryption with LUKS2

Arno Wagner arno at wagner.name
Fri Feb 5 16:15:50 CET 2016


On Fri, Feb 05, 2016 at 14:49:38 CET, Zaolin wrote:
> Hi,
> 
> > On Fri, Feb 05, 2016 at 14:13:21 CET, Yves-Alexis Perez wrote:
> > > On ven., 2016-02-05 at 12:02 +0100, Arno Wagner wrote:
> > > > > Think external drives / removable storage?
> > > > 
> > > > An attacker with physical access that you do not notice has 
> > > > won. Storage encryption does not protect here. Think, for 
> > > > example, "evil maid" type attacks. Storage encryption
> > > > is only for theft of the device (which you notice) or 
> > > > attacker access which you notice in other ways.
> > > 
> > > This is exactly why integrity matters? The point is to have an usb
> > > drive /
> > > external disk *fully* encrypted.  The decryption is done by the
> > > host
> > > (which is trusted).  In that case, confidentiality and integrity
> > > are both
> > > important.
> > 
> > No. You are trying to solve the wrong problem. First, disk 
> > encryption with 1:1 mapping will never give you integrity 
> > protection and the other variants kill performance.
> I partially agree. What's about using GCM or CCM mode of operation for
> disk encryption ? ;) In order to solve the evil maid issue you need
> hardware security and a secure boot process.

GCM needs extra storage and so does CCM. The problem is that
a simple entropy-argument shows that integrity protection is
infeasible in the general case without extra storage.

The effect is that unless you want to mess with effective
disk block size (not a good idea), you do not get integrity
protection in block-level disk encryption. On the other hand,
there is a file-level alternative: eCryptFS. It serves somewhat
different needs and has different performance characteristics.
It basically does automated per-file PGP-like encryption. (The 
format is even derived from PGP.) It does have some drawbacks 
though, for example filenames, the filesystem (think evil maid) 
and some metadata and information about file changes are not 
protected.

Regards,
Arno

-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
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