ZFS + GELI data integrity

[Pawel Jakub Dawidek]

On Thu, Sep 16, 2010 at 03:22:27PM -0400, Andriy Bakay wrote:
> Hi list(s),
> 
> I am using ZFS on top of GELI. Does exists any practical reason to enable  
> GELI data authentication (data integrity) underneath of ZFS? I understand  
> GELI data integrity is cryptographically strong -- up to HMAC/SHA512, but  
> ZFS has SHA256 checksum. GELI linked data to sector and will detect if  
> somebody move data around, but my understanding is to move data around  
> consistently one need to decrypt it which is very difficult. Correct me if  
> I wrong.
> 
> Any thoughts?

ZFS blocks form z merkle tree (http://en.wikipedia.org/wiki/Hash_tree),
so if you're using cryptographically strong hash, like sha256 within
your pool, I believe it is safe not to use GELI data authentication, but
only encryption. Note, that I'm not cryptographer and this is quite
complex scenario, so what I believe in here might not be true.
Alternatively you could use GELI authetication and turn off ZFS
checksum. When I personally use ZFS on top of GELI, I do just that: GELI
does encryption only and ZFS does authentication with SHA256 checksum.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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