[collectd] Authentication/Encryption for the network plugin.

[Florian Forster]

Hi,

On Sun, Apr 12, 2009 at 08:41:17PM +0200, Florian Forster wrote:
> Encryption is done without initialization vector (IV) and AES is set
> up to work in cipher-block chaining mode (CBC). When talking with
> Sebastian yesterday we realized that this allows for known plaintext
> attacks if you have the network plugin set up to forward data using
> encryption. So I will probably add a 16 byte IV and possibly rearrange
> the parts a bit.

actually, I didn't think enough. Using an IV doesn't help against known
plaintext attacks. While the use of an IV doesn't prevent an attacker to
use known plaintext attacks, it should prevent chosen plaintext attacks
on the cypher itself, so it's probably a good thing nonetheless.

Currently, the use of an IV is implemented using this layout:
 +-+-+----+-+------+---------+
 !T!L! IV !l! Hash ! Padding !
 +-+-+----+-+------+---------+
           ^^^^^^^^^^^^^^^^^^
  IV == initialization vector (16 bytes)
The part marked with ‘^’ is encrypted. Maybe we could improve the
situation by using no IV and simply encrypt the ‘IV’ field in the
header.

We should think about using a different mode of operation, though:
Output feedback mode (OFB) doesn't require input data to be a multiple
of 16 bytes long, so we could avoid all that padding business. It
results in some opaque buffer length calculations and feels quite error
prone.

Regards,
-octo
-- 
Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
http://verplant.org/
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