Re: AES MAC security question

From: Rein Anders Apeland (apeland_at_mivu.no)
Date: 07/04/05 

Date: Mon, 04 Jul 2005 00:46:40 +0200

On Sun, 2005-07-03 at 22:20 +0000, Mike Amling wrote:

<snip>
> > I am planning on using AES for generating the MAC, since for other
> > reasons the transmitter software already implements AES for other
> > puproses, and I cannot affort an increase in code size for adding
> > e.g. a secure hash algorithm for use as a MAC.
> >
> > Since the RF packet is so small that it fits inside one AES block,
> > I am thinking of padding the packet to full 128 bits, encrypt it
> > and then truncate the result to e.g. 32 bits and use that as a MAC.
> > Bacause of the low bandwidth of the system, I believe truncating is
> > ok in this case.
>
> What protects against a man-in-the-middle attack?

Could you give some examples? I do not claim to be a crypto-expert,
but would like a discussion on my planned solution. :D

<snip>

> >
> > And finally, if you want to know, all fobs have different encryption
> > keys, and the receiver/car has a list of ID/key pairs of accepted fobs.
>
> Is your method of adding a new remote-keyless-entry-key for a
> receiver/car better than the current method for getting a conventional
> remote to work on a particular car?
>

Currently, I am thinking of requiring a physical connection for
adding new keys. This operation could very well be restricted to
be performed by service personnell only. Do you have other
suggestions? I would like other perspectives than my own here. :D 

-- 
Mvh / Regards
Rein Anders Apeland
MIVU Solutions

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