Re: AES MAC security question

From: Joseph Ashwood (ashwood_at_msn.com)
Date: 07/07/05 

Date: Thu, 07 Jul 2005 00:51:00 GMT

"Rein Anders Apeland" <apeland@mivu.no> wrote in message
news:1120497172.5120.85.camel@localhost.localdomain...
> On Mon, 2005-07-04 at 00:00 +0000, Andrew Swallow wrote:
> Maybe I am missing something here, but why do I need an IV if
> the packet is smaller than the AES block size? Can't I just
> encrypt it with the shared key? The receiver just decrypts whatever
> packet it gets, and _then_ it can have a look at IDs and counters.

The IVs purpose is to avoid having information leaked due to repeated
sending. In your case there is actually no need for an external one, you
actually have an internal IV in the form of the usage counter. It's a usage
form that has not been significantly studied so may have flaws, but none are
immediately apparent because of the additional restrictions around the
usage.
                    Joe

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