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Re: Reasons for AH & ESP
On Fri, 02 Jun 2000, Paul Koning wrote:
> >>>>> "Sankar" == Sankar Ramamoorthi <sankar@nexsi.com> writes:
>
> Sankar> I am not sure if any one is using AH and ESP this way, but
> Sankar> this is one reasoning I was given some time back.
>
> Sankar> RFC 2401 section 4.3 talks about combining security
> Sankar> associations (iterated tunneling). It talks of a case (case
> Sankar> 2) where an end-point could apply ESP with the outer gateway
> Sankar> and AH with a host behind the gateway. Thus the packet could
> Sankar> be authenticated and encrypted over the internet and just
> Sankar> authenticated inside the network behind the gateway allowing
> Sankar> for any traffic analysis.
>
> I think you lose confidentiality doing this, because it leaves the
> packets vulnerable to Steve Bellovin's splicing attack on ESP. To
> defeat that attack, you have to do authentication in the same box that
> does the decryption.
>
Yes, ESP trailer based authentication could be done on the box that does the
decryption (the outer gateway) - though it will be reduntant to do both AH and
ESP authentication. However it still will be useful if one wants encryption and
authentication for traffic on the internet and just authentication on the
inside (though it looks too fancy to me - that seems to be potential use one can
infer from reading 2401).
> paul
--
sankar ramamoorthi
email: sankar@nexsi.com
phone: 408-579-5718 (w)
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