Subject: [MSEC] Re: TESLA comments

From: Mark Baugher <[email-masked]>
Date: Mon, 08 Apr 2002 09:51:43 -0700

Hi Adrian
    I have a comment below.

At 09:22 AM 4/8/2002 -0700, Adrian Perrig wrote:
>Thanks Mark for addressing some of the issues, I am currently also
>traveling. Below are additional comments.
>
> >   So, in this case where data security treatments are externalized
> >   from the receivers, within a gateway, it seems to me that it would
> >   be better, for performance and cost reasons, to provide these
> >   security treatments at IP layer, instead of crossing all the gateway
> >   TCP/IP stack up to the application layer.
> >
> > Security is end-to-end and I think a better security solution is
> > end-to-end rather than using what is essentially a firewall.  A
> > packet-filtering firewall typically operates on the IP or transport
> > headers, but an application firewall operates at the application layer
> > at the cost of increased complexity of the middle box.  That being
> > said, I understand your point but think that TESLA is better suited to
> > the application layer since there is so much buffering that is needed.
>
>The buffering in the network layer is not much different from the
>buffering that TCP performs (in the case a packet did not arrive, TCP
>buffers subsequent data packets).

I think we are in agreement that TESLA should not be performed
at the IP layer, though perhaps at the transport layer.  But I
think that TESLA would be most useful in an SRTP or
AMESP than it would be in AH or ESP.

cheers, Mark

> >   Ran, I do not clearly understand why you mention a TCP hypothesis,
> >   since multicast goes with UDP. See TESLA draft, section 5 (drawbacks
> >   attached to TCP delays) ?
>
>TESLA can also be used in point-to-point authentication. A published
>key of the TESLA keychain acts as a public key, which allows a
>receiver to authenticate any subsequent packets (assuming synchronized
>clocks). The advantage is that if N nodes in a network want to
>authenticate their pairwise communication, you would need n*(n+1)/2
>shared keys, but if you use TESLA, you would only need to distribute n
>public keys.
>
>So if you use TESLA to authenticate point-to-point TCP communication,
>one should put TESLA in the network layer.
>
>Greetings,
>   Adrian

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