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Re: [tcpm] Review of draft-ietf-tcpm-tcp-auth-opt-01

Eric Rescorla <ekr@networkresonance.com> Mon, 28 July 2008 17:00 UTC

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Date: Mon, 28 Jul 2008 10:00:26 -0700
From: Eric Rescorla <ekr@networkresonance.com>
To: Adam Langley <agl@imperialviolet.org>
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Cc: tcpm@ietf.org, Joe Touch <touch@isi.edu>
Subject: Re: [tcpm] Review of draft-ietf-tcpm-tcp-auth-opt-01
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At Mon, 28 Jul 2008 09:48:11 -0700,
Adam Langley wrote:
> 
> On Mon, Jul 28, 2008 at 9:42 AM, Eric Rescorla <ekr@networkresonance.com> wrote:
> > It depends what you mean by rekeying. If it involves a new protocol
> > exchange it is incredibly painful. If you mean just running the kdf
> > again, I agree that's fine.
> 
> It would just be rerunning the KDF every 2**31 bytes. I'd suggest
> something along the lines of this:
> 
> For keys k1, k2, k3, ... and a manually configured master key K:
> 
> H(x) is some hash function (say SHA1)
> H2(x) = H(x | "\x00")
> 
> k1 = H2(K)
> k2 = H2(H(K))
> k3 = H2(H(H(k)))
> ...

Obviously there are a number of ways to do this. I think I would
prefer to use an ESN, but I agree this would work.

-Ekr
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