Re: [tcpm] tcp-auth-opt issue: support for NATs

Eric Rescorla <ekr@networkresonance.com> Thu, 07 August 2008 01:08 UTC

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Date: Wed, 06 Aug 2008 18:18:12 -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] tcp-auth-opt issue: support for NATs
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At Wed, 6 Aug 2008 17:42:19 -0700,
Adam Langley wrote:
> 
> On Tue, Aug 5, 2008 at 7:02 PM, Eric Rescorla <ekr@networkresonance.com> wrote:
> > Isn't the whole point of the key-ids to avoid requiring this?
> 
> Well, keyids would be required too. Here's how I see it working.
> 
> Define a synchronisation range, R, say 1 minute. We require that the
> maximum skew between two clocks is R.
> 
> Define a key rotation timespan, T, say 1 minute. Let N be the maximum
> number of keys that exist in a timespan of 2R. In our example, this is
> two.
> 
> Define a function K(master, t) that maps a timestamp to a key derived
> from a master key and a keyid in [0, N). For example, F(master, t) =
> SHA1(master + uint32be (t/T)) with keyid (t/T) `mod` N.
> 
> At any time, a client transmits with key and keyid from F(master,
> currentTime). At any time, the server accepts SYN signed with any
> keyid and key in a span of 2R centered around the current time.
> 
> So one can only connect if one's clock skew is acceptable and one
> knows the master key.
> 
> The keys for the resulting connection would be connection specific,
> probably hashing in the SEQ/ACK numbers, other stuff etc.

I'm sorry, I must be missing something. what problem are you trying to
solve?

-Ekr
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