Re: Fixing exchange of host keys in the SSH key exchange

Mouse <mouse@Rodents-Montreal.ORG> Tue, 25 April 2017 05:36 UTC

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Date: Mon, 24 Apr 2017 22:55:05 -0400 (EDT)
From: Mouse <mouse@Rodents-Montreal.ORG>
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To: ietf-ssh@netbsd.org
Subject: Re: Fixing exchange of host keys in the SSH key exchange
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References: <201703251227.IAA20189@Stone.Rodents-Montreal.ORG> <2216143EDEE342A3A5C9BB786F7FEF7A@Khan> <1490340148872.12344@cs.auckland.ac.nz>
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Back on March 25th, I wrote (in the thread about making the client tell
the server what host keys it's able to authenticate using, pre-kex)

> Hmm, I think I'll give moussh a configuration option to send things
> before the ID string, for exactly that reason.

I've now done this.  See the -pre-banner command-line option and the
pre-banner config-file variable.

As the manpage notes,

                             Generating a line beginning `SSH-' with this
             mechanism will break the protocol; moussh contains no checks to
             ensure this isn't done.

I'm not sure whether I think this is the Right Thing.  I came down in
favour of this behaviour, but not by much; if anyone cares to argue in
favour of either position (either the above stance or making sure that
doesn't happen), I'd be interested.

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