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Re: applying AES-GCM to secure shell: proposed "tweak"



--On Wednesday, April 08, 2009 10:57:49 PM -0500 Nicolas Williams <Nicolas.Williams%sun.com@localhost> wrote:

On Thu, Apr 09, 2009 at 03:51:35PM +1200, Peter Gutmann wrote:
Nicolas Williams <Nicolas.Williams%sun.com@localhost> writes:

> [So far the only extensibility mechanisms that we have at that point
> in the protocol are: new protocol version number (not going to happen)
> and magic algorithm names (which have been used successfully).]

... and the completely unused 32-bit flags field in the first message,
which I mentioned previously :-).

This:

      uint32       0 (reserved for future extension)

?

Yes, that could be used too.

I admit we haven't left ourself much room for pre-keyex negotiation, but there is some. In addition to the bits already mentioned, we can use magic token in the "comments" field of the version banner, and there are also several unused messages in both the transport-generic and algorithm-negotiation layers, which implementations are REQUIRED to ignore except for sending an SSH_MSG_UNIMPLEMENTED (see RFC4253 11.4)

-- Jeff



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