Re: [POSH] Comments/questions on draft-miller-posh-00

[Michael Procter <[e-mail]>]

On 28 July 2013 20:09, Philipp Hancke <[e-mail]> wrote:
> Am 27.07.2013 19:22, schrieb Peter Saint-Andre:
>
>>> Similarly, I can't see anything obviously wrong with letting the
>>> application handshake complete, then performing the POSH
>>> operations before deciding the application connection is not
>>> suitable and should be terminated before being used.  Is the MUST
>>> in this section mandating the order of operations necessary for
>>> some other reason?
>>
>>
>> As mentioned above, the MUST here is perhaps a bit silly because it's
>> so obvious. I think there is a better way to word it...
>
>
> It isn't. In server-to-server XMPP what is typically done is to let the tls
> handshake succeed and only offer sasl external if the peer certificate is
> "valid". The same could be done for POSH... after the handshake is complete,
> look at the verification result. If it is valid, send stream features
> including external; if not, do the POSH dance.

Thanks, Philipp.  That is the sort of scenario I was thinking about,
which is why I questioned the MUST.  Doing the POSH lookup after the
TLS handshake seems fine, as long as the application doesn't try to
use the not-yet-verified connection until POSH completes.  I can't
think of a protocol reason why the TLS handshake must be held off
until POSH completes, unless you wish to withold a client cert until
the server is trusted.  That obviously doesn't apply if you aren't
doing mutual auth.

Regards,

Michael