Re: [TLS] Confirming consensus about one

Martin Rex <mrex@sap.com> Thu, 28 January 2010 14:56 UTC

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From: Martin Rex <mrex@sap.com>
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To: ynir@checkpoint.com (Yoav Nir)
Date: Thu, 28 Jan 2010 15:56:47 +0100 (MET)
In-Reply-To: <02F6A83D-6FE0-4095-8523-A91C95BE1481@checkpoint.com> from "Yoav Nir" at Jan 28, 10 07:40:03 am
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Cc: DPKemp@missi.ncsc.mil, tls@ietf.org
Subject: Re: [TLS] Confirming consensus about one
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Yoav Nir wrote:
> 
> A new version of TLS (4.0?  It's time to stop explaining that
> three-point-one-means-one-point-zero) would have to be certified
> again anyway, so it might as well change the way Finished is
> calculated. Then you don't need either SCSV or RI.
> 
> Of course as long as you support older versions of TLS, you still
> need them, but fully 4.0 handshakes will need neither SCSV nor RI.

I could imagine that a part of the installed base might have an
interop problems with protcol_versions where the major_number
is != 0x03.  (I believe ours does). 

In order to allow servers to perform some plausibility tests on
the initial incoming data of a connection to recognize ClientHellos
and distinguish them from e.g. HTTP GET/PUT/... the protocol_version
at the record layer should IMHO use the lowest(!) protocol_version
acceptable to the client.

I'm also wondering about one thing I encountered not so long ago
during interop tests:  when a Server aborts a handshake while
processing the initial ClientHello on a connection, there seems
to be an uncertainty what protocol_version that alert will
use at the record layer and from which set of available alerts
it will be chosen.

If possible, the protocol_version for that alert (and therefore
the set of avaiable alert numbers) should --if possible-- be chosen
to match a protocol version _not_ exceeding the highest protocol_version
proposed by the client in client_version.  There may be TLS server
implementations that do not account for this yet.


-Martin