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Re: [TLS] Last Call: draft-ietf-tls-renegotiation - deployment in

Nelson B Bolyard <nelson@bolyard.me> Mon, 07 December 2009 00:21 UTC

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Subject: Re: [TLS] Last Call: draft-ietf-tls-renegotiation - deployment in
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On 2009-12-05 20:19 PST, Marsh Ray wrote:
> (The quoting got too much for me, check archives for thread context.)
> 
> The language in the TLS 1.0 and 1.1 specs is something like:
> 
>> TLS versions 1.1 and 1.0, and SSL 3.0 are very similar; thus,
>> supporting both is easy.  TLS clients who wish to negotiate with such
>> older servers SHOULD ...
> 
> Notice the conditional SHOULD there. It seems to support the view that
> successful negotiation with an SSLv3 server (especially a broken one)
> is not considered a MUST for a conformant TLS implementation.

Right, ESPECIALLY not a broken one.

> What if we adapt the proposed language thusly:
> 
> Clients that wish to be compatible with the maximum number of older
> servers (including SSLv3 servers not supporting TLS), SHOULD signal
> using the special TLS cipher suite value rather than including an
> extension on the initial Client Hello. 

Not "rather than", but "in addition to".  "Rather than" mandates fallback.

> (Note that this does not apply to
> any subsequent Client Hello messages sent.) Any such client MUST be
> prepared to receive in response a Server Hello message of any negotiable
> version (subject to the usual rules) which contains the extension.
> Clients are not required to offer support back to SSLv3, but if they do,
> they MUST implement the behaviors described in this specification.
> 
> - Marsh

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