Re: [TLS] PR#625: Change alert requirements

Martin Thomson <martin.thomson@gmail.com> Sat, 10 September 2016 10:43 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Sat, 10 Sep 2016 20:43:33 +1000
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To: Hannes Tschofenig <hannes.tschofenig@gmx.net>
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Subject: Re: [TLS] PR#625: Change alert requirements
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On 10 September 2016 at 00:35, Hannes Tschofenig
<hannes.tschofenig@gmx.net>; wrote:
> I personally would find it more useful to have an alert saying
> "missing_server_name_extension" instead of just returning
> "missing_extension" for a number of different extensions since this gives
> the client no chance to fix the problem without human intervention.


In this case, this is the only use of missing_extension that would be
due to the extension being optional.  In all other cases,
missing_extension is used for a protocol violation: missing
signature_algorithms, for instance, is always a direct result of
problems that are inherent to the ClientHello.  Thus, a well-behaved
implementation can (currently) infer that this is the reason for
missing_extension.

I wouldn't say that this is a great argument, but it's one that could
be made.  Generally, I've given up on TLS error codes being useful, or
even making them useful; we've been stung in the past by being overly
specific about what went wrong.