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Re: [TLS] Protocol version for inappropriate_fallback alerts

mrex@sap.com (Martin Rex) Sat, 15 November 2014 04:23 UTC

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To: Bodo Moeller <bmoeller@acm.org>
Date: Sat, 15 Nov 2014 05:23:06 +0100
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From: mrex@sap.com
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Cc: Florian Weimer <fweimer@redhat.com>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Protocol version for inappropriate_fallback alerts
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Bodo Moeller wrote:
> Martin Rex <mrex@sap.com>:
> 
>> Creating specification with ambiguities or undefined behaviour,
>> pushing the buck to implementors, is never a good idea.
> 
> Now I am thoroughly confused by what you're saying. A bit earlier you
> argued *against* specifying a MUST for the record-layer version number to
> be used with the inappropriate_fallback alert (as it appears in
> draft-ietf-tls-downgrade-scsv-02), proposing instead a wording that you
> said was "vague on purpose". I can't reconcile that with what you're saying
> here. The only constant theme I can make out is that whatever you're saying
> at a given time is undoubtedly right.


Giving a implementors a guidance by describing the issue at hand
calling for reasonable trade-offs and and recommending, but not mandating
certain behaviour, promotes interop.


Using imperatives where this isn't necessary is not only squarly in
conflict with rfc2119, it will also result in interop failures, because
it gives (some) implementors poor excuses for why their code aborts or
fails interop in a neither useful nor reasonable fashion.


-Martin

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