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Re: [TLS] draft-ietf-tls-tls13-16

Stephen Checkoway <s@pahtak.org> Wed, 28 September 2016 16:18 UTC

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From: Stephen Checkoway <s@pahtak.org>
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Date: Wed, 28 Sep 2016 11:18:45 -0500
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To: "Salz, Rich" <rsalz@akamai.com>
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Cc: "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] draft-ietf-tls-tls13-16
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> On Sep 28, 2016, at 11:08 AM, Salz, Rich <rsalz@akamai.com> wrote:
> 
> 
>> C.2 Negotiating with an older client says, "If the
>>   "supported_versions" extension is present, the server MUST negotiate
>>   the highest server-supported version found in that extension."
> 
> I agree that an appendix is the wrong place to put this.  And that specifying the client order is pointless.
> 
> But I disagree with this being a MUST.  There may be times when the server knows more than the client and will know that a lower version is more appropriate.  E.g., interfering middleboxes or regulatory regimes.

Seems reasonable. How about making selection from the list (if the extension is present) a MUST and selecting the highest server-supported version is RECOMMENDED? Perhaps the second part is unnecessary.

-- 
Stephen Checkoway

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