Re: [TLS] Commentary on the client authentication presentation slides

Yoav Nir <ynir.ietf@gmail.com> Mon, 10 August 2015 17:28 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Mon, 10 Aug 2015 20:28:14 +0300
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To: Andrei Popov <Andrei.Popov@microsoft.com>
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Subject: Re: [TLS] Commentary on the client authentication presentation slides
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> On Aug 10, 2015, at 8:10 PM, Andrei Popov <Andrei.Popov@microsoft.com> wrote:
> 
> Hi Ilari,
> 
>> What sort of usecase you have in mind for this?
> This is to support a fairly common website design where the landing page does not require client auth, but subsequent request to a protected resource triggers client authentication within an existing TLS connection.
> In TLS<=1.2, this was accomplished via renegotiation. In TLS1.3, there is no renegotiation, so we need an alternative solution if we want to support these existing sites over TLS1.3.

I’d like to point out that I am very interested in this use case, but I’m not sure that this is the solution.

Such sites were first broken by HTTP/2 which forbade renegotiation. Then they were broken again by TLS 1.3 that does not include renegotiation.

Ideally a solution would work with HTTP/1 over TLS 1.3, HTTP/2 over TLS 1.3, HTTP/2 over TLS 1.2, and for completeness HTTP/1 over TLS 1.2. 

Assuming that HTTP/2 is the HTTP of the future (meaning that relegating these sites to HTTP/1 is a temporary thing), I don’t think that this new mechanism fixes the issue with renegotiation that caused httpbis to reject its usage. We still get a race condition where several requests might be answered before, after or during authentication depending on the timing of the TLS handshake message vs the HTTP messages.

It would be useless IMO to create an alternate renegotiation in TLS only for it to not be used in HTTP/2.

Yoav