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Re: [TLS] Enforcing stronger server side signature/hash combinations in TLS 1.2

Eric Rescorla <ekr@rtfm.com> Fri, 24 March 2017 13:01 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 24 Mar 2017 06:00:29 -0700
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Subject: Re: [TLS] Enforcing stronger server side signature/hash combinations in TLS 1.2
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On Thu, Mar 23, 2017 at 10:23 PM, Viktor Dukhovni <ietf-dane@dukhovni.org>
wrote:

>
> > On Mar 24, 2017, at 1:08 AM, Martin Thomson <martin.thomson@gmail.com>
> wrote:
> >
> >> I've never seen
> >> a TLS server that has multiple chains to choose from for the same
> >> server identity.
>
> Both chains of course use SHA256.
>

I am too lazy to check if it's still true but at least for a while
https://www.mozilla.org/
had both a SHA-1 and a SHA-256 certificate so that we could serve Firefox to
people on very downrev browsers (e.g., XP).

-Ekr


> Sorry I meant to say multiple digest algorithms for otherwise
> identical chains (same public key algorithm and server name).
>
> Even in the SMTP space some servers have both RSA and ECDSA certs.
> When that's the case, cipher negotiation ensures that the selected
> EE certificate's public key algorithm is mutually supported.
>
> There's still little need to pay attention to the client's signature
> algorithms in choosing the EE-certificate and associated chain.
>
> --
> --
>         Viktor.
>
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