Re: [TLS] Signature Algorithms Extension Clarification

Eric Rescorla <ekr@rtfm.com> Thu, 22 September 2016 12:41 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 22 Sep 2016 05:30:43 -0700
Message-ID: <CABcZeBPScjajGQAe0sST_PTfR-TKCPf5kXSJU-KOg6bvLXJpgg@mail.gmail.com>
To: Hannes Tschofenig <hannes.tschofenig@gmx.net>
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Subject: Re: [TLS] Signature Algorithms Extension Clarification
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On Thu, Sep 22, 2016 at 2:33 AM, Hannes Tschofenig <
hannes.tschofenig@gmx.net>; wrote:

> Hi all,
>
> I need a clarification regarding the use of the signature algorithms.
>
> Reading Section 4.2.3. "Signature Algorithms" I got the impression that
> there is a new extension being defined called 'supported_signature_algorithms',
> which replaces the previous 'signature_algorithm' extension.
>
> The difference between the 'signature_algorithm' extension in RFC 5246 and
> the newly defined 'supported_signature_algorithms' extension is that the
> new extension only contains the digital signature algorithm and not the
> hash function anymore.
>

> If that's indeed the intention I would prefer if the text uses the
> 'supported_signature_algorithms' rather than 'signature_algorithms'.
> (as it is done in Section 4.4.2. "Certificate Verify"). Unfortunately the
> term 'signature_algorithms' is used in many other places in the document
> itself, including the IANA consideration section that makes a reference to
> RFC 5246.
>
> Is it correct that the 'supported_signature_algorithms' extension
> replaces the 'signature_algorithm' extension from RFC 5246?
>

Yes and no :)

We've redefined the structure to be "signature and hash and curve in one
code point" but we're just
retconning the existing values and extension code point.

-Ekr


> Ciao
> Hannes
>
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