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Re: [TLS] Key Hierarchy TLS 1.3 RFC8446(bis)

Hugo Krawczyk <hugo@ee.technion.ac.il> Sun, 17 December 2023 20:05 UTC

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From: Hugo Krawczyk <hugo@ee.technion.ac.il>
Date: Sun, 17 Dec 2023 15:05:03 -0500
Message-ID: <CADi0yUP27w+gcLvfWjn=+EqxfiWebFiyaNa1aUomVai8AUAU5w@mail.gmail.com>
To: Muhammad Usama Sardar <muhammad_usama.sardar@tu-dresden.de>
Cc: tls@ietf.org
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/KSUJywY6WZpnVnLNRf0tpIBXGjk>
Subject: Re: [TLS] Key Hierarchy TLS 1.3 RFC8446(bis)
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See full thread here
https://mailarchive.ietf.org/arch/msg/tls/cS4vdMvENOGdpall7uos9iwZ5OA/

See also how this helped analysis here (search for reference [73]
https://inria.hal.science/hal-01528752v3/file/RR-9040.pdf

On Sat, Dec 16, 2023 at 1:16 PM Muhammad Usama Sardar <
muhammad_usama.sardar@tu-dresden.de> wrote:

> Hi all,
> In the key schedule (section 7.1) of RFC8446(bis), what is the rationale
> for using *Derive-Secret(., "derived", "")* in the derivations of
> Handshake and Master Secrets? Since this change was made in draft 19, I
> expect there should be some reasoning of why this was added. Specifically,
> what are the security implications if this step is missed, i.e.,
>
>    - if Early Secret is directly used as the Salt argument for
>    HKDF-Extract of Handshake Secret;
>    - and similarly if Handshake Secret is directly used as the Salt
>    argument for HKDF-Extract of Master Secret.
>
> Regards,
>
> Usama
>
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