Re: [TLS] Draft-22 and Post-Handshake Authentication

Eric Rescorla <ekr@rtfm.com> Tue, 02 January 2018 17:23 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Tue, 2 Jan 2018 09:22:50 -0800
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To: "Short, Todd" <tshort@akamai.com>
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Subject: Re: [TLS] Draft-22 and Post-Handshake Authentication
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Yes, that is correct

On Tue, Jan 2, 2018 at 9:06 AM, Short, Todd <tshort@akamai.com> wrote:

> Question on Post-Handshake Authentication (PHA):
>
> PHA can occur multiple times over a connection. The description for the
> "Handshake Context” is as follows (4.4):
>
>    |           |                            |                          |
>    | Post-     | ClientHello ... client     | client_application_traff |
>    | Handshake | Finished +                 | ic_secret_N              |
>    |           | CertificateRequest         |                          |
>    +-----------+----------------------------+--------------------------+
>
>
> Now, PHA costs of:
>
> S>C: CertificateRequest
>
> followed by:
>
> C>S: Certificate+CertificateVerify+client Finished
>
> This could be interpreted to mean that these PHA messages are included in
> the Handshake Context. However, Section 4.4.1 states:
>
>    For concreteness, the transcript hash is always taken from the
>    following sequence of handshake messages, starting at the first
>    ClientHello and including only those messages that were sent:
>    ClientHello, HelloRetryRequest, ClientHello, ServerHello,
>    EncryptedExtensions, server CertificateRequest, server Certificate,
>
>    server CertificateVerify, server Finished, EndOfEarlyData, client
>    Certificate, client CertificateVerify, client Finished.
>
>
>
> I want to confirm that the PHA handshake context consists only of the
> messages listed in section 4.4.1 from the initial handshake, and do not
> include any of the messages from intermediate PHA exchanges.
>
> Thank you,
>
> --
> -Todd Short
> // tshort@akamai.com
> // "One if by land, two if by sea, three if by the Internet."
>
>
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