Re: [TLS] [Emu] Fwd: Benjamin Kaduk's Discuss on draft-ietf-emu-eap-tls13-13: (with DISCUSS and COMMENT)

Alan DeKok <aland@deployingradius.com> Mon, 01 February 2021 19:55 UTC

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From: Alan DeKok <aland@deployingradius.com>
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Date: Mon, 01 Feb 2021 14:55:26 -0500
Cc: Eric Rescorla <ekr@rtfm.com>, EMU WG <emu@ietf.org>, Benjamin Kaduk <kaduk@mit.edu>, "<tls@ietf.org>" <tls@ietf.org>
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To: Joseph Salowey <joe@salowey.net>
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Subject: Re: [TLS] [Emu] Fwd: Benjamin Kaduk's Discuss on draft-ietf-emu-eap-tls13-13: (with DISCUSS and COMMENT)
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On Feb 1, 2021, at 2:32 PM, Joseph Salowey <joe@salowey.net> wrote:
> 
> 
> 
> On Mon, Feb 1, 2021 at 11:25 AM Alan DeKok <aland@deployingradius.com> wrote:
> On Feb 1, 2021, at 11:26 AM, Eric Rescorla <ekr@rtfm.com> wrote:
> > Yes, this is what I have in mind. So, maybe there's never any need for the server to say "I won't say anything more" after just one round trip?
> 
>   I think so, yes.
> 
>   That means of course EAP-TLS will always require 4.5 round trips.
> 
> [Joe] I don't follow why this means 4.5 round trips would be required.  

  If the CloseNotify signal is sent by the server *after* it receives the client certs, then another round trip is required.  At least, according to Figure 1 of draft-13.

  The CloseNotify can't be sent with the EAP-Success, because the EAP-Success can't carry data.  So the packet flow looks something like this:

   EAP-TLS Peer                                      EAP-TLS Server

                                                        EAP-Request/
                                <--------                  Identity
   EAP-Response/
   Identity (Privacy-Friendly)  -------->
                                                        EAP-Request/
                                                   EAP-Type=EAP-TLS
                                <--------                (TLS Start)
   EAP-Response/
   EAP-Type=EAP-TLS
  (TLS ClientHello)             -------->
                                                        EAP-Request/
                                                   EAP-Type=EAP-TLS
                                                   (TLS ServerHello,
                                            TLS EncryptedExtensions,
                                             TLS CertificateRequest,
                                                    TLS Certificate,
                                              TLS CertificateVerify,
                                <-------            TLS Finished)
   EAP-Response/
   EAP-Type=EAP-TLS
  (TLS Certificate,
   TLS CertificateVerify,
   TLS Finished)                -------->

                                                            EAP-Request/
                                                   EAP-Type=EAP-TLS
                            <--------        (TLS CloseNotify)

   EAP-Response/
   EAP-Type=EAP-TLS
    (TLS Ack)                 -------->
                                <--------               EAP-Success