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List: ietf-tls
Subject: Re: [TLS] ServerHello extensions
From: R du Toit <r () nerd ! ninja>
Date: 2018-01-18 22:06:59
Message-ID: D35AD71E-5FEE-470F-BD57-3FC84769E612 () nerd ! ninja
[Download RAW message or body]
https://github.com/tlswg/tls13-spec/pull/1143
From: Eric Rescorla <ekr@rtfm.com>
Date: Thursday, January 18, 2018 at 1:25 PM
To: R du Toit <r@nerd.ninja>
Cc: "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] ServerHello extensions
Thanks. These are good points. I would welcome a PR.
On Thu, Jan 18, 2018 at 10:21 AM, R du Toit <r@nerd.ninja> wrote:
Issue#1: Section "4.1.3 Server Hello" currently states:
extensions A list of extensions. The ServerHello MUST only include extensions which \
are required to establish the cryptographic context. Currently the only such \
extensions are "key_share" and "pre_shared_key". All current TLS 1.3 ServerHello \
messages will contain one of these two extensions, or both when using a PSK with \
(EC)DHE key establishment. The remaining extensions are sent separately in the \
EncryptedExtensions message.
"supported_versions" should be added to the list of required extensions for a session \
that negotiates TLS 1.3.
Issue#2: Section "4.1.4 Hello Retry Request" currently states:
Upon receiving the ServerHello, clients MUST check that the cipher suite supplied in \
the ServerHello is the same as that in the HelloRetryRequest and otherwise abort the \
handshake with an "illegal_parameter" alert.
There is no rule about checking that SH.supported_versions.selected_version matches \
HRR.supported_versions.selected_version. I am currently adding draft 23 support, \
and want to enforce that rule to make sure the protocol state machine does not have \
to jump back and forth between TLS 1.2 and TLS 1.3.
I can add a PR for both issues, if you agree.
--Roelof
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style='font-size:11.0pt;font-family:Calibri'><a \
href="https://github.com/tlswg/tls13-spec/pull/1143">https://github.com/tlswg/tls13-spec/pull/1143</a><o:p></o:p></span></p><p \
class=MsoNormal><span \
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class=MsoNormal style='margin-left:.5in'><b><span \
style='font-family:Calibri;color:black'>From: </span></b><span \
style='font-family:Calibri;color:black'>Eric Rescorla \
<ekr@rtfm.com><br><b>Date: </b>Thursday, January 18, 2018 at 1:25 PM<br><b>To: \
</b>R du Toit <r@nerd.ninja><br><b>Cc: </b>"tls@ietf.org" \
<tls@ietf.org><br><b>Subject: </b>Re: [TLS] ServerHello \
extensions<o:p></o:p></span></p></div><div><p class=MsoNormal \
style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal \
style='margin-left:.5in'>Thanks. These are good points. I would welcome a \
PR.<o:p></o:p></p></div><div><p class=MsoNormal \
style='margin-left:.5in'><o:p> </o:p></p><div><p class=MsoNormal \
style='margin-left:.5in'>On Thu, Jan 18, 2018 at 10:21 AM, R du Toit <<a \
href="mailto:r@nerd.ninja" target="_blank">r@nerd.ninja</a>> \
wrote:<o:p></o:p></p><blockquote style='border:none;border-left:solid #CCCCCC \
1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><div><div><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'>Issue#1: \
Section "4.1.3 Server Hello" currently states:<o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'><i>extensions \
A list of extensions. The ServerHello MUST only include extensions which are required \
to establish the cryptographic context. Currently the only such extensions are \
“key_share” and “pre_shared_key”. All current TLS 1.3 \
ServerHello messages will contain one of these two extensions, or both when using a \
PSK with (EC)DHE key establishment. The remaining extensions are sent separately in \
the EncryptedExtensions message.</i><o:p></o:p></p><p class=MsoNormal \
style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'> <o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'>"supported_versions" \
should be added to the list of required extensions for a session that negotiates TLS \
1.3.<o:p></o:p></p><p class=MsoNormal \
style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'> <o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'> <o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'>Issue#2: \
Section "4.1.4 Hello Retry Request" currently states:<o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'><i>Upon \
receiving the ServerHello, clients MUST check that the cipher suite supplied in the \
ServerHello is the same as that in the HelloRetryRequest and otherwise abort the \
handshake with an “illegal_parameter” alert.</i><o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'> <o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'>There \
is no rule about checking that <b>SH.supported_versions.selected_version</b> matches \
<b>HRR.supported_versions.selected_version</b>. I am currently adding \
draft 23 support, and want to enforce that rule to make sure the protocol state \
machine does not have to jump back and forth between TLS 1.2 and TLS \
1.3.<o:p></o:p></p><p class=MsoNormal \
style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'> <o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'>I \
can add a PR for both issues, if you agree.<o:p></o:p></p><p class=MsoNormal \
style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'> <o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'>--Roelof<o:p></o:p></p><p \
class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:.5in'> <o:p></o:p></p></div></div><p \
class=MsoNormal style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:12.0pt;margin-left:.5in'><br>_______________________________________________<br>TLS \
mailing list<br><a href="mailto:TLS@ietf.org">TLS@ietf.org</a><br><a \
href="https://www.ietf.org/mailman/listinfo/tls" \
target="_blank">https://www.ietf.org/mailman/listinfo/tls</a><o:p></o:p></p></blockquote></div><p \
class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div></div></body></html>
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