Re: [quicwg/base-drafts] Prohibit TLS 1.3 middlebox compatibility mode (#3595)

ekr <notifications@github.com> Fri, 08 May 2020 20:20 UTC

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Date: Fri, 08 May 2020 13:20:30 -0700
From: ekr <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Prohibit TLS 1.3 middlebox compatibility mode (#3595)
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@ekr approved this pull request.



> @@ -213,6 +209,11 @@ own key update mechanism {{key-update}}.
 ~~~
 {: #tls-full title="TLS Handshake with 0-RTT"}
 
+{{tls-full}} omits the EndOfEarlyData message, which is not used in QUIC; see
+{{remove-eoed}}. Likewise, neither ChangeCipherSpec nor KeyUpdate messages are
+used by QUIC. ChangeCipherSpec is redundant in TLS 1.3; see {{compat-mode}}.
+QUIC has its own key update mechanism; see {{key-update}}.

Worth noting that it's not possible to send CCS anywya?

> @@ -1631,6 +1632,21 @@ PROTOCOL_VIOLATION.
 As a result, EndOfEarlyData does not appear in the TLS handshake transcript.
 
 
+## Prohibit TLS Middlebox Compatibility Mode {#compat-mode}
+
+Appendix D.4 of {{!TLS13}} describes an alteration to the TLS 1.3 handshake as
+a workaround for bugs in some middleboxes. The TLS 1.3 middlebox compatibility
+mode involves setting the legacy_session_id field to a 32-byte value in the
+ClientHello and ServerHello, then sending a change_cipher_spec record. Both
+field and record carry no semantic content and are ignored.
+
+This mode has no use in QUIC as it only applies to middleboxes that interfere
+with TLS over TCP. A client MUST NOT request the use of the TLS 1.3
+compatibility mode. A server SHOULD treat the receipt of a TLS ClientHello that
+requests the use of the TLS 1.3 middlebox compatibility mode as a connection

```suggestion
with a non-empty legacy_session_id field as a connection
```

> @@ -1631,6 +1632,21 @@ PROTOCOL_VIOLATION.
 As a result, EndOfEarlyData does not appear in the TLS handshake transcript.
 
 
+## Prohibit TLS Middlebox Compatibility Mode {#compat-mode}
+
+Appendix D.4 of {{!TLS13}} describes an alteration to the TLS 1.3 handshake as
+a workaround for bugs in some middleboxes. The TLS 1.3 middlebox compatibility
+mode involves setting the legacy_session_id field to a 32-byte value in the
+ClientHello and ServerHello, then sending a change_cipher_spec record. Both
+field and record carry no semantic content and are ignored.
+
+This mode has no use in QUIC as it only applies to middleboxes that interfere
+with TLS over TCP. A client MUST NOT request the use of the TLS 1.3
+compatibility mode. A server SHOULD treat the receipt of a TLS ClientHello that
+requests the use of the TLS 1.3 middlebox compatibility mode as a connection

This way you don't need to dig into D.4 to see what the signal is.

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