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Re: STARTTLS & EHLO: Errata text?

2009-01-29 14:12:39

Hi Tony,

Some of the text in this message is from from RFC 3207.

At 09:04 29-01-2009, Tony Hansen wrote:

If we were to write an Errata against RFC 3207, I'd suggest text such as
the following (in Errata format):

Section:
   4.2 Result of the STARTTLS Command

Old text:
   The server MUST discard any knowledge obtained from the client, such
   as the argument to the EHLO command, which was not obtained from the
   TLS negotiation itself.

New text:
   The server MUST discard any knowledge obtained from the client that
   was not obtained from the TLS negotiation itself. The server state
   is otherwise as if the connection had just been opened.

Reason:
   The example is misleading and has lead some people to think that
   knowledge of an EHLO having been sent previously should be
   remembered.

Quoting the entire paragraph from the RFC:

  "Upon completion of the TLS handshake, the SMTP protocol is reset to
   the initial state (the state in SMTP after a server issues a 220
   service ready greeting).  The server MUST discard any knowledge
   obtained from the client, such as the argument to the EHLO command,
   which was not obtained from the TLS negotiation itself.  The client
   MUST discard any knowledge obtained from the server, such as the list
   of SMTP service extensions, which was not obtained from the TLS
   negotiation itself.  The client SHOULD send an EHLO command as the
   first command after a successful TLS negotiation."

Updated text:

   Upon completion of the TLS handshake, the SMTP protocol is reset to
   the initial state (the state in SMTP after a server issues a 220
   service ready greeting).  The server MUST discard any knowledge obtained
   from the client, such as command verbs and their arguments, that was
   not obtained from the TLS negotiation itself.  The client MUST discard any
knowledge obtained from the server, such as the list of SMTP service extensions, which was not obtained from the TLS negotiation itself. As the server state is as when a SMTP session is initiated, the client SHOULD send an EHLO command as the
   first command after a successful TLS negotiation.

New text:
   The client MUST send either an EHLO command or a HELO command as the
   first command after a successful TLS negotiation.

As the two ends are support EHLO, there is no need to have HELO there. I suggest leaving the MUST to the next revision.

Reason:
   Since the state is reset to that of a connection having just been
   opened, the requirement from RFC 5321 applies:

        In any event, a client MUST issue HELO or EHLO before starting a
        mail transaction.

I didn't use MUST for the EHLO because there isn't any restriction on whether the client can only perform mail transactions in RFC 3207 or RFC 5321. In the updated text, it is implied that the client must not forget that the server supports the STARTTLS extension. Do we expressly need to say that? :-)

Section:
   4. The STARTTLS Command

Old text:
   The format for the STARTTLS command is:

   STARTTLS

   with no parameters.

New text:
   The format for the STARTTLS command is:

   STARTTLS

   with no parameters.

   Because the server state machine is reset to an initial connection
   state after negotiating TLS, and any modifications to the server
   state will be lost, the client SHOULD NOT issue any MAIL
   FROM or RCPT TO commands prior to using the STARTTLS command.

Agreed.

Now for the $64k questions:

1) Is there consensus behind this viewpoint?

See updated text.

3) If so, who wants to file the Errata?

You have already volunteered. :-)

Regards,
-sm