Re: [Sip] Using TLS in the first hop - Bug in RFC 5630

Iñaki Baz Castillo <> Thu, 15 September 2011 13:36 UTC

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Date: Thu, 15 Sep 2011 15:38:44 +0200
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From: =?UTF-8?Q?I=C3=B1aki_Baz_Castillo?= <>
To: "Olle E. Johansson" <>
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Subject: Re: [Sip] Using TLS in the first hop - Bug in RFC 5630
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2011/9/15 Olle E. Johansson <>et>:
>> As a personal comment, I would like to say that nobody understands the
>> usage of "sips" schema, just nobody. And the specs do not help.
> With the deprecation of "transport=tls" it becomes even more strange.

AFAIK "transport=tls" has never been deprecated. Instead, it has never
been an standard. Note for example that RFC 3261 says:

      Note that in the SIPS URI scheme, transport is independent of TLS,
      and thus ";transport=tcp" and
      ";transport=sctp" are both valid (although
      note that UDP is not a valid transport for SIPS).  The use of
      "transport=tls" has consequently been deprecated, partly because
      it was specific to a single hop of the request.  This is a change
      since RFC 2543.

"A change since RFC 2543"?? transport=tls has never been defined in
RFC 2543. Check yourself:

> We should really spend some time on a "hitch hikers guide to SIP with TLS" and write an RFC to reinstate transtport=tls, which is what we all use.

Or spend some time in a new draft that *correctly* explains how to use
TLS in the first hop (without requiring security in the whole path).
This is *very* easy:

As I've explained in my first mail:

  Via: SIP/2.0/TLS
  Contact: sips:alice@;transport=tcp

That's all. Just:
- Set TLS in Via transport.
- Use "sip" schema in every URI.
- But use "sips" schema in Contact URI.

And it works.

Iñaki Baz Castillo