One document matched: draft-ietf-mmusic-udptl-dtls-08.xml
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<rfc ipr="trust200902" category="std" docName="draft-ietf-mmusic-udptl-dtls-08" obsoletes="" updates="" submissionType="IETF" xml:lang="en">
<front>
<title abbrev="UDPTL over DTLS">
UDP Transport Layer (UDPTL) over Datagram Transport Layer Security (DTLS)
</title>
<author initials="C.H." surname="Holmberg" fullname="Christer Holmberg">
<organization>Ericsson</organization>
<address>
<postal>
<street>Hirsalantie 11</street>
<code>02420</code>
<city>Jorvas</city>
<country>Finland</country>
</postal>
<email>christer.holmberg@ericsson.com</email>
</address>
</author>
<author initials="I.S." surname="Sedlacek" fullname="Ivo Sedlacek">
<organization>Ericsson</organization>
<address>
<postal>
<street>Sokolovska 79</street>
<code>18600</code>
<city>Praha</city>
<country>Czech Republic</country>
</postal>
<email>ivo.sedlacek@ericsson.com</email>
</address>
</author>
<author initials="G.S" surname="Salgueiro" fullname="Gonzalo Salgueiro">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street>7200-12 Kit Creek Road</street>
<city>Research Triangle Park</city>
<region>NC</region>
<code>27709</code>
<country>US</country>
</postal>
<email>gsalguei@cisco.com</email>
</address>
</author>
<date year="2014" />
<area>Transport</area>
<workgroup>MMUSIC Working Group</workgroup>
<keyword>SDP</keyword>
<keyword>SIP</keyword>
<keyword>DTLS</keyword>
<keyword>UDPTL</keyword>
<keyword>fax</keyword>
<keyword>transport</keyword>
<abstract>
<t>
This document specifies how the UDP Transport Layer (UDPTL) protocol,
the predominant transport protocol for T.38 fax, can be transported
over the Datagram Transport Layer Security (DTLS) protocol, how the
usage of UDPTL over DTLS is indicated in the Session Description
Protocol (SDP), and how UDPTL over DTLS is negotiated in a session
established using the Session Initiation Protocol (SIP).
</t>
</abstract>
</front>
<middle>
<section title="Introduction" toc="default">
<t>
While it is possible to transmit highly sensitive documents using
traditional telephony encryption devices, secure fax on the Public
Switched Telephone Network (PSTN) was never widely considered or
prioritized. This was mainly because of the challenges involved
with malevolent physical access to telephony equipment. As real-time
communications transition to IP networks, where information might
potentially be intercepted or spoofed, an appropriate level of
security for fax that offers integrity and confidentiality protection
is vital.
</t>
<t>
The overwhelmingly predominant fax transport protocol is UDPTL-based,
as described in section 9.1 of <xref target="ITU.T38.2010" pageno="false"
format="default" />. The protocol stack for fax transport using UDPTL is
shown in <xref target="figure_UDPTL_UDP_stack" pageno="false" format="default"/>.
</t>
<figure anchor="figure_UDPTL_UDP_stack" title="Protocol stack for UDPTL over UDP">
<artwork><![CDATA[
+-----------------------------+
| Internet facsimile protocol |
+-----------------------------+
| UDPTL |
+-----------------------------+
| UDP |
+-----------------------------+
| IP |
+-----------------------------+
]]></artwork>
</figure>
<t>
The following mechanisms are available for securing fax:
</t>
<t>
<list style="symbols">
<t>
<xref target="ITU.T30.2005" pageno="false" format="default" /> Annex H specifies
a transport protocol-independent application-layer integrity and confidentiality
protection of fax based on the RSA algorithm for use with the T.30 telephony protocol
by Group 3 facsimile equipment (G3FE).
</t>
<t>
<xref target="ITU.T38.2010" pageno="false" format="default" /> specifies fax transport
over RTP/SAVP which enables integrity and confidentiality protection of fax in IP network.
</t>
</list>
</t>
<t>
Both of these mechanisms have been available for many years and never
gained any significant adoption in the market. This has prompted an
effort to develop an open standards-based approach to secure fax
communications over an IP-based transport.
</t>
<t>
Telephony-based protocols like T.30 offer application-level security
options like the RSA-based approached detailed in Annex H of the T.30
specification. The problem is that it is very sparingly implemented
and not enforced at the transport level.
</t>
<t>
It is worth noting that while T.38 over RTP offers a very viable
option for such standards-based IP security solution using SRTP, this
fax over IP transport never gained any traction in the market place
and accounts for a negligible percentage of fax over IP
implementations.
</t>
<t>
Thus, security mechanisms offering integrity and confidentiality
protection should be limited to UDPTL-based fax transport, which is
the only broad-based fax over IP solution. The 3rd Generation
Partnership Project (3GPP) launched a study on how best to provide
secure fax in the IP Multimedia Subsystem (IMS) for UDPTL. Results
of the study confirmed that this security was best achieved by using
UDPTL over DTLS.
</t>
<t>
This document specifies fax transport using UDPTL over DTLS <xref target="RFC6347"
pageno="false" format="default"/>, which enables integrity and confidentiality
protection of fax in IP networks. The protocol stack which enhances fax transport
to offer integrity and confidentiality using UDPTL over DTLS is shown in
<xref target="figure_UDPTL_DTLS_UDP_stack" pageno="false" format="default"/>.
</t>
<figure anchor="figure_UDPTL_DTLS_UDP_stack" title="Protocol stack for UDPTL over DTLS over UDP">
<artwork><![CDATA[
+-----------------------------+
| Internet facsimile protocol |
+-----------------------------+
| UDPTL |
+-----------------------------+
| DTLS |
+-----------------------------+
| UDP |
+-----------------------------+
| IP |
+-----------------------------+
]]></artwork>
</figure>
<t>
The primary motivations for the mechanism in this document are:
<list style="symbols">
<t>
The design of DTLS <xref target="RFC6347" pageno="false" format="default"/> is
clearly defined and well understood and implementations are widely available.
</t>
<t>
No DTLS extensions are required in order to enable UDPTL transport over DTLS.
</t>
<t>
Fax transport using UDPTL over DTLS only requires insertion of the DTLS layer between
the UDPTL layer and the UDP layer, as shown in <xref target="figure_UDPTL_DTLS_UDP_stack"
pageno="false" format="default"/>. The UDPTL layer and the layers above the UDPTL layer
require no modifications.
</t>
<t>
UDPTL <xref target="ITU.T38.2010" pageno="false" format="default" /> is by far the
most widely deployed fax transport protocol in IP networks.
</t>
<t>
3GPP and the IP fax community need a mechanism to transport UDPTL over DTLS in order to
provide secure fax in SIP-based networks (including IMS).
</t>
</list>
</t>
<t>
This document specifies the transport of UDPTL over DTLS using the DTLS record
layer "application_data" packets <xref target="RFC5246" pageno="false" format="default"/>
<xref target="RFC6347" pageno="false" format="default"/>.
</t>
<t>
Since the DTLS record layer "application_data" packet does not indicate whether
it carries UDPTL, or some other protocol, the usage of a dedicated DTLS association
for transport of UDPTL needs to be negotiated, e.g. using the Session Description
Protocol (SDP) <xref target="RFC4566" pageno="false" format="default"/> and the SDP
offer/answer mechanism <xref target="RFC3264" pageno="false" format="default"/>.
</t>
<t>
Therefore, this document specifies a new <proto> value <xref target="RFC4566"
pageno="false" format="default"/> for the SDP media description ("m=" line)
<xref target="RFC3264" pageno="false" format="default"/>, in order to indicate
UDPTL over DTLS in SDP messages <xref target="RFC4566" pageno="false" format="default"/>.
</t>
</section>
<section title="Conventions" toc="default">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted
as described in BCP 14, RFC 2119 <xref target="RFC2119" pageno="false" format="default" />.
</t>
<t>
DTLS uses the term "session" to refer to a long-lived set of
keying material that spans DTLS associations. In this document,
in order to be consistent with SIP/SDP usage of "session" terminology,
we use "session" to refer to a multimedia session and use the term "DTLS session"
to refer to the DTLS construct. We use the term "DTLS association" to refer
to a particular DTLS cipher suite and keying material set that is associated
with a single host/port quartet. The same DTLS session can be used to
establish the keying material for multiple DTLS associations. For
consistency with other SIP/SDP usage, we use the term "connection" when
what's being referred to is a multimedia stream that is not specifically
DTLS.
</t>
</section>
<section title="Secure Channel" toc="default">
<t>
The UDPTL over DTLS media stream is negotiated using the SDP
offer/answer mechanism <xref target="RFC3264" pageno="false"
format="default" />. See <xref target="sec-sdp-of" pageno="false"
format="default" /> for more details.
</t>
<t>
DTLS is used as specified in <xref target="RFC6347" pageno="false"
format="default" />. Once the DTLS handshake is successfully completed
(in order to prevent facsimile data from being transmitted insecurely), the
UDPTL packets MUST be transported in DTLS record layer "application_data"
packets.
</t>
</section>
<section anchor="sec-sdp-of" title="SDP Offerer/Answerer Procedures" toc="default">
<section title="General" toc="default">
<t>
An endpoint (i.e. both the offerer and the answerer) MUST create an SDP
media description ("m=" line) for each UDPTL over DTLS media stream, and
MUST assign a UDP/TLS/UDPTL value (see <xref target="table_SDP_proto_values"
pageno="false" format="default" />) to the "proto" field of the "m=" line.
</t>
<t>
The procedures in this section apply to an "m=" line associated with a UDPTL over DTLS
media stream.
</t>
<t>
In order to negotiate a UDPTL over DTLS media stream, the following SDP attributes are used:
<list style="symbols">
<t>
The SDP attributes defined for UDPTL over UDP, as described in
<xref target="ITU.T38.2010" pageno="false" format="default" />; and
</t>
<t>
The SDP attributes, defined in <xref target="RFC4145" pageno="false"
format="default" /> and <xref target="RFC4572" pageno="false"
format="default" />, as described in this section.
</t>
</list>
</t>
<t>
The endpoint MUST NOT use the SDP "connection" attribute
<xref target="RFC4145" pageno="false" format="default" />.
</t>
<t>
In order to negotiate the TLS roles for the UDPTL over DTLS transport
connection, the endpoint MUST use the SDP "setup" attribute
<xref target="RFC4145" pageno="false" format="default" />.
</t>
<t>
If the endpoint supports, and is willing to use, a cipher suite with an
associated certificate, the endpoint MUST include an SDP "fingerprint" attribute
<xref target="RFC4572" pageno="false" format="default" />. The endpoint MUST support
SHA-256 for generating and verifying the SDP "fingerprint" attribute
value. The use of SHA-256 is preferred.
UPDPTL over DTLS, at a minimum, MUST support TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
and MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256. UDPTL over DTLS MUST
prefer TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and any other Perfect Forward Secrecy
(PFS) cipher suites over non-PFS cipher suites. Implementations SHOULD disable
TLS-level compression.
</t>
<t>
If a cipher suite with an associated certificate is selected during the
DTLS handshake, the certificate received during the DTLS handshake MUST match
the fingerprint received in the SDP "fingerprint" attribute. If the fingerprint
does not match the hashed certificate, then the endpoint MUST tear down the media
session immediately. Note that it is permissible to wait until the other side's
fingerprint has been received before establishing the connection; however, this
may have undesirable latency effects.
</t>
</section>
<section title="Generating the Initial Offer" toc="default">
<t>
The offerer SHOULD assign the SDP "setup" attribute with a value of
"actpass", unless the offerer insists on being either the sender or
receiver of the DTLS ClientHello message, in which case the offerer
can use either a value of "active" (the offerer will be the sender of
ClientHello) or "passive" (the offerer will be the receiver of ClientHello).
The offerer MUST NOT assign an SDP "setup" attribute with a "holdconn"
value.
</t>
<t>
If the offerer assigns the SDP "setup" attribute with a
value of "actpass" or "passive", the offerer
MUST be prepared to receive a DTLS ClientHello message
before it receives the SDP answer.
</t>
</section>
<section title="Generating the Answer" toc="default">
<t>
If the answerer accepts the offered UDPTL over DTLS transport
connection, in the associated SDP answer the answerer MUST assign
an SDP "setup" attribute with a value of either "active" or
"passive", according to the procedures in
<xref target="RFC4145" pageno="false" format="default" />.
The answerer MUST NOT assign an SDP "setup" attribute with a
value of "holdconn".
</t>
<t>
If the answerer assigns an SDP "setup" attribute with a value of
"active" value, the answerer MUST initiate a DTLS handshake by
sending a DTLS ClientHello message on the negotiated media stream,
towards the IP address and port of the offerer.
</t>
</section>
<section title="Offerer Processing of the Answer" toc="default">
<t>
When the offerer receives an SDP answer, if the offerer ends
up being active it MUST initiate a DTLS handshake by
sending a DTLS ClientHello message on the negotiated media
stream, towards the IP address and port of the answerer.
</t>
</section>
<section title="Modifying the Session" toc="default">
<t>
Once an offer/answer exchange has been completed, either
endpoint MAY send a new offer in order to modify the session.
The endpoints can reuse the existing DTLS association if
the key fingerprint values and transport parameters indicated
by each endpoint are unchanged. Otherwise, following
the rules as for the initial offer/answer exchange, the endpoints
can negotiate and create a new DTLS association and, once created,
delete the previous DTLS association, following the same rules
for the initial offer/answer exchange. Each endpoint needs
to be prepared to receive data on both the new and old DTLS associations,
as long as both are alive.
</t>
</section>
</section>
<section title="Miscellaneous Considerations" toc="default">
<section title="Anonymous Calls" toc="default">
<t>
When making anonymous calls, a new self-signed certificate SHOULD be
used for each call and attributes inside the certificate MUST NOT contain
information that either allows correlation or identification of the user making
anonymous calls. This is particularly important for the subjectAltName
and commonName attributes.
</t>
</section>
<section title="NAT Traversal" toc="default">
<section title="ICE Usage" toc="default">
<t>
When ICE <xref target="RFC5245" pageno="false" format="default" /> is being
used, the ICE connectivity checks are performed before the DTLS
handshake begins. Note that if aggressive nomination mode is used,
multiple candidate pairs may be marked valid before ICE finally
converges on a single candidate pair. UAs MUST treat all
ICE candidate pairs associated with a single component as part of the
same DTLS association. Thus, there will be only one DTLS handshake
even if there are multiple valid candidate pairs. Note that this may
mean adjusting the endpoint IP addresses if the selected candidate
pair shifts, just as if the DTLS packets were an ordinary media stream.
In case of an ICE restart, the DTLS handshake procedure is repeated and
a new DTLS association is created. Once the DTLS handshake is completed
,and the new DTLS association has been created, the previous DTLS association
is deleted.
</t>
</section>
<section title="STUN Interaction" toc="default">
<t>
The UA MUST send the STUN packets <xref target="RFC5389" pageno="false" format="default" />
directly over UDP, not over DTLS.
</t>
<t>
The UA MUST support the following mechanism for demultiplexing packets arriving on
the IP address and port associated with the DTLS association:
<list style="symbols">
<t>
If the value of the first byte of the packet is 0 or 1, then the packet is STUN.
</t>
<t>
If the value of the first byte of the packet is between 20 and 63 (inclusive),
the packet is DTLS.
</t>
</list>
</t>
</section>
</section>
<section title="Rekeying" toc="default">
<t>
During rekeying, packets protected by the previous set of keys can
arrive after the DTLS handshake caused by rekeying has completed,
because packets can be reordered on the wire.
To compensate for this fact, receivers MUST maintain both sets of keys
for some time in order to be able to decrypt and verify older packets. The duration
of maintaining the previous set of keys after the finish of the DTLS handshake is
out of scope for this document.
</t>
</section>
<section title="Compatibility With UDPTL over UDP" toc="default">
<t>
If a user requires fax to be transported securely using UDPTL over DTLS, and
if the remote user does not support UDPTL over DTLS, then a fax media stream
cannot be established.
</t>
<t>
If a user prefers fax to be transported securely using UDPTL over DTLS, but is willing
to transport the fax insecurely in case the remote user does not support UDPTL over
DTLS, then the SDP Capability Negotiation mechanism [RFC5939] can be used to offer
both UDPTL over DTLS and UDPTL over UDP. Alternatively, if the remote user rejects
an SDP offer for UDPTL over DTLS, a new SDP offer for a UDPTL over UDP media stream can be sent.
</t>
</section>
</section>
<section anchor="section.sec" title="Security Considerations">
<t>
Fax may be used to transmit a wide range of sensitive data, including
personal, corporate, and governmental information. It is therefore
critical to be able to protect against threats to the confidentiality
and integrity of the transmitted data.
</t>
<t>
The mechanism in this document provides integrity and confidentiality
protection for fax by specifying fax transport using UDPTL over DTLS
<xref target="RFC6347" pageno="false" format="default" />.
</t>
<t>
DTLS media stream negotiated using SIP/SDP requires a mechanism to ensure
that the certificate received via DTLS was issued by the remote
party of the SIP session.
</t>
<t>
The standard DTLS strategy for authenticating the communicating
parties is to give the server (and optionally the client) a PKIX
<xref target="RFC5280" pageno="false" format="default" /> certificate.
The client then verifies the certificate and checks that the name in
the certificate matches the server's domain name. This works because
there are a relatively small number of servers and the cost for issuing
and deploying PKIX certificates can be justified. Issuing and deploying
PKIX certificates to all clients is not realistic in most deployment scenarios.
</t>
<t>
The design described in this document is intended to leverage the
integrity protection of the SIP signaling, while not requiring
confidentiality. As long as each side of the connection can verify
the integrity of the SDP received from the other side, then the DTLS
handshake cannot be hijacked via a man-in-the-middle attack. This
integrity protection is easily provided by the caller to the callee
via the SIP Identity <xref target="RFC4474"
pageno="false" format="default" /> mechanism. Other mechanisms, such as the
S/MIME mechanism <xref target="RFC3261" pageno="false" format="default" />,
or perhaps future mechanisms yet to be specified could also serve this purpose.
</t>
<t>
While this mechanism can still be used without such integrity
mechanisms, the security provided is limited to defense against
passive attack by intermediaries. An active attack on the signaling
plus an active attack on the media plane can allow an attacker to
attack the connection (R-SIG-MEDIA in the notation of <xref target="RFC5479"
pageno="false" format="default" />).
</t>
</section>
<section anchor="section.iana" title="IANA Considerations">
<t>
This document updates the "Session Description Protocol (SDP) Parameters" registry as
specified in Section 8.2.2 of <xref target="RFC4566" pageno="false" format="default"/>.
Specifically, it adds the values in <xref target="table_SDP_proto_values"
pageno="false" format="default"/> to the table for the SDP "proto" field
registry.
</t>
<texttable anchor="table_SDP_proto_values" title='SDP "proto" field values'>
<ttcol align='center'>Type</ttcol>
<ttcol align='center'>SDP Name</ttcol>
<ttcol align='center'>Reference</ttcol>
<c>proto</c>
<c>UDP/TLS/UDPTL</c>
<c>[RFC-XXXX]</c>
</texttable>
<t>
[RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this document.]
</t>
</section>
<section title="Acknowledgments">
<t>
Special thanks to Peter Dawes, who provided comments on the initial version of the draft, and to
Paul E. Jones, James Rafferty, Albrecht Schwarz, Oscar Ohlsson, David Hanes, Adam Gensler, Ari
Keranen, Flemming Andreasen and John Mattsson who provided valuable feedback and input.
Barry Leiba, Spencer Dawkins, Pete Resnick, Kathleen Moriarty and Stephen Farrell provided valuable
feedback during the IESG review. Thanks to Scott Brim for performing the Gen-ART review. Thanks to
Alissa Cooper for her help as sponsoring Area Director.
</t>
</section>
<section title="Change Log">
<t>
[RFC EDITOR NOTE: Please remove this section when publishing]
</t>
<t>
Changes from draft-ietf-mmusic-udptl-dtls-07
<list style="symbols">
<t>Changes based on IESG comments by Barry Leiba:</t>
<t>- SHALL replaced with MUST.</t>
<t>- Text modifications in sections 4.2, 4.4, 5.2.2, 5.3 and 6.</t>
<t>Changes based on IESG comments by Pete Resnick and Kathleen Moriarty:</t>
<t>- Additional text on existing mechanisms for securing fax in section 1.</t>
<t>Changes based on IESG comments by Stephen Farrell:</t>
<t>- Added text regarding MTI cipher suites.</t>
</list>
</t>
<t>
Changes from draft-ietf-mmusic-udptl-dtls-06
<list style="symbols">
<t>Changes based on WGLC comments by Paul Kyzivat</t>
<t>- Indicating that, when a new and an old DTLS association exist, each endpoint needs
to be prepared to receive data on both.</t>
<t>- Editorial nit.</t>
</list>
</t>
<t>
Changes from draft-ietf-mmusic-udptl-dtls-05
<list style="symbols">
<t>Changes based on comments by Flemming Andreasen</t>
<t>- SDP Offer/Answer sections structured according to RFC 3264.</t>
<t>- Clarified that ICE considerations also apply to ICE restart.</t>
<t>- Editorial changes.</t>
</list>
</t>
<t>
Changes from draft-ietf-mmusic-udptl-dtls-04
<list style="symbols">
<t>Changes based on comments by Flemming Andreasen</t>
<t>- Addition of SDP Offer/Answer procedure section.</t>
<t>- Removal of non-ICE NAT traversal procedures.</t>
<t>- Addition of guidance regarding compatibility with UDPTL over UDP.</t>
<t>- Editorial corrections.</t>
<t>Minor editorial corrections</t>
<t>-Spelling of Ari's family name.</t>
</list>
</t>
<t>
Changes from draft-ietf-mmusic-udptl-dtls-03
<list style="symbols">
<t>Changes based on comments by Adam Gensler (http://www.ietf.org/mail-archive/web/mmusic/current/msg12945.html)</t>
<t>-Indicating that, in case of rekeying, entities MUST maintain both set of keys for some time (previously SHOULD).</t>
<t>-Explicit mentioning of the commonName attribute in text about correlation/identification of users.</t>
<t>Changes based on comments by Ari Keranen (http://www.ietf.org/mail-archive/web/mmusic/current/msg12966.html)</t>
<t>-Informative reference to RFC 5246 added.</t>
<t>-Re-naming of sections 4.2.1 and 4.2.2.</t>
<t>-Clarifying that documented STUN/DTLS demux mechanism is only one way of doing the demux.</t>
<t>-Editorial corrections.</t>
</list>
</t>
<t>
Changes from draft-ietf-mmusic-udptl-dtls-02
<list style="symbols">
<t>Editorial comments based on review comments by James Rafferty (http://www.ietf.org/mail-archive/web/mmusic/current/msg12890.html)</t>
<t>Editorial comments based on review comments by David Hanes (http://www.ietf.org/mail-archive/web/mmusic/current/msg12886.html)</t>
<t>Editorial comments based on review comments by Oscar Ohlsson (http://www.ietf.org/mail-archive/web/mmusic/current/msg12882.html)</t>
<t>Editorial comments based on review comments by Albrecht Schwartz (http://www.ietf.org/mail-archive/web/mmusic/current/msg12900.html)</t>
</list>
</t>
<t>
Changes from draft-ietf-mmusic-udptl-dtls-01
<list style="symbols">
<t>Usage of the SDP fingerprint attribute depends on whether a cipher suite with
an associated certificate is used.</t>
<t>Editor's note in section 4.2 removed. Procedure text added.</t>
</list>
</t>
<t>
Changes from draft-ietf-mmusic-udptl-dtls-00
<list style="symbols">
<t>SDP offerer is allowed to assign an a=setup:active or a=setup:passive value, in
addition to the recommended a=setup:actpass (http://www.ietf.org/mail-archive/web/mmusic/current/msg12331.html).</t>
<t>The example for secure fax replacing audio stream in audio-only session
added (http://www.ietf.org/mail-archive/web/mmusic/current/msg12428.html).</t>
<t>Editor's note on the connection attribute resolved by prohibiting usage of the
SDP connection attribute (http://www.ietf.org/mail-archive/web/mmusic/current/msg12772.html).</t>
<t>Editorial corrections.</t>
</list>
</t>
<t>
Changes from draft-holmberg-mmusic-udptl-dtls-02
<list style="symbols">
<t>Milestone adopted - draft-ietf-mmusic version of the draft submitted.</t>
</list>
</t>
<t>
Changes from draft-holmberg-mmusic-udptl-dtls-01
<list style="symbols">
<t>Gonzalo Salgueiro added as co-author.</t>
<t>PSTN comparison text and Introduction text modified.</t>
</list>
</t>
<t>
Changes from draft-holmberg-mmusic-udptl-dtls-00
<list style="symbols">
<t>Text about T.30 added.</t>
<t>Latest version of T.38 referenced.</t>
<t>Additional text about the need for secure fax in IP networks.</t>
</list>
</t>
<t>
Changes from draft-holmberg-dispatch-udptl-dtls-00
<list style="symbols">
<t>WG changed to MMUSIC.</t>
<t>Added text about 3GPP need for UDPTL/DTLS.</t>
</list>
</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.3261"?>
<?rfc include="reference.RFC.3264"?>
<?rfc include="reference.RFC.4145"?>
<?rfc include="reference.RFC.4474"?>
<?rfc include="reference.RFC.4566"?>
<?rfc include="reference.RFC.4572"?>
<?rfc include="reference.RFC.5245"?>
<?rfc include="reference.RFC.5280"?>
<?rfc include="reference.RFC.5389"?>
<?rfc include="reference.RFC.6347"?>
<reference anchor="ITU.T30.2005">
<front>
<title>Procedures for document facsimile transmission in the general switched telephone network</title>
<author>
<organization>International Telecommunications Union</organization>
</author>
<date month="September" year="2005"/>
</front>
<seriesInfo name="ITU-T" value="Recommendation T.30"/>
</reference>
<reference anchor="ITU.T38.2010">
<front>
<title>Procedures for real-time Group 3 facsimile communication over IP networks</title>
<author>
<organization>International Telecommunications Union</organization>
</author>
<date month="September" year="2010"/>
</front>
<seriesInfo name="ITU-T" value="Recommendation T.38"/>
</reference>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.5246"?>
<?rfc include="reference.RFC.5479"?>
<?rfc include="reference.RFC.5939"?>
</references>
<section anchor="section.example" title="Examples">
<section title="General">
<t>
Prior to establishing the session, both Alice and Bob generate self-signed certificates
which are used for a single session or, more likely, reused for multiple sessions.
</t>
<t>
The SIP signaling from Alice to her proxy is transported over TLS to ensure an integrity
protected channel between Alice and her identity service. Alice's identity service asserts
identity of Alice and protects the SIP message, e.g. using SIP Identity. Transport between
proxies should also be protected, e.g. by use of TLS.
</t>
<t>
In order to simplify the flow, only one element is shown for Alice's and Bob's proxies.
</t>
<t>
For the sake of brevity and simplicity, only the mandatory SDP T.38
attributes are shown.
</t>
</section>
<section title="Basic Message Flow">
<t>
<xref target="example_1_figure" pageno="false" format="default" /> shows an example message flow of session
establishment for T.38 fax securely transported using UDPTL over DTLS.
</t>
<t>
In this example flow, Alice acts as the passive endpoint of the DTLS association and Bob acts as
the active endpoint of the DTLS association.
</t>
<t>
<figure anchor="example_1_figure" title="Basic message flow">
<artwork><![CDATA[
Alice Proxies Bob
| (1) SIP INVITE | |
|----------------------->| |
| | (2) SIP INVITE |
| |----------------------->|
| | (3) DTLS ClientHello |
|<------------------------------------------------|
| (4) remaining messages of DTLS handshake |
|<----------------------------------------------->|
| | |
| | |
| | (5) SIP 200 OK |
| |<-----------------------|
| (6) SIP 200 OK | |
|<-----------------------| |
| (7) SIP ACK | |
|------------------------------------------------>|
| (8) T.38 message using UDPTL over DTLS |
|<----------------------------------------------->|
| | |
]]></artwork>
</figure>
</t>
<t>
<list style="hanging">
<t hangText="Message (1):">
<vspace blankLines="1"/>
<xref target="example_1_message_1" pageno="false" format="default" /> shows the initial INVITE request
sent by Alice to Alice's proxy. The initial INVITE request contains an SDP offer.
</t>
<t>
<vspace blankLines="1"/>
The "m=" line in the SDP offer indicates T.38 fax using UDPTL over DTLS.
</t>
<t>
<vspace blankLines="1"/>
The SDP "setup" attribute with a value of "actpass" in the SDP
offer indicates that Alice has requested to be either the active
or passive endpoint.
</t>
<t>
<vspace blankLines="1"/>
The SDP "fingerprint" attribute in the SDP offer contains the
certificate fingerprint computed from Alice's self-signed
certificate.
</t>
<t>
<vspace blankLines="2"/>
</t>
<t>
<figure anchor="example_1_message_1" title="Message (1)">
<artwork><![CDATA[
INVITE sip:bob@example.com SIP/2.0
To: <sip:bob@example.com>
From: "Alice"<sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
Contact: <sip:alice@ua1.example.com>
Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: xxxx
Supported: from-change
v=0
o=- 1181923068 1181923196 IN IP4 ua1.example.com
s=-
c=IN IP4 ua1.example.com
t=0 0
m=image 6056 UDP/TLS/UDPTL t38
a=setup:actpass
a=fingerprint: SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF
]]></artwork>
</figure>
<vspace blankLines="1"/>
</t>
<t hangText="Message (2):">
<vspace blankLines="1"/>
<xref target="example_1_message_2" pageno="false" format="default" /> shows the SIP INVITE request sent by Bob's proxy to Bob.
</t>
<t>
<vspace blankLines="1"/>
When received, Bob verifies the identity provided in the SIP INVITE request.
<vspace blankLines="2"/>
<figure anchor="example_1_message_2" title="Message (2)">
<artwork><![CDATA[
INVITE sip:bob@ua2.example.com SIP/2.0
To: <sip:bob@example.com>
From: "Alice"<sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS proxy.example.com;branch=z9hG4bK-0e53sadfkasldk
Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
Record-Route: <sip:proxy.example.com;lr>
Contact: <sip:alice@ua1.example.com>
Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE
Max-Forwards: 69
Content-Type: application/sdp
Content-Length: xxxx
Supported: from-change
v=0
o=- 1181923068 1181923196 IN IP4 ua1.example.com
s=-
c=IN IP4 ua1.example.com
t=0 0
m=image 6056 UDP/TLS/UDPTL t38
a=setup:actpass
a=fingerprint: SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF
]]></artwork>
</figure>
<vspace blankLines="1"/>
</t>
<t hangText="Message (3):">
<vspace blankLines="1"/>
Assuming that Alice's identity is valid, Bob sends a DTLS ClientHello directly to Alice.
<vspace blankLines="1"/>
</t>
<t hangText="Message (4):">
<vspace blankLines="1"/>
Alice and Bob exchange further messages of DTLS handshake (HelloVerifyRequest, ClientHello,
ServerHello, Certificate, ServerKeyExchange, CertificateRequest, ServerHelloDone, Certificate,
ClientKeyExchange, CertificateVerify, ChangeCipherSpec, Finished).
</t>
<t>
<vspace blankLines="1"/>
When Bob receives the certificate of Alice via DTLS, Bob checks whether the certificate fingerprint
calculated from Alice's certificate received via DTLS matches the certificate fingerprint received
in the a=fingerprint SDP attribute of <xref target="example_1_message_2" pageno="false" format="default" />.
In this message flow, the check is successful and thus session setup continues.
</t>
<t>
<vspace blankLines="1"/>
Note that, unlike in this example, it is not necessary to wait for the DTLS handshake to finish before
the SDP answer is sent. If Bob has sent the SIP 200 (OK) response and later detects that the certificate
fingerprints do not match, he will terminate the session.
<vspace blankLines="1"/>
</t>
<t hangText="Message (5):">
<vspace blankLines="1"/>
<xref target="example_1_message_5" pageno="false" format="default" /> shows a SIP 200 (OK) response to the initial
SIP INVITE request, sent by Bob to Bob's proxy. The SIP 200 (OK) response contains an SDP answer.
</t>
<t>
<vspace blankLines="1"/>
The "m=" line in the SDP answer indicates T.38 fax using UDPTL over DTLS.
</t>
<t>
<vspace blankLines="1"/>
The SDP "setup" attribute with a value of "active" in the SDP
answer indicates that Bob has requested to be the active endpoint.
</t>
<t>
<vspace blankLines="1"/>
The SDP "fingerprint" attribute in the SDP answer contains the
certificate fingerprint computed from Bob's self-signed
certificate.
</t>
<t>
<vspace blankLines="2"/>
</t>
<t>
<figure anchor="example_1_message_5" title="Message (5)">
<artwork><![CDATA[
SIP/2.0 200 OK
To: <sip:bob@example.com>;tag=6418913922105372816
From: "Alice" <sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS proxy.example.com:5061;branch=z9hG4bK-0e53sadfkasldk
Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
Record-Route: <sip:proxy.example.com;lr>
Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE
Contact: <sip:bob@ua2.example.com>
Content-Type: application/sdp
Content-Length: xxxx
Supported: from-change
v=0
o=- 8965454521 2105372818 IN IP4 ua2.example.com
s=-
c=IN IP4 ua2.example.com
t=0 0
m=image 12000 UDP/TLS/UDPTL t38
a=setup:active
a=fingerprint: SHA-1 \
FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF
]]></artwork>
</figure>
<vspace blankLines="1"/>
</t>
<t hangText="Message (6):">
<vspace blankLines="1"/>
<xref target="example_1_message_6" pageno="false" format="default" /> shows a SIP 200 (OK) response
to the initial SIP INVITE request, sent by Alice's proxy to Alice. Alice checks if the certificate
fingerprint calculated from the Bob's certificate received via DTLS is the same as the certificate
fingerprint received in the a=fingerprint SDP attribute of <xref target="example_1_message_6" pageno="false" format="default" />.
In this message flow, the check is successful and thus the session setup continues.
<vspace blankLines="1"/>
</t>
<t>
<figure anchor="example_1_message_6" align="center" title="Message (6)">
<artwork><![CDATA[
SIP/2.0 200 OK
To: <sip:bob@example.com>;tag=6418913922105372816
From: "Alice" <sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
Record-Route: <sip:proxy.example.com;lr>
Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE
Contact: <sip:bob@ua2.example.com>
Content-Type: application/sdp
Content-Length: xxxx
Supported: from-change
v=0
o=- 8965454521 2105372818 IN IP4 ua2.example.com
s=-
c=IN IP4 ua2.example.com
t=0 0
m=image 12000 UDP/TLS/UDPTL t38
a=setup:active
a=fingerprint: SHA-1 \
FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF
]]></artwork>
</figure>
<vspace blankLines="1"/>
</t>
<t hangText="Message (7):">
<vspace blankLines="1"/>
Alice sends the SIP ACK request to Bob.
<vspace blankLines="1"/>
</t>
<t hangText="Message (8):">
<vspace blankLines="1"/>
At this point, Bob and Alice can exchange T.38 fax securely transported using UDPTL over DTLS.
<vspace blankLines="1"/>
</t>
</list>
</t>
</section>
<section title="Message Flow Of T.38 Fax Replacing Audio Media Stream in An Existing Audio-Only Session">
<t>
Traditionally, most sessions with non-secure transport of T.38 fax,
transported using UDPTL, are established by modifying an ongoing
audio session into a fax session. <xref target="example_2_figure"
pageno="false" format="default" /> shows an example message flow of
modifying an existing audio session into a session with T.38 fax
securely transported using UDPTL over DTLS.
</t>
<t>
In this example flow, Alice acts as the passive endpoint of the DTLS association
and Bob acts as the active endpoint of the DTLS association.
</t>
<t>
<figure anchor="example_2_figure" title="Message Flow Of T.38 Fax Replacing Audio Media Stream in An Existing Audio-Only Session">
<artwork><![CDATA[
Alice Proxies Bob
| | |
| (1) Audio-only session initiation |
|<-----------------------+----------------------->|
| | |
| (2) SIP re-INVITE | |
|------------------------------------------------>|
| | (3) DTLS ClientHello |
|<------------------------------------------------|
| (4) remaining messages of DTLS handshake |
|<----------------------------------------------->|
| | |
| | |
| | (5) SIP 200 OK |
|<------------------------------------------------|
| (6) SIP ACK | |
|------------------------------------------------>|
| (7) T.38 message using UDPTL over DTLS |
|<----------------------------------------------->|
| | |
]]></artwork>
</figure>
</t>
<t>
<list style="hanging">
<t hangText="Message (1):">
<vspace blankLines="1"/>
Session establishment of audio-only session. The proxies decide not to record-route.
<vspace blankLines="1"/>
</t>
<t hangText="Message (2):">
<vspace blankLines="1"/>
Alice sends SIP re-INVITE request. The SDP offer included in the SIP re-INVITE
request is shown in <xref target="example_2_message_2" pageno="false" format="default" />.
</t>
<t>
<vspace blankLines="1"/>
The first "m=" line in the SDP offer indicates audio media stream being removed.
The second "m=" line in the SDP offer indicates T.38 fax using UDPTL over DTLS being added.
</t>
<t>
<vspace blankLines="1"/>
The SDP "setup" attribute with a value of "actpass" in the SDP offer indicates
that Alice has requested to be either the active or passive endpoint.
</t>
<t>
<vspace blankLines="1"/>
The SDP "fingerprint" attribute in the SDP offer contains the certificate
fingerprint computed from Alice's self-signed certificate.
</t>
<t>
<vspace blankLines="2"/>
</t>
<t>
<figure anchor="example_2_message_2" title="SDP offer of message (2)">
<artwork><![CDATA[
v=0
o=- 2465353433 3524244442 IN IP4 ua1.example.com
s=-
c=IN IP4 ua1.example.com
t=0 0
m=audio 0 UDP/TLS/RTP/SAVP 0
m=image 46056 UDP/TLS/UDPTL t38
a=setup:actpass
a=fingerprint: SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF
]]></artwork>
</figure>
<vspace blankLines="1"/>
</t>
<t hangText="Message (3):">
<vspace blankLines="1"/>
Bob sends a DTLS ClientHello directly to Alice.
<vspace blankLines="1"/>
</t>
<t hangText="Message (4):">
<vspace blankLines="1"/>
Alice and Bob exchange further messages of DTLS handshake (HelloVerifyRequest,
ClientHello, ServerHello, Certificate, ServerKeyExchange, CertificateRequest,
ServerHelloDone, Certificate, ClientKeyExchange, CertificateVerify,
ChangeCipherSpec, Finished).
</t>
<t>
<vspace blankLines="1"/>
When Bob receives the certificate of Alice via DTLS, Bob checks whether the
certificate fingerprint calculated from Alice's certificate received via
DTLS matches the certificate fingerprint received in the SDP "fingerprint"
attribute of <xref target="example_2_message_2" pageno="false" format="default" />.
In this message flow, the check is successful and thus session setup continues.
<vspace blankLines="1"/>
</t>
<t hangText="Message (5):">
<vspace blankLines="1"/>
Bob sends a SIP 200 (OK) response to the SIP re-INVITE request. The SIP 200 (OK)
response contains an SDP answer shown in <xref target="example_2_message_5" pageno="false" format="default" />.
</t>
<t>
<vspace blankLines="1"/>
The first "m=" line in the SDP offer indicates audio media stream being removed.
The second "m=" line in the SDP answer indicates T.38 fax using UDPTL over DTLS being added.
</t>
<t>
<vspace blankLines="1"/>
The SDP "setup" attribute with a value of "active" in the SDP answer indicates
that Bob has requested to be the active endpoint.
</t>
<t>
<vspace blankLines="1"/>
The SDP "fingerprint" attribute in the SDP answer contains the certificate
fingerprint computed from Bob's self-signed certificate.
</t>
<t>
<vspace blankLines="2"/>
</t>
<t>
<figure anchor="example_2_message_5" title="SDP answer of message (5)">
<artwork><![CDATA[
v=0
o=- 4423478999 5424222292 IN IP4 ua2.example.com
s=-
c=IN IP4 ua2.example.com
t=0 0
m=audio 0 UDP/TLS/RTP/SAVP 0
m=image 32000 UDP/TLS/UDPTL t38
a=setup:active
a=fingerprint: SHA-1 \
FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF
]]></artwork>
</figure>
<vspace blankLines="1"/>
</t>
<t hangText="Message (6):">
<vspace blankLines="1"/>
Alice sends the SIP ACK request to Bob.
<vspace blankLines="1"/>
</t>
<t hangText="Message (7):">
<vspace blankLines="1"/>
At this point, Bob and Alice can exchange T.38 fax securely
transported using UDPTL over DTLS.
<vspace blankLines="1"/>
</t>
</list>
</t>
</section>
</section>
</back>
</rfc>
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