draft-ietf-mmusic-udptl-dtls-10.txt   rfc7345.txt 
MMUSIC Working Group C. Holmberg Internet Engineering Task Force (IETF) C. Holmberg
Internet-Draft I. Sedlacek Request for Comments: 7345 I. Sedlacek
Intended status: Standards Track Ericsson Category: Standards Track Ericsson
Expires: December 22, 2014 G. Salgueiro ISSN: 2070-1721 G. Salgueiro
Cisco Cisco
June 20, 2014 August 2014
UDP Transport Layer (UDPTL) over Datagram Transport Layer Security UDP Transport Layer (UDPTL)
(DTLS) over Datagram Transport Layer Security (DTLS)
draft-ietf-mmusic-udptl-dtls-10
Abstract Abstract
This document specifies how the UDP Transport Layer (UDPTL) protocol, This document specifies how the UDP Transport Layer (UDPTL) protocol,
the predominant transport protocol for T.38 fax, can be transported the predominant transport protocol for T.38 fax, can be transported
over the Datagram Transport Layer Security (DTLS) protocol, how the over the Datagram Transport Layer Security (DTLS) protocol, how the
usage of UDPTL over DTLS is indicated in the Session Description usage of UDPTL over DTLS is indicated in the Session Description
Protocol (SDP), and how UDPTL over DTLS is negotiated in a session Protocol (SDP), and how UDPTL over DTLS is negotiated in a session
established using the Session Initiation Protocol (SIP). established using the Session Initiation Protocol (SIP).
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on December 22, 2014. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7345.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction ....................................................3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Conventions .....................................................5
3. Secure Channel . . . . . . . . . . . . . . . . . . . . . . . 5 3. Secure Channel ..................................................5
4. SDP Offerer/Answerer Procedures . . . . . . . . . . . . . . . 5 4. SDP Offerer/Answerer Procedures .................................6
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. General ....................................................6
4.2. Generating the Initial Offer . . . . . . . . . . . . . . 6 4.2. Generating the Initial Offer ...............................7
4.3. Generating the Answer . . . . . . . . . . . . . . . . . . 6 4.3. Generating the Answer ......................................7
4.4. Offerer Processing of the Answer . . . . . . . . . . . . 7 4.4. Offerer Processing of the Answer ...........................7
4.5. Modifying the Session . . . . . . . . . . . . . . . . . . 7 4.5. Modifying the Session ......................................7
5. Miscellaneous Considerations . . . . . . . . . . . . . . . . 7 5. Miscellaneous Considerations ....................................8
5.1. Anonymous Calls . . . . . . . . . . . . . . . . . . . . . 7 5.1. Anonymous Calls ............................................8
5.2. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 7 5.2. NAT Traversal ..............................................8
5.2.1. ICE Usage . . . . . . . . . . . . . . . . . . . . . . 7 5.2.1. ICE Usage ...........................................8
5.2.2. STUN Interaction . . . . . . . . . . . . . . . . . . 8 5.2.2. STUN Interaction ....................................8
5.3. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3. Rekeying ...................................................9
5.4. Compatibility With UDPTL over UDP . . . . . . . . . . . . 8 5.4. Compatibility with UDPTL over UDP ..........................9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations .........................................9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. IANA Considerations ............................................10
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 8. Acknowledgments ................................................10
9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 10 9. References .....................................................11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.1. Normative References ......................................11
10.1. Normative References . . . . . . . . . . . . . . . . . . 13 9.2. Informative References ....................................12
10.2. Informative References . . . . . . . . . . . . . . . . . 14 Appendix A. Examples .............................................13
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 14 A.1. General ...................................................13
A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 14 A.2. Basic Message Flow ........................................13
A.2. Basic Message Flow . . . . . . . . . . . . . . . . . . . 15 A.3. Message Flow of T.38 Fax Replacing Audio Media Stream in
A.3. Message Flow Of T.38 Fax Replacing Audio Media Stream in an Existing Audio-Only Session ............................20
An Existing Audio-Only Session . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction 1. Introduction
While it is possible to transmit highly sensitive documents using While it is possible to transmit highly sensitive documents using
traditional telephony encryption devices, secure fax on the Public traditional telephony encryption devices, secure fax on the Public
Switched Telephone Network (PSTN) was never widely considered or Switched Telephone Network (PSTN) was never widely considered or
prioritized. This was mainly because of the challenges involved with prioritized. This was mainly because of the challenges involved with
malevolent physical access to telephony equipment. As real-time malevolent physical access to telephony equipment. As real-time
communications transition to IP networks, where information might communications transition to IP networks, where information might
potentially be intercepted or spoofed, an appropriate level of potentially be intercepted or spoofed, an appropriate level of
security for fax that offers integrity and confidentiality protection security for fax that offers integrity and confidentiality protection
is vital. is vital.
The overwhelmingly predominant fax transport protocol is UDPTL-based, The overwhelmingly predominant fax transport protocol is UDPTL-based,
as described in section 9.1 of [ITU.T38.2010]. The protocol stack as described in Section 9.1 of [ITU.T38.2010]. The protocol stack
for fax transport using UDPTL is shown in Figure 1. for fax transport using UDPTL is shown in Figure 1.
+-----------------------------+ +-----------------------------+
| Internet facsimile protocol | | Internet facsimile protocol |
+-----------------------------+ +-----------------------------+
| UDPTL | | UDPTL |
+-----------------------------+ +-----------------------------+
| UDP | | UDP |
+-----------------------------+ +-----------------------------+
| IP | | IP |
+-----------------------------+ +-----------------------------+
Figure 1: Protocol stack for UDPTL over UDP Figure 1: Protocol Stack for UDPTL over UDP
The following mechanisms are available for securing fax: The following mechanisms are available for securing fax:
o [ITU.T30.2005] Annex H specifies a transport protocol-independent o Annex H of [ITU.T30.2005] specifies an application-layer integrity
application-layer integrity and confidentiality protection of fax and confidentiality protection of fax that is independent of the
based on the RSA algorithm for use with the T.30 telephony transport protocol and is based on the RSA algorithm for use with
protocol by Group 3 facsimile equipment (G3FE). the T.30 telephony protocol by Group 3 facsimile equipment (G3FE).
o [ITU.T38.2010] specifies fax transport over RTP/SAVP which enables
integrity and confidentiality protection of fax in IP network. o [ITU.T38.2010] specifies fax transport over RTP/SAVP, which
enables integrity and confidentiality protection of fax in IP
networks.
Both of these mechanisms have been available for many years and never Both of these mechanisms have been available for many years and never
gained any significant adoption in the market. This has prompted an gained any significant adoption in the market. This has prompted an
effort to develop an open standards-based approach to secure fax effort to develop an approach, based on open standards, for securing
communications over an IP-based transport. fax communications over an IP-based transport.
Telephony-based protocols like T.30 offer application-level security Telephony-based protocols like T.30 offer application-level security
options like the RSA-based approached detailed in Annex H of the T.30 options like the RSA-based approach detailed in Annex H of the T.30
specification. The problem is that it is very sparingly implemented specification [ITU.T30.2005]. The problem is that it is very
and not enforced at the transport level. sparingly implemented and not enforced at the transport level.
It is worth noting that while T.38 over RTP offers a very viable 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 option for such standards-based IP security solution using Secure
fax over IP transport never gained any traction in the market place Realtime Transport Protocol (SRTP), this fax-over-IP transport never
and accounts for a negligible percentage of fax over IP gained any traction in the marketplace and accounts for a negligible
implementations. percentage of fax-over-IP implementations.
Thus, security mechanisms offering integrity and confidentiality Thus, security mechanisms offering integrity and confidentiality
protection should be limited to UDPTL-based fax transport, which is protection should be limited to UDPTL-based fax transport, which is
the only broad-based fax over IP solution. The 3rd Generation the only broad-based fax-over-IP solution. The 3rd Generation
Partnership Project (3GPP) launched a study on how best to provide Partnership Project (3GPP) launched a study on how best to provide
secure fax in the IP Multimedia Subsystem (IMS) for UDPTL. Results secure fax in the IP Multimedia Subsystem (IMS) for UDPTL. Results
of the study confirmed that this security was best achieved by using of the study confirmed that this security was best achieved by using
UDPTL over DTLS. UDPTL over DTLS.
This document specifies fax transport using UDPTL over DTLS This document specifies fax transport using UDPTL over DTLS
[RFC6347], which enables integrity and confidentiality protection of [RFC6347], which enables integrity and confidentiality protection of
fax in IP networks. The protocol stack which enhances fax transport fax in IP networks. The protocol stack that enhances fax transport
to offer integrity and confidentiality using UDPTL over DTLS is shown to offer integrity and confidentiality using UDPTL over DTLS is shown
in Figure 2. in Figure 2.
+-----------------------------+ +-----------------------------+
| Internet facsimile protocol | | Internet facsimile protocol |
+-----------------------------+ +-----------------------------+
| UDPTL | | UDPTL |
+-----------------------------+ +-----------------------------+
| DTLS | | DTLS |
+-----------------------------+ +-----------------------------+
| UDP | | UDP |
+-----------------------------+ +-----------------------------+
| IP | | IP |
+-----------------------------+ +-----------------------------+
Figure 2: Protocol stack for UDPTL over DTLS over UDP Figure 2: Protocol Stack for UDPTL over DTLS over UDP
The primary motivations for the mechanism in this document are: The primary motivations for the mechanism in this document are:
o The design of DTLS [RFC6347] is clearly defined and well o The design of DTLS [RFC6347] is clearly defined and well
understood and implementations are widely available. understood, and implementations are widely available.
o No DTLS extensions are required in order to enable UDPTL transport o No DTLS extensions are required in order to enable UDPTL transport
over DTLS. over DTLS.
o Fax transport using UDPTL over DTLS only requires insertion of the o Fax transport using UDPTL over DTLS only requires insertion of the
DTLS layer between the UDPTL layer and the UDP layer, as shown in DTLS layer between the UDPTL layer and the UDP layer, as shown in
Figure 2. The UDPTL layer and the layers above the UDPTL layer Figure 2. The UDPTL layer and the layers above the UDPTL layer
require no modifications. require no modifications.
o UDPTL [ITU.T38.2010] is by far the most widely deployed fax o UDPTL [ITU.T38.2010] is by far the most widely deployed fax
transport protocol in IP networks. transport protocol in IP networks.
o 3GPP and the IP fax community need a mechanism to transport UDPTL o 3GPP and the IP fax community need a mechanism to transport UDPTL
over DTLS in order to provide secure fax in SIP-based networks over DTLS in order to provide secure fax in SIP-based networks
(including IMS). (including IMS).
This document specifies the transport of UDPTL over DTLS using the This document specifies the transport of UDPTL over DTLS using the
DTLS record layer "application_data" packets [RFC5246] [RFC6347]. DTLS record layer "application_data" packets [RFC5246] [RFC6347].
Since the DTLS record layer "application_data" packet does not Since the DTLS record layer "application_data" packet does not
indicate whether it carries UDPTL, or some other protocol, the usage indicate whether it carries UDPTL or some other protocol, the usage
of a dedicated DTLS association for transport of UDPTL needs to be of a dedicated DTLS association for transport of UDPTL needs to be
negotiated, e.g. using the Session Description Protocol (SDP) negotiated, e.g., using the Session Description Protocol (SDP)
[RFC4566] and the SDP offer/answer mechanism [RFC3264]. [RFC4566] and the SDP offer/answer mechanism [RFC3264].
Therefore, this document specifies a new <proto> value [RFC4566] for Therefore, this document specifies a new <proto> value [RFC4566] for
the SDP media description ("m=" line) [RFC3264], in order to indicate the SDP media description ("m=" line) [RFC3264], in order to indicate
UDPTL over DTLS in SDP messages [RFC4566]. UDPTL over DTLS in SDP messages [RFC4566].
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
skipping to change at page 5, line 26 skipping to change at page 5, line 46
session" to refer to the DTLS construct. We 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 association" to refer to a particular DTLS cipher suite and keying
material set that is associated with a single host/port quartet. The material set that is associated with a single host/port quartet. The
same DTLS session can be used to establish the keying material for same DTLS session can be used to establish the keying material for
multiple DTLS associations. For consistency with other SIP/SDP multiple DTLS associations. For consistency with other SIP/SDP
usage, we use the term "connection" when what's being referred to is usage, we use the term "connection" when what's being referred to is
a multimedia stream that is not specifically DTLS. a multimedia stream that is not specifically DTLS.
3. Secure Channel 3. Secure Channel
The UDPTL over DTLS media stream is negotiated using the SDP offer/ The UDPTL-over-DTLS media stream is negotiated using the SDP offer/
answer mechanism [RFC3264]. See Section 4 for more details. answer mechanism [RFC3264]. See Section 4 for more details.
DTLS is used as specified in [RFC6347]. Once the DTLS handshake is DTLS is used as specified in [RFC6347]. Once the DTLS handshake is
successfully completed (in order to prevent facsimile data from being successfully completed (in order to prevent facsimile data from being
transmitted insecurely), the UDPTL packets MUST be transported in transmitted insecurely), the UDPTL packets MUST be transported in
DTLS record layer "application_data" packets. DTLS record layer "application_data" packets.
4. SDP Offerer/Answerer Procedures 4. SDP Offerer/Answerer Procedures
4.1. General 4.1. General
An endpoint (i.e. both the offerer and the answerer) MUST create an An endpoint (i.e., both the offerer and the answerer) MUST create an
SDP media description ("m=" line) for each UDPTL over DTLS media SDP media description ("m=" line) for each UDPTL-over-DTLS media
stream, and MUST assign a UDP/TLS/UDPTL value (see Table 1) to the stream and MUST assign a UDP/TLS/UDPTL value (see Table 1) to the
"proto" field of the "m=" line. "proto" field of the "m=" line.
The procedures in this section apply to an "m=" line associated with The procedures in this section apply to an "m=" line associated with
a UDPTL over DTLS media stream. a UDPTL-over-DTLS media stream.
In order to negotiate a UDPTL over DTLS media stream, the following In order to negotiate a UDPTL-over-DTLS media stream, the following
SDP attributes are used: SDP attributes are used:
o The SDP attributes defined for UDPTL over UDP, as described in o The SDP attributes defined for UDPTL over UDP, as described in
[ITU.T38.2010]; and [ITU.T38.2010]; and
o The SDP attributes, defined in [RFC4145] and [RFC4572], as o The SDP attributes, defined in [RFC4145] and [RFC4572], as
described in this section. described in this section.
The endpoint MUST NOT use the SDP "connection" attribute [RFC4145]. The endpoint MUST NOT use the SDP "connection" attribute [RFC4145].
In order to negotiate the TLS roles for the UDPTL over DTLS transport In order to negotiate the TLS roles for the UDPTL-over-DTLS transport
connection, the endpoint MUST use the SDP "setup" attribute connection, the endpoint MUST use the SDP "setup" attribute
[RFC4145]. [RFC4145].
If the endpoint supports, and is willing to use, a cipher suite with If the endpoint supports, and is willing to use, a cipher suite with
an associated certificate, the endpoint MUST include an SDP an associated certificate, the endpoint MUST include an SDP
"fingerprint" attribute [RFC4572]. The endpoint MUST support SHA-256 "fingerprint" attribute [RFC4572]. The endpoint MUST support SHA-256
for generating and verifying the SDP "fingerprint" attribute value. for generating and verifying the SDP "fingerprint" attribute value.
The use of SHA-256 is preferred. UPDPTL over DTLS, at a minimum, The use of SHA-256 is preferred. UDPTL over DTLS, at a minimum, MUST
MUST support TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 and MUST support 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. UDPTL over DTLS MUST prefer
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and any other Perfect Forward TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and any other Perfect Forward
Secrecy (PFS) cipher suites over non-PFS cipher suites. Secrecy (PFS) cipher suites over non-PFS cipher suites.
Implementations SHOULD disable TLS-level compression. Implementations SHOULD disable TLS-level compression.
If a cipher suite with an associated certificate is selected during If a cipher suite with an associated certificate is selected during
the DTLS handshake, the certificate received during the DTLS the DTLS handshake, the certificate received during the DTLS
handshake MUST match the fingerprint received in the SDP handshake MUST match the fingerprint received in the SDP
"fingerprint" attribute. If the fingerprint does not match the "fingerprint" attribute. If the fingerprint does not match the
hashed certificate, then the endpoint MUST tear down the media hashed certificate, then the endpoint MUST tear down the media
skipping to change at page 6, line 47 skipping to change at page 7, line 21
ClientHello) or "passive" (the offerer will be the receiver of ClientHello) or "passive" (the offerer will be the receiver of
ClientHello). The offerer MUST NOT assign an SDP "setup" attribute ClientHello). The offerer MUST NOT assign an SDP "setup" attribute
with a "holdconn" value. with a "holdconn" value.
If the offerer assigns the SDP "setup" attribute with a value of If the offerer assigns the SDP "setup" attribute with a value of
"actpass" or "passive", the offerer MUST be prepared to receive a "actpass" or "passive", the offerer MUST be prepared to receive a
DTLS ClientHello message before it receives the SDP answer. DTLS ClientHello message before it receives the SDP answer.
4.3. Generating the Answer 4.3. Generating the Answer
If the answerer accepts the offered UDPTL over DTLS transport If the answerer accepts the offered UDPTL-over-DTLS transport
connection, in the associated SDP answer the answerer MUST assign an connection, in the associated SDP answer, the answerer MUST assign an
SDP "setup" attribute with a value of either "active" or "passive", SDP "setup" attribute with a value of either "active" or "passive",
according to the procedures in [RFC4145]. The answerer MUST NOT according to the procedures in [RFC4145]. The answerer MUST NOT
assign an SDP "setup" attribute with a value of "holdconn". assign an SDP "setup" attribute with a value of "holdconn".
If the answerer assigns an SDP "setup" attribute with a value of If the answerer assigns an SDP "setup" attribute with a value of
"active" value, the answerer MUST initiate a DTLS handshake by "active" value, the answerer MUST initiate a DTLS handshake by
sending a DTLS ClientHello message on the negotiated media stream, sending a DTLS ClientHello message on the negotiated media stream,
towards the IP address and port of the offerer. towards the IP address and port of the offerer.
4.4. Offerer Processing of the Answer 4.4. Offerer Processing of the Answer
skipping to change at page 7, line 23 skipping to change at page 7, line 45
active it MUST initiate a DTLS handshake by sending a DTLS active it MUST initiate a DTLS handshake by sending a DTLS
ClientHello message on the negotiated media stream, towards the IP ClientHello message on the negotiated media stream, towards the IP
address and port of the answerer. address and port of the answerer.
4.5. Modifying the Session 4.5. Modifying the Session
Once an offer/answer exchange has been completed, either endpoint MAY Once an offer/answer exchange has been completed, either endpoint MAY
send a new offer in order to modify the session. The endpoints can send a new offer in order to modify the session. The endpoints can
reuse the existing DTLS association if the key fingerprint values and reuse the existing DTLS association if the key fingerprint values and
transport parameters indicated by each endpoint are unchanged. transport parameters indicated by each endpoint are unchanged.
Otherwise, following the rules as for the initial offer/answer Otherwise, following the rules for the initial offer/answer exchange,
exchange, the endpoints can negotiate and create a new DTLS the endpoints can negotiate and create a new DTLS association and,
association and, once created, delete the previous DTLS association, once created, delete the previous DTLS association, following the
following the same rules for the initial offer/answer exchange. Each same rules for the initial offer/answer exchange. Each endpoint
endpoint needs to be prepared to receive data on both the new and old needs to be prepared to receive data on both the new and old DTLS
DTLS associations, as long as both are alive. associations as long as both are alive.
5. Miscellaneous Considerations 5. Miscellaneous Considerations
5.1. Anonymous Calls 5.1. Anonymous Calls
When making anonymous calls, a new self-signed certificate SHOULD be When making anonymous calls, a new self-signed certificate SHOULD be
used for each call and attributes inside the certificate MUST NOT used for each call, and attributes inside the certificate MUST NOT
contain information that either allows correlation or identification contain information that allows either correlation or identification
of the user making anonymous calls. This is particularly important of the user making anonymous calls. This is particularly important
for the subjectAltName and commonName attributes. for the "subjectAltName" and "commonName" attributes.
5.2. NAT Traversal 5.2. NAT Traversal
5.2.1. ICE Usage 5.2.1. ICE Usage
When ICE [RFC5245] is being used, the ICE connectivity checks are When Interactive Connectivity Establishment (ICE) [RFC5245] is being
performed before the DTLS handshake begins. Note that if aggressive used, the ICE connectivity checks are performed before the DTLS
nomination mode is used, multiple candidate pairs may be marked valid handshake begins. Note that if aggressive nomination mode is used,
before ICE finally converges on a single candidate pair. UAs MUST multiple candidate pairs may be marked valid before ICE finally
treat all ICE candidate pairs associated with a single component as converges on a single candidate pair. User Agents (UAs) MUST treat
part of the same DTLS association. Thus, there will be only one DTLS 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 handshake even if there are multiple valid candidate pairs. Note
that this may mean adjusting the endpoint IP addresses if the that this may mean adjusting the endpoint IP addresses if the
selected candidate pair shifts, just as if the DTLS packets were an selected candidate pair shifts, just as if the DTLS packets were an
ordinary media stream. In case of an ICE restart, the DTLS handshake ordinary media stream. In the case of an ICE restart, the DTLS
procedure is repeated and a new DTLS association is created. Once handshake procedure is repeated, and a new DTLS association is
the DTLS handshake is completed ,and the new DTLS association has created. Once the DTLS handshake is completed and the new DTLS
been created, the previous DTLS association is deleted. association has been created, the previous DTLS association is
deleted.
5.2.2. STUN Interaction 5.2.2. STUN Interaction
The UA MUST send the STUN packets [RFC5389] directly over UDP, not The UA MUST send the Session Traversal Utilities for NAT (STUN)
over DTLS. packets [RFC5389] directly over UDP, not over DTLS.
The UA MUST support the following mechanism for demultiplexing The UA MUST support the following mechanism for demultiplexing
packets arriving on the IP address and port associated with the DTLS packets arriving on the IP address and port associated with the DTLS
association: association:
o If the value of the first byte of the packet is 0 or 1, then the o If the value of the first byte of the packet is 0 or 1, then the
packet is STUN. packet is STUN.
o If the value of the first byte of the packet is between 20 and 63 o If the value of the first byte of the packet is between 20 and 63
(inclusive), the packet is DTLS. (inclusive), the packet is DTLS.
5.3. Rekeying 5.3. Rekeying
During rekeying, packets protected by the previous set of keys can During rekeying, packets protected by the previous set of keys can
arrive after the DTLS handshake caused by rekeying has completed, arrive after the DTLS handshake caused by rekeying has completed,
because packets can be reordered on the wire. To compensate for this because packets can be reordered on the wire. To compensate for this
fact, receivers MUST maintain both sets of keys for some time in fact, receivers MUST maintain both sets of keys for some time in
order to be able to decrypt and verify older packets. The duration order to be able to decrypt and verify older packets. The duration
skipping to change at page 8, line 31 skipping to change at page 9, line 13
(inclusive), the packet is DTLS. (inclusive), the packet is DTLS.
5.3. Rekeying 5.3. Rekeying
During rekeying, packets protected by the previous set of keys can During rekeying, packets protected by the previous set of keys can
arrive after the DTLS handshake caused by rekeying has completed, arrive after the DTLS handshake caused by rekeying has completed,
because packets can be reordered on the wire. To compensate for this because packets can be reordered on the wire. To compensate for this
fact, receivers MUST maintain both sets of keys for some time in fact, receivers MUST maintain both sets of keys for some time in
order to be able to decrypt and verify older packets. The duration 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 of maintaining the previous set of keys after the finish of the DTLS
handshake is out of scope for this document. handshake is out of the scope of this document.
5.4. Compatibility With UDPTL over UDP 5.4. Compatibility with UDPTL over UDP
If a user requires fax to be transported securely using UDPTL over 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 DTLS, and if the remote user does not support UDPTL over DTLS, then a
fax media stream cannot be established. fax media stream cannot be established.
If a user prefers fax to be transported securely using UDPTL over If a user prefers fax to be transported securely using UDPTL over
DTLS, but is willing to transport the fax insecurely in case the DTLS but is willing to transport the fax insecurely in case the
remote user does not support UDPTL over DTLS, then the SDP Capability remote user does not support UDPTL over DTLS, then the SDP Capability
Negotiation mechanism [RFC5939] can be used to offer both UDPTL over Negotiation mechanism [RFC5939] can be used to offer both UDPTL over
DTLS and UDPTL over UDP. Alternatively, if the remote user rejects 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 an SDP offer for UDPTL over DTLS, a new SDP offer for a UDPTL-over-
UDP media stream can be sent. UDP media stream can be sent.
6. Security Considerations 6. Security Considerations
Fax may be used to transmit a wide range of sensitive data, including Fax may be used to transmit a wide range of sensitive data, including
personal, corporate, and governmental information. It is therefore personal, corporate, and governmental information. It is therefore
critical to be able to protect against threats to the confidentiality critical to be able to protect against threats to the confidentiality
and integrity of the transmitted data. and integrity of the transmitted data.
The mechanism in this document provides integrity and confidentiality The mechanism in this document provides integrity and confidentiality
skipping to change at page 9, line 31 skipping to change at page 10, line 12
be justified. Issuing and deploying PKIX certificates to all clients be justified. Issuing and deploying PKIX certificates to all clients
is not realistic in most deployment scenarios. is not realistic in most deployment scenarios.
The design described in this document is intended to leverage the The design described in this document is intended to leverage the
integrity protection of the SIP signaling, while not requiring integrity protection of the SIP signaling, while not requiring
confidentiality. As long as each side of the connection can verify confidentiality. As long as each side of the connection can verify
the integrity of the SDP received from the other side, then the DTLS 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 handshake cannot be hijacked via a man-in-the-middle attack. This
integrity protection is easily provided by the caller to the callee integrity protection is easily provided by the caller to the callee
via the SIP Identity [RFC4474] mechanism. Other mechanisms, such as via the SIP Identity [RFC4474] mechanism. Other mechanisms, such as
the S/MIME mechanism [RFC3261], or perhaps future mechanisms yet to the S/MIME mechanism [RFC3261] or perhaps future mechanisms yet to be
be specified could also serve this purpose. specified, could also serve this purpose.
While this mechanism can still be used without such integrity While this mechanism can still be used without such integrity
mechanisms, the security provided is limited to defense against mechanisms, the security provided is limited to defense against
passive attack by intermediaries. An active attack on the signaling passive attack by intermediaries. An active attack on the signaling
plus an active attack on the media plane can allow an attacker to plus an active attack on the media plane can allow an attacker to
attack the connection (R-SIG-MEDIA in the notation of [RFC5479]). attack the connection (R-SIG-MEDIA in the notation of [RFC5479]).
7. IANA Considerations 7. IANA Considerations
This document updates the "Session Description Protocol (SDP) This document updates the "Session Description Protocol (SDP)
Parameters" registry as specified in Section 8.2.2 of [RFC4566]. Parameters" registry as specified in Section 8.2.2 of [RFC4566].
Specifically, it adds the values in Table 1 to the table for the SDP Specifically, the values in Table 1 have been added to the SDP
"proto" field registry. "proto" field registry.
+-------+---------------+------------+ +-------+---------------+-----------+
| Type | SDP Name | Reference | | Type | SDP Name | Reference |
+-------+---------------+------------+ +-------+---------------+-----------+
| proto | UDP/TLS/UDPTL | [RFC-XXXX] | | proto | UDP/TLS/UDPTL | [RFC7345] |
+-------+---------------+------------+ +-------+---------------+-----------+
Table 1: SDP "proto" field values
[RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this Table 1: SDP "proto" Field Values
document.]
8. Acknowledgments 8. Acknowledgments
Special thanks to Peter Dawes, who provided comments on the initial Special thanks to Peter Dawes, who provided comments on the initial
version of the draft, and to Paul E. Jones, James Rafferty, Albrecht draft version of the document, and to Paul E. Jones, James Rafferty,
Schwarz, Oscar Ohlsson, David Hanes, Adam Gensler, Ari Keranen, Albrecht Schwarz, Oscar Ohlsson, David Hanes, Adam Gensler, Ari
Flemming Andreasen, John Mattsson and Marc Petit-Huguenin who Keranen, Flemming Andreasen, John Mattsson, and Marc Petit-Huguenin,
provided valuable feedback and input. Barry Leiba, Spencer Dawkins, who provided valuable feedback and input. Barry Leiba, Spencer
Pete Resnick, Kathleen Moriarty and Stephen Farrell provided valuable Dawkins, Pete Resnick, Kathleen Moriarty, and Stephen Farrell
feedback during the IESG review. Thanks to Scott Brim for performing provided valuable feedback during the IESG review. Thanks to Scott
the Gen-ART review. Thanks to Alissa Cooper for her help as Brim for performing the Gen-ART review. Thanks to Alissa Cooper for
sponsoring Area Director. her help as sponsoring Area Director.
9. Change Log
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-mmusic-udptl-dtls-09
o Removal of previous changes based on comments by Marc Petit-
Huguenin:
o - Future correction might be needed based on generic NAT traversal
work in IETF.
Changes from draft-ietf-mmusic-udptl-dtls-08
o Changes based on comments by Marc Petit-Huguenin:
o - Corrected text on how to distinguish STUN, TURN and DTLS
packets.
Changes from draft-ietf-mmusic-udptl-dtls-07
o Changes based on IESG comments by Barry Leiba:
o - SHALL replaced with MUST.
o - Text modifications in sections 4.2, 4.4, 5.2.2, 5.3 and 6.
o Changes based on IESG comments by Pete Resnick and Kathleen
Moriarty:
o - Additional text on existing mechanisms for securing fax in
section 1.
o Changes based on IESG comments by Stephen Farrell:
o - Added text regarding MTI cipher suites.
Changes from draft-ietf-mmusic-udptl-dtls-06
o Changes based on WGLC comments by Paul Kyzivat
o - Indicating that, when a new and an old DTLS association exist,
each endpoint needs to be prepared to receive data on both.
o - Editorial nit.
Changes from draft-ietf-mmusic-udptl-dtls-05
o Changes based on comments by Flemming Andreasen
o - SDP Offer/Answer sections structured according to RFC 3264.
o - Clarified that ICE considerations also apply to ICE restart.
o - Editorial changes.
Changes from draft-ietf-mmusic-udptl-dtls-04
o Changes based on comments by Flemming Andreasen
o - Addition of SDP Offer/Answer procedure section.
o - Removal of non-ICE NAT traversal procedures.
o - Addition of guidance regarding compatibility with UDPTL over
UDP.
o - Editorial corrections.
o Minor editorial corrections
o -Spelling of Ari's family name.
Changes from draft-ietf-mmusic-udptl-dtls-03
o Changes based on comments by Adam Gensler (http://www.ietf.org/
mail-archive/web/mmusic/current/msg12945.html)
o -Indicating that, in case of rekeying, entities MUST maintain both
set of keys for some time (previously SHOULD).
o -Explicit mentioning of the commonName attribute in text about
correlation/identification of users.
o Changes based on comments by Ari Keranen (http://www.ietf.org/
mail-archive/web/mmusic/current/msg12966.html)
o -Informative reference to RFC 5246 added.
o -Re-naming of sections 4.2.1 and 4.2.2.
o -Clarifying that documented STUN/DTLS demux mechanism is only one
way of doing the demux.
o -Editorial corrections.
Changes from draft-ietf-mmusic-udptl-dtls-02
o Editorial comments based on review comments by James Rafferty
(http://www.ietf.org/mail-archive/web/mmusic/current/
msg12890.html)
o Editorial comments based on review comments by David Hanes
(http://www.ietf.org/mail-archive/web/mmusic/current/
msg12886.html)
o Editorial comments based on review comments by Oscar Ohlsson
(http://www.ietf.org/mail-archive/web/mmusic/current/
msg12882.html)
o Editorial comments based on review comments by Albrecht Schwartz
(http://www.ietf.org/mail-archive/web/mmusic/current/
msg12900.html)
Changes from draft-ietf-mmusic-udptl-dtls-01
o Usage of the SDP fingerprint attribute depends on whether a cipher
suite with an associated certificate is used.
o Editor's note in section 4.2 removed. Procedure text added.
Changes from draft-ietf-mmusic-udptl-dtls-00
o 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).
o The example for secure fax replacing audio stream in audio-only
session added (http://www.ietf.org/mail-
archive/web/mmusic/current/msg12428.html).
o 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).
o Editorial corrections.
Changes from draft-holmberg-mmusic-udptl-dtls-02
o Milestone adopted - draft-ietf-mmusic version of the draft
submitted.
Changes from draft-holmberg-mmusic-udptl-dtls-01
o Gonzalo Salgueiro added as co-author.
o PSTN comparison text and Introduction text modified.
Changes from draft-holmberg-mmusic-udptl-dtls-00
o Text about T.30 added.
o Latest version of T.38 referenced.
o Additional text about the need for secure fax in IP networks.
Changes from draft-holmberg-dispatch-udptl-dtls-00 9. References
o WG changed to MMUSIC. 9.1. Normative References
o Added text about 3GPP need for UDPTL/DTLS.
10. References [ITU.T30.2005]
International Telecommunications Union, "Procedures for
document facsimile transmission in the general switched
telephone network", ITU-T Recommendation T.30, September
2005.
10.1. Normative References [ITU.T38.2010]
International Telecommunications Union, "Procedures for
real-time Group 3 facsimile communication over IP
networks", ITU-T Recommendation T.38, September 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
skipping to change at page 14, line 12 skipping to change at page 12, line 17
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008. (CRL) Profile", RFC 5280, May 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389, "Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008. October 2008.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012. Security Version 1.2", RFC 6347, January 2012.
[ITU.T30.2005] 9.2. Informative References
International Telecommunications Union, "Procedures for
document facsimile transmission in the general switched
telephone network", ITU-T Recommendation T.30, September
2005.
[ITU.T38.2010]
International Telecommunications Union, "Procedures for
real-time Group 3 facsimile communication over IP
networks", ITU-T Recommendation T.38, September 2010.
10.2. Informative References
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5479] Wing, D., Fries, S., Tschofenig, H., and F. Audet, [RFC5479] Wing, D., Fries, S., Tschofenig, H., and F. Audet,
"Requirements and Analysis of Media Security Management "Requirements and Analysis of Media Security Management
Protocols", RFC 5479, April 2009. Protocols", RFC 5479, April 2009.
[RFC5939] Andreasen, F., "Session Description Protocol (SDP) [RFC5939] Andreasen, F., "Session Description Protocol (SDP)
Capability Negotiation", RFC 5939, September 2010. Capability Negotiation", RFC 5939, September 2010.
Appendix A. Examples Appendix A. Examples
A.1. General A.1. General
Prior to establishing the session, both Alice and Bob generate self- Prior to establishing the session, both Alice and Bob generate self-
signed certificates which are used for a single session or, more signed certificates that are used for a single session or, more
likely, reused for multiple sessions. likely, reused for multiple sessions.
The SIP signaling from Alice to her proxy is transported over TLS to The SIP signaling from Alice to her proxy is transported over TLS to
ensure an integrity protected channel between Alice and her identity ensure an integrity-protected channel between Alice and her identity
service. Alice's identity service asserts identity of Alice and service. Alice's identity service asserts identity of Alice and
protects the SIP message, e.g. using SIP Identity. Transport between protects the SIP message, e.g., using SIP Identity. Transport
proxies should also be protected, e.g. by use of TLS. between proxies should also be protected, e.g., by use of TLS.
In order to simplify the flow, only one element is shown for Alice's In order to simplify the flow, only one element is shown for Alice's
and Bob's proxies. and Bob's proxies.
For the sake of brevity and simplicity, only the mandatory SDP T.38 For the sake of brevity and simplicity, only the mandatory SDP T.38
attributes are shown. attributes are shown.
A.2. Basic Message Flow A.2. Basic Message Flow
Figure 3 shows an example message flow of session establishment for Figure 3 shows an example message flow of session establishment for
T.38 fax securely transported using UDPTL over DTLS. T.38 fax securely transported using UDPTL over DTLS.
In this example flow, Alice acts as the passive endpoint of the DTLS 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, and Bob acts as the active endpoint of the DTLS
association. association.
Alice Proxies Bob Alice Proxies Bob
| (1) SIP INVITE | | | (1) SIP INVITE | |
|----------------------->| | |----------------------->| |
| | (2) SIP INVITE | | | (2) SIP INVITE |
| |----------------------->| | |----------------------->|
| | (3) DTLS ClientHello | | | (3) DTLS ClientHello |
|<------------------------------------------------| |<------------------------------------------------|
| (4) remaining messages of DTLS handshake | | (4) remaining messages of DTLS handshake |
|<----------------------------------------------->| |<----------------------------------------------->|
| | | | | |
| | | | | |
| | (5) SIP 200 OK | | | (5) SIP 200 OK |
| |<-----------------------| | |<-----------------------|
| (6) SIP 200 OK | | | (6) SIP 200 OK | |
|<-----------------------| | |<-----------------------| |
| (7) SIP ACK | | | (7) SIP ACK | |
|------------------------------------------------>| |------------------------------------------------>|
| (8) T.38 message using UDPTL over DTLS | | (8) T.38 message using UDPTL over DTLS |
|<----------------------------------------------->| |<----------------------------------------------->|
| | | | | |
Figure 3: Basic message flow Figure 3: Basic Message Flow
Message (1): Message (1):
Figure 4 shows the initial INVITE request sent by Alice to Alice's Figure 4 shows the initial INVITE request sent by Alice to Alice's
proxy. The initial INVITE request contains an SDP offer. proxy. The initial INVITE request contains an SDP offer.
The "m=" line in the SDP offer indicates T.38 fax using UDPTL over The "m=" line in the SDP offer indicates T.38 fax using UDPTL over
DTLS. DTLS.
The SDP "setup" attribute with a value of "actpass" in the SDP The SDP "setup" attribute with a value of "actpass" in the SDP
skipping to change at page 17, line 44 skipping to change at page 17, line 16
Assuming that Alice's identity is valid, Bob sends a DTLS Assuming that Alice's identity is valid, Bob sends a DTLS
ClientHello directly to Alice. ClientHello directly to Alice.
Message (4): Message (4):
Alice and Bob exchange further messages of DTLS handshake Alice and Bob exchange further messages of DTLS handshake
(HelloVerifyRequest, ClientHello, ServerHello, Certificate, (HelloVerifyRequest, ClientHello, ServerHello, Certificate,
ServerKeyExchange, CertificateRequest, ServerHelloDone, ServerKeyExchange, CertificateRequest, ServerHelloDone,
Certificate, ClientKeyExchange, CertificateVerify, Certificate, ClientKeyExchange, CertificateVerify,
ChangeCipherSpec, Finished). ChangeCipherSpec, and Finished).
When Bob receives the certificate of Alice via DTLS, Bob checks When Bob receives the certificate of Alice via DTLS, Bob checks
whether the certificate fingerprint calculated from Alice's whether the certificate fingerprint calculated from Alice's
certificate received via DTLS matches the certificate fingerprint certificate received via DTLS matches the certificate fingerprint
received in the a=fingerprint SDP attribute of Figure 5. In this received in the a=fingerprint SDP attribute of Figure 5. In this
message flow, the check is successful and thus session setup message flow, the check is successful; thus, session setup
continues. continues.
Note that, unlike in this example, it is not necessary to wait for 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 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 Bob has sent the SIP 200 (OK) response and later detects that the
certificate fingerprints do not match, he will terminate the certificate fingerprints do not match, he will terminate the
session. session.
Message (5): Message (5):
skipping to change at page 19, line 38 skipping to change at page 19, line 12
Figure 6: Message (5) Figure 6: Message (5)
Message (6): Message (6):
Figure 7 shows a SIP 200 (OK) response to the initial SIP INVITE Figure 7 shows a SIP 200 (OK) response to the initial SIP INVITE
request, sent by Alice's proxy to Alice. Alice checks if the request, sent by Alice's proxy to Alice. Alice checks if the
certificate fingerprint calculated from the Bob's certificate certificate fingerprint calculated from the Bob's certificate
received via DTLS is the same as the certificate fingerprint received via DTLS is the same as the certificate fingerprint
received in the a=fingerprint SDP attribute of Figure 7. In this received in the a=fingerprint SDP attribute of Figure 7. In this
message flow, the check is successful and thus the session setup message flow, the check is successful; thus, the session setup
continues. continues.
SIP/2.0 200 OK SIP/2.0 200 OK
To: <sip:bob@example.com>;tag=6418913922105372816 To: <sip:bob@example.com>;tag=6418913922105372816
From: "Alice" <sip:alice@example.com>;tag=843c7b0b From: "Alice" <sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
Record-Route: <sip:proxy.example.com;lr> Record-Route: <sip:proxy.example.com;lr>
Call-ID: 6076913b1c39c212@REVMTEpG Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE CSeq: 1 INVITE
Contact: <sip:bob@ua2.example.com> Contact: <sip:bob@ua2.example.com>
skipping to change at page 20, line 39 skipping to change at page 20, line 5
Message (7): Message (7):
Alice sends the SIP ACK request to Bob. Alice sends the SIP ACK request to Bob.
Message (8): Message (8):
At this point, Bob and Alice can exchange T.38 fax securely At this point, Bob and Alice can exchange T.38 fax securely
transported using UDPTL over DTLS. transported using UDPTL over DTLS.
A.3. Message Flow Of T.38 Fax Replacing Audio Media Stream in An A.3. Message Flow of T.38 Fax Replacing Audio Media Stream in an
Existing Audio-Only Session Existing Audio-Only Session
Traditionally, most sessions with non-secure transport of T.38 fax, Traditionally, most sessions with non-secure transport of T.38 fax,
transported using UDPTL, are established by modifying an ongoing transported using UDPTL, are established by modifying an ongoing
audio session into a fax session. Figure 8 shows an example message audio session into a fax session. Figure 8 shows an example message
flow of modifying an existing audio session into a session with T.38 flow of modifying an existing audio session into a session with T.38
fax securely transported using UDPTL over DTLS. fax securely transported using UDPTL over DTLS.
In this example flow, Alice acts as the passive endpoint of the DTLS 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, and Bob acts as the active endpoint of the DTLS
association. association.
Alice Proxies Bob Alice Proxies Bob
| | | | | |
| (1) Audio-only session initiation | | (1) Audio-only session initiation |
|<-----------------------+----------------------->| |<-----------------------+----------------------->|
| | | | | |
| (2) SIP re-INVITE | | | (2) SIP re-INVITE | |
|------------------------------------------------>| |------------------------------------------------>|
| | (3) DTLS ClientHello | | | (3) DTLS ClientHello |
|<------------------------------------------------| |<------------------------------------------------|
| (4) remaining messages of DTLS handshake | | (4) remaining messages of DTLS handshake |
|<----------------------------------------------->| |<----------------------------------------------->|
| | | | | |
| | | | | |
| | (5) SIP 200 OK | | | (5) SIP 200 OK |
|<------------------------------------------------| |<------------------------------------------------|
| (6) SIP ACK | | | (6) SIP ACK | |
|------------------------------------------------>| |------------------------------------------------>|
| (7) T.38 message using UDPTL over DTLS | | (7) T.38 message using UDPTL over DTLS |
|<----------------------------------------------->| |<----------------------------------------------->|
| | | | | |
Figure 8: Message Flow Of T.38 Fax Replacing Audio Media Stream in An Figure 8: Message Flow of T.38 Fax Replacing Audio Media Stream in an
Existing Audio-Only Session Existing Audio-Only Session
Message (1): Message (1):
Session establishment of audio-only session. The proxies decide Session establishment of audio-only session. The proxies decide
not to record-route. not to record-route.
Message (2): Message (2):
Alice sends SIP re-INVITE request. The SDP offer included in the Alice sends SIP re-INVITE request. The SDP offer included in the
skipping to change at page 22, line 21 skipping to change at page 21, line 29
s=- s=-
c=IN IP4 ua1.example.com c=IN IP4 ua1.example.com
t=0 0 t=0 0
m=audio 0 UDP/TLS/RTP/SAVP 0 m=audio 0 UDP/TLS/RTP/SAVP 0
m=image 46056 UDP/TLS/UDPTL t38 m=image 46056 UDP/TLS/UDPTL t38
a=setup:actpass a=setup:actpass
a=fingerprint: SHA-1 \ a=fingerprint: SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF a=T38FaxRateManagement:transferredTCF
Figure 9: SDP offer of message (2) Figure 9: SDP Offer of Message (2)
Message (3): Message (3):
Bob sends a DTLS ClientHello directly to Alice. Bob sends a DTLS ClientHello directly to Alice.
Message (4): Message (4):
Alice and Bob exchange further messages of DTLS handshake Alice and Bob exchange further messages of DTLS handshake
(HelloVerifyRequest, ClientHello, ServerHello, Certificate, (HelloVerifyRequest, ClientHello, ServerHello, Certificate,
ServerKeyExchange, CertificateRequest, ServerHelloDone, ServerKeyExchange, CertificateRequest, ServerHelloDone,
Certificate, ClientKeyExchange, CertificateVerify, Certificate, ClientKeyExchange, CertificateVerify,
ChangeCipherSpec, Finished). ChangeCipherSpec, and Finished).
When Bob receives the certificate of Alice via DTLS, Bob checks When Bob receives the certificate of Alice via DTLS, Bob checks
whether the certificate fingerprint calculated from Alice's whether the certificate fingerprint calculated from Alice's
certificate received via DTLS matches the certificate fingerprint certificate received via DTLS matches the certificate fingerprint
received in the SDP "fingerprint" attribute of Figure 9. In this received in the SDP "fingerprint" attribute of Figure 9. In this
message flow, the check is successful and thus session setup message flow, the check is successful; thus, session setup
continues. continues.
Message (5): Message (5):
Bob sends a SIP 200 (OK) response to the SIP re-INVITE request. Bob sends a SIP 200 (OK) response to the SIP re-INVITE request.
The SIP 200 (OK) response contains an SDP answer shown in The SIP 200 (OK) response contains an SDP answer shown in
Figure 10. Figure 10.
The first "m=" line in the SDP offer indicates audio media stream The first "m=" line in the SDP offer indicates audio media stream
being removed. The second "m=" line in the SDP answer indicates being removed. The second "m=" line in the SDP answer indicates
skipping to change at page 23, line 32 skipping to change at page 22, line 34
s=- s=-
c=IN IP4 ua2.example.com c=IN IP4 ua2.example.com
t=0 0 t=0 0
m=audio 0 UDP/TLS/RTP/SAVP 0 m=audio 0 UDP/TLS/RTP/SAVP 0
m=image 32000 UDP/TLS/UDPTL t38 m=image 32000 UDP/TLS/UDPTL t38
a=setup:active a=setup:active
a=fingerprint: SHA-1 \ a=fingerprint: SHA-1 \
FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF a=T38FaxRateManagement:transferredTCF
Figure 10: SDP answer of message (5) Figure 10: SDP Answer of Message (5)
Message (6): Message (6):
Alice sends the SIP ACK request to Bob. Alice sends the SIP ACK request to Bob.
Message (7): Message (7):
At this point, Bob and Alice can exchange T.38 fax securely At this point, Bob and Alice can exchange T.38 fax securely
transported using UDPTL over DTLS. transported using UDPTL over DTLS.
Authors' Addresses Authors' Addresses
Christer Holmberg Christer Holmberg
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: christer.holmberg@ericsson.com EMail: christer.holmberg@ericsson.com
Ivo Sedlacek Ivo Sedlacek
Ericsson Ericsson
Sokolovska 79 Sokolovska 79
Praha 18600 Praha 18600
Czech Republic Czech Republic
Email: ivo.sedlacek@ericsson.com EMail: ivo.sedlacek@ericsson.com
Gonzalo Salgueiro Gonzalo Salgueiro
Cisco Systems, Inc. Cisco Systems, Inc.
7200-12 Kit Creek Road 7200-12 Kit Creek Road
Research Triangle Park, NC 27709 Research Triangle Park, NC 27709
US US
Email: gsalguei@cisco.com EMail: gsalguei@cisco.com
 End of changes. 71 change blocks. 
324 lines changed or deleted 199 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/