draft-ietf-mmusic-udptl-dtls-02.txt   draft-ietf-mmusic-udptl-dtls-03.txt 
MMUSIC Working Group C. Holmberg MMUSIC Working Group C. Holmberg
Internet-Draft I. Sedlacek Internet-Draft I. Sedlacek
Intended status: Standards Track Ericsson Intended status: Standards Track Ericsson
Expires: June 8, 2014 G. Salgueiro Expires: July 21, 2014 G. Salgueiro
Cisco Cisco
December 5, 2013 January 17, 2014
UDP Transport Layer (UDPTL) over Datagram Transport Layer Security UDP Transport Layer (UDPTL) over Datagram Transport Layer Security
(DTLS) (DTLS)
draft-ietf-mmusic-udptl-dtls-02 draft-ietf-mmusic-udptl-dtls-03
Abstract Abstract
This document specifies how the UDP Transport Layer (UDPTL) protocol This document specifies how the UDP Transport Layer (UDPTL) protocol,
can be transported over the Datagram Transport Layer Security (DTLS) the predominant transport protocol for T.38 fax, can be transported
protocol, how the usage of UDPTL over DTLS is indicated in the over the Datagram Transport Layer Security (DTLS) protocol, how the
Session Description Protocol (SDP), and how UDPTL over DTLS is usage of UDPTL over DTLS is indicated in the Session Description
negotiated in a session established using the Session Initiation Protocol (SDP), and how UDPTL over DTLS is negotiated in a session
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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 8, 2014. This Internet-Draft will expire on July 21, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 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
skipping to change at page 2, line 27 skipping to change at page 2, line 27
4.1. Anonymous Calls . . . . . . . . . . . . . . . . . . . . . 6 4.1. Anonymous Calls . . . . . . . . . . . . . . . . . . . . . 6
4.2. Middlebox Interaction . . . . . . . . . . . . . . . . . . 6 4.2. Middlebox Interaction . . . . . . . . . . . . . . . . . . 6
4.2.1. ICE Interaction . . . . . . . . . . . . . . . . . . . 6 4.2.1. ICE Interaction . . . . . . . . . . . . . . . . . . . 6
4.2.2. Latching Control without ICE . . . . . . . . . . . . 6 4.2.2. Latching Control without ICE . . . . . . . . . . . . 6
4.2.3. STUN Interaction . . . . . . . . . . . . . . . . . . 7 4.2.3. STUN Interaction . . . . . . . . . . . . . . . . . . 7
4.3. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 7 4.3. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 8 8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 10 9.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 10 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 11
A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 11 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 11
A.2. Basic Message Flow with Identity . . . . . . . . . . . . 11 A.2. Basic Message Flow . . . . . . . . . . . . . . . . . . . 11
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 . . . . . . . . . . . . . 16 An Existing Audio-Only Session . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
While telephony encryption devices have been traditionally used for While it is possible to transmit highly sensitive documents using
highly sensitive documents, secure fax on the Public Switched traditional telephony encryption devices, secure fax on the Public
Telephone Network (PSTN) was not as widely considered or prioritized Switched Telephone Network (PSTN) was never widely considered or
because of the challenges involved with physical access to telephony prioritized. This was mainly because of the challenges involved with
equipment. As real-time communications transition to IP networks, physical access to telephony equipment. As real-time communications
where information might potentially be intercepted or spoofed, an transition to IP networks, where information might potentially be
appropriate level of security for fax that offers integrity and intercepted or spoofed, an appropriate level of security for fax that
confidentiality protection is vital. Some of the security mechanisms offers integrity and confidentiality protection is vital.
for securing fax include:
o [ITU.T30.2005] Annex H specifies integrity and confidentiality
protection of fax in application layer, independent of protocol
for fax transport.
o [ITU.T38.2010] specifies fax transport over RTP/SAVP which enables
integrity and confidentiality protection of fax in IP network.
Despite these mechanisms to secure fax, there is no transport layer The overwhelmingly predominant fax transport protocol is UDPTL-based
security offering integrity and confidentiality protection for UDPTL [ITU.T38.2010]. The protocol stack for fax transport using UDPTL is
[ITU.T38.2010], the overwhelmingly predominant fax transport shown in Table 1.
protocol. The protocol stack for fax transport using UDPTL is shown
in Table 1.
+-----------------------------+ +-----------------------------+
| Protocol |
+-----------------------------+
| Internet facsimile protocol | | Internet facsimile protocol |
+-----------------------------+ +-----------------------------+
| UDPTL | | UDPTL |
+-----------------------------+ +-----------------------------+
| UDP | | UDP |
+-----------------------------+ +-----------------------------+
| IP | | IP |
+-----------------------------+ +-----------------------------+
Table 1: Protocol stack for UDPTL over UDP Table 1: Protocol stack for UDPTL over UDP
The 3rd Generation Partnership Project (3GPP) has performed a study Implementations exist today for securing this fax transport type.
on how to provide secure fax in the IP Multimedia Subsystem (IMS) and Some of these mechanisms are:
concluded that secure fax shall be transported using UDPTL over DTLS.
o [ITU.T30.2005] Annex H specifies integrity and confidentiality
protection of fax in the application layer, independent of
protocol for fax transport.
o [ITU.T38.2010] specifies fax transport over RTP/SAVP which enables
integrity and confidentiality protection of fax in IP network.
Despite these mechanisms to secure fax, there is no transport layer
security offering integrity and confidentiality protection for UDPTL.
This issue was addressed in a study by the 3rd Generation Partnership
Project (3GPP) on how to provide secure fax in the IP Multimedia
Subsystem (IMS). They concluded that secure fax shall be transported
using 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 for integrity and fax in IP networks. The protocol stack which enhances fax transport
confidentiality protected fax transport using UDPTL over DTLS is to offer integrity and confidentiality using UDPTL over DTLS is shown
shown in Table 2. in Table 2.
+-----------------------------+ +-----------------------------+
| Protocol |
+-----------------------------+
| Internet facsimile protocol | | Internet facsimile protocol |
+-----------------------------+ +-----------------------------+
| UDPTL | | UDPTL |
+-----------------------------+ +-----------------------------+
| DTLS | | DTLS |
+-----------------------------+ +-----------------------------+
| UDP | | UDP |
+-----------------------------+ +-----------------------------+
| IP | | IP |
+-----------------------------+ +-----------------------------+
Table 2: Protocol stack for UDPTL over UDP Table 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, well understood o The design of DTLS [RFC6347] is clearly defined, well understood
and implementations are widely available. 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
Table 2. The UDPTL layer and layers above UDPTL layer require no Table 2. The UDPTL layer and layers above UDPTL layer require no
modification. modification.
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 needs a mechanism to transport UDPTL over DTLS, in order to o 3GPP and the IP fax community need a mechanism to transport UDPTL
provide secure fax in IMS networks. over DTLS in order to provide secure fax in IMS and other SIP-
based networks.
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 [RFC6347]. DTLS record layer "application_data" packets [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].
skipping to change at page 4, line 42 skipping to change at page 4, line 43
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
document are to be interpreted as described in BCP 14, RFC 2119 document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119]. [RFC2119].
DTLS uses the term "session" to refer to a long-lived set of keying 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 material that spans DTLS associations. In this document, in order to
be consistent with SIP/SDP usage of "session" terminology, we use it be consistent with SIP/SDP usage of "session" terminology, we use
to refer to a multimedia session and use the term "DTLS session" to "session" to refer to a multimedia session and use the term "DTLS
refer to the DTLS construct. We use the term "DTLS association" to session" to refer to the DTLS construct. We use the term "DTLS
refer to a particular DTLS cipher suite and keying material set that association" to refer to a particular DTLS cipher suite and keying
is associated with a single host/port quartet. The same DTLS session material set that is associated with a single host/port quartet. The
can be used to establish the keying material for multiple DTLS same DTLS session can be used to establish the keying material for
associations. For consistency with other SIP/SDP usage, we use the multiple DTLS associations. For consistency with other SIP/SDP
term "connection" when what's being referred to is a multimedia usage, we use the term "connection" when what's being referred to is
stream that is not specifically DTLS. a multimedia stream that is not specifically DTLS.
3. Secure Channel 3. Secure Channel
3.1. Secure Channel Establishment 3.1. Secure Channel Establishment
The SDP offer/answer mechanism [RFC3264] is used by other protocols, The SDP offer/answer mechanism [RFC3264] is used by other protocols,
e.g. the Session Initiation Protocol (SIP) [RFC3261], to negotiate e.g. the Session Initiation Protocol (SIP) [RFC3261], to negotiate
and establish multimedia sessions. and establish multimedia sessions.
In addition to the usual contents of an SDP media description ("m=" In addition to the usual contents of an SDP media description ("m="
line) specified for UDPTL over the UDP, each SDP media description line) specified for UDPTL over UDP, each SDP media description for
for UDPTL over DTLS over the UDP will also contain several SDP UDPTL over DTLS over UDP will also contain several SDP attributes,
attributes, as specified in [RFC4145] and [RFC4572]. which were introduced in the context of TCP [RFC4145] and TLS
[RFC4572], and are re-used in this document.
The SDP offer and SDP answer MUST conform to the following The SDP offer and the SDP answer MUST conform to the following
requirements: requirements:
o The endpoint MUST set the "proto" field of the "m=" line to the o The endpoint MUST set the "proto" field of the "m=" line to the
token specified in Table 3. token specified in Table 3.
o The endpoint MUST use the SDP setup attribute [RFC4145]. The o In order to negotiate the TLS roles, the endpoint MUST use the SDP
offerer SHOULD assign the SDP setup attribute with a setup:actpass setup attribute [RFC4145]. The offerer SHOULD assign the SDP
value, and MAY assign the SDP setup attribute with a setup:active setup attribute with a setup:actpass value, and MAY assign the SDP
value or setup:passive value. The offerer MUST NOT assign the SDP setup attribute with a setup:active value or setup:passive value.
setup attribute with a setup:holdconn value. If the offerer The offerer MUST NOT assign the SDP setup attribute with a
assigns the SDP setup attribute with a setup:actpass value or setup:holdconn value. If the offerer assigns the SDP setup
setup:passive value, it MUST be prepared to receive a DTLS attribute with a setup:actpass value or setup:passive value, it
client_hello message before it receives the SDP answer. If the MUST be prepared to receive a DTLS client_hello message before it
answerer accepts the media stream, then it MUST assign the SDP receives the SDP answer. If the answerer accepts the media
setup attribute with either a setup:active value or setup:passive stream, then it MUST assign the SDP setup attribute with either a
value, according to the procedures in [RFC4145]. The answerer setup:active value or setup:passive value, according to the
MUST NOT assign an SDP setup attribute with a setup:holdconn procedures in [RFC4145]. The answerer MUST NOT assign an SDP
value. Whichever party is active, it MUST initiate a DTLS setup attribute with a setup:holdconn value. Whichever party is
handshake by sending a ClientHello over each flow (host/port active, it MUST initiate a DTLS handshake by sending a ClientHello
quartet). over each flow (host/port quartet).
o If the endpoint supports, and is willing to use, a cipher suite o If the endpoint supports, and is willing to use, a cipher suite
with an associated certificate, it MUST include an SDP fingerprint with an associated certificate, it MUST include an SDP fingerprint
attribute [RFC4572] in the SDP. attribute [RFC4572] in the SDP.
o If a cipher suite with an associated certificate is selected o If a cipher suite with an associated certificate is selected
during the DTLS handshake, the certificate received during the during the DTLS handshake, the certificate received during the
DTLS handshake MUST match the fingerprint received in the SDP DTLS 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
session immediately. Note that it is permissible to wait until session immediately. Note that it is permissible to wait until
the other side's fingerprint has been received before establishing the other side's fingerprint has been received before establishing
the connection; however, this may have undesirable latency the connection; however, this may have undesirable latency
effects. effects.
o The endpoint MUST NOT use the SDP connection attribute [RFC4145]. o The endpoint MUST NOT use the SDP connection attribute [RFC4145].
3.2. Secure Channel Usage 3.2. Secure Channel Usage
DTLS is used as specified in [RFC6347]. Once the DTLS handshake is DTLS is used as specified in [RFC6347]. Once the DTLS handshake is
completed, the UDPTL packets SHALL be transported in DTLS record successfully completed (in order to prevent facsimile data from being
layer "application_data" packets. transmitted insecurely), the UDPTL packets SHALL be transported in
DTLS record layer "application_data" packets.
4. Miscellaneous Considerations 4. Miscellaneous Considerations
4.1. Anonymous Calls 4.1. 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 the content of the subjectAltName attribute used for each call and the content of the subjectAltName attribute
inside the certificate MUST NOT contain information that either inside the certificate MUST NOT contain information that either
allows correlation or identification of the user making anonymous allows correlation or identification of the user making anonymous
calls. calls.
skipping to change at page 7, line 30 skipping to change at page 7, line 30
After the DTLS handshake caused by rekeying has completed, because of After the DTLS handshake caused by rekeying has completed, because of
possible packet reordering on the wire, packets protected by the possible packet reordering on the wire, packets protected by the
previous set of keys can arrive. To compensate for this fact, previous set of keys can arrive. To compensate for this fact,
receivers SHOULD maintain both sets of keys for some time in order to receivers SHOULD maintain both sets of keys for some time in order to
be able to decrypt and verify older packets. The duration of be able to decrypt and verify older packets. The duration of
maintaining the previous set of keys after the finish of the DTLS maintaining the previous set of keys after the finish of the DTLS
handshake is out of scope for this document. handshake is out of scope for this document.
5. Security Considerations 5. Security Considerations
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.
The mechanism in this document provides integrity and confidentiality
protection for fax by specifying fax transport using UDPTL over DTLS
[RFC6347].
DTLS media signaled with SIP requires a mechanism to ensure that the DTLS media signaled with SIP requires a mechanism to ensure that the
communicating peers' certificates are correct. communicating peers' certificates are correct.
The standard DTLS strategy for authenticating the communicating The standard DTLS strategy for authenticating the communicating
parties is to give the server (and optionally the client) a PKIX parties is to give the server (and optionally the client) a PKIX
[RFC5280] certificate. The client then verifies the certificate and [RFC5280] certificate. The client then verifies the certificate and
checks that the name in the certificate matches the server's domain checks that the name in the certificate matches the server's domain
name. This works because there are a relatively small number of name. This works because there are a relatively small number of
servers with well-defined names; a situation that does not usually servers with well-defined names; a situation that does not usually
occur in the VoIP context. occur in the VoIP context.
The design described in this document is intended to leverage the The design described in this document is intended to leverage the
authenticity of the signaling channel (while not requiring authenticity of the signaling channel (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
(see sample message flow in Annex A.2) via the SIP Identity [RFC4474] via the SIP Identity [RFC4474] mechanism. Other mechanisms, such as
mechanism. Other mechanisms, such as the S/MIME mechanism [RFC3261], the S/MIME mechanism [RFC3261], or perhaps future mechanisms yet to
or perhaps future mechanisms yet to be specified could also serve be specified could also serve this purpose.
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]).
6. IANA Considerations 6. 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 3 to the table for the SDP Specifically, it adds the values in Table 3 to the table for 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" | [RFC-XXXX] |
+-------+---------------+------------+ +-------+-----------------+------------+
Table 3: SDP "proto" field values Table 3: SDP "proto" field values
[RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this [RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this
document.] document.]
7. Acknowledgments 7. 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 version of the draft, and to Paul E. Jones, James Rafferty, Albrecht
Schwarz and Oscar Ohlsson who provided valuable feedback and input on Schwarz, Oscar Ohlsson and David Hanes who provided valuable feedback
the MMUSIC mailing list. and input on the MMUSIC mailing list.
8. Change Log 8. Change Log
[RFC EDITOR NOTE: Please remove this section when publishing] [RFC EDITOR NOTE: Please remove this section when publishing]
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 Changes from draft-ietf-mmusic-udptl-dtls-01
o Usage of the SDP fingerprint attribute depends on whether a cipher o Usage of the SDP fingerprint attribute depends on whether a cipher
suite with an associated certificate is used. suite with an associated certificate is used.
o Editor's note in section 4.2 removed. Procedure text added. o Editor's note in section 4.2 removed. Procedure text added.
Changes from draft-ietf-mmusic-udptl-dtls-00 Changes from draft-ietf-mmusic-udptl-dtls-00
o SDP offerer is allowed to assign an a=setup:active or o SDP offerer is allowed to assign an a=setup:active or
a=setup:passive value, in addition to the recommended a=setup:passive value, in addition to the recommended
skipping to change at page 10, line 50 skipping to change at page 11, line 25
International Telecommunications Union, "Procedures for International Telecommunications Union, "Procedures for
real-time Group 3 facsimile communication over IP real-time Group 3 facsimile communication over IP
networks", ITU-T Recommendation T.38, September 2010. networks", ITU-T Recommendation T.38, September 2010.
9.2. Informative References 9.2. Informative References
[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.
Appendix A. Example 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 which 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. Transport between proxies should also be protected somehow. 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 somehow.
Only one element is shown for Alice's and Bob's proxies for the Only one element is shown for Alice's and Bob's proxies for the
purposes of simplification. purposes of simplification.
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 with Identity A.2. Basic Message Flow
Figure 1 shows an example message flow of session establishment for Figure 1 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 DTLS In this example flow, Alice acts as the passive endpoint of the DTLS
association and Bob acts as the active endpoint of DTLS association. association and Bob acts as the active endpoint of the DTLS
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 |
|<----------------------------------------------->| |<----------------------------------------------->|
skipping to change at page 11, line 49 skipping to change at page 12, line 26
| | (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 1: Basic message flow with Identity Figure 1: Basic message flow
Message (1): Message (1):
Figure 2 shows the initial INVITE request sent by Alice to Alice's Figure 2 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:actpass attribute in the SDP offer indicates that The SDP setup:actpass attribute in the SDP offer indicates that
Alice has requested to be either the active or passive endpoint. Alice has requested to be either the active or passive endpoint.
The SDP fingerprint attribute in the SDP offer indicates the The SDP fingerprint attribute in the SDP offer contains the
certificate fingerprint computed from Alice's self-signed certificate fingerprint computed from Alice's self-signed
certificate. certificate.
INVITE sip:bob@example.com SIP/2.0 INVITE sip:bob@example.com SIP/2.0
To: <sip:bob@example.com> To: <sip:bob@example.com>
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
Contact: <sip:alice@ua1.example.com> Contact: <sip:alice@ua1.example.com>
Call-ID: 6076913b1c39c212@REVMTEpG Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE CSeq: 1 INVITE
skipping to change at page 13, line 7 skipping to change at page 13, line 35
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 2: Message (1) Figure 2: Message (1)
Message (2): Message (2):
Figure 3 shows the SIP INVITE request sent by Bob's proxy to Bob. Figure 3 shows the SIP INVITE request sent by Bob's proxy to Bob.
The SIP INVITE request contains an Identity header field and an
Identity-Info header fields inserted by Alice's proxy.
When received, Bob verifies the identity provided in the SIP When received, Bob verifies the identity provided in the SIP
INVITE request. INVITE request.
INVITE sip:bob@ua2.example.com SIP/2.0 INVITE sip:bob@ua2.example.com SIP/2.0
To: <sip:bob@example.com> To: <sip:bob@example.com>
From: "Alice"<sip:alice@example.com>;tag=843c7b0b From: "Alice"<sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS proxy.example.com;branch=z9hG4bK-0e53sadfkasldk Via: SIP/2.0/TLS proxy.example.com;branch=z9hG4bK-0e53sadfkasldk
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>
Contact: <sip:alice@ua1.example.com> Contact: <sip:alice@ua1.example.com>
Call-ID: 6076913b1c39c212@REVMTEpG Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE CSeq: 1 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE
Max-Forwards: 69 Max-Forwards: 69
Identity: CyI4+nAkHrH3ntmaxgr01TMxTmtjP7MASwliNRdupRI1vpkXRvZXx1ja9k
3W+v1PDsy32MaqZi0M5WfEkXxbgTnPYW0jIoK8HMyY1VT7egt0kk4XrKFC
HYWGCl0nB2sNsM9CG4hq+YJZTMaSROoMUBhikVIjnQ8ykeD6UXNOyfI=
Identity-Info: https://example.com/cert
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: xxxx Content-Length: xxxx
Supported: from-change Supported: from-change
v=0 v=0
o=- 1181923068 1181923196 IN IP4 ua1.example.com o=- 1181923068 1181923196 IN IP4 ua1.example.com
s=- s=-
c=IN IP4 ua1.example.com c=IN IP4 ua1.example.com
t=0 0 t=0 0
m=image 6056 UDP/TLS/UDPTL t38 m=image 6056 UDP/TLS/UDPTL t38
skipping to change at page 14, line 14 skipping to change at page 14, line 47
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, 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 the 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 3. In this received in the a=fingerprint SDP attribute of Figure 3. In this
message flow, the check is successful and thus session setup message flow, the check is successful and thus session setup
continues. continues.
Message (5): Message (5):
Figure 4 shows a SIP 200 (OK) response to the initial SIP INVITE Figure 4 shows a SIP 200 (OK) response to the initial SIP INVITE
request, sent by Bob to Bob's proxy. The SIP 200 (OK) response request, sent by Bob to Bob's proxy. The SIP 200 (OK) response
contains an SDP answer. contains an SDP answer.
The "m=" line in the SDP answer indicates T.38 fax using UDPTL The "m=" line in the SDP answer indicates T.38 fax using UDPTL
over DTLS. over DTLS.
The SDP setup:active attribute in the SDP answer indicates that The SDP setup:active attribute in the SDP answer indicates that
Bob has requested to be the active endpoint. Bob has requested to be the active endpoint.
The SDP fingerprint attribute in the SDP answer indicates the The SDP fingerprint attribute in the SDP answer contains the
certificate fingerprint computed from Bob's self-signed certificate fingerprint computed from Bob's self-signed
certificate. certificate.
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 proxy.example.com:5061;branch=z9hG4bK-0e53sadfkasldk Via: SIP/2.0/TLS proxy.example.com:5061;branch=z9hG4bK-0e53sadfkasldk
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
skipping to change at page 15, line 31 skipping to change at page 17, line 5
Message (6): Message (6):
Figure 5 shows a SIP 200 (OK) response to the initial SIP INVITE Figure 5 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 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 and thus 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>
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: xxxx Content-Length: xxxx
Supported: from-change Supported: from-change
v=0 v=0
o=- 8965454521 2105372818 IN IP4 ua2.example.com o=- 8965454521 2105372818 IN IP4 ua2.example.com
s=- s=-
c=IN IP4 ua2.example.com c=IN IP4 ua2.example.com
t=0 0 t=0 0
m=image 12000 UDP/TLS/UDPTL t38 m=image 12000 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 5: Message (6) Figure 5: Message (6)
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
Figure 6 focuses on T.38 fax securely transported using UDPTL over Traditionally, most session with non-secure transport of T.38 fax,
DTLS replacing audio media stream in an existing audio-only session. transported using UDPTL, are established by modifying an ongoing
audio session into a fax session. Figure 6 shows an example message
flow of modifying an existing audio session into a session with T.38
fax securely transported using UDPTL over DTLS.
In this example flow, Alice acts as the passive endpoint of DTLS In this example flow, Alice acts as the passive endpoint of the DTLS
association and Bob acts as the active endpoint of DTLS association. association and Bob acts as the active endpoint of the DTLS
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 |
|<------------------------------------------------| |<------------------------------------------------|
skipping to change at page 17, line 12 skipping to change at page 18, line 40
Figure 6: Message Flow Of T.38 Fax Replacing Audio Media Stream in An Figure 6: 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. SDP offer included in the SIP Alice sends SIP re-INVITE request. The SDP offer included in the
re-INVITE request shown in Figure 7. SIP re-INVITE request is shown in Figure 7.
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 offer indicates being removed. The second "m=" line in the SDP offer indicates
T.38 fax using UDPTL over DTLS being added. T.38 fax using UDPTL over DTLS being added.
The SDP setup:actpass attribute in the SDP offer indicates that The SDP setup:actpass attribute in the SDP offer indicates that
Alice has requested to be either the active or passive endpoint. Alice has requested to be either the active or passive endpoint.
The SDP fingerprint attribute in the SDP offer indicates the The SDP fingerprint attribute in the SDP offer contains the
certificate fingerprint computed from Alice's self-signed certificate fingerprint computed from Alice's self-signed
certificate. certificate.
v=0 v=0
o=- 2465353433 3524244442 IN IP4 ua1.example.com o=- 2465353433 3524244442 IN IP4 ua1.example.com
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
skipping to change at page 18, line 11 skipping to change at page 19, line 35
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, Finished).
When Bob receives Alice's certificate via DTLS, Bob checks whether When Bob receives the certificate of Alice via DTLS, Bob checks
the certificate fingerprint calculated from Alice's certificate whether the certificate fingerprint calculated from Alice's
received via DTLS matches the certificate fingerprint received in certificate received via DTLS matches the certificate fingerprint
the a=fingerprint SDP attribute of Figure 7. In this message received in the a=fingerprint SDP attribute of Figure 7. In this
flow, the check is successful and thus session setup continues. message flow, the check is successful and thus session setup
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 Figure The SIP 200 (OK) response contains an SDP answer shown in
8. Figure 8.
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
T.38 fax using UDPTL over DTLS being added. T.38 fax using UDPTL over DTLS being added.
The SDP setup:active attribute in the SDP answer indicates that The SDP setup:active attribute in the SDP answer indicates that
Bob has requested to be the active endpoint. Bob has requested to be the active endpoint.
The SDP fingerprint attribute in the SDP answer indicates the The SDP fingerprint attribute in the SDP answer contains the
certificate fingerprint computed from Bob's self-signed certificate fingerprint computed from Bob's self-signed
certificate. certificate.
v=0 v=0
o=- 4423478999 5424222292 IN IP4 ua2.example.com o=- 4423478999 5424222292 IN IP4 ua2.example.com
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
 End of changes. 46 change blocks. 
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