draft-ietf-mmusic-dtls-sdp-24.txt   draft-ietf-mmusic-dtls-sdp-25.txt 
Network Working Group C. Holmberg Network Working Group C. Holmberg
Internet-Draft Ericsson Internet-Draft Ericsson
Updates: 5763,7345 (if approved) R. Shpount Updates: 5763,7345 (if approved) R. Shpount
Intended status: Standards Track TurboBridge Intended status: Standards Track TurboBridge
Expires: October 22, 2017 April 20, 2017 Expires: December 23, 2017 June 21, 2017
Using the SDP Offer/Answer Mechanism for DTLS Using the SDP Offer/Answer Mechanism for DTLS
draft-ietf-mmusic-dtls-sdp-24.txt draft-ietf-mmusic-dtls-sdp-25.txt
Abstract Abstract
This document defines the SDP offer/answer procedures for negotiating This document defines the SDP offer/answer procedures for negotiating
and establishing a DTLS association. The document also defines the and establishing a DTLS association. The document also defines the
criteria for when a new DTLS association must be established. The criteria for when a new DTLS association must be established. The
document updates RFC 5763 and RFC 7345, by replacing common SDP document updates RFC 5763 and RFC 7345, by replacing common SDP
offer/answer procedures with a reference to this specification. offer/answer procedures with a reference to this specification.
This document defines a new SDP media-level attribute, 'tls-id'. This document defines a new SDP media-level attribute, 'tls-id'.
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This Internet-Draft will expire on October 22, 2017. This Internet-Draft will expire on December 23, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Establishing a new DTLS Association . . . . . . . . . . . . . 4 3. Establishing a new DTLS Association . . . . . . . . . . . . . 4
3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Change of Local Transport Parameters . . . . . . . . . . 4 3.2. Change of Local Transport Parameters . . . . . . . . . . 4
3.3. Change of ICE ufrag value . . . . . . . . . . . . . . . . 5 3.3. Change of ICE ufrag value . . . . . . . . . . . . . . . . 5
4. SDP tls-id Attribute . . . . . . . . . . . . . . . . . . . . 5 4. SDP tls-id Attribute . . . . . . . . . . . . . . . . . . . . 5
5. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 6 5. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 6
5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Generating the Initial SDP Offer . . . . . . . . . . . . 8 5.2. Generating the Initial SDP Offer . . . . . . . . . . . . 8
5.3. Generating the Answer . . . . . . . . . . . . . . . . . . 8 5.3. Generating the Answer . . . . . . . . . . . . . . . . . . 9
5.4. Offerer Processing of the SDP Answer . . . . . . . . . . 9 5.4. Offerer Processing of the SDP Answer . . . . . . . . . . 10
5.5. Modifying the Session . . . . . . . . . . . . . . . . . . 10 5.5. Modifying the Session . . . . . . . . . . . . . . . . . . 10
6. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 10 6. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Transport Protocol Considerations . . . . . . . . . . . . . . 11 7. Transport Protocol Considerations . . . . . . . . . . . . . . 11
7.1. Transport Re-Usage . . . . . . . . . . . . . . . . . . . 11 7.1. Transport Re-Usage . . . . . . . . . . . . . . . . . . . 11
8. TLS Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. TLS Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 12 9. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . . 13 10. RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. General . . . . . . . . . . . . . . . . . . . . . . . . 13 10.1. General . . . . . . . . . . . . . . . . . . . . . . . . 14
10.2. Update to RFC 5763 . . . . . . . . . . . . . . . . . . . 13 10.2. Update to RFC 5763 . . . . . . . . . . . . . . . . . . . 14
10.2.1. Update to section 5 . . . . . . . . . . . . . . . . 13 10.2.1. Update to section 5 . . . . . . . . . . . . . . . . 14
10.2.2. Update to section 6.6 . . . . . . . . . . . . . . . 17 10.2.2. Update to section 6.6 . . . . . . . . . . . . . . . 15
10.2.3. Update to section 6.7.1 . . . . . . . . . . . . . . 17 10.2.3. Update to section 6.7.1 . . . . . . . . . . . . . . 16
10.3. Update to RFC 7345 . . . . . . . . . . . . . . . . . . . 18 10.3. Update to RFC 7345 . . . . . . . . . . . . . . . . . . . 16
10.3.1. Update to section 4 . . . . . . . . . . . . . . . . 18 10.3.1. Update to section 4 . . . . . . . . . . . . . . . . 16
10.3.2. Update to section 5.2.1 . . . . . . . . . . . . . . 21 10.3.2. Update to section 5.2.1 . . . . . . . . . . . . . . 16
11. Security Considerations . . . . . . . . . . . . . . . . . . . 21 11. Security Considerations . . . . . . . . . . . . . . . . . . . 17
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
14. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 22 14. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 17
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
15.1. Normative References . . . . . . . . . . . . . . . . . . 26 15.1. Normative References . . . . . . . . . . . . . . . . . . 22
15.2. Informative References . . . . . . . . . . . . . . . . . 27 15.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction 1. Introduction
[RFC5763] defines SDP offer/answer procedures for SRTP-DTLS. [RFC5763] defines SDP offer/answer procedures for SRTP-DTLS.
[RFC7345] defines SDP offer/answer procedures for UDPTL-DTLS. This [RFC7345] defines SDP offer/answer procedures for UDPTL-DTLS. This
specification defines general offer/answer procedures for DTLS, based specification defines general offer/answer procedures for DTLS, based
on the procedures in [RFC5763]. Other specifications, defining on the procedures in [RFC5763]. Other specifications, defining
specific DTLS usages, can then reference this specification, in order specific DTLS usages, can then reference this specification, in order
to ensure that the DTLS aspects are common among all usages. Having to ensure that the DTLS aspects are common among all usages. Having
common procedures is essential when multiple usages share the same common procedures is essential when multiple usages share the same
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always require a new DTLS association to be established, but always require a new DTLS association to be established, but
currently there is no way to explicitly indicate in an SDP offer or currently there is no way to explicitly indicate in an SDP offer or
answer whether a new DTLS association is required. To solve that answer whether a new DTLS association is required. To solve that
problem, this document defines a new SDP attribute, 'tls-id'. The problem, this document defines a new SDP attribute, 'tls-id'. The
pair of SDP 'tls-id' attribute values (the attribute values of the pair of SDP 'tls-id' attribute values (the attribute values of the
offerer and the answerer) uniquely identifies the DTLS association. offerer and the answerer) uniquely identifies the DTLS association.
Providing a new value of the 'tls-id' attribute in an SDP offer or Providing a new value of the 'tls-id' attribute in an SDP offer or
answers can be used to indicate whether a new DTLS association is to answers can be used to indicate whether a new DTLS association is to
be established. be established.
The SDP 'tls-id' attribute can also be used for negotiating a TLS The SDP 'tls-id' attribute can be specified when negotiating a TLS
connection, using the procedures in this document in conjunction with connection, using the procedures in this document in conjunction with
the procedures in [RFC5763] and [RFC8122]. The TLS specific the procedures in [RFC5763] and [RFC8122]. The unique combination of
considerations are described in Section 8. SDP 'tls-id' attribute values can be used to identity the negotiated
TLS connection. The unique value can be used, for example, within
TLS protocol extensions to differentiate between multiple TLS
connections and correlate those connections with specific offer/
answer exchanges. The TLS specific considerations are described in
Section 8.
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 [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Establishing a new DTLS Association 3. Establishing a new DTLS Association
3.1. General 3.1. General
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permissible to wait until the other side's fingerprint(s) has been permissible to wait until the other side's fingerprint(s) has been
received before establishing the connection; however, this may have received before establishing the connection; however, this may have
undesirable latency effects. undesirable latency effects.
SDP offerers and answerers might reuse certificates across multiple SDP offerers and answerers might reuse certificates across multiple
DTLS associations, and provide identical fingerprint values for each DTLS associations, and provide identical fingerprint values for each
DTLS association. The combination of the SDP 'tls-id' attribute DTLS association. The combination of the SDP 'tls-id' attribute
values of the SDP offerer and answerer identifies each individual values of the SDP offerer and answerer identifies each individual
DTLS association. DTLS association.
NOTE: There are cases where the SDP a€˜tls-ida€™
attribute value generated by the offerer will end up being used for
multiple DTLS associations. For that reason the combination of the
attribute values of the offerer and answerer is needed in order to
identity a DTLS association. An example of such case is where the
offerer sends an updated offer (Section 5.5), without modifying its
attribute value, but the answerer determines that a new DTLS
association is to be created. The answerer will generate a new local
attribute value for the new DTLS association (Section 5.3), while the
offerer will use the same attribute value that it used for the
current association. Another example is when the Session Initiation
Protocol (SIP) [RFC3261] is used for signalling, and an offer is
forked to multiple answerers. The attribute value generated by the
offerer will be used for DTLS associations established by each
answerer.
5.2. Generating the Initial SDP Offer 5.2. Generating the Initial SDP Offer
When an offerer sends the initial offer, the offerer MUST insert an When an offerer sends the initial offer, the offerer MUST insert an
SDP 'setup' attribute according to the procedures in [RFC4145], and SDP 'setup' attribute [RFC4145] with an 'actpass' attribute value,
one or more SDP 'fingerprint' attributes according to the procedures and one or more SDP 'fingerprint' attributes according to the
in [RFC8122]. In addition, the offerer MUST insert in the offer an procedures in [RFC8122]. In addition, the offerer MUST insert in the
SDP 'tls-id' attribute with a unique value. offer an SDP 'tls-id' attribute with a unique attribute value.
If the offerer inserts the SDP 'setup' attribute with an 'actpass' or As the offerer inserts the SDP 'setup' attribute with an 'actpass'
'passive' attribute value, the offerer MUST be prepared to receive a attribute value, the offerer MUST be prepared to receive a DTLS
DTLS ClientHello message (if a new DTLS association is established by ClientHello message (if a new DTLS association is established by the
the answerer) from the answerer before the offerer receives the SDP answerer) from the answerer before the offerer receives the SDP
answer. answer.
If the offerer receives a DTLS ClientHello message, and a DTLS
association is established, before the offerer receives the SDP
Answer carrying the fingerprint associated with the DTLS association,
any data received on the DTLS association before the fingerprint MUST
be considered coming from an unverified source. The processing of
such data, and sending of data by the offerer to the unverified
source, is outside the scope of this document.
5.3. Generating the Answer 5.3. Generating the Answer
When an answerer sends an answer, the answerer MUST insert in the When an answerer sends an answer, the answerer MUST insert in the
answer an SDP 'setup' attribute according to the procedures in answer an SDP 'setup' attribute according to the procedures in
[RFC4145], and one or more SDP 'fingerprint' attributes according to [RFC4145], and one or more SDP 'fingerprint' attributes according to
the procedures in [RFC8122]. If the answerer determines, based on the procedures in [RFC8122]. If the answerer determines, based on
the criteria specified in Section 3.1, that a new DTLS association is the criteria specified in Section 3.1, that a new DTLS association is
to be established, the answerer MUST insert in the associated answer to be established, the answerer MUST insert in the associated answer
an SDP 'tls-id' attribute with a new unique value. Note that the an SDP 'tls-id' attribute with a new unique attribute value. Note
offerer and answerer generate their own local 'tls-id' attribute that the offerer and answerer generate their own local 'tls-id'
values, and the combination of both values identify the DTLS attribute values, and the combination of both values identify the
association. DTLS association.
If the answerer receives an offer that requires establishment of a If the answerer receives an offer that requires establishment of a
new DTLS association, and if the answerer does not accept the new DTLS association, and if the answerer does not accept the
establishment of a new DTLS association, the answerer MUST reject the establishment of a new DTLS association, the answerer MUST reject the
"m=" lines associated with the suggested DTLS association [RFC3264]. "m=" lines associated with the suggested DTLS association [RFC3264].
If an answerer receives an offer that does not require the If an answerer receives an offer that does not require the
establishment of a new DTLS association, and if the answerer establishment of a new DTLS association, and if the answerer
determines that a new DTLS association is not to be established, the determines that a new DTLS association is not to be established, the
answerer MUST insert an SDP 'tls-id' attribute with the previously answerer MUST insert an SDP 'tls-id' attribute with the previously
assigned value in the associated answer. In addition, the answerer assigned attribute value in the associated answer. In addition, the
MUST insert an SDP 'setup' attribute with a value that does not answerer MUST insert an SDP 'setup' attribute with an attribute value
change the previously negotiated DTLS roles, and one or more SDP that does not change the previously negotiated DTLS roles, and one or
'fingerprint' attributes values that do not change the previously more SDP 'fingerprint' attributes values that do not change the
sent fingerprint set, in the associated answer. previously sent fingerprint set, in the associated answer.
If the answerer receives an offer that does not contain an SDP 'tls- If the answerer receives an offer that does not contain an SDP 'tls-
id' attribute, the answerer MUST NOT insert a 'tls-id' attribute in id' attribute, the answerer MUST NOT insert a 'tls-id' attribute in
the answer. the answer.
If a new DTLS association is to be established, and if the answerer If a new DTLS association is to be established, and if the answerer
inserts an SDP 'setup' attribute with an 'active' value in the inserts an SDP 'setup' attribute with an 'active' attribute value in
answer, the answerer MUST initiate a DTLS handshake by sending a DTLS the answer, the answerer MUST initiate a DTLS handshake by sending a
ClientHello message towards the offerer. DTLS ClientHello message towards the offerer.
Eventhough an offerer is required to insert an 'SDP' setup attribute
with an 'actpass' attribute value in initial offers (Section 5.2) and
subsequent offers (Section 5.5), the answerer MUST be able to receive
initial and subsequent offers with other attribute values, in order
to be backward compatible with older implementations that might
insert other attribute values in initial and subsequent offers.
5.4. Offerer Processing of the SDP Answer 5.4. Offerer Processing of the SDP Answer
When an offerer receives an answer that establishes a new DTLS When an offerer receives an answer that establishes a new DTLS
association based on criteria defined in Section 3.1, and if the association based on criteria defined in Section 3.1, and if the
offerer becomes DTLS client (based on the value of the SDP 'setup' offerer becomes DTLS client (based on the value of the SDP 'setup'
attribute value [RFC4145]), the offerer MUST establish a DTLS attribute value [RFC4145]), the offerer MUST establish a DTLS
association. If the offerer becomes DTLS server, it MUST wait for association. If the offerer becomes DTLS server, it MUST wait for
the answerer to establish the DTLS association. the answerer to establish the DTLS association.
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NOTE: A new DTLS association can be established based on changes in NOTE: A new DTLS association can be established based on changes in
either an SDP offer or answer. When communicating with legacy either an SDP offer or answer. When communicating with legacy
endpoints, an offerer can receive an answer that includes the same endpoints, an offerer can receive an answer that includes the same
fingerprint set and setup role. A new DTLS association MUST still be fingerprint set and setup role. A new DTLS association MUST still be
established if such an answer was received as a response to an offer established if such an answer was received as a response to an offer
which requested the establishment of a new DTLS association. which requested the establishment of a new DTLS association.
5.5. Modifying the Session 5.5. Modifying the Session
When the offerer sends a subsequent offer, and if the offerer wants When an offerer sends a subsequent offer, and if the offerer wants to
to establish a new DTLS association, the offerer MUST insert an SDP establish a new DTLS association, the offerer MUST insert an SDP
'setup' attribute according to the procedures in [RFC4145], and one 'setup' attribute [RFC4145] with an 'actpass' attribute value, and
or more SDP 'fingerprint' attributes according to the procedures in one or more SDP 'fingerprint' attributes according to the procedures
[RFC8122]. In addition, the offerer MUST insert in the offer an SDP in [RFC8122]. In addition, the offerer MUST insert in the offer an
'tls-id' attribute with a new unique value. SDP 'tls-id' attribute with a new unique attribute value.
When the offerer sends a subsequent offer, and the offerer does not When an offerer sends a subsequent offer, and the offerer does not
want to establish a new DTLS association, and if a previously want to establish a new DTLS association, and if a previously
established DTLS association exists, the offerer MUST insert an SDP established DTLS association exists, the offerer MUST insert an SDP
'tls-id' attribute with the previously assigned value in the offer. 'setup' attribute with an 'actpass' attribute value, and one or more
In addition, the offerer MUST insert an SDP 'setup' attribute, and SDP 'fingerprint' attributes with attribute values that do not change
one or more SDP 'fingerprint' attributes with values that do not the previously sent fingerprint set, in the offer. In addition, the
change the previously sent fingerprint set, in the offer. The value offerer MUST insert an SDP 'tls-id' attribute with the previously
of the 'setup' attribute SHOULD be set to 'actpass', in order to assigned attribute value in the offer.
allow the answerer to establish a new DTLS association with a
different role, but MAY be set to the current negotiated role
('active' or 'passive'). It MUST NOT be set to a value that changes
the current negotiated role.
NOTE: When a new DTLS association is being established, each endpoint NOTE: When a new DTLS association is being established, each endpoint
needs to be prepared to receive data on both the new and old DTLS needs to be prepared to receive data on both the new and old DTLS
associations as long as both are alive. associations as long as both are alive.
6. ICE Considerations 6. ICE Considerations
When the Interactive Connectivity Establishment (ICE) mechanism When the Interactive Connectivity Establishment (ICE) mechanism
[I-D.ietf-ice-rfc5245bis] is used, the ICE connectivity checks are [I-D.ietf-ice-rfc5245bis] is used, the ICE connectivity checks are
performed before the DTLS handshake begins. Note that if aggressive performed before the DTLS handshake begins. Note that if aggressive
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As specified in [RFC4145], the SDP 'connection' attribute is used to As specified in [RFC4145], the SDP 'connection' attribute is used to
indicate whether to establish a new TLS connection. An offerer and indicate whether to establish a new TLS connection. An offerer and
answerer MUST ensure that the 'connection' attribute value and the answerer MUST ensure that the 'connection' attribute value and the
'tls-id' attribute value does not cause a conflict regarding whether 'tls-id' attribute value does not cause a conflict regarding whether
a new TLS connection is to be established or not. a new TLS connection is to be established or not.
NOTE: Even though the SDP 'connection' attribute can be used to NOTE: Even though the SDP 'connection' attribute can be used to
indicate whether a new TLS connection is to be established, the indicate whether a new TLS connection is to be established, the
unique combination of SDP 'tls-id' attribute values can be used to unique combination of SDP 'tls-id' attribute values can be used to
identity a TLS connection. The unique value can be used e.g., within identity a TLS connection. The unique value can be used e.g., within
TLS protocol extensions to differentiate between mulitple TLS TLS protocol extensions to differentiate between multiple TLS
connections and correlate those connections with specific offer/ connections and correlate those connections with specific offer/
answer exchanges. answer exchanges.
If an offerer or answerer inserts an SDP 'connection' attribute with If an offerer or answerer inserts an SDP 'connection' attribute with
a 'new' value in the offer/answer and also inserts an SDP 'tls-id' a 'new' value in the offer/answer and also inserts an SDP 'tls-id'
attribute, the value of tls-id' attribute MUST be new and unique. attribute, the value of tls-id' attribute MUST be new and unique.
If an offerer or answerer inserts an SDP 'connection' attribute with If an offerer or answerer inserts an SDP 'connection' attribute with
a 'existing' value in the offer/answer, if a previously established a 'existing' value in the offer/answer, if a previously established
TLS connection exists, and if the offerer/answerer previously TLS connection exists, and if the offerer/answerer previously
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9. SIP Considerations 9. SIP Considerations
When the Session Initiation Protocol (SIP) [RFC3261] is used as the When the Session Initiation Protocol (SIP) [RFC3261] is used as the
signal protocol for establishing a multimedia session, dialogs signal protocol for establishing a multimedia session, dialogs
[RFC3261] might be established between the caller and multiple [RFC3261] might be established between the caller and multiple
callees. This is referred to as forking. If forking occurs, callees. This is referred to as forking. If forking occurs,
separate DTLS associations will be established between the caller and separate DTLS associations will be established between the caller and
each callee. each callee.
When forking occurs, an SDP offerer can receive DTLS ClientHello
messages and SDP answerers from multiple remote locations. Because
of this, the offerer might have to wait for multiple SDP answers
(from different remote locations) until it receives a certificate
fingerprint that matches the certificate associated with a specific
DTLS handshake. The offerer MUST NOT decleare a fingerprint mismatch
until it determines that it will not receive SDP answers from any
additional remote locations.
It is possible to send an INVITE request which does not contain an It is possible to send an INVITE request which does not contain an
SDP offer. Such an INVITE request is often referred to as an 'empty SDP offer. Such an INVITE request is often referred to as an 'empty
INVITE', or an 'offer-less INVITE'. The receiving endpoint will INVITE', or an 'offer-less INVITE'. The receiving endpoint will
include the SDP offer in a response to the request. When the include the SDP offer in a response to the request. When the
endpoint generates such SDP offer, if a previously established DTLS endpoint generates such SDP offer, if a previously established DTLS
association exists, the offerer MUST insert an SDP 'tls-id' association exists, the offerer MUST insert an SDP 'tls-id'
attribute, and one or more SDP 'fingerprint' attributes, with attribute, and one or more SDP 'fingerprint' attributes, with
previously assigned attribute values. If a previously established previously assigned attribute values. If a previously established
DTLS association did not exist, the offer MUST be generated based on DTLS association did not exist, the offer MUST be generated based on
the same rules as a new offer (see Section 5.2). Regardless of the the same rules as a new offer (see Section 5.2). Regardless of the
skipping to change at page 13, line 23 skipping to change at page 14, line 16
10.1. General 10.1. General
This section updates specifications that use DTLS-protected media, in This section updates specifications that use DTLS-protected media, in
order to reflect the procedures defined in this specification. order to reflect the procedures defined in this specification.
10.2. Update to RFC 5763 10.2. Update to RFC 5763
10.2.1. Update to section 5 10.2.1. Update to section 5
OLD TEXT: The text in section 5 (Establishing a Secure Channel) is replaced
with the new text below:
5. Establishing a Secure Channel
The two endpoints in the exchange present their identities as part of
the DTLS handshake procedure using certificates. This document uses
certificates in the same style as described in "Connection-Oriented
Media Transport over the Transport Layer Security (TLS) Protocol in
the Session Description Protocol (SDP)" [RFC4572].
If self-signed certificates are used, the content of the
subjectAltName attribute inside the certificate MAY use the uniform
resource identifier (URI) of the user. This is useful for debugging
purposes only and is not required to bind the certificate to one of
the communication endpoints. The integrity of the certificate is
ensured through the fingerprint attribute in the SDP. The
subjectAltName is not an important component of the certificate
verification.
The generation of public/private key pairs is relatively expensive.
Endpoints are not required to generate certificates for each session.
The offer/answer model, defined in [RFC3264], is used by protocols
like the Session Initiation Protocol (SIP) [RFC3261] to set up
multimedia sessions. In addition to the usual contents of an SDP
[RFC4566] message, each media description ("m=" line and associated
parameters) will also contain several attributes as specified in
[RFC5764], [RFC4145], and [RFC4572].
When an endpoint wishes to set up a secure media session with another
endpoint, it sends an offer in a SIP message to the other endpoint.
This offer includes, as part of the SDP payload, the fingerprint of
the certificate that the endpoint wants to use. The endpoint SHOULD
send the SIP message containing the offer to the offerer's SIP proxy
over an integrity protected channel. The proxy SHOULD add an
Identity header field according to the procedures outlined in
[RFC4474]. The SIP message containing the offer SHOULD be sent to
the offerer's SIP proxy over an integrity protected channel. When
the far endpoint receives the SIP message, it can verify the identity
of the sender using the Identity header field. Since the Identity
header field is a digital signature across several SIP header fields,
in addition to the body of the SIP message, the receiver can also be
certain that the message has not been tampered with after the digital
signature was applied and added to the SIP message.
The far endpoint (answerer) may now establish a DTLS association with
the offerer. Alternately, it can indicate in its answer that the
offerer is to initiate the TLS association. In either case, mutual
DTLS certificate-based authentication will be used. After completing
the DTLS handshake, information about the authenticated identities,
including the certificates, are made available to the endpoint
application. The answerer is then able to verify that the offerer's
certificate used for authentication in the DTLS handshake can be
associated to the certificate fingerprint contained in the offer in
the SDP. At this point, the answerer may indicate to the end user
that the media is secured. The offerer may only tentatively accept
the answerer's certificate since it may not yet have the answerer's
certificate fingerprint.
When the answerer accepts the offer, it provides an answer back to
the offerer containing the answerer's certificate fingerprint. At
this point, the offerer can accept or reject the peer's certificate
and the offerer can indicate to the end user that the media is
secured.
Note that the entire authentication and key exchange for securing the
media traffic is handled in the media path through DTLS. The
signaling path is only used to verify the peers' certificate
fingerprints.
The offer and answer MUST conform to the following requirements.
o The endpoint MUST use the setup attribute defined in [RFC4145].
The endpoint that is the offerer MUST use the setup attribute
value of setup:actpass and be prepared to receive a client_hello
before it receives the answer. The answerer MUST use either a
setup attribute value of setup:active or setup:passive. Note that
if the answerer uses setup:passive, then the DTLS handshake will
not begin until the answerer is received, which adds additional
latency. setup:active allows the answer and the DTLS handshake to
occur in parallel. Thus, setup:active is RECOMMENDED. Whichever
party is active MUST initiate a DTLS handshake by sending a
ClientHello over each flow (host/port quartet).
o The endpoint MUST NOT use the connection attribute defined in
[RFC4145].
o The endpoint MUST use the certificate fingerprint attribute as
specified in [RFC4572].
o The certificate presented during the DTLS handshake MUST match the
fingerprint exchanged via the signaling path in the SDP. The
security properties of this mechanism are described in Section 8.
o If the fingerprint does not match the hashed certificate, then the
endpoint MUST tear down the media session immediately. Note that
it is permissible to wait until the other side's fingerprint has
been received before establishing the connection; however, this
may have undesirable latency effects.
NEW TEXT: NEW TEXT:
5. Establishing a Secure Channel
The two endpoints in the exchange present their identities as part of The two endpoints in the exchange present their identities as part of
the DTLS handshake procedure using certificates. This document uses the DTLS handshake procedure using certificates. This document uses
certificates in the same style as described in "Connection-Oriented certificates in the same style as described in "Connection-Oriented
Media Transport over the Transport Layer Security (TLS) Protocol in Media Transport over the Transport Layer Security (TLS) Protocol in
the Session Description Protocol (SDP)" [RFC4572]. the Session Description Protocol (SDP)" [RFC4572].
If self-signed certificates are used, the content of the If self-signed certificates are used, the content of the
subjectAltName attribute inside the certificate MAY use the uniform subjectAltName attribute inside the certificate MAY use the uniform
resource identifier (URI) of the user. This is useful for debugging resource identifier (URI) of the user. This is useful for debugging
purposes only and is not required to bind the certificate to one of purposes only and is not required to bind the certificate to one of
skipping to change at page 17, line 7 skipping to change at page 15, line 38
Note that the entire authentication and key exchange for securing Note that the entire authentication and key exchange for securing
the media traffic is handled in the media path through DTLS. The the media traffic is handled in the media path through DTLS. The
signaling path is only used to verify the peers' certificate signaling path is only used to verify the peers' certificate
fingerprints. fingerprints.
The offerer and answerer MUST follow the SDP offer/answer procedures The offerer and answerer MUST follow the SDP offer/answer procedures
defined in [RFCXXXX]. defined in [RFCXXXX].
10.2.2. Update to section 6.6 10.2.2. Update to section 6.6
OLD TEXT: The text in section 6.6 (Session Modification) is replaced with the
new text below:
6.6. Session Modification
Once an answer is provided to the offerer, either endpoint MAY
request a session modification that MAY include an updated offer.
This session modification can be carried in either an INVITE or
UPDATE request. The peers can reuse the existing associations if
they are compatible (i.e., they have the same key fingerprints and
transport parameters), or establish a new one following the same
rules are for initial exchanges, tearing down the existing
association as soon as the offer/answer exchange is completed. Note
that if the active/passive status of the endpoints changes, a new
connection MUST be established.
NEW TEXT:
6.6. Session Modification NEW TEXT:
Once an answer is provided to the offerer, either endpoint MAY Once an answer is provided to the offerer, either endpoint MAY
request a session modification that MAY include an updated offer. request a session modification that MAY include an updated offer.
This session modification can be carried in either an INVITE or This session modification can be carried in either an INVITE or
UPDATE request. The peers can reuse an existing DTLS association, UPDATE request. The peers can reuse an existing DTLS association,
or establish a new one, following the procedures in [RFCXXXX]. or establish a new one, following the procedures in [RFCXXXX].
10.2.3. Update to section 6.7.1 10.2.3. Update to section 6.7.1
OLD TEXT:
6.7.1. ICE Interaction
Interactive Connectivity Establishment (ICE), as specified in
[RFC5245], provides a methodology of allowing participants in
multimedia sessions to verify mutual connectivity. When ICE is being
used, the ICE connectivity checks are performed before the DTLS
handshake begins. Note that if aggressive nomination mode is used,
multiple candidate pairs may be marked valid before ICE finally
converges on a single candidate pair. Implementations MUST treat all
ICE candidate pairs associated with a single component as part of the
same DTLS association. Thus, there will be only one DTLS handshake
even if there are multiple valid candidate pairs. Note that this may
mean adjusting the endpoint IP addresses if the selected candidate
pair shifts, just as if the DTLS packets were an ordinary media
stream.
Note that Simple Traversal of the UDP Protocol through NAT (STUN)
packets are sent directly over UDP, not over DTLS. [RFC5764]
describes how to demultiplex STUN packets from DTLS packets and SRTP
packets.
NEW TEXT: The text in section 6.7.1 (ICE Interaction) is replaced with the new
text below:
6.7.1. ICE Interaction NEW TEXT:
The Interactive Connectivity Establishment (ICE) The Interactive Connectivity Establishment (ICE)
[I-D.ietf-ice-rfc5245bis] considerations for DTLS-protected media [I-D.ietf-ice-rfc5245bis] considerations for DTLS-protected media
are described in [RFCXXXX]. are described in [RFCXXXX].
10.3. Update to RFC 7345 10.3. Update to RFC 7345
10.3.1. Update to section 4 10.3.1. Update to section 4
OLD TEXT: The subsections (4.1.-4.5.) in section 4 (SDP Offerer/Answerer
Procedures) are removed, and replaced with the new text below:
4. SDP Offerer/Answerer Procedures
4.1. General
An endpoint (i.e., both the offerer and the answerer) MUST create an
SDP media description ("m=" line) for each UDPTL-over-DTLS media
stream and MUST assign a UDP/TLS/UDPTL value (see Table 1) to the
"proto" field of the "m=" line.
The procedures in this section apply to an "m=" line associated with
a UDPTL-over-DTLS media stream.
In order to negotiate a UDPTL-over-DTLS media stream, the following
SDP attributes are used:
o The SDP attributes defined for UDPTL over UDP, as described in
[ITU.T38.2010]; and
o The SDP attributes, defined in [RFC4145] and [RFC4572], as
described in this section.
The endpoint MUST NOT use the SDP "connection" attribute [RFC4145].
In order to negotiate the TLS roles for the UDPTL-over-DTLS transport
connection, the endpoint MUST use the SDP "setup" attribute
[RFC4145].
If the endpoint supports, and is willing to use, a cipher suite with
an associated certificate, the endpoint MUST include an SDP
"fingerprint" attribute [RFC4572]. The endpoint MUST support SHA-256
for generating and verifying the SDP "fingerprint" attribute value.
The use of SHA-256 is preferred. UDPTL over DTLS, at a minimum, MUST
support TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 and MUST support
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256. UDPTL over DTLS MUST prefer
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and any other Perfect Forward
Secrecy (PFS) cipher suites over non-PFS cipher suites.
Implementations SHOULD disable TLS-level compression.
If a cipher suite with an associated certificate is selected during
the DTLS handshake, the certificate received during the DTLS
handshake MUST match the fingerprint received in the SDP
"fingerprint" attribute. If the fingerprint does not match the
hashed certificate, then the endpoint MUST tear down the media
session immediately. Note that it is permissible to wait until the
other side's fingerprint has been received before establishing the
connection; however, this may have undesirable latency effects.
4.2. Generating the Initial Offer
The offerer SHOULD assign the SDP "setup" attribute with a value of
"actpass", unless the offerer insists on being either the sender or
receiver of the DTLS ClientHello message, in which case the offerer
can use either a value of "active" (the offerer will be the sender of
ClientHello) or "passive" (the offerer will be the receiver of
ClientHello). The offerer MUST NOT assign an SDP "setup" attribute
with a "holdconn" value.
If the offerer assigns the SDP "setup" attribute with a value of
"actpass" or "passive", the offerer MUST be prepared to receive a
DTLS ClientHello message before it receives the SDP answer.
4.3. Generating the Answer
If the answerer accepts the offered UDPTL-over-DTLS transport
connection, in the associated SDP answer, the answerer MUST assign an
SDP "setup" attribute with a value of either "active" or "passive",
according to the procedures in [RFC4145]. The answerer MUST NOT
assign an SDP "setup" attribute with a value of "holdconn".
If the answerer assigns an SDP "setup" attribute with a value of
"active" value, the answerer MUST initiate a DTLS handshake by
sending a DTLS ClientHello message on the negotiated media stream,
towards the IP address and port of the offerer.
4.4. Offerer Processing of the Answer
When the offerer receives an SDP answer, if the offerer ends up being
active it MUST initiate a DTLS handshake by sending a DTLS
ClientHello message on the negotiated media stream, towards the IP
address and port of the answerer.
4.5. Modifying the Session
Once an offer/answer exchange has been completed, either endpoint MAY
send a new offer in order to modify the session. The endpoints can
reuse the existing DTLS association if the key fingerprint values and
transport parameters indicated by each endpoint are unchanged.
Otherwise, following the rules for the initial offer/answer exchange,
the endpoints can negotiate and create a new DTLS association and,
once created, delete the previous DTLS association, following the
same rules for the initial offer/answer exchange. Each endpoint
needs to be prepared to receive data on both the new and old DTLS
associations as long as both are alive.
NEW TEXT:
4. SDP Offerer/Answerer Procedures NEW TEXT:
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 offerer and answerer MUST follow the SDP offer/answer procedures The offerer and answerer MUST follow the SDP offer/answer procedures
defined in [RFCXXXX] in order to negotiate the DTLS association defined in [RFCXXXX] in order to negotiate the DTLS association
associated with the UDPTL-over-DTLS media stream. In addition, associated with the UDPTL-over-DTLS media stream. In addition,
the offerer and answerer MUST use the SDP attributes defined for the offerer and answerer MUST use the SDP attributes defined for
UDPTL over UDP, as defined in [ITU.T38.2010]. UDPTL over UDP, as defined in [ITU.T38.2010].
10.3.2. Update to section 5.2.1 10.3.2. Update to section 5.2.1
OLD TEXT: The text in section 5.2.1 (ICE Usage) is replaced with the new text
below:
5.2.1. ICE Usage
When Interactive Connectivity Establishment (ICE) [RFC5245] is being
used, the ICE connectivity checks are performed before the DTLS
handshake begins. Note that if aggressive nomination mode is used,
multiple candidate pairs may be marked valid before ICE finally
converges on a single candidate pair. User Agents (UAs) MUST treat
all ICE candidate pairs associated with a single component as part
of the same DTLS association. Thus, there will be only one DTLS
handshake even if there are multiple valid candidate pairs. Note
that this may mean adjusting the endpoint IP addresses if the
selected candidate pair shifts, just as if the DTLS packets were an
ordinary media stream. In the case of an ICE restart, the DTLS
handshake procedure is repeated, and a new DTLS association is
created. Once the DTLS handshake is completed and the new DTLS
association has been created, the previous DTLS association is
deleted.
NEW TEXT:
5.2.1. ICE Usage NEW TEXT:
The Interactive Connectivity Establishment (ICE) The Interactive Connectivity Establishment (ICE)
[I-D.ietf-ice-rfc5245bis] considerations for DTLS-protected media [I-D.ietf-ice-rfc5245bis] considerations for DTLS-protected media
are described in [RFCXXXX]. are described in [RFCXXXX].
[RFC EDITOR NOTE: Througout the document, please replace RFCXXXX [RFC EDITOR NOTE: Througout the document, please replace RFCXXXX
with the RFC number of this document.] with the RFC number of this document.]
11. Security Considerations 11. Security Considerations
This specification does not modify the security considerations This specification does not modify the security considerations
associated with DTLS, or the SDP offer/answer mechanism. In addition associated with DTLS, or the SDP offer/answer mechanism. In addition
to the introduction of the SDP 'tls-id' attribute, the specification to the introduction of the SDP 'tls-id' attribute, the specification
simply clarifies the procedures for negotiating and establishing a simply clarifies the procedures for negotiating and establishing a
DTLS association. DTLS association.
12. IANA Considerations 12. IANA Considerations
skipping to change at page 22, line 32 skipping to change at page 17, line 49
Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat, Jens Guballa, Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat, Jens Guballa,
Charles Eckel, Gonzalo Salgueiro and Paul Jones for providing Charles Eckel, Gonzalo Salgueiro and Paul Jones for providing
comments and suggestions on the document. Ben Campbell performed an comments and suggestions on the document. Ben Campbell performed an
AD review. AD review.
14. Change Log 14. 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-sdp-dtls-24
o Changes based on 2nd WGLC comments from Roman S and Martin T:
o - RFC update structure shortened (old text removed).
o - Guidance regarding receiving ClientHello before SDP answer
added.
o - Additional SIP condierations regarding forking.
o - SDP setup attribute value restriction in initial and subsequent
offers based on comment from Ekr.
Changes from draft-ietf-mmusic-sdp-dtls-23 Changes from draft-ietf-mmusic-sdp-dtls-23
o Editrial change to make it clear that the document does not modify o Editrial change to make it clear that the document does not modify
the procedures in RFC 8122. the procedures in RFC 8122.
Changes from draft-ietf-mmusic-sdp-dtls-22 Changes from draft-ietf-mmusic-sdp-dtls-22
o Support for TLS added. o Support for TLS added.
o Editorial changes based on sec-dir review by Rich Salz. o Editorial changes based on sec-dir review by Rich Salz.
skipping to change at page 27, line 26 skipping to change at page 23, line 9
[RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media [RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media
Transport over the Transport Layer Security (TLS) Protocol Transport over the Transport Layer Security (TLS) Protocol
in the Session Description Protocol (SDP)", RFC 8122, in the Session Description Protocol (SDP)", RFC 8122,
DOI 10.17487/RFC8122, March 2017, DOI 10.17487/RFC8122, March 2017,
<http://www.rfc-editor.org/info/rfc8122>. <http://www.rfc-editor.org/info/rfc8122>.
[I-D.ietf-ice-rfc5245bis] [I-D.ietf-ice-rfc5245bis]
Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", draft-ietf-ice- Address Translator (NAT) Traversal", draft-ietf-ice-
rfc5245bis-08 (work in progress), December 2016. rfc5245bis-10 (work in progress), May 2017.
[I-D.ietf-mmusic-sdp-mux-attributes] [I-D.ietf-mmusic-sdp-mux-attributes]
Nandakumar, S., "A Framework for SDP Attributes when Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16
(work in progress), December 2016. (work in progress), December 2016.
[I-D.ietf-mmusic-sdp-bundle-negotiation] [I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings, Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session "Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle- Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
 End of changes. 40 change blocks. 
351 lines changed or deleted 157 lines changed or added

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