One document matched: draft-ietf-mmusic-dtls-sdp-14.xml
<?xml version="1.0" encoding="iso-8859-1"?>
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<!DOCTYPE rfc SYSTEM "rfc2629.dtd"[]>
<?rfc toc="yes" ?>
<?rfc compact="yes" ?>
<?rfc sortrefs="no" ?>
<rfc ipr="trust200902" category="std" docName="draft-ietf-mmusic-dtls-sdp-14.txt" updates="5763,7345" submissionType="IETF" xml:lang="en">
<front>
<title>
Using the SDP Offer/Answer Mechanism for DTLS
</title>
<author fullname="Christer Holmberg" initials="C.H." surname="Holmberg">
<organization abbrev="Ericsson">Ericsson</organization>
<address>
<postal>
<street>Hirsalantie 11</street>
<city>Jorvas</city>
<region></region>
<code>02420</code>
<country>Finland</country>
</postal>
<phone></phone>
<email>christer.holmberg@ericsson.com</email>
</address>
</author>
<author fullname="Roman Shpount" initials="R.S." surname="Shpount">
<organization abbrev="TurboBridge">TurboBridge</organization>
<address>
<postal>
<street>4905 Del Ray Avenue, Suite 300</street>
<city>Bethesda</city>
<region>MD</region>
<code>20814</code>
<country>USA</country>
</postal>
<phone>+1 (240) 292-6632</phone>
<email>rshpount@turbobridge.com</email>
</address>
</author>
<date year="2016" />
<area>RAI</area>
<abstract>
<t>
This draft defines the SDP offer/answer procedures for negotiating and establishing
a DTLS association. The draft also defines the criteria for when a new DTLS association
must be established. The draft updates RFC 5763 and RFC 7345, by replacing common
SDP offer/answer procedures with a reference to this specification.
</t>
<t>
This draft defines a new SDP media-level attribute, 'dtls-id'.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
<xref format="default" pageno="false" target="RFC5763"/> defines SDP Offer/Answer
procedures for SRTP-DTLS. <xref format="default" pageno="false" target="RFC7345"/>
defines SDP offer/answer procedures for UDPTL-DTLS. This specification
defines general offer/answer procedures for DTLS, based on the procedures in
<xref format="default" pageno="false" target="RFC5763"/>. Other specifications,
defining specific DTLS usages, can then reference this specification, in order
to ensure that the DTLS aspects are common among all usages. Having common
procedures is essential when multiple usages share the same
DTLS association <xref target="I-D.ietf-mmusic-sdp-bundle-negotiation"/>.
The draft updates <xref format="default" pageno="false" target="RFC5763"/>
and <xref format="default" pageno="false" target="RFC7345"/>, by replacing common
SDP offer/answer procedures with a reference to this specification.
</t>
<t>
As defined in <xref format="default" pageno="false" target="RFC5763"/>, a new DTLS association
MUST be established when transport parameters are changed. Transport parameter change is not
well defined when Interactive Connectivity Establishment (ICE) <xref format="default"
pageno="false" target="RFC5245"/> is used. One possible way to determine a transport change is
based on ufrag change, but the ufrag value is changed both when ICE is negotiated
and when ICE restart <xref format="default" pageno="false" target="RFC5245"/> occurs. These events
do not always require a new DTLS association to be established, but currently there is no way
to explicitly indicate in an SDP offer or answer whether a new DTLS association is required.
To solve that problem, this draft defines a new SDP attribute, 'dtls-id'. The attribute
contains a unique value associated with a DTLS association, and by providing a new value
in SDP offers and answers the attribute can be used to indicate whether a new DTLS
association is to be established/re-established.
</t>
</section>
<section title="Conventions">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref target="RFC2119"></xref>.
</t>
</section>
<section title="Establishing a new DTLS Association">
<section title="General" anchor="sec-dtls-gen">
<t>
A new DTLS association MUST be established in the following cases:
<list style="symbols">
<t>
The DTLS roles change;
</t>
<t>
One or more fingerprint values are modified, added
or removed; or
</t>
<t>
The intent to establish a new DTLS association is
explicitly signaled;
</t>
</list>
</t>
<t>
NOTE: The first two items list above are based on the procedures
in <xref format="default" pageno="false" target="RFC5763"/>.
This specification adds the support for explicit signaling.
</t>
<t>
Whenever an entity determines, based on the criteria above, that a new DTLS association
is required, the entity MUST initiate an associated SDP offer/answer transaction, following the
procedures in <xref target="sec-oa"/>.
</t>
<t>
The sections below describe typical cases where a new DTLS association needs to be established.
</t>
</section>
<section title="Change of Local Transport Parameters" anchor="sec-dtls-transport">
<t>
If an endpoint modifies its local transport parameters (address and/or port), and if the modification
requires a new DTLS association, the endpoint MUST change its DTLS role, change its fingerprint value, and/or
use the SDP 'dtls-id' attribute with a new value <xref target="sec-dcon-attr"/>.
</t>
<t>
If the underlying transport explicitly prohibits a DTLS association to span multiple transports, and if
the transport is changed, a new value MUST be assigned to the the SDP 'dtls-id' attribute.
An example of such case is when DTLS is carried over SCTP, as described in <xref format="default" pageno="false" target="RFC6083"/>.
</t>
</section>
<section title="Change of ICE ufrag value" anchor="sec-dtls-ufrag">
<t>
If an endpoint uses ICE, and modifies a local ufrag value, and if the modification
requires a new DTLS association, the endpoint MUST either change its DTLS role, a fingerprint value and/or
assign a new value to the SDP 'dtls-id' attribute <xref target="sec-dcon-attr"/>.
</t>
</section>
</section>
<section title="SDP dtls-id Attribute" anchor="sec-dcon-attr">
<t>
The SDP 'dtls-id' attribute contains a unique value associated with a
DTLS association.
</t>
<figure>
<artwork align="left"><![CDATA[
Name: dtls-id
Value: conn-value
Usage Level: media
Charset Dependent: no
Syntax:
conn-value = 1*256alphanum
Example:
a=dtls-id:abc3dl
]]></artwork>
</figure>
<t>
A 'dtls-id' attribute that contains a new value indicates an intention
to establish a new DTLS association. A 'dtls-id' attribute
that contains a previously assigned value indicates an intention to reuse an existing
association.
</t>
<t>
There is no default value defined for the SDP 'dtls-id' attribute.
Implementations that wish to use the attribute MUST explicitly include it
in SDP offers and answers. If an offer or answer does not contain an
attribute (this could happen if the offerer or answerer represents an
existing implementation that has not been updated to support the attribute
defined in this specification or an implementation which allocates a new
temporary certificate for each association and uses change in fingerprint
to indicate new association), other means needs to be used in order for
endpoints to determine whether an offer or answer is associated with an
event that requires the DTLS association to be re-established.
</t>
<t>
The mux category <xref target="I-D.ietf-mmusic-sdp-mux-attributes"/>
for the 'dtls-id' attribute is 'IDENTICAL', which means that
the attribute value must be identical across all media descriptions
being multiplexed <xref target="I-D.ietf-mmusic-sdp-bundle-negotiation"/>.
</t>
<t>
For RTP-based media, the 'dtls-id' attribute apply to whole associated
media description. The attribute MUST NOT be defined per source (using the
SDP 'ssrc' attribute <xref format="default" pageno="false" target="RFC5576"/>).
</t>
<t>
The SDP offer/answer <xref format="default" pageno="false" target="RFC3264"/>
procedures associated with the attribute are defined in <xref target="sec-oa"/>
</t>
</section>
<section title="SDP Offer/Answer Procedures" anchor="sec-oa">
<section title="General">
<t>
This section defines the generic SDP offer/answer procedures for negotiating
a DTLS association. Additional procedures (e.g. regarding usage of specific SDP
attributes etc) for individual DTLS usages (e.g. SRTP-DTLS) are outside the scope
of this specification, and need to be specified in a usage specific specification.
</t>
<t>
NOTE: The procedures in this section are generalizations of procedures first
specified in SRTP-DTLS <xref format="default" pageno="false" target="RFC5763"/>,
with the addition of usage of the SDP 'dtls-id' attribute. That document is
herein revised to make use of these new procedures.
</t>
<t>
The procedures in this section apply to an SDP media description ("m=" line) associated
a DTLS-protected media/data.
</t>
<t>
When an offerer needs to establish a new DTLS association, and if an unordered transport (e.g. UDP)
is used, the offerer MUST allocate a new transport for the offer in such a way that the offerer can
disambiguate any packets associated with the new DTLS association from any packets associated with
any other DTLS association. This typically means using a local address and or port, or a set of
ICE candidates (see <xref format="default" pageno="false" target="sec-dtls-reest-ice"/>), which were
not recently used for any other DTLS association.
</t>
<t>
When an answerer needs to establish a new DTLS association, if an unordered transport is used, and if
the offerer did not allocate a new transport, the answerer MUST allocate a new transport for the offer
in answer a way that it can disambiguate any packets associated with new DTLS association from any
packets associated with any other DTLS association. This typically means using a local address and
or port, or a set of ICE candidates (see <xref format="default" pageno="false" target="sec-dtls-reest-ice"/>),
which were not recently used for any other DTLS association.
</t>
<t>
In order to negotiate a DTLS association, the following SDP attributes are used:
<list style="symbols">
<t>
The SDP 'setup' attribute, defined in <xref target="RFC4145" pageno="false"
format="default" />, is used to negotiate the DTLS roles;
</t>
<t>
The SDP 'fingerprint' attribute, defined in <xref target="RFC4572"
pageno="false" format="default" />, is used to provide a fingerprint
value; and
</t>
<t>
The SDP 'dtls-id' attribute, defined in this specification, indicates
a unique value associated with the DTLS association. The attribute value can
be used to explicitly indicate the intention of establishing a new DTLS association.
</t>
</list>
</t>
<t>
This specification does not define the usage of the SDP 'connection' attribute
<xref target="RFC4145" pageno="false" format="default" /> for negotiating a DTLS
connection. However, the attribute MAY be used if the DTLS association is used
together with another protocol, e.g. SCTP or TCP, for which the usage of the
attribute has been defined.
</t>
<t>
Unlike for TCP and TLS connections, endpoints MUST NOT use the
SDP 'setup' attribute 'holdconn' value when negotiating a DTLS association.
</t>
<t>
Endpoints MUST support SHA-256 for generating and verifying any fingerprint
value associated with the DTLS association. The use of SHA-256 is preferred.
</t>
<t>
Endpoints MUST, at a minimum, support TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
and MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256. UDPTL over DTLS MUST
prefer TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and any other Perfect Forward Secrecy
(PFS) cipher suites over non-PFS cipher suites. Implementations SHOULD disable
TLS-level compression.
</t>
<t>
The certificate received during the DTLS handshake MUST match at least
one of the certificate fingerprints received in SDP 'fingerprint' attributes.
If no fingerprint matches the hashed certificate, then an endpoint MUST tear
down the media session immediately. Note that it is permissible to wait until
the other side's fingerprint has been received before establishing the connection;
however, this may have undesirable latency effects.
</t>
<t>
SDP offerers and answerers might reuse certificates across multiple DTLS
associations, and provide identical fingerprint values for each DTLS
association. It MUST be ensured that the combination of the fingerprint values
and the SDP 'dtls-id' attribute value is unique across all
DTLS associations.
</t>
<t>
If an SDP offerer or answerer generates a new temporary self-signed certificate for
each new DTLS association, they can omit the SDP 'dtls-id' attribute.
</t>
</section>
<section title="Generating the Initial SDP Offer" anchor="sec-oa-offer">
<t>
When the offerer sends the initial offer, and the offerer wants to establish a
DTLS association, it MUST insert an SDP 'dtls-id' attribute with a new value
in the offer. In addition, the offerer MUST insert an SDP 'setup' attribute according
to the procedures in <xref format="default" pageno="false" target="RFC4145"/>, and
one or more SDP 'fingerprint' attributes according to the procedures in <xref format="default"
pageno="false" target="RFC4572"/>, in the offer.
</t>
<t>
If the offerer inserts the SDP 'setup' attribute with an 'actpass' or 'passive' value, the
offerer MUST be prepared to receive a DTLS ClientHello message (if a new DTLS association
is established by the answerer) from the answerer before it receives the SDP answer.
</t>
</section>
<section title="Generating the Answer">
<t>
If an answerer receives an offer that contains an SDP 'dtls-id' attribute with a new
value, or if the answerer receives an offer that contains an 'dtls-id' attribute with a
previously assigned value and the answerer determines (based on the criteria for establishing
a new DTLS association) that a new DTLS association is to be established, the answerer MUST
insert a new value in the associated answer. In addition, the answerer MUST insert an
SDP 'setup' attribute according to the procedures in <xref format="default" pageno="false"
target="RFC4145"/>, and one or more SDP 'fingerprint' attributes according to the procedures in
<xref format="default" pageno="false" target="RFC4572"/>, in the answer.
</t>
<t>
If an answerer receives an offer that contains an SDP 'dtls-id' attribute with a new
value, and if the answerer does not accept the establishment of a new DTLS association, the
answerer MUST reject the "m=" lines associated with the suggested DTLS association
<xref format="default" pageno="false" target="RFC3264"/>.
</t>
<t>
If an answerer receives an offer that contains a 'dtls-id' attribute with a previously assigned value,
and if the answerer determines that a new DTLS association is not to be established,
the answerer MUST insert a 'dtls-id' attribute with the previously assigned value in the
associated answer. In addition, the answerer MUST insert an SDP 'setup' attribute with a
value that does not change the previously negotiated DTLS roles, and one or more SDP 'fingerprint'
attributes values that do not change the previously sent fingerprints, in the answer.
</t>
<t>
If the answerer receives an offer that does not contain an SDP 'dtls-id' attribute,
the answerer MUST NOT insert a 'dtls-id' attribute in the answer.
</t>
<t>
If a new DTLS association is to be established, and if the answerer inserts an SDP 'setup'
attribute with an 'active' value in the answer, the answerer MUST initiate a DTLS handshake by
sending a DTLS ClientHello message towards the offerer.
</t>
</section>
<section title="Offerer Processing of the SDP Answer">
<t>
When an offerer receives an answer that contains an SDP 'dtls-id' attribute with
a new value, and if the offerer becomes DTLS client (based on the value of the SDP 'setup'
attribute value <xref format="default" pageno="false" target="RFC4145"/>), the offerer MUST
establish a DTLS association. If the offerer becomes DTLS server, it MUST wait for the answerer
to establish the DTLS association.
</t>
<t>
If the answer contains an SDP 'dtls-id' attribute with a previously assigned value, the offerer
will continue using the previously established DTLS association. It is considered an error
case if the answer contains a 'dtls-id' attribute with a previously assigned value, and a DTLS
association does not exist.
</t>
<t>
An offerer needs to be able to handle error conditions that can occur during an offer/answer
transaction, e.g. if an answer contains an SDP 'dtls-id' attribute with a previosuly assigned value even
if no DTLS association exists, or if the answer contains one or more new fingerprint values for an existing DTLS association.
If such error case occurs, the offerer SHOULD terminate the associated DTLS association (if it exists) and send
a new offer in order to terminate each media stream using the DTLS association, by setting the associated
port value to zero <xref format="default" pageno="false" target="RFC4145"/>.
</t>
</section>
<section title="Modifying the Session">
<t>
When the offerer sends a subsequent offer, and if the offerer wants to establish a new
DTLS association, the offerer MUST insert an SDP 'dtls-id' attribute with a new
value in the offer. In addition, the offerer MUST insert an SDP 'setup' attribute
according to the procedures in <xref format="default" pageno="false" target="RFC4145"/>,
and one or more SDP 'fingerprint' attributes according to the procedures in <xref format="default"
pageno="false" target="RFC4572"/>, in the offer.
</t>
<t>
when the offerer sends a subsequent offer, and the offerer does not want to establish
a new DTLS association, and if a previously established DTLS association exists, the
offerer MUST insert an SDP 'dtls-id' attribute with a previously assigned value in the offer.
In addition, the offerer MUST insert an SDP 'setup' attribute with a value that does
not change the previously negotiated DTLS roles, and one or more SDP 'fingerprint' attributes with
values that do not change the previously sent fingerprints, in the offer.
</t>
<t>
NOTE: When a new DTLS association is established, each endpoint needs to be prepared to receive
data on both the new and old DTLS associations as long as both are alive.
</t>
</section>
</section>
<section title="ICE Considerations" anchor="sec-dtls-reest-ice">
<t>
When ICE is 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.
</t>
<t>
NOTE: Aggressive nomination has been deprecated from ICE, but must still be
supported for backwards compatibility reasons.
</t>
<t>
When new DTLS association is established over an unordered transport, in order to
disambiguate any packets associated with newly established DTLS association, at least
one of the endpoints MUST allocate a completely new set of ICE candidates which
were not recently used for any other DTLS association. This means that answerer
cannot initiate a new DTLS association unless the offerer initiated ICE restart
<xref format="default" pageno="false" target="RFC5245"/>. If the answerer wants
to initiate a new DTLS association, it needs to initiate an ICE restart
on its own. However, an ICE restart does not by default require a new DTLS association
to be established.
</t>
<t>
NOTE: Simple Traversal of the UDP Protocol through NAT (STUN) packets are sent directly
over UDP, not over DTLS. <xref format="default" pageno="false" target="RFC3261"/> describes
how to demultiplex STUN packets from DTLS packets and SRTP packets.
</t>
<t>
Each ICE candidate associated with a component is treated as being part of the
same DTLS association. Therefore, from a DTLS perspective it is not considered
a change of local transport parameters when an endpoint switches between those
ICE candidates.
</t>
</section>
<section title="Transport Protocol Considerations" anchor="sec-dtls-cons-trans">
<section title="Transport Re-Usage" anchor="sec-dtls-cons-trans-reuse">
<t>
If DTLS is transported on top of a connection-oriented transport protocol (e.g. TCP or SCTP),
where all IP packets are acknowledged, all DTLS packets associated with a previous
DTLS association MUST be acknowledged (or timed out) before a new DTLS association
can be established on the same transport.
</t>
</section>
</section>
<section title="SIP Considerations">
<t>
When the Session Initiation Protocol (SIP) <xref format="default" pageno="false"
target="RFC3261"/> is used as the signal protocol for establishing a multimedia
session, dialogs <xref format="default" pageno="false" target="RFC3261"/> might be
established between the caller and multiple callees. This is referred to as forking.
If forking occurs, separate DTLS associations MUST be established between the caller
and each callee.
</t>
<t>
It is possible to send an INVITE request which does not contain an SDP offer. Such
INVITE request is often referred to as an 'empty INVITE', or an 'offer-less INVITE'.
The receiving endpoint will include the SDP offer in a response associated with the
response. When the endpoint generates such SDP offer, if a previously established
DTLS association exists, the offerer SHOULD insert an SDP 'dtls-id'
attribute, and one or more SDP 'fingerprint' attributes, with previously assigned
attribute values. If a previously established DTLS association did not exists
offer SHOULD be generated based on the same rules as new offer <xref target="sec-oa-offer"/>.
Regardless of the previous existence of DTLS association, the SDP 'setup' attribute
MUST be included according to rules defiend in <xref format="default" pageno="false"
target="RFC4145"/> and if ICE is used, ICE restart MUST be initiated.
</t>
</section>
<section title="RFC Updates">
<section title="General">
<t>
This section updates specifications that use DTLS-protected media, in
order to reflect the procedures defined in this specification.
</t>
</section>
<section title="Update to RFC 5763">
<figure>
<artwork align="left" alt="" height="" name="" type="" width="" xml:space="preserve"><![CDATA[
Update to section 5:
--------------------
OLD TEXT:
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:
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 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.
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, a fingerprint of
a 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 DTLS 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 offerer and answerer MUST follow the SDP offer/answer procedures
defined in [RFCXXXX].
Update to section 6.6:
----------------------
OLD TEXT:
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
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 an existing DTLS association,
or establish a new one, following the procedures in [RFCXXXX].
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:
6.7.1. ICE Interaction
The Interactive Connectivity Establishment (ICE) [RFC5245]
considerations for DTLS-protected media are described in
[RFCXXXX].
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.
]]></artwork>
</figure>
</section>
<section title="Update to RFC 7345">
<figure>
<artwork align="left" alt="" height="" name="" type="" width="" xml:space="preserve"><![CDATA[
Update to section 4:
--------------------
OLD TEXT:
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
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 offerer and answerer MUST follow the SDP offer/answer procedures
defined in [RFCXXXX] in order to negotiate the DTLS association
associated with the UDPTL-over-DTLS media stream. In addition,
the offerer and answerer MUST use the SDP attributes defined for
UDPTL over UDP, as defined in [ITU.T38.2010].
Update to section 5.2.1:
------------------------
OLD TEXT:
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
The Interactive Connectivity Establishment (ICE) [RFC5245]
considerations for DTLS-protected media are described in
[RFCXXXX].
]]></artwork>
</figure>
</section>
</section>
<section title="Security Considerations">
<t>
This specification does not modify the security considerations associated with DTLS, or
the SDP offer/answer mechanism. In addition to the introduction of the SDP
'dtls-id' attribute, the specification simply clarifies the procedures for
negotiating and establishing a DTLS association.
</t>
</section>
<section anchor="section.iana" title="IANA Considerations">
<t>
This document updates the "Session Description Protocol Parameters" registry
as specified in Section 8.2.2 of <xref target="RFC4566" pageno="false" format="default"/>.
Specifically, it adds the SDP dtls-id attribute to the table for SDP
media level attributes.
</t>
<figure>
<artwork align="left"><![CDATA[
Attribute name: dtls-id
Type of attribute: media-level
Subject to charset: no
Purpose: Indicate whether a new DTLS association is to be
established/re-established.
Appropriate Values: see Section 4
Contact name: Christer Holmberg
Category: IDENTICAL
]]></artwork>
</figure>
</section>
<section title="Acknowledgements">
<t>
Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat, Jens Guballa,
Charles Eckel and Gonzalo Salgueiro for providing comments and
suggestions on the draft.
</t>
</section>
<section title="Change Log">
<t>[RFC EDITOR NOTE: Please remove this section when publishing]</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-13
<list style="symbols">
<t>Text about the updated RFCs added to Abstract and Introduction</t>
<t>Reference to RFC 5763 removed from section 6 (ICE Considerations)</t>
<t>Reference to RFC 5763 removed from section 8 (SIP Considerations)</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-12
<list style="symbols">
<t>"unreliable" changed to "unordered"</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-11
<list style="symbols">
<t>Attribute name changed to dtls-id</t>
<t>Additional text based on comments from Roman Shpount.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-10
<list style="symbols">
<t>Modified document to use dtls-id instead of dtls-connection</t>
<t>Changes are based on comments from Eric Rescorla, Justin Uberti, and Paul Kyzivat.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-08
<list style="symbols">
<t>Offer/Answer section modified in order to allow sending of multiple SDP 'fingerprint' attributes.</t>
<t>Terminology made consistent: 'DTLS connection' replaced with 'DTLS association'.</t>
<t>Editorial changes based on comments from Paul Kyzivat.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-07
<list style="symbols">
<t>Reference to RFC 7315 replaced with reference to RFC 7345.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-06
<list style="symbols">
<t>Text on restrictions regarding spanning a DTLS association over multiple transports added.</t>
<t>Mux category added to IANA Considerations.</t>
<t>Normative text regarding mux category and source-specific applicability added.</t>
<t>Reference to RFC 7315 added.</t>
<t>Clarified that offerer/answerer that has not been updated to support this specification will
not include the dtls-id attribute in offers and answers.</t>
<t>Editorial corrections based on WGLC comments from Charles Eckel.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-05
<list style="symbols">
<t>Text on handling offer/answer error conditions added.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-04
<list style="symbols">
<t>Editorial nits fixed based on comments from Paul Kyzivat:</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-03
<list style="symbols">
<t>Changes based on comments from Paul Kyzivat:</t>
<t>- Modification of dtls-id attribute section.</t>
<t>- Removal of IANA considerations subsection.</t>
<t>- Making note into normative text in o/a section.</t>
<t>Changes based on comments from Martin Thompson:</t>
<t>- Abbreviations section removed.</t>
<t>- Clarify that a new DTLS association requires a new o/a transaction.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-02
<list style="symbols">
<t>- Updated RFCs added to boilerplate.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-01
<list style="symbols">
<t>- Annex regarding 'dtls-id-id' attribute removed.</t>
<t>- Additional SDP offer/answer procedures, related to certificates, added.</t>
<t>- Updates to RFC 5763 and RFC 7345 added.</t>
<t>- Transport protocol considerations added.</t>
</list>
</t>
<t>Changes from draft-ietf-mmusic-sdp-dtls-00
<list style="symbols">
<t>- SDP 'connection' attribute replaced with new 'dtls-id' attribute.</t>
<t>- IANA Considerations added.</t>
<t>- E-mail regarding 'dtls-id-id' attribute added as Annex.</t>
</list>
</t>
<t>Changes from draft-holmberg-mmusic-sdp-dtls-01
<list style="symbols">
<t>- draft-ietf-mmusic version of draft submitted.</t>
<t>- Draft file name change (sdp-dtls -> dtls-sdp) due to collision with another expired draft.</t>
<t>- Clarify that if ufrag in offer is unchanged, it must be unchanged in associated answer.</t>
<t>- SIP Considerations section added.</t>
<t>- Section about multiple SDP fingerprint attributes added.</t>
</list>
</t>
<t>Changes from draft-holmberg-mmusic-sdp-dtls-00
<list style="symbols">
<t>- Editorial changes and clarifications.</t>
</list>
</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.3261"?>
<?rfc include="reference.RFC.3264"?>
<?rfc include="reference.RFC.4145"?>
<?rfc include="reference.RFC.4566"?>
<?rfc include="reference.RFC.4572"?>
<?rfc include="reference.RFC.5245"?>
<?rfc include="reference.RFC.5763"?>
<?rfc include="reference.RFC.7345"?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.5576"?>
<?rfc include="reference.RFC.6083"?>
<?rfc include="reference.I-D.draft-ietf-mmusic-sdp-mux-attributes-13"?>
<?rfc include="reference.I-D.draft-ietf-mmusic-sdp-bundle-negotiation-31"?>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 19:47:49 |