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Versions: (draft-holmberg-mmusic-sdp-dtls) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Draft is active
In: MissingRef
Network Working Group                                        C. Holmberg
Internet-Draft                                                  Ericsson
Updates: 5763,7315 (if approved)                              R. Shpount
Intended status: Standards Track                             TurboBridge
Expires: June 10, 2016                                  December 8, 2015


             Using the SDP Offer/Answer Mechanism for DTLS
                   draft-ietf-mmusic-dtls-sdp-03.txt

Abstract

   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.

   This draft defines a new SDP media-level attribute, 'dtls-
   connection'.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 10, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Establishing a new DTLS Association . . . . . . . . . . . . .   3
     4.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.2.  Change of Local Transport Parameters  . . . . . . . . . .   4
     4.3.  Change of ICE ufrag value . . . . . . . . . . . . . . . .   4
     4.4.  Multiple SDP fingerprint attributes . . . . . . . . . . .   4
   5.  SDP dtls-connection Attribute . . . . . . . . . . . . . . . .   4
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.2.  ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . .   5
     6.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.2.  Generating the Initial SDP Offer  . . . . . . . . . . . .   6
     6.3.  Generating the Answer . . . . . . . . . . . . . . . . . .   6
     6.4.  Offerer Processing of the SDP Answer  . . . . . . . . . .   7
     6.5.  Modifying the Session . . . . . . . . . . . . . . . . . .   7
   7.  ICE Considerations  . . . . . . . . . . . . . . . . . . . . .   8
   8.  Transport Protocol Considerations . . . . . . . . . . . . . .   8
     8.1.  Transport Re-Usage  . . . . . . . . . . . . . . . . . . .   8
   9.  SIP Considerations  . . . . . . . . . . . . . . . . . . . . .   8
   10. RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  General  . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.2.  Update to RFC 5763 . . . . . . . . . . . . . . . . . . .   9
     10.3.  Update to RFC 7345 . . . . . . . . . . . . . . . . . . .  14
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  17
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     12.1.  Registration of New SDP Attribute  . . . . . . . . . . .  17
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   14. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  18
   15. Normative References  . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   [RFC5763] defines SDP Offer/Answer procedures for SRTP-DTLS.  This
   draft defines the SDP Offer/Answer [RFC3264] procedures for
   negotiation DTLS in general, based on the procedures in [RFC5763].

   This draft also defines a new SDP attribute, 'dtls-connection'.  The
   attribute is used in SDP offers and answers to explicitly indicate
   whether a new DTLS association is to be established.




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   As defined in [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)
   [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 [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-
   connection'.  The attribute is used in SDP offers and answers to
   explicitly indicate whether a new DTLS association is to be
   established/re-established.  The attribute can be used both with and
   without ICE.

2.  Abbreviations

   TBD

3.  Conventions

   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 [RFC2119].

4.  Establishing a new DTLS Association

4.1.  General

   A new DTLS association MUST be established in the following cases:

   o  The DTLS roles change;

   o  The fingerprint (certificate) value changes; or

   o  The establishment of a new DTLS association is explicitly
      signaled;

   NOTE: The first two items list above are based on the procedures in
   [RFC5763].  This draft adds the support for explicit signaling.

   The sections below describe typical cases where a new DTLS
   association needs to be established.








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4.2.  Change of Local Transport Parameters

   If an endpoint modifies its local transport parameters (IP address
   and/or port), and if the modification requires a new DTLS
   association, the endpoint MUST either change its DTLS role, its
   fingerprint value and/or use the SDP 'dtls-connection' attribute with
   a 'new' value Section 5.

4.3.  Change of ICE ufrag value

   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, its fingerprint value and/or use the SDP
   'dtls-connection' attribute with a 'new' value Section 5.

4.4.  Multiple SDP fingerprint attributes

   It is possible to associate multiple SDP fingerprint attribute values
   to an 'm-' line.  If any of the attribute values associated with an
   'm-' line are removed, or if any new attribute values are added, it
   is considered a fingerprint value change.

5.  SDP dtls-connection Attribute

5.1.  General

   The SDP 'connection' attribute [RFC4145] was originally defined for
   connection-oriented protocols, e.g.  TCP and TLS.  This section
   defines a similar attribute, 'dtls-connection', to be used with DTLS.

   A 'dtls-connection' attribute value of 'new' indicates that a new
   DTLS association MUST be established.  A 'dtls-connection' attribute
   value of 'existing' indicates that a new DTLS association MUST NOT be
   established.

   Unlike the SDP 'connection' attribute for TLS, there is no default
   value defined for the 'dtls-connection' 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, 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.

   The SDP Offer/Answer [RFC3264] procedures associated with the
   attribute are defined in Section 6






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5.2.  ABNF

   The ABNF [RFC5234] grammar for the SDP 'dtls-connection' attributes
   is:


       dtls-connection-attr   = "a=dtls-connection:" conn-value
       conn-value             = "new" / "existing"


6.  SDP Offer/Answer Procedures

6.1.  General

   This section defines the generic SDP offer/answer procedures for
   negotiating a DTLS association.  Additional procedures (e.g.
   regarding usage of usage specific SDP attributes etc) for individual
   DTLS usages (e.g.  SRTP-DTLS) are outside the scope of this
   specification, and needs to be specified in a usage specific
   specification.

   NOTE: The procedures in this section are based on the procedures for
   SRTP-DTLS [RFC5763], with the addition of usage of the SDP 'dtls-
   connection' attribute.

   The procedures in this section apply to an SDP media description
   ("m=" line) associated a DTLS-protected media/data stream.

   In order to negotiate a DTLS association, the following SDP
   attributes are used:

   o  The SDP 'setup' attribute, defined in [RFC4145], is used to
      negotiate the DTLS roles;

   o  The SDP 'fingerprint' attribute, defined in [RFC4572], is used to
      provide the fingerprint value; and

   o  The SDP 'dtls-connection' attribute, defined in this
      specification, is used to explicitly indicate whether a new DTLS
      association is to be established or whether a previous association
      is to be used.

   Endpoints MUST NOT use the SDP 'connection' attribute [RFC4145] when
   negotiating a DTLS association.

   NOTE: The SDP 'connection' attribute may be used if the usage is
   associated with another protocol layer, e.g.  SCTP or TCP, used
   together with DTLS.



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   Unlike for TCP and TLS connections, endpoints MUST NOT use the SDP
   'setup' attribute 'holdconn' value when negotiating a DTLS
   association.

   Endpoints MUST support SHA-256 for generating and verifying the
   fingerprint value associated with the DTLS association.  The use of
   SHA-256 is preferred.

   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.

   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.

6.2.  Generating the Initial SDP Offer

   When the offerer sends the initial offer, and the offerer wants to
   establish a DTLS association, it MUST insert an SDP 'dtls-connection'
   attribute with a 'new' value in the offer.  In addition, the offerer
   MUST insert an SDP 'setup' attribute according to the procedures in
   [RFC4145], and an SDP 'fingerprint' attribute according to the
   procedures in [RFC4572], in the offer.

   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.

6.3.  Generating the Answer

   If an answerer receives an offer that contains an SDP 'dtls-
   connection' attribute with a 'new' value, or if the answerer receives
   and offer that contains an 'dtls-connection' attribute with an
   'existing' 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 [RFC4145], and an




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   SDP 'fingerprint' attribute according to the procedures in [RFC4572],
   in the answer.

   If an answerer receives an offer that contains an SDP 'dtls-
   connection' 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 [RFC3264].

   If an answerer receives an offer that contains a 'dtls-connection'
   attribute with an 'existing' value, and if the answerer determines
   that a new DTLS association is not to be established, the answerer
   MUST insert a 'dtls-connection' attribute with an 'existing' 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 an SDP 'fingerprint' attribute with a
   value that does not change the previously sent fingerprint, in the
   answer.

   If the answerer receives an offer that does not contain an SDP 'dtls-
   connection' attribute, the answerer MUST NOT insert a 'dtls-
   connection' attribute in the answer.

   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 the offerer.

6.4.  Offerer Processing of the SDP Answer

   When an offerer receives an answer that contains an SDP 'dtls-
   connection' attribute with a 'new' value, and if the offerer becomes
   DTLS client, the offerer MUST establish a DTLS association.  If the
   offerer becomes DTLS server, it MUST wait for the answerer to
   establish the DTLS association.

   If the answer contains an SDP 'dtls-connection' attribute with an
   'existing' value, the offerer will continue using the previously
   established DTLS association.  It is considered an error case if the
   answer contains a 'dtls-connection' attribute with an 'existing'
   value, and a DTLS association does not exist.

6.5.  Modifying the Session

   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-connection' attribute with a 'new' value in the offer.  In
   addition, the offerer MUST insert an SDP 'setup' attribute according



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   to the procedures in [RFC4145], and an SDP 'fingerprint' attribute
   according to the procedures in [RFC4572], in the offer.

   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-connection' attribute with an 'existing' 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
   an SDP 'fingerprint' attribute with a value that does not change the
   previously sent fingerprint, in the offer.

   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.

7.  ICE Considerations

   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.

   An ICE restart [RFC5245] does not by default require a new DTLS
   association to be established.

   As defined in [RFC5763], 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.

8.  Transport Protocol Considerations

8.1.  Transport Re-Usage

   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.

9.  SIP Considerations

   When the Session Initiation Protocol (SIP) [RFC3261] is used as the
   signal protocol for establishing a multimedia session, dialogs
   [RFC3261] might be established between the caller and multiple
   callees.  This is referred to as forking.  If forking occurs,



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   separate DTLS associations MUST be established between the caller and
   each callee.

   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 'offerless INVITE'.  The receiving endpoint will
   include the SDP offer in a response associated with the response.
   When the endpoint generates such SDP offer, it MUST assign an SDP
   connection attribute, with a 'new' value, to each 'm-' line that
   describes DTLS protected media.  If ICE is used, the endpoint MUST
   allocate a new set of ICE candidates, in order to ensure that two
   DTLS association would not be running over the same transport.

10.  RFC Updates

10.1.  General

   This section updates specifications that use DTLS-protected media, in
   order to reflect the procedures defined in this specification.

10.2.  Update to RFC 5763


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.




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   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.




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   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
   subjectAltName is not an important component of the certificate



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   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.

   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



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   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



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   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.


10.3.  Update to RFC 7345


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:



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   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




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   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:



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------------------------

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].


11.  Security Considerations

   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-connection' attribute, the
   specification simply clarifies the procedures for negotiating and
   establishing a DTLS association.

12.  IANA Considerations

12.1.  Registration of New SDP Attribute

   This document updates the "Session Description Protocol Parameters"
   registry as specified in Section 8.2.2 of [RFC4566].  Specifically,
   it adds the SDP attributes in Section 12.1 to the table for SDP media
   level attributes.



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       Attribute name: dtls-connection
       Type of attribute: media-level
       Subject to charset: no
       Purpose: TBD
       Appropriate Values: see Section X
       Contact name: Christer Holmberg


13.  Acknowledgements

   Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat and Jens
   Guballa for providing comments and suggestions on the draft.

14.  Change Log

   [RFC EDITOR NOTE: Please remove this section when publishing]

   Changes from draft-ietf-mmusic-sdp-dtls-02

   o  - Updated RFCs added to boilerplate.

   Changes from draft-ietf-mmusic-sdp-dtls-01

   o  - Annex regarding 'dtls-connection-id' attribute removed.

   o  - Additional SDP offer/answer procedures, related to certificates,
      added.

   o  - Updates to RFC 5763 and RFC 7345 added.

   o  - Transport protocol considerations added.

   Changes from draft-ietf-mmusic-sdp-dtls-00

   o  - SDP 'connection' attribute replaced with new 'dtls-connection'
      attribute.

   o  - IANA Considerations added.

   o  - E-mail regarding 'dtls-connection-id' attribute added as Annex.

   Changes from draft-holmberg-mmusic-sdp-dtls-01

   o  - draft-ietf-mmusic version of draft submitted.

   o  - Draft file name change (sdp-dtls -> dtls-sdp) due to collision
      with another expired draft.




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   o  - Clarify that if ufrag in offer is unchanged, it must be
      unchanged in associated answer.

   o  - SIP Considerations section added.

   o  - Section about multiple SDP fingerprint attributes added.

   Changes from draft-holmberg-mmusic-sdp-dtls-00

   o  - Editorial changes and clarifications.

15.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <http://www.rfc-editor.org/info/rfc3264>.

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              DOI 10.17487/RFC4145, September 2005,
              <http://www.rfc-editor.org/info/rfc4145>.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572,
              DOI 10.17487/RFC4572, July 2006,
              <http://www.rfc-editor.org/info/rfc4572>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.



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   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              DOI 10.17487/RFC5245, April 2010,
              <http://www.rfc-editor.org/info/rfc5245>.

   [RFC5763]  Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
              for Establishing a Secure Real-time Transport Protocol
              (SRTP) Security Context Using Datagram Transport Layer
              Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
              2010, <http://www.rfc-editor.org/info/rfc5763>.

Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com


   Roman Shpount
   TurboBridge
   4905 Del Ray Avenue, Suite 300
   Bethesda, MD  20814
   USA

   Phone: +1 (240) 292-6632
   Email: rshpount@turbobridge.com




















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