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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 4567

Internet Engineering Task Force                                 J. Arkko
MMUSIC Working Group                                          E. Carrara
INTERNET-DRAFT                                               F. Lindholm
Expires: February 2004                                        M. Naslund
                                                              K. Norrman
                                                             August 2003

            Key Management Extensions for Session Description
          Protocol (SDP) and Real Time Streaming Protocol (RTSP)

Status of this memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   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 cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.


   This document defines general extensions for SDP and RTSP to carry
   the security information needed by a key management protocol, in
   order to secure the media. These extensions are presented as a
   framework, to be used by one or more key management protocols. As

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   such, its use is meaningful only when it is completed by the key
   management protocol in use.

   General guidelines are also given on how the framework should be used
   together with SIP and RTSP.


   1. Introduction.....................................................2
   1.1. Notational Conventions.........................................3
   2. Extensions to SDP and RTSP.......................................4
   2.1. SDP Extensions.................................................4
   2.2. RTSP Extensions................................................4
   3. Usage with SIP and RTSP..........................................5
   3.1. General SDP processing.........................................5
   3.2. SIP usage......................................................7
   3.3. RTSP usage.....................................................8
   3.4. Example scenarios..............................................9
   4. Adding further Key management protocols.........................11
   5. Security Considerations.........................................12
   6. IANA Considerations.............................................13
   6.1. SDP Attribute Registration....................................13
   6.2. Protocol Identifier Registration..............................13
   8. Acknowledgments.................................................14
   9. Author's Addresses..............................................14
   10. References.....................................................15
   10.1. Normative References.........................................15
   10.2. Informative References.......................................15

1. Introduction

      [Editor remark] All instances of RFC xxxx should be replaced with
      the RFC number of this document, when published. Furthermore, all
      instances of RFC yyyy should be replaced with the RFC number of
      the MIKEY (Multimedia Internet KEYing) document [MIKEY], when

   There has recently been work to define a security framework for the
   protection of real-time applications running over RTP, [SRTP].
   However, a security protocol needs a key management infrastructure to
   exchange keys and security parameters, manage and refresh keys, etc.

   A key management protocol is executed prior to the security protocol
   execution. The key management protocol's main goal is to, in a secure
   and reliable way, establish a security association for the security
   protocol. This includes one or more cryptographic keys and the set of
   necessary parameters for the security protocol, e.g., cipher and
   authentication algorithm to be used. The key management protocol has
   similarities with, e.g., SIP [SIP] and RTSP [RTSP] in the sense that

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   it negotiates necessary information in order to be able to setup the

   The focus in the following sections is to describe a new SDP
   attribute and RTSP header extension to support key management, and
   the integration within SIP and RTSP. A framework is therefore
   described in the following. This framework is completed by one or
   more key management protocols, to describe how the framework is used,
   e.g. which is the data to be carried in the extensions.

   Some of the motivations to create a framework with the possibility to
   include the key management in the session establishment are:

   * Just as the codec information is a description of how to encode and
      decode the audio (or video) stream, the key management data is a
      description of how to encrypt and decrypt the data.

   * The possibility to negotiate the security for the entire multimedia
      session at the same time.

   * The knowledge of the media at the session establishment makes it
      easy to tie the key management to the multimedia sessions.

   * This approach may be more efficient than setting up the security
      later, as that approach might force extra roundtrips, possibly
      also a separate set-up for each stream, hence implying more delay
      to the actual setup of the media session.

   * The possibility to negotiate keying material end-to-end without
      applying end-to-end protection of the SDP (instead, hop-by-hop
      security mechanisms can be used which may be useful if
      intermediate proxies needs access to the SDP).

   Currently in SDP [SDPnew], one field exists to transport keys, i.e.
   the "k=" field. However, this is not enough for a key management
   protocol as there are many more parameters that need to be
   transported. The approach here is to use and extend the SDP
   description to transport the key management offer/answer and also to
   associate it with the media sessions. SIP uses the offer/answer model
   [OAM] whereby extensions to SDP will be enough. However, RTSP
   [RTSP]does not use the offer/answer model with SDP, so a new header
   is introduced to convey key management data.

1.1. Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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2. Extensions to SDP and RTSP

   This section describes common attributes that are to be included in
   an SDP description or in an RTSP header when an integrated key
   management protocol is used. The attribute values MUST follow the
   general SDP or RTSP guidelines (see [SDPnew] and [RTSP]).

   For both SDP and RTSP, the general method of adding the key
   management protocol is to introduce new attributes, one identifier to
   identify the specific key management protocol, and one data field
   where the key management protocol data is placed. The key management
   protocol data contains the necessary information to establish the
   security protocol, e.g., keys and cryptographic parameters. All
   parameters and keys are protected by the key management.

2.1. SDP Extensions

   This section provides an Augmented Backus-Naur Form (ABNF) grammar
   (as used in [SDPnew]) for the key management extensions to SDP.

   Note that the new definitions are compliant with the definition of an
   attribute field, i.e.

   attribute    = (att-field ":" att-value) | att-field

   One new attribute for SDP is defined:

   key-mgmt     = "key-mgmt: " prtcl-id keymgmt-data

   prtcl-id     = non-ws-string
                  ; e.g. "mikey"

   keymgmt-data = text

   where non-ws-string and text are as defined in SDP [SDPnew]. The
   attribute may be used at session level, media level, or at both
   levels. An attribute defined at media level overrides an attribute
   defined at session level. Note that the prtcl-id name will be case
   sensitive and it is therefore RECOMMENDED that attributes registered
   are in lower case letters. Section 3 describes in detail how the
   attributes are used and how the SDP is handled in different usage

2.2. RTSP Extensions

   To support the needed attribute, the following RTSP header is

   KeyMgmt = "keymgmt" ":" 1#key-mgmt-spec

   key-mgmt-spec = "prot" "=" token ";" "data" "=" quoted-string

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   "token" and "quoted-string" are as defined in the RTSP specification

   The KeyMgmt header should be possible to use in the messages
   described in the table below.

   Method      Direction     Requirement
   DESCRIBE    C->S          required
   SETUP       C->S          required
   ANNOUNCE    C->S, S->C    optional (required: if re-key is supported)

   Note: Section 3 describes in detail how the RTSP extensions are used.

3. Usage with SIP and RTSP

   This section gives recommendations of how/when to include the defined
   key management attribute when SIP and/or RTSP are used together with

   When a key management protocol is integrated with SIP/SDP and RTSP,
   the following requirements are placed on the key management:

   * It MUST be possible to execute the key management protocol in at
      most one roundtrip in case the answerer accepts the offer.

   * It MUST be possible from the SIP/SDP and RTSP application, using
      the key management API, to receive key management data, and
      information of whether a message is accepted or not.

   Today, the MIKEY protocol [MIKEY] has adopted the key management
   extensions to work together with SIP and RTSP. Other protocols MAY
   use the described attribute and header, e.g. Kerberos [KERB].

3.1. General SDP processing

   When an SDP message is created, the following procedure should be

   * The identifier of the key management protocol used (e.g. MIKEY or
      Kerberos) MUST be placed in the prtcl-id field.

   * The keymgmt-data field MUST be created as follows. The key
      management protocol MUST be used to create the key management
      message. This message SHALL be base64 encoded [RFC3548] by the SDP
      application and then encapsulated in the keymgmt-data attribute.
      The data may e.g. be a MIKEY message (see [MIKEY], Section 7) or
      Kerberos ticket.

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   A received SDP message that contains the key management attributes
   SHOULD be processed in the following manner:

   * The key management protocol is identified according to the prtcl-id

   * The key management data from the keymgmt-data field MUST be
      extracted, base64 decoded to reconstruct the original message, and
      then passed to the key management protocol. Note that depending on
      key management protocol, some extra parameters might of course be
      requested by the specific API, such as the source/destination
      network address/port(s) for the specified media (however, this
      will be implementation specific depending on the actual API).

   * Depending on the outcome of the key management processing (i.e.
      whether it was successful or not), the processing can proceed
      according to normal rules (e.g. according to the offer/answer
      model, see also Section 3.2).

   Note that the key management attribute MAY be repeated more than once
   (e.g., one at session level and one at media level). Consequently,
   the process is repeated for each key management attribute detected.
   However, in case of failure of the key management (on either session
   or media level), the session setup SHALL be aborted (see also Section
   3.2 and Section 3.3 for more details).

   If more than one key management protocol is supported, multiple
   instances of the key management attribute MAY be included in the
   initial offer, each transporting a different key management data,
   thus indicating supported alternatives.

   If the sender includes more than one key management protocol
   attribute at session level (analogous for the media level), these
   SHOULD be listed in order of preference (the first being the
   preferred). The receiver selects the key management protocol it
   wishes to use and includes only that attribute in the answer. If the
   receiver does not support any of the sender's suggested key
   management protocols, the receiver returns an error message (see
   section 3.2 and section 3.3), whereby the sender MUST abort the
   current setup procedure.

   Note that the placement of multiple key management offers in a single
   message has the disadvantage that the message expands and the
   computational workload for the offerer will increase drastically.

   The possibility to support multiple key management protocols may
   introduce bidding down attacks. To avoid this, the list of
   identifiers of the proposed key management protocols MUST be
   authenticated. The authentication MUST be done separately by each key
   management protocol (see e.g. Section 7.1 in [MIKEY]).

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   Accordingly, it MUST be specified (in the key management protocol
   specification itself or in a companion document) how the list of key
   management protocol identifiers can be authenticated from the offerer
   to the answerer by the specific key management protocol. Note that
   even if only one key management protocol is used, that still MUST
   authenticate its own protocol identifier.

   The list of protocol identifiers MUST be given to the selected key
   management protocol by the SDP application with ";" separated
   identifiers. All the offered protocol identifiers MUST be included,
   in the same order as they appear in the corresponding SDP

   The protocol list can formally be described as

   prtcl-list   =  prtcl-id *(";" prtcl-id)

   prtcl-id     = non-ws-string

   For example, if the SDP is:

        o=alice 2891092738 2891092738 IN IP4 lost.example.com
        s=Secret discussion
        t=0 0
        c=IN IP4 lost.example.com
        a=key-mgmt:mikey <data1>
        a=key-mgmt:keyp1 <data2>
        a=key-mgmt:keyp2 <data3>
        m=audio 39000 RTP/SAVP 98
        a=rtpmap:98 AMR/8000
        m=video 42000 RTP/SAVP 31
        a=rtpmap:31 H261/90000

        The protocol list, "mikey;keyp1;keyp2", would be generated from
        the SDP description and used as input to each specified key
        management protocol (together with the data for that protocol).

   If more than one protocol is supported by the offerer, it is
   RECOMMENDED that all acceptable protocols are included in the first
   offer, rather than making single, subsequent alternative offers in
   response to error messages, see "Security Considerations".

3.2. SIP usage

   When used with SIP and the offer/answer model, the offerer SHOULD
   include the key management data within an offer that contains the
   media description it should apply to. The answerer MUST check with
   the key management protocol if the attribute values are valid, and
   then obtain from the key management the data to include in the

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   If the offer is not accepted, the answerer SHOULD return a "606 Not
   Acceptable" message, including one or more Warning headers (at least
   a 306 "Attribute not understood"). The session is then aborted (and
   it is up to local policy or end user to decide how to continue).

   Re-keying can be handled as a new offer, i.e. a re-INVITE should be
   sent with the new proposed parameters. The answerer treats this as a
   new offer where the key management is the issue of change. In
   general, the re-INVITE (and the key exchange) must be finalized
   before the security protocol can change the keys. The same key
   management protocol used in the original INVITE SHALL also be used in
   the re-INVITE carrying re-keying. If the re-INVITE carrying re-keying
   fails (e.g., the authentication verification fails), the answerer
   SHOULD send a "606 Not Acceptable" message, including one or more
   Warning headers (at least a 306). The offer MUST then abort the
   security setup.

3.3. RTSP usage

   RTSP does not use the offer/answer model, as SIP does. This causes
   some problems, as it is not possible (without abusing RTSP) to send
   back an answer to the server (as the server will in most cases be the
   one initiating the security parameter exchange). To solve this, a new
   header has been introduced (Section 2.2). This also assumes that the
   key management also has some kind of binding to the media, so that
   the response to the server will be processed as required.

   The initial key management message from a server should be sent to
   the client using SDP. When responding to this, the client uses the
   new RTSP header to send back an answer (included in the SETUP
   message). If a server receives a SETUP message in which it expects a
   key management message, but none is included, a 403 Forbidden SHOULD
   be returned to the client, whereby the current setup MUST be aborted.

   The processing of creating a key management header in RTSP SHOULD be
   as follow:

   * The identifier of the key management protocol used (e.g. MIKEY or
      Kerberos) MUST be placed in the "prot" field of the header.

   * The keymgmt-data field MUST be created as follows. The key
      management protocol MUST be used to create the key management
      message. This message SHALL be base64 encoded by the SDP
      application and then encapsulated in the "data" field of the
      header. The data may e.g. be a MIKEY message (see [MIKEY], Section
      7) or Kerberos ticket.

   A received key management header SHOULD be processed in the following

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   * The key management protocol is identified according to the "prot"

   * The key management data from the "data" field MUST be extracted,
      base64 decoded to reconstruct the original message, and then
      passed to the key management protocol. Note that depending on the
      key management protocol, some extra parameters might of course be
      requested by the specific API, such as the source/destination
      network address/port(s) for the specified media (however, this
      will be implementation specific depending on the actual API).

   * Depending on the outcome of the key management processing (i.e.
      whether it was successful or not), the processing can proceed
      according to normal rules (see also below).

   The server MAY provide re-keying/updating facilities by sending a new
   key management message in an ANNOUNCE messages. The ANNOUNCE message
   contains an SDP message including the key management parameters. The
   response message is put in the new RTSP header in the response from
   the client to the server. Note that the ANNOUNCE messages MUST be
   supported if this feature is to be used.

3.4. Example scenarios

   Example 1 (SIP)

   A SIP call is taking place between Alice and Bob. Alice sends an
   Invite message consisting of the following offer:

   o=alice 2891092738 2891092738 IN IP4 w-land.example.com
   s=Cool stuff
   t=0 0
   c=IN IP4 w-land.example.com
   a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...
   m=audio 49000 RTP/SAVP 98
   a=rtpmap:98 AMR/8000
   m=video 52230 RTP/SAVP 31
   a=rtpmap:31 H261/90000

   i.e. Alice proposes to set up one audio stream and one video stream
   that run over SRTP. To set up the security parameters for SRTP, she
   uses MIKEY. Note that MIKEY is negotiating the crypto suite for both
   streams (as it is placed at the session level).

   Bob accepts the offer and sends an answer back to Alice:

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   o=bob 2891092897 2891092897 IN IP4 foo.example.com
   s=Cool stuff
   t=0 0
   c=IN IP4 foo.example.com
   a=key-mgmt:mikey skaoqDeMkdwRW278HjKVB...
   m=audio 49030 RTP/SAVP 98
   a=rtpmap:98 AMR/8000
   m=video 52230 RTP/SAVP 31
   a=rtpmap:31 H261/90000

   Example 2 (SDP)

   This example shows how Alice would have done if she wished to protect
   only the audio stream.

   o=alice 2891092738 2891092738 IN IP4 w-land.example.com
   s=Cool stuff
   t=0 0
   c=IN IP4 w-land.example.com
   m=audio 49000 RTP/SAVP 98
   a=rtpmap:98 AMR/8000
   a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...
   m=video 52230 RTP/AVP 31
   a=rtpmap:31 H261/90000

   Note that even if the key management attribute were specified at
   session level, the video part would not be affected by this (as a
   security profile is not used).

   Example 3 (RTSP)

   A client wants to set up a streaming session and requests a media
   description from the streaming server.

   DESCRIBE rtsp://server.example.com/fizzle/foo RTSP/1.0
   CSeq: 312
   Accept: application/sdp
   From: user@example.com

   The server sends back an OK message including an SDP description.

   RTSP/1.0 200 OK
   CSeq: 312
   Date: 23 Jan 1997 15:35:06 GMT
   Content-Type: application/sdp

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   o=actionmovie 2891092738 2891092738 IN IP4 movie.example.com
   s=Action Movie
   t=0 0
   c=IN IP4 movie.example.com
   a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...
   m=audio 0 RTP/SAVP 98
   a=rtpmap:98 AMR/8000
   m=video 0 RTP/SAVP 31
   a=rtpmap:31 H261/90000

   The client is now ready to setup the sessions. It includes the key
   management data in the first message going back to the server (i.e.
   the SETUP message).

   SETUP rtsp://movie.example.com/action/audio RTSP/1.0
   CSeq: 313
   Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057
   keymgmt: prot=mikey; data="skaoqDeMkdwRW278HjKVB..."

   The server processes the request including checking the validity of
   the key management header.

   RTSP/1.0 200 OK
   CSeq: 313
   Session: 12345678
   Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057;

   The RTSP then proceeds as usual (with e.g. a SETUP message for the
   video followed by a PLAY message).

4. Adding further Key management protocols

   This framework cannot be used with all key management protocols. The
   key management protocol needs to comply with the requirements
   described in Section 3. To be able to use a key management protocol
   with this framework, the following MUST be specified:

   * the key management protocol identifier that should be used in the
      protocol identifier fields in both SDP and RTSP (e.g. "mikey" for

   * the information the key management needs from SDP and RTSP (Section
      3 gives a guideline of what SDP and RTSP needs from the key
      management). The exact API is implementation specific, but it
      SHOULD at least support to exchange the specified information.

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      Note that in particular, the key management MUST always be given
      the protocol identifier(s) of the key management protocol(s)
      included in the offer in the correct order as they appear.

   The key management data MUST be base64 encoded in the SDP and RTSP
   fields. Therefore, considerations of possible conversion from the
   normal key management representation to base64 SHOULD be taken into

5. Security Considerations

   The nature of this document is to allow SDP and RTSP to support
   negotiation of the security of the media sessions. It is therefore
   not a primary intention of this document to describe possible
   security solutions or to define possible security problems. The
   defined SDP and RTSP extensions are not believed to introduce any new
   security risks to SDP and RTSP, if used as specified.

   Note that the purpose of the key management fields is to provide
   information to secure the media streams. Under the assumption that
   the key management schemes are secure, the SDP can be passed along
   unprotected without affecting the key management, and the media
   streams will still be secure even if some attackers gained knowledge
   of the SDP contents.

   However, if the SDP messages are not sent authenticated between the
   parties, it is possible for an active attacker to change attributes
   without being detected. As the key management protocol may
   (indirectly) rely on some of the session information from SDP (e.g.,
   address information), an attack on SDP may have indirect consequences
   on the key management. Even if the key management protocol does not
   rely on parameters of SDP and will not be affected by manipulation of
   these, different DoS attacks aimed at SDP (e.g. the SIMCAP
   extensions) may lead to undesired interruption in the setup.

   In general, it is therefore a good thing, not only to try to secure
   the session, but also to secure the session setup. However, the
   security of the session setup might not possible on an end-to-end
   basis, but may require to be protected on a hop-by-hop basis (this is
   generally the case for SIP/SDP when intermediate proxies needs to
   obtain information about the sessions etc). In fact, the focus of
   this framework is mainly when end-to-end protection of the session
   setup is not used, but where the media streams needs to be end-to-end

   Note that it is impossible to assure the authenticity of a declined
   offer, since even if it comes from the true respondent, the fact that
   the answerer declines the offer usually means that he does not
   support the protocol(s) offered, and consequently cannot be expected

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   to authenticate the response either. This means that if the initiator
   is unsure of which protocol(s) the responder supports, we RECOMMEND
   that the initiator offers all acceptable protocols in a single offer.
   If not, this opens up the possibility for a "man-in-the-middle"
   (MITM) to affect the outcome of the eventually agreed upon protocol,
   by faking unauthenticated error messages until the initiator
   eventually offers a protocol "to the liking" of the MITM. This is not
   really a security problem, but rather a mild form of denial of
   service that can be avoided by following the above recommendation.

6. IANA Considerations

6.1. SDP Attribute Registration

   A new SDP attribute needs to be registered for the purpose of key
   management protocol integration with SDP.

        Contact:      Fredrik Lindholm
                      mailto: fredrik.lindholm@ericsson.com
                      tel: +46 8 58531705

      SDP Attribute ("att-field"):

        Name:               key-mgmt
        Long form:          key management protocol
        Type of name:       att-field
        Type of attribute:  Media and session level
        Purpose:            See RFC xxxx, Section 2.
        Reference:          RFC xxxx, Section 2.1
        Values:             See registrations below

6.2. Protocol Identifier Registration

   This document defines one new name space associated with the above
   registered key-mgmt attribute i.e., the protocol identifier (see also
   Section 2.1 and Section 2.2).

   A new registry needs to be set up for "prtcl-id" parameter of the
   "key-mgmt" attribute, with the following registration created
   initially: "mikey".

        Contact:      Fredrik Lindholm
                      mailto: fredrik.lindholm@ericsson.com
                      tel: +46 8 58531705

        Value name:     mikey
        Long name:      Multimedia Internet KEYing
        Purpose:        Usage of MIKEY with the key-mgmt attribute
        Reference:      Section 7 in RFC yyyy

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   Further entries may be registered according to the "Specification
   Required" policy as defined in [RFC2434]. Each new registration needs
   to indicate the parameter name and the syntax of possible additional
   arguments. Note that the parameter name is case sensitive and it is
   recommended that the name should be in lower case letters. For each
   new registration, it is mandatory that a permanent, stable, and
   publicly accessible document exists that specifies the semantics of
   the registered parameter, the syntax and semantics of its parameters
   as well as all the requested details of interaction between the key
   management protocol and SDP, as specified in this document.

8. Acknowledgments

   Thanks to: Rolf Blom, Magnus Westerlund, and the rest involved in the
   MMUSIC WG and the MSEC WG.

   A special thanks to Joerg Ott and Colin Perkins.

9. Author's Addresses

     Jari Arkko
     02420 Jorvas             Phone:  +358 40 5079256
     Finland                  Email:  jari.arkko@ericsson.com

     Elisabetta Carrara
     Ericsson Research
     SE-16480 Stockholm       Phone:  +46 8 50877040
     Sweden                   EMail:  elisabetta.carrara@ericsson.com

     Fredrik Lindholm
     Ericsson Research
     SE-16480 Stockholm       Phone:  +46 8 58531705
     Sweden                   EMail:  fredrik.lindholm@ericsson.com

     Mats Naslund
     Ericsson Research
     SE-16480 Stockholm       Phone:  +46 8 58533739
     Sweden                   EMail:  mats.naslund@ericsson.com

     Karl Norrman
     Ericsson Research
     SE-16480 Stockholm       Phone:  +46 8 4044502
     Sweden                   EMail:  karl.norrman@ericsson.com

Arkko, et al.                                                  [Page 14]

INTERNET-DRAFT            mmusic-kmgmt-ext-08               August 2003

10. References

10.1. Normative References

   [OAM] Rosenberg, J. and Schulzrinne, H., "An Offer/Answer Model with
   the Session Description Protocol (SDP)", IETF, RFC 3264.

   [RTSP] Schulzrinne, H., Rao, A., and Lanphier, R., "Real Time
   Streaming Protocol (RTSP)", IETF, RFC 2326.

   [RFC2119] Bradner, S. "Key words for use in RFCs to Indicate
   Requirement Levels", IETF, RFC 2119.

   [SDPnew] Handley, M., Jacobson, V., and Perkins, C., "SDP: Session
   Description Protocol", Internet Draft, IETF, Work in progress
   (MMUSIC), draft-ietf-mmusic-sdp-new-13.txt.

   [SIP] Handley, M., Schulzrinne, H., Schooler, E., and Rosenberg, J.,
   "SIP: Session Initiation Protocol", IETF, RFC 3261.

   [RFC2434] Narten, T. and Alvestrand, H., "Guidelines for Writing an
   IANA Considerations Section in RFCs", IETF, RFC 2434.

   [RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data
   Encodings", IETF, RFC 3548.

10.2. Informative References

   [KERB] Kohl, J., Neuman, C., "The Kerberos Network Authentication
   Service (V5)", IETF, RFC 1510.

   [MIKEY] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and
   Norrman, K., "MIKEY: Multimedia Internet KEYing", IETF, RFC yyyy,
   [Internet Draft, Work in progress (MSEC)].

   [SRTP] Baugher, M., Blom, R., Carrara, E., McGrew, D., Naslund, M,
   Norrman, K., and Oran, D., "The Secure Real Time Transport Protocol",
   Internet Draft, IETF, Work in Progress (AVT).

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing

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INTERNET-DRAFT            mmusic-kmgmt-ext-08               August 2003

   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

   This Internet-Draft expires in February 2004.

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