[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

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: August 2004                                          M. Naslund
                                                              K. Norrman
                                                                Ericsson
                                                           February 2004






            Key Management Extensions for Session Description
          Protocol (SDP) and Real Time Streaming Protocol (RTSP)
                   <draft-ietf-mmusic-kmgmt-ext-10.txt>


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
   http://www.ietf.org/ietf/lid-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html


Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.


Abstract

   This document defines general extensions for SDP and RTSP to carry
   messages, as specified 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 such, their use



Arkko, et al.                                                   [Page 1]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   is meaningful only when complemented by an appropriate key management
   protocol.

   General guidelines are also given on how the framework should be used
   together with SIP and RTSP. The usage with the MIKEY key management
   protocol is also defined.



TABLE OF CONTENTS

   1. Introduction.....................................................2
   1.1. Notational Conventions.........................................4
   2. Extensions to SDP and RTSP.......................................4
   2.1. SDP Extensions.................................................4
   2.2. RTSP Extensions................................................5
   3. Usage with SDP, SIP, RTSP, and SAP...............................6
   3.1. Use of SDP.....................................................7
   3.1.1 General processing............................................7
   3.1.2 Use of SDP with offer/answer and SIP..........................8
   3.1.3 Use of SDP with SAP..........................................10
   3.1.4 Bidding-down attack prevention...............................10
   3.2. RTSP usage....................................................12
   4. Example scenarios...............................................14
   5. Adding further Key management protocols.........................18
   6. Integration of MIKEY............................................18
   6.1 MIKEY Interface................................................19
   7. Security Considerations.........................................20
   8. IANA Considerations.............................................21
   8.1. SDP Attribute Registration....................................21
   8.2. RTSP Registration.............................................21
   8.3. Protocol Identifier Registration..............................22
   9. Acknowledgments.................................................23
   10. Author's Addresses.............................................23
   11. References.....................................................24
   11.1. Normative References.........................................24
   11.2. Informative References.......................................24


1. Introduction

      [RFC 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
      published.

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



Arkko, et al.                                                   [Page 2]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004



   A key management protocol is executed prior to the security
   protocol's 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 algorithms to be used. The key management
   protocol has similarities with, e.g., SIP [SIP] and RTSP [RTSP] in
   the sense that it negotiates necessary information in order to be
   able to setup the session.

   The focus in the following sections is to describe a new SDP
   attribute and RTSP header extension to support key management, and to
   show how these can be integrated within SIP and RTSP. The resulting
   framework is completed by one or more key management protocols, which
   use the extensions provided.

   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 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], there exists one field to transport keys,
   the "k=" field. However, this is not enough for a key management
   protocol as there are many more parameters that need to be
   transported, and the "k=" field is not extendible. The approach used
   is to extend the SDP description through a number of attributes that
   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 RTSP header is
   introduced to convey key management data.




Arkko, et al.                                                   [Page 3]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   The document also defines the use of the described framework together
   with the key management protocol Multimedia Internet KEYing (MIKEY)
   [MIKEY].

1.1. Notational 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].


2. Extensions to SDP and RTSP

   This section describes common attributes that can be included in SDP
   or RTSP when an integrated key management protocol is used. The
   attribute values follow the general SDP and 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 protocol.

   The key management data SHALL be base64 [RFC3548] encoded and comply
   with the base64 grammar as defined in [SDPnew]. The key management
   protocol identifier, KMID, is defined as below in Augmented Backus-
   Naur Form grammar (ABNF) [RFC2234].

   KMID =  1*(ALPHA / DIGIT)

   Values for the identifier, KMID, are registered and defined in
   accordance to Section 8. Note that the KMID will be case sensitive
   and it is RECOMMENDED that values registered are lower case letters.

2.1. SDP Extensions

   This section provides an 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

   The att-field and att-value for the key management extensions are as
   follow:

   key-mgmt-att-field = "key-mgmt"



Arkko, et al.                                                   [Page 4]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   key-mgmt-att-value = 0*1SP prtcl-id SP keymgmt-data

   prtcl-id     = KMID
                  ; e.g. "mikey"

   keymgmt-data = base64
   SP           = 0x20

   where KMID is as defined in Section 2 of this memo, base64 is as
   defined in SDP [SDPnew]. Prtcl-id refers to the set of values defined
   for KMID in Section 7.

   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. In other words, if the media level
   attribute is present, the session level attribute MUST be ignored for
   this media. Section 3.1 describes in detail how the attributes are
   used and how the SDP is handled in different usage scenarios.

2.2. RTSP Extensions

   To support the key management attributes, the following RTSP header
   is defined:

   KeyMgmt = "KeyMgmt" ":" key-mgmt-spec 0*("," key-mgmt-spec)

   key-mgmt-spec = "prot" "=" KMID ";" ["uri" "=" <"> rtsp_URL <"> ";"]
   "data" "=" base64

   where KMID is as defined in Section 2 of this memo, "base64" as
   defined in [SDPnew], and "rtsp_URL" as defined in [RTSP].

   The "uri" parameter identifies the context for which the key
   management data applies, and the RTSP URI SHALL match a (session or
   media) URI present in the description of the session. If the RTSP
   aggregated control URI is included it indicates that the key
   management message is on session level (and similarly the RTSP media
   control URI, that it applies to the media level). If no "uri"
   parameter is present in a key-mgmt-spec the specification applies to
   the context identified by the RTSP request URI.

   The KeyMgmt header MAY be used in the messages and directions
   described in the table below.


   Method            | Direction  |  Requirement
   ---------------------------------------------
   DESCRIBE response |   S->C     |  RECOMMENDED
   SETUP             |   C->S     |  REQUIRED
   SETUP Response    |   S->C     |  REQUIRED (error)




Arkko, et al.                                                   [Page 5]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   Note: Section 3.2 describes in detail how the RTSP extensions are
   used.

   We define one new RTSP status code to report error due to any failure
   during the key management processing (Section 3.2):

   Status-Code  =  "463" ; Key management failure

   A 463 response MAY contain a KeyMgmt header with a key management
   protocol message that further indicates the nature of the error.


3. Usage with SDP, SIP, RTSP, and SAP

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

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

   * It MUST be possible to execute the key management protocol in at
      most one request-response message exchange.

   * 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.

   The content of the key management messages depends on the key
   management protocol that is used. However, the content of such key
   management messages might be expected to be roughly as follow. The
   key management Initiator (e.g. the offerer) includes the key
   management data in a first message, containing the media description
   it should apply to. This data in general consists of the security
   parameters (including key material) needed to secure the
   communication, together with the necessary authentication information
   (to assure that the message is authentic).

   At the Responder's side, the key management protocol checks the
   validity of the key management message, together with the
   availability of the parameters offered, and then provides the key
   management data to be included in the answer. This answer may
   typically authenticate the Responder to the Initiator, and also state
   if the initial offer was accepted or not. Certain protocols might
   require the Responder to include a selection of the security
   parameters that he is willing to support. Again, the actual content
   of such response is dependent on the particular key management
   protocol.






Arkko, et al.                                                   [Page 6]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   Section 6 describes a realization of the MIKEY protocol using these
   mechanisms. Procedures to be used when mapping new key management
   protocols onto this framework are described in Section 5.

3.1. Use of SDP

   This section describes the processing rules for the different
   applications which use SDP for the key management.

3.1.1 General processing

   The processing when SDP is used is slightly different according to
   the way SDP is transported, and if it uses an offer/answer or
   announcement. The processing can be divided into four different
   steps:

   1) How to create the initial offer.
   2) How to handle a received offer.
   3) How to create an answer.
   4) How to handle a received answer.

   It should be noted that the last two steps may not always be
   applicable, as there are cases where an answer can not or will not be
   sent back.

   The general processing for creating an initial offer SHALL follow the
   following actions:

   * The identifier of the key management protocol used MUST be placed
      in the prtcl-id field of SDP. A table of legal protocols
      identifiers is maintained by IANA (see Section 8).

   * 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.
      Note though that the semantics of the encapsulated message is
      dependent on the key management protocol that is used.

   The general processing for handling a received offer SHALL follow the
   following actions:

   * The key management protocol is identified according to the prtcl-id
      field. A table of legal protocols identifiers is maintained by
      IANA (Section 8).

   * 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 for processing. Note
      that depending on key management protocol, some extra parameters
      might also be requested by the specific API, such as the



Arkko, et al.                                                   [Page 7]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


      source/destination network address/port(s) for the specified media
      (however, this will be implementation specific depending on the
      actual API). The extra parameters that a key management protocol
      might need (other than the ones defined here) SHOULD be
      documented, describing their use, as well as the interaction of
      that key management protocol with SDP and RTSP.

   * If errors occur, or the key management offer is rejected, the
       session SHALL be aborted. Possible error messages are dependent
       on the specific session establishment protocol.

   At this stage, the key management will have either accepted or
   rejected the offered parameters. This MAY cause a response message to
   be generated, depending on the key management protocol and the
   application scenario.

   If an answer is to be generated, the following general actions SHALL
   be performed:

   * The identifier of the key management protocol used 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 semantics of the encapsulated message is dependent on the key
      management protocol that is used.

   The general processing for handling a received answer SHALL follow
   the following actions:

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

   * 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 for processing.

   * If errors occur, or the key management offer is rejected, the
       session SHALL be aborted. If possible an error message indicating
       the failure SHOULD be sent back. Otherwise, if all the steps are
       successful, the normal setup proceeds.

3.1.2 Use of SDP with offer/answer and SIP

   This section defines additional processing rules, to the general one
   defined in Section 3.1.1, applicable only to applications using SDP
   with the offer-answer model [OAM] (and in particular SIP).





Arkko, et al.                                                   [Page 8]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   When an initial offer is created, the following offer-answer specific
   procedure SHALL be applied:

   * Before creating the key management data field, the list of protocol
      identifiers MUST be provided by the SDP application to (each) key
      management protocol, as defined in Section 3.1.4 (to defeat
      bidding-down attacks).

   For a received SDP offer that contains the key management attributes,
   the following offer-answer specific procedure SHALL be applied:

   * Before, or in conjunction with, passing the key management data to
      the key management protocol, the complete list of protocol
      identifier from the offer message is provided by the SDP
      application to the key management protocol (as defined in Section
      3.1.4).

   When an answer is created, the following offer-answer specific
   procedure SHALL be applied:

   * If the key management rejects the offer, the answerer SHOULD return
      a "606 Not Acceptable" message and optionally also including one
      or more Warning headers (a 306 "Attribute not understood" when one
      of the parameters is not supported, and a 399 "Miscellaneous
      warning" with arbitrary information to be presented to a human
      user or logged, see Section 20.43 in [SIP]). Further details about
      the cause of failure MAY be described in an included message from
      the key management protocol. The session is then aborted (and it
      is up to local policy or end user to decide how to continue).

   Note that the key management attribute (related to the same key
   management protocol) MAY be present both at session level and at
   media level. Consequently, the process SHALL be repeated for each
   such key management attribute detected. In case the key management
   processing of any such attribute does not succeed (e.g.
   authentication failure, parameters not supported etc.), on either
   session or media level, the entire session setup SHALL be aborted,
   including those parts of the session which successfully completed
   their part of the key management.

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

   If the offerer 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 answerer selects the key management protocol it
   wishes to use, and processes only it, on either session or media



Arkko, et al.                                                   [Page 9]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   level, or on both, according to where located. If the answerer does
   not support any of the offerer's suggested key management protocols,
   the receiver returns a "606 Not Acceptable" error message, 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.
   Unless the guidelines of Section 3.1.4 are followed, multiple lines
   may open up bidding-down attacks.

   The offerer MUST include the key management data within an offer that
   contains the media description it applies to.

   Re-keying MUST be handled as a new offer, with the new proposed
   parameters. The answerer treats this as a new offer where the key
   management is the issue of change. The re-keying exchange MUST be
   finalized before the security protocol can change the keys. The same
   key management protocol used in the original offer SHALL also be used
   in the new offer carrying re-keying. If the new offer 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 offerer MUST then abort
   the session.

   Note that, in multicast scenarios, unlike unicast, there is only a
   single view of the stream [OAM], hence there MUST be a uniform
   agreement of the security parameters.

3.1.3 Use of SDP with SAP

   There are cases where SDP is used without conforming to the
   offer/answer model; instead it is a one-way SDP distribution (i.e.
   without back channel), such as when used with SAP and HTTP.

   The processing follows the two first steps of the general SDP
   processing (see Section 3.1.1). It can be noted that the processing
   in this case differs from the offer/answer case in the fact that only
   one key management protocol SHALL be offered (i.e. no negotiation
   will be possible). This implies that the bidding down attack is not
   an issue; therefore the countermeasure is not needed.  The key
   management protocol used MUST support one-way messages.

3.1.4 Bidding-down attack prevention

   The possibility to support multiple key management protocols may,
   unless properly handled, introduce bidding-down attacks.
   Specifically, a man-in-the-middle could "peel off" cryptographically
   strong offers (deleting the key management lines from the message),
   leaving only weaker ones as the Responder's choice. To avoid this,
   the list of identifiers of the proposed key management protocols MUST



Arkko, et al.                                                  [Page 10]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   be authenticated. The authentication MUST be done separately by each
   key management protocol.

   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 processed to 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 then be given to each of the
   selected (offered) key management protocols by the application with
   ";" separated identifiers. All the offered protocol identifiers MUST
   be included, in the same order as they appear in the corresponding
   SDP description.

   The protocol list can formally be described as

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

   where KMID is as defined in Section 2.

   For example, if the offered protocols are MIKEY and two yet-to-be-
   invented protocols KEYP1, KEYP2, the SDP is:

        v=0
        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).
   Each of the three protocols includes this protocol identifier
   list in its authentication coverage (according to its protocol
   specification).

   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".





Arkko, et al.                                                  [Page 11]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


3.2. RTSP usage

   RTSP does not use the offer/answer model, as SIP does. This causes
   some problems, as it is not possible (without modifying RTSP) to send
   back an answer. 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 server SHALL be the Initiator of the key management exchange for
   sessions in PLAY mode, i.e. transporting media from server to client.
   The below text describes the behavior for PLAY mode. For any other
   mode the behavior is not defined in this specification.

   To obtain a session description, the client initially contacts the
   server via a DESCRIBE message (according to RTSP, a media description
   could also be obtained by other means e.g. using http). The initial
   key management message from the RTSP server is sent to the client in
   the SDP of the 200 OK in response to the DESCRIBE. Note that only one
   key management protocol SHALL be used per session / media level. A
   server MAY allow the SDP with key-management attribute(s) to be
   distributed to the client though other means than RTSP.

   The "uri" parameter of the KeyMgmt header is used to indicate for the
   key management protocol on what context the carried message applies.
   For key management messages on the SDP session level, the answer MUST
   contain the RTSP aggregated control URL to indicate this. For Key
   management messages initially on SDP media level, the key management
   response message in the KeyMgmt header MAY use the RTSP media level
   URL. For RTSP sessions not using aggregated control, i.e. no session
   level control URI is defined, the key management protocol SHALL only
   be invoked on individual media streams. In this case also, the key
   management response SHALL be on individual media streams (i.e. one
   RTSP key management header per media).

   When responding to the initial key management message, the client
   uses the new RTSP header (KeyMgmt) to send back an answer. How this
   is done depends on the usage context.

   * Key management protocol responses for the initial establishment of
      security parameters for an aggregated RTSP session SHALL be sent
      in the first SETUP of the session. This means that if the key
      management is declared for the whole session but is setup in non-
      aggregated fashion, i.e. one media per RTSP session, each SETUP
      MUST carry the same response for the session level context. When
      performing a setup of the second or any subsequent media in a RTSP
      session the same key management parameters as established for the
      first media also applies to these setups.






Arkko, et al.                                                  [Page 12]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   * Key management responses for the initial establishment of security
      parameters for an individual media SHALL only be included in SETUP
      for the corresponding media stream.

   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.

   When the server creates an initial SDP message, the procedure SHALL
   be the same as described in Section 3.1.1.

   The client processing of the initial SDP message from the server
   SHALL follow the same procedures as described in Section 3.1.1,
   except that, if there is an error, the session is aborted (no error
   is sent back).

   The client SHALL create the response, using the key management header
   in RTSP, as follows:

   * The identifier of the key management protocol used (e.g. MIKEY)
      MUST be placed in the "prot" field of the header. The prot values
      are maintained by IANA (Section 8).

   * 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 RTSP
      application and then encapsulated in the "data" field of the
      header. The semantic of the encapsulated message is dependent on
      the key management protocol that is used.

   * Include if necessary the URL to indicate the context in the "uri"
      parameter.

   The server SHALL process a received key management header in RTSP as
   follow:

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

   * 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 for processing.

   * If the key management protocol is successful, the processing can
      proceed according to normal rules.

   * Otherwise, if the key management fails (e.g. due to authentication
      failure or parameter not supported), an error is sent back as the
      SETUP response using RTSP error code 463 (see Section 2.2) and the
      session is aborted. It is up to the key management protocol to
      specify (within the RTSP status code message or through key



Arkko, et al.                                                  [Page 13]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


      management messages) details about the type of error that
      occurred.

   Re-keying within RTSP is for further study, given that media updating
   mechanisms within RTSP are unspecified at the time this document is
   written.


4. Example scenarios

   The following examples utilizes MIKEY [MIKEY] as key management
   protocol to be integrated into SDP and RTSP (see Section 5.1.).

   Example 1 (SIP/SDP)

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

   v=0
   o=alice 2891092738 2891092738 IN IP4 w-land.example.com
   s=Cool stuff
   e=alice@w-land.example.com
   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 (signaled by the use of the SAVP profile). She
   uses MIKEY to set up the security parameters for SRTP (Section 6).
   The MIKEY message contains the security parameters, together with the
   necessary key material. Note that MIKEY is exchanging the crypto
   suite for both streams, as it is placed at the session level. Also,
   MIKEY provides its own security, i.e. when Bob processes Alice's
   MIKEY message, he will also find the signaling of the security
   parameters used to secure the MIKEY exchange. Alice's authentication
   information is also carried within the MIKEY message, to prove that
   the message is authentic.

   Upon receiving the offer, Bob checks the validity of the received
   MIKEY message, and, in case of successful verification, he accepts
   the offer and sends an answer back to Alice (with his authentication
   information, and, if necessary, also some key material from his
   side):

   v=0
   o=bob 2891092897 2891092897 IN IP4 foo.example.com
   s=Cool stuff



Arkko, et al.                                                  [Page 14]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   e=bob@foo.example.com
   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

   Upon receiving the answer, Alice verifies the correctness of it. In
   case of success, at this point Alice and Bob share the security
   parameters and the keys needed for a secure RTP communication.


   Example 2 (SDP)

   This example shows how Alice would have done if she wished to protect
   only the audio stream. She would have placed the MIKEY line at media
   level for the audio stream only (also specifying the use of the SRTP
   profile there, SAVP). The semantic of the MIKEY messages is as in the
   previous case, but applies only to the audio stream.

   v=0
   o=alice 2891092738 2891092738 IN IP4 w-land.example.com
   s=Cool stuff
   e=alice@w-land.example.com
   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

   Bob would then act as described in the previous example, including
   the MIKEY answer at the media level for the audio stream (as Alice
   did).

   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, instead the RTP/AVP profile is
   signaled).


   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



Arkko, et al.                                                  [Page 15]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   Accept: application/sdp
   From: user@example.com

   The server sends back an OK message including an SDP description,
   together with the MIKEY message. The MIKEY message contains the
   necessary security parameters that the server is willing of offering
   to the client, together with authentication information (to prove
   that the message is authentic) and the key material. The SAVP profile
   also signals the use of SRTP for securing the media sessions.

   RTSP/1.0 200 OK
   CSeq: 312
   Date: 23 Jan 1997 15:35:06 GMT
   Content-Type: application/sdp
   Content-Length: 478
   v=0
   o=actionmovie 2891092738 2891092738 IN IP4 movie.example.com
   s=Action Movie
   e=action@movie.example.com
   t=0 0
   c=IN IP4 movie.example.com
   a=control:rtsp://movie.example.com/action
   a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD..
   m=audio 0 RTP/SAVP 98
   a=rtpmap:98 AMR/8000
   a=control:rtsp://movie.example.com/action/audio
   m=video 0 RTP/SAVP 31
   a=rtpmap:31 H261/90000
   a=control:rtsp://movie.example.com/action/video

   The client checks the validity of the received MIKEY message, and, in
   case of successful verification, it accept the message. The client
   then includes its key management data in the SETUP request going back
   to the server, the client authentication information (to prove that
   the message is authentic) and, if necessary, some key material.

   SETUP rtsp://movie.example.com/action/audio RTSP/1.0
   CSeq: 313
   Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057
   keymgmt: prot=mikey; uri="rtsp://movie.example.com/action";
   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;
                         server_port=5000-5001




Arkko, et al.                                                  [Page 16]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   Note than in this case the key management line was specified at the
   session level, the key management information only goes into the
   SETUP related to the first stream. The "uri" indicates to the server
   that the context is for the whole aggregated session the key
   management applies. The RTSP client  then proceeds setting up the
   second media (video) in aggregation with the audio. As the two media
   are run in aggregation and the key context was established in the
   first exchange, no more key management messages are needed.


   Example 4 (RTSP)

   The use of the MIKEY message at the media level would change the
   previous example as follows.

   The 200 OK would contain the two distinct SDP attributes for MIKEY at
   the media level:

   RTSP/1.0 200 OK
   CSeq: 312
   Date: 23 Jan 1997 15:35:06 GMT
   Content-Type: application/sdp
   Content-Length: 561
   v=0
   o=actionmovie 2891092738 2891092738 IN IP4 movie.example.com
   s=Action Movie
   e=action@movie.example.com
   t=0 0
   c=IN IP4 movie.example.com
   a=control:rtsp://movie.example.com/action
   m=audio 0 RTP/SAVP 98
   a=rtpmap:98 AMR/8000
   a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD..
   a=control:rtsp://movie.example.com/action/audio
   m=video 0 RTP/SAVP 31
   a=rtpmap:31 H261/90000
   a=key-mgmt:mikey dhsoKkdOokdo7eWsnDSJDuiSDF9sdhs727ghsd/..
   a=control:rtsp://movie.example.com/action/video

   Each RTSP header are inserted in the SETUP related to the audio and
   video separately:

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

   and similarly for the video session:

   SETUP rtsp://movie.example.com/action/video RTSP/1.0



Arkko, et al.                                                  [Page 17]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   CSeq: 315
   Transport: RTP/SAVP/UDP;unicast;client_port=3058-3059
   keymgmt: prot=mikey; uri="rtsp://movie.example.com/action/video";
   data="RW278HjKVBskaoqDeMkdw..."

   Note: The "uri" parameter could be excluded from the two SETUP
   messages in this example.


5. 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. In addition to this, the following needs to
   be defined:

   * The key management protocol identifier to be used as the protocol
      identifier should be registered at IANA according to Section 8.

   * The information that the key management needs from SDP and RTSP,
      and vice versa, as described in Section 3. The exact API is
      implementation specific, but it SHOULD at least support the
      exchange of the specified information.

   * The key management protocol to be added MUST be such, that the
      processing in Section 3 (describing its interactions with SDP and
      RTSP) can be applied. Note in particular, Section 3.1.4 requires
      each key management protocol to specify how the list of protocol
      identifiers is authenticated inside that key management protocol.
      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.

   Finally, it is obviously crucial to analyze possible security
   implications induced by the introduction of a new key management
   protocol in the described framework.

   Today, the MIKEY protocol [MIKEY] has adopted the key management
   extensions to work together with SIP and RTSP (see Section 6). Other
   protocols MAY use the described attribute and header, e.g. Kerberos
   [KERB], however this is subject to future standardization.


6. Integration of MIKEY

   [MIKEY] describes a key management protocol for real-time
   applications (both for peer-to-peer communication and group
   communication). MIKEY can be integrated within SDP and RTSP,
   following the rules and guidelines described in this document.





Arkko, et al.                                                  [Page 18]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   MIKEY satisfies the requirements described in Section 3. The MIKEY
   message is formed as defined in [MIKEY], then passed from MIKEY to
   the SDP application that base64 encodes it, and encapsulates it in
   the keymgmt-data attribute. The examples in Section 4 use MIKEY,
   where the semantic of the exchange is also briefly explained.

   The key management protocol identifier (KMID) to be used as the
   protocol identifier SHALL be "mikey" and is registered at IANA, see
   in detail Section 8.

   The information that the key management needs from SDP and RTSP, and
   vice versa, follows Section 3. To avoid bidding-down attacks, the
   directives in Section 3.1.4 are followed. The list of protocol
   identifiers is authenticated within MIKEY by placing such list in a
   General Extension Payload (of type "SDP IDs", [MIKEY]), which then
   automatically will be integrity protected/signed. The receiver SHALL
   then match the list in the General Extension Payload with the list
   included in SDP and SHOULD (according to policy) if they differ, or
   if integrity/signature verification fails, reject the offer.

   To signal the MIKEY identity of the client to the server in the
   DESCRIBE, it is RECOMMENDED to include the From header field in RTSP.

6.1 MIKEY Interface

   This subsection describes some aspects, which implementers SHOULD
   consider. If the MIKEY implementation is separate from the
   SDP/SIP/RTSP, an application programming interface (API) between
   MIKEY and those protocols is needed with certain functionality
   (however, exactly what it looks like is implementation dependent).

   Implementers of MIKEY are RECOMMENDED to consider providing at least
   the following functionality:

   * the possibility for MIKEY to receive information about the sessions
      negotiated. This is to some extent implementation dependent. But
      it is RECOMMENDED that, in the case of SRTP streams, the number of
      SRTP streams is included (and the direction of these). It is also
      RECOMMENDED to provide the destination addresses and ports to
      MIKEY. When referring to streams described in SDP, MIKEY allocated
      two consecutive numbers for the related Crypto Session indexes (as
      each stream can be bi-directional). An example: if the SDP
      contains two m lines (specifying whatever direction of the
      streams), and MIKEY is at the session level, then MIKEY allocates
      e.g. the CS IDs '1' and '2' for the first m line, and '3' and '4'
      for the second m line.

   * the possibility for MIKEY to receive incoming MIKEY messages and
      return a status code from/to the SIP/RTSP application.





Arkko, et al.                                                  [Page 19]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   * the possibility for the SIP or RTSP applications to receive
      information from MIKEY. This would typically include the receiving
      of the CSB ID (to later be able to identify the active MIKEY
      session), and the SSRCs and the ROC for SRTP usage. It is also
      RECOMMENDED that extra information about errors can be received.

   * the possibility for the SIP or RTSP application to receive outgoing
      MIKEY messages.

   * the possibility to tear down a MIKEY CSB (e.g. if the SIP session
      is closed, the CSB SHOULD also be closed).


7. Security Considerations

   The framework for transfer of key management data as described here
   is intended to provide the security parameters for the end-to-end
   protection of the media session. It is furthermore good practice to
   secure the session setup (e.g. SDP, SIP, RTSP, SAP).  However, it
   might be that the security of the session setup is not possible to
   achieve end-to-end, but only hop-by-hop. For example, SIP requires
   intermediate proxies to have access to part of the SIP message, and
   sometimes also to the SDP description (c.f. [E2M]). General security
   considerations for the session setup can be found in SDP [SDPnew],
   SIP [SIP], and RTSP [RTSP]. The framework defined in this memo is
   useful when the session setup is not protected in an end-to-end
   fashion, but the media streams needs to be end-to-end protected,
   hence the security parameters such as keys are not wanted revealed to
   intermediaries.

   The security will also depend on the encapsulated level of security
   the key management protocol offers. It follows that, under the
   assumption that the key management schemes are secure, the SDP can be
   passed along unprotected without affecting the key management as
   such, and the media streams will still be secure even if some
   attackers gained knowledge of the SDP contents. Further security
   considerations can be found for each key management protocol (for
   MIKEY these can be found in [MIKEY]).

   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 may lead to undesired
   interruption in the setup.

   The use of multiple key management protocols in the same offer may
   open up the possibility of a bidding-down attack, as specified in



Arkko, et al.                                                  [Page 20]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   Section 3.1.4. To exclude such possibility, the authentication of the
   protocol identifier list is used. Note though, that the security
   level of the authenticated protocol identifier will be as high (or
   low), as the "weakest" protocol. Therefore, it is discouraged to
   offer protocols with too different security levels.

   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
   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. In
   the case that the response declines any security (therefore there is
   impossibility of authenticating it), the session setup SHALL be
   aborted.


8. IANA Considerations

8.1. 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 Field ("att-field"):

        Name:               key-mgmt-att-field
        Long form:          key management protocol attribute field
        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 RFC xxxx, Section 2.1 and 8.3.

8.2. RTSP Registration

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





Arkko, et al.                                                  [Page 21]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   Following the guidelines of [RTSP], the registration is defined as
   follows:

   Header name:      keymgmt
   Header syntax:    see RFC xxxx, Section 2.2
   Intended usage:   see RFC xxxx, Section 2.2
   Proxy treatment:  Proxies SHALL NOT add, change, or delete the
                      header. The proxy does not need to read this
                      header.
   Purpose:          see RFC xxxx, Section 2

   The RTSP Status-Code "463" [RFC xxxx], with the default string "Key
   management failure", needs to be registered.

8.3. Protocol Identifier Registration

   This document defines one new name space, the "SDP/RTSP key
   management protocol identifier", associated with the protocol
   identifier, KMID, defined in Section 2 to be used with the above
   registered attributes in SDP and RTSP.

   A new registry needs to be set up for the KMID parameter, 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-att-field
                         attribute and the keymgmt RTSP header
        Reference:      Section 7 in RFC yyyy

   Note that this registration will imply that the protocol identifier,
   KMID, name space will be shared between SDP and RTSP.

   Further values may be registered according to the "Specification
   Required" policy as defined in [RFC2434]. Each new registration needs
   to indicate the parameter name, and register it within IANA. Note
   that the parameter name is case sensitive and it is RECOMMENDED that
   the name to 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 and the requested details of interaction between the key
   management protocol and SDP, as specified in RFC xxxx.

   The registration itself of new values should be sent to IANA.
   Registrations SHALL include the following information:





Arkko, et al.                                                  [Page 22]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   * Contact: the contact name and email address
   * Value name: the name of the value being registered (which MUST
      comply with the KMID as defined in Section 2)
   * Long Name: long-form name in English
   * Purpose: short explanation of the purpose of the registered name.
   * Reference: a reference to the specification (e.g. RFC number)
      providing the usage guidelines in accordance to Section 5 (and
      also complying to the specified requirements).


9. Acknowledgments

   The authors would like to thank Joerg Ott, Rolf Blom, Magnus Brolin,
   Johan Bilien, Jon-Olov Vatn, and Erik Eliasson. A special thanks to
   Colin Perkins and Magnus Westerlund, who contributed in many
   sections.


10. Author's Addresses

     Jari Arkko
     Ericsson
     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 23]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


11. References

11.1. Normative References

   [MIKEY] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and
   Norrman, K., "MIKEY: Multimedia Internet KEYing", IETF, RFC yyyy,
   [Internet Draft, <draft-ietf-msec-mikey-08.txt> ].

   [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, draft-ietf-mmusic-sdp-
   new-15.txt.

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

   [RFC2234] Crocker, D. and Overell, P., "Augmented BNF for Syntax
   Specifications: ABNF", RFC 2234, November 1997.

   [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.

11.2. Informative References

   [E2M] Ono, K. and Tachimoto, S., "End-to-middle security in the
   Session Initiation Protocol (SIP)", Internet Draft, IETF, draft-ono-
   sipping-end2middle-security-00.

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

   [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, <draft-ietf-avt-srtp-09.txt>.


IPR Notices

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to



Arkko, et al.                                                  [Page 24]

INTERNET-DRAFT            mmusic-kmgmt-ext-10             February 2004


   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights. Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive
   Director.

Copyright Notice

   Copyright (C) The Internet Society (2004). 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
   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
   English.

   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
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


   This Internet-Draft expires in August 2004.






Arkko, et al.                                                  [Page 25]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/