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rfc:rfc4567

Network Working Group J. Arkko Request for Comments: 4567 F. Lindholm Category: Standards Track M. Naslund

                                                            K. Norrman
                                                              Ericsson
                                                            E. Carrara
                                         Royal Institute of Technology
                                                             July 2006
         Key Management Extensions for Session Description
       Protocol (SDP) and Real Time Streaming Protocol (RTSP)

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 This document defines general extensions for Session Description
 Protocol (SDP) and Real Time Streaming Protocol (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
 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 Multimedia Internet
 KEYing (MIKEY) key management protocol is also defined.

Arkko, et al. Standards Track [Page 1] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

Table of Contents

 1. Introduction ....................................................3
    1.1. Notational Conventions .....................................4
 2. Applicability ...................................................4
 3. Extensions to SDP and RTSP ......................................5
    3.1. SDP Extensions .............................................5
    3.2. RTSP Extensions ............................................6
 4. Usage with SDP, SIP, RTSP, and SAP ..............................7
    4.1. Use of SDP .................................................8
         4.1.1. General Processing ..................................8
         4.1.2. Use of SDP with Offer/Answer and SIP ...............10
         4.1.3. Use of SDP with SAP ................................13
         4.1.4. Bidding-Down Attack Prevention .....................13
    4.2. RTSP Usage ................................................14
 5. Example Scenarios ..............................................17
    5.1. Example 1 (SIP/SDP) .......................................17
    5.2. Example 2 (SDP) ...........................................18
    5.3. Example 3 (RTSP) ..........................................18
    5.4. Example 4 (RTSP) ..........................................20
 6. Adding Further Key Management Protocols ........................21
 7. Integration of MIKEY ...........................................22
    7.1. MIKEY Interface ...........................................22
 8. Security Considerations ........................................23
 9. IANA Considerations ............................................25
    9.1. SDP Attribute Registration ................................25
    9.2. RTSP Registration .........................................26
    9.3. Protocol Identifier Registration ..........................26
 10. Acknowledgements ..............................................27
 11. References ....................................................27
    11.1. Normative References .....................................27
    11.2. Informative References ...................................28

Arkko, et al. Standards Track [Page 2] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

1. Introduction

 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.
 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 set up 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 setup 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 need access to the SDP).

Arkko, et al. Standards Track [Page 3] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 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 extensible.  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.  [SDES] uses the approach
 of extending SDP, to carry the security parameters for the media
 streams.  However, the mechanism defined in [SDES] requires end-to-
 end protection of the SDP by some security protocol such as S/MIME,
 in order to get end-to-end protection.  The solution described here
 focuses only on the end-to-end protection of key management
 parameters and as a consequence does not require external end-to-end
 protection means.  It is important to note though, and we stress this
 again, that only the key management parameters are protected.
 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. Applicability

 [SDES] provides similar cryptographic key distribution capabilities,
 and it is intended for use when keying material is protected along
 with the signaling.
 In contrast, this specification expects endpoints to have
 preconfigured keys or common security infrastructure.  It provides
 its own security and is independent of the protection of signaling
 (if any).  As a result, it can be applied in environments where
 signaling protection is not turned on, or used hop-by-hop (i.e.,
 scenarios where the SDP is not protected end-to-end).  This
 specification will, independently of the signaling protection
 applied, ensure end-to-end security establishment for the media.

Arkko, et al. Standards Track [Page 4] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

3. 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, KMPID, is defined as below in Augmented Backus-
 Naur Form grammar (ABNF) [RFC4234].
 KMPID =  1*(ALPHA / DIGIT)
 Values for the identifier, KMPID, are registered and defined in
 accordance to Section 9.  Note that the KMPID is case sensitive, and
 it is RECOMMENDED that values registered are lowercase letters.

3.1. 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 ABNF for the key management extensions (conforming to the
 att-field and att-value) are as follows:
    key-mgmt-attribute = key-mgmt-att-field ":" key-mgmt-att-value
    key-mgmt-att-field = "key-mgmt"
    key-mgmt-att-value = 0*1SP prtcl-id SP keymgmt-data
    prtcl-id     = KMPID
                   ; e.g., "mikey"

Arkko, et al. Standards Track [Page 5] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

    keymgmt-data = base64
    SP           = %x20
 where KMPID is as defined in Section 3 of this memo, and base64 is as
 defined in SDP [SDPnew].  Prtcl-id refers to the set of values
 defined for KMPID in Section 9.
 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 4.1 describes in detail how the attributes are
 used and how the SDP is handled in different usage scenarios.  The
 choice of the level depends, for example, on the particular key
 management protocol.  Some protocols may not be able to derive enough
 key material for all the sessions; furthermore, possibly a different
 protection to each session could be required.  The particular
 protocol might achieve this only by specifying it at the media level.
 Other protocols, such as MIKEY, have instead those capabilities (as
 it can express multiple security policies and derive multiple keys),
 so it may use the session level.

3.2. 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" "=" KMPID ";" ["uri" "=" %x22 URI %x22 ";"]
 where KMPID is as defined in Section 3 of this memo, "base64" as
 defined in [SDPnew], and "URI" as defined in Section 3 of [RFC3986].
 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.

Arkko, et al. Standards Track [Page 6] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 Method            | Direction  |  Requirement
 ---------------------------------------------
 DESCRIBE response |   S->C     |  RECOMMENDED
 SETUP             |   C->S     |  REQUIRED
 SETUP Response    |   S->C     |  REQUIRED (error)
 Note: Section 4.2 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 4.2):
 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.

4. 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:
  • At the current time, it MUST be possible to execute the key

management protocol in at most one request-response message

   exchange.  Future relaxation of this requirement is possible but
   would introduce significant complexity for implementations
   supporting multi-roundtrip mechanisms.
  • 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 or not a message is accepted.
 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 follows: 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 ensure that the message is authentic).

Arkko, et al. Standards Track [Page 7] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 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 responses is dependent on the particular key management
 protocol.
 Section 7 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 6.

4.1. Use of SDP

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

4.1.1. 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 cannot 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 9).

Arkko, et al. Standards Track [Page 8] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

  • 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 9).
  • 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
   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) MUST 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.

Arkko, et al. Standards Track [Page 9] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 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 the key management offer is rejected and the intent is to re-

negotiate it, it MUST be done through another Offer/Answer

   exchange.  It is RECOMMENDED to NOT abort the session in that case,
   but to re-negotiate using another Offer/Answer exchange.  For
   example, in [SIP], the "security precondition" as defined in
   [SPREC] solves the problem for a session initiation.  The
   procedures in [SPREC] are outside the scope of this document.  In
   an established session, an additional Offer/Answer exchange using a
   re-INVITE or UPDATE as appropriate MAY be used
  • If errors occur, or the key management offer is rejected and there

is no intent to re-negotiate it, 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.

4.1.2. Use of SDP with Offer/Answer and SIP

 This section defines additional processing rules, to the general
 rules defined in Section 4.1.1, applicable only to applications using
 SDP with the offer/answer model [OAM] (and in particular SIP).
 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 4.1.4 (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:

Arkko, et al. Standards Track [Page 10] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

  • Before, or in conjunction with, passing the key management data to

the key management protocol, the complete list of protocol

   identifiers from the offer message is provided by the SDP
   application to the key management protocol (as defined in Section
   4.1.4).
 When an answer is created, the following offer/answer-specific
 procedure SHALL be applied:
  • If the key management rejects the offer and the intent is to re-

negotiate it, the Answer SHOULD include the cause of failure in an

   included message from the key management protocol.  The
   renegotiation MUST be done through another Offer/Answer exchange
   (e.g., using [SPREC]).  In an established session, it can also be
   done through a re-INVITE or UPDATE as appropriate.
  • If the key management rejects the offer and the session needs to be

aborted, the answerer SHOULD return a "488 Not Acceptable Here"

   message, 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 that 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. Standards Track [Page 11] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 level, or on both, according to where located.  If the answerer does
 not support any of the offerer's suggested key management protocols,
 the answerer indicates this to the offerer so a new Offer/Answer can
 be triggered; alternatively, it may return a "488 Not Acceptable
 Here" 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 4.1.4 are followed, multiple lines
 may open up bidding-down attacks.  Note also that the multiple-offer
 option has been added to optimize signaling overhead in case the
 Initiator knows some key (e.g., a public key) that the Responder has,
 but is unsure of what protocol the Responder supports.  The mechanism
 is not intended to negotiate options within one and the same
 protocol.
 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 "488 Not Acceptable Here" 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.
 After the offer is issued, the offerer SHOULD be prepared to receive
 media, as the media may arrive prior to the answer.  However, this
 brings issues, as the offerer does not know yet the answerer's choice
 in terms of, e.g., algorithms, or possibly the key is known.  This
 can cause delay or clipping can occur; if this is unacceptable, the
 offerer SHOULD use mechanisms outside the scope of this document,
 e.g., the security preconditions for SIP [SPREC].

Arkko, et al. Standards Track [Page 12] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

4.1.3. 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 4.1.1).  It can be noted that the processing
 in this case differs from the offer/answer case in 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.

4.1.4. 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
 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   =  KMPID *(";" KMPID)
 where KMPID is as defined in Section 3.
 For example, if the offered protocols are MIKEY and two yet-to-be-
 invented protocols KEYP1, KEYP2, the SDP is:

Arkko, et al. Standards Track [Page 13] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 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 AQAFgM0XflABAAAAAAAAAAAAAAsAyO...
 a=key-mgmt:keyp1 727gkdOshsuiSDF9sdhsdKnD/dhsoSJokdo7eWD...
 a=key-mgmt:keyp2 DFsnuiSDSh9sdh Kksd/dhsoddo7eOok727gWsJD...
 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".
 End-to-end integrity protection of the key-mgmt attributes
 altogether, provided externally to the key management itself, also
 protects against this bidding-down attack.  This is, for example, the
 case if SIP uses S/MIME [RFC3851] to end-to-end integrity protect the
 SDP description.  However, as this end-to-end protection is not an
 assumption of the framework, the mechanisms defined in this section
 SHALL be applied.

4.2. 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 3.2).  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.

Arkko, et al. Standards Track [Page 14] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 To obtain a session description, the client initially contacts the
 server via a DESCRIBE message.  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 through other means than RTSP, although this is not specified
 here.
 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 set up 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 an RTSP
   session, the same key management parameters as established for the
   first media also apply to these setups.
  • 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 4.1.1.

Arkko, et al. Standards Track [Page 15] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 The client processing of the initial SDP message from the server
 SHALL follow the same procedures as described in Section 4.1.1,
 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 9).
  • 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 semantics 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
 follows:
  • 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 3.2) and the
   session is aborted.  It is up to the key management protocol to
   specify (within the RTSP status code message or through key
   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 was
 written.

Arkko, et al. Standards Track [Page 16] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

5. Example Scenarios

 The following examples utilize MIKEY [MIKEY] as the key management
 protocol to be integrated into SDP and RTSP.

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 AQAFgM0XflABAAAAAAAAAAAAAAsAyONQ6gAAAAAGEEoo2pee4hp2
 UaDX8ZE22YwKAAAPZG9uYWxkQGR1Y2suY29tAQAAAAAAAQAk0JKpgaVkDaawi9whVBtBt
 0KZ14ymNuu62+Nv3ozPLygwK/GbAV9iemnGUIZ19fWQUOSrzKTAv9zV
 m=audio 49000 RTP/SAVP 98
 a=rtpmap:98 AMR/8000
 m=video 52230 RTP/SAVP 31
 a=rtpmap:31 H261/90000
 That is, 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
 7).  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
 endpoint's authentication information is also carried within the
 MIKEY message, to prove that the message is authentic.  The above
 MIKEY message is an example of message when the pre-shared method
 MIKEY is used.
 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
 e=bob@foo.example.com

Arkko, et al. Standards Track [Page 17] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 t=0 0
 c=IN IP4 foo.example.com
 a=key-mgmt:mikey AQEFgM0XflABAAAAAAAAAAAAAAYAyONQ6gAAAAAJAAAQbWlja2
 V5QG1vdXNlLmNvbQABn8HdGE5BMDXFIuGEga+62AgY5cc=
 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.

5.2. Example 2 (SDP)

 This example shows what 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 semantics 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 AQAFgM0XflABAAAAAAAAAAAAAAsAy...
 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 the
 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).

5.3. 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

Arkko, et al. Standards Track [Page 18] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 CSeq: 312
 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 to offer 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 AQAFgM0XflABAAAAAAAAAAAAAAsAy...
 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="AQEFgM0XflABAAAAAAAAAAAAAAYAyONQ6g..."
 The server processes the request including checking the validity of
 the key management header.

Arkko, et al. Standards Track [Page 19] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 RTSP/1.0 200 OK
 CSeq: 313
 Session: 12345678
 Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057;
                       server_port=5000-5001
 Note that in this case the key management line was specified at the
 session level, and 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.

5.4. 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 AQAFgM0XflABAAAAAAAAAAAAA...
 a=control:rtsp://movie.example.com/action/audio
 m=video 0 RTP/SAVP 31
 a=rtpmap:31 H261/90000
 a=key-mgmt:mikey AQAFgM0AdlABAAAAAAAAAAAAA...
 a=control:rtsp://movie.example.com/action/video

Arkko, et al. Standards Track [Page 20] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 Each RTSP header is 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="AQEFgM0XflABAAAAAAAAAAAAA..."
 and similarly for the video session:
 SETUP rtsp://movie.example.com/action/video RTSP/1.0
 CSeq: 315
 Transport: RTP/SAVP/UDP;unicast;client_port=3058-3059
 keymgmt: prot=mikey; uri="rtsp://movie.example.com/action/video";
          data="AQEFgM0AdlABAAAAAAAAAAAAAA..."
 Note: The "uri" parameter could be excluded from the two SETUP
 messages in this example.

6. 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 4.  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 9.

  • The information that the key management needs from SDP and RTSP,

and vice versa, as described in Section 4. The exact API is

   implementation specific, but it MUST at least support the exchange
   of the specified information.
  • The key management protocol to be added MUST be such that the

processing in Section 4 (describing its interactions with SDP and

   RTSP) can be applied.  Note in particular, Section 4.1.4 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.

Arkko, et al. Standards Track [Page 21] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 Today, the MIKEY protocol [MIKEY] has adopted the key management
 extensions to work together with SIP and RTSP (see Section 7).  Other
 protocols MAY use the described attribute and header, e.g., Kerberos
 [KERB]; however, this is subject to future standardization.

7. Integration of MIKEY

 [MIKEY] describes a key management protocol for real-time
 applications (both for peer-to-peer communication and group
 communication).  MIKEY carries the security parameters needed for
 setting up the security protocol (e.g., SRTP) protecting the media
 stream.  MIKEY can be integrated within SDP and RTSP, following the
 rules and guidelines described in this document.
 MIKEY satisfies the requirements described in Section 4.  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 5 use MIKEY,
 where the semantics of the exchange is also briefly explained.
 The key management protocol identifier (KMPID) to be used as the
 protocol identifier SHALL be "mikey" and is registered at IANA; see
 Section 9 for details.
 The information that the key management needs from SDP and RTSP, and
 vice versa, follows Section 4.  To avoid bidding-down attacks, the
 directives in Section 4.1.4 are followed.  The list of protocol
 identifiers is authenticated within MIKEY by placing the 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.
 The server will need to be able to know the identity of the client
 before creating and sending a MIKEY message.  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.  Other methods
 to establish the identity could be using the IP address or retrieving
 the identity from the RTSP authentication if used.

7.1. 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).

Arkko, et al. Standards Track [Page 22] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 The following aspects need to be considered:
  • 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 SHALL
   allocate 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 Crypto Sessions Identifiers (CS IDs; see [MIKEY]) '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.

  • the possibility for the SIP or RTSP applications to receive

information from MIKEY. This would typically include the receiving

   of the Crypto Session Bundle Identifier (CSB ID; see [MIKEY], to
   later be able to identify the active MIKEY session), and the SSRCs
   and the rollover counter (ROC; see [SRTP]) 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).

8. 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 (cf. [E2M]), although end-to-
 end confidentiality can hide bodies from intermediaries.  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-

Arkko, et al. Standards Track [Page 23] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 end fashion, but the media streams need to be end-to-end protected;
 hence the security parameters (such as keys) are not wanted revealed
 to or manipulated by intermediaries.
 The security will also depend on the 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 unencrypted 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
 integrity protected 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 denial-of-service
 (DoS) attacks aimed at SDP may lead to undesired interruption in the
 setup.  See also the attacks described at the end of this section.
 The only integrity-protected attribute of the media stream is, in the
 framework proposed here, the set of key management protocols.  For
 instance, it is possible to (1) swap key management offers across SDP
 messages, or (2) inject a previous key management offer into a new
 SDP message.  Making the (necessary) assumption that all involved key
 management protocols are secure, the second attack will be detected
 by replay protection mechanisms of the key management protocol(s).
 Making the further assumption that, according to normal best current
 practice, the production of each key management offer is done with
 independent (pseudo)random choices (for session keys and other
 parameters), the first attack will either be detected in the
 Responder's (now incorrect) verification reply message (if such is
 used) or be a pure DoS attack, resulting in Initiator and Responder
 using different keys.
 It is RECOMMENDED for the identity at the SPD level to be the one
 authenticated at the key management protocol level.  However, this
 might need to keep into consideration privacy aspects, which are out
 of scope for this framework.
 The use of multiple key management protocols in the same offer may
 open up the possibility of a bidding-down attack, as specified in
 Section 4.1.4.  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

Arkko, et al. Standards Track [Page 24] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 low), as the "weakest" protocol.  Therefore, the offer MUST NOT
 contain any security protocols (or configurations thereof) weaker
 than permitted by local security policy.
 Note that it is impossible to ensure 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.  Note also that the declined offer could be the
 result of an attacker who sits on the path and removes all the key
 management offers.  The bidding-down attack prevention, as described
 above, would not work in this case (as the answerer receives no key
 management attribute).  Also, here it is impossible to ensure the
 authenticity of a declined offer, though here the reason is the
 "peeling-off" attack.  It is up to the local policy to decide the
 behavior in the case that the response declines any security
 (therefore, there is impossibility of authenticating it).  For
 example, if the local policy requires a secure communication and
 cannot accept an unsecured one, then the session setup SHALL be
 aborted.

9. IANA Considerations

9.1. SDP Attribute Registration

 The IANA has created a new subregistry for the purpose of key
 management protocol integration with SDP.
    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 4567, Section 3.
      Reference:          RFC 4567, Section 3.1
      Values:             See RFC 4567, Sections 3.1 and 9.3.

Arkko, et al. Standards Track [Page 25] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

9.2. RTSP Registration

 The IANA has created a new subregistry for the purpose of key
 management protocol integration with RTSP.
 Following the guidelines of [RTSP], the registration is defined as
 follows:
 Header name:      keymgmt
 Header syntax:    see RFC 4567, Section 3.2
 Intended usage:   see RFC 4567, Section 3.2
 Proxy treatment:  Proxies SHALL NOT add, change, or delete the
                    header.  The proxy does not need to read this
                    header.
 Purpose:          see RFC 4567, Section 3
 The RTSP Status-Code "463" (RFC 4567), with the default string "Key
 management failure", needs to be registered.

9.3. Protocol Identifier Registration

 This document defines one new name space, the "SDP/RTSP key
 management protocol identifier", associated with the protocol
 identifier, KMPID, defined in Section 3 to be used with the above
 registered attributes in SDP and RTSP.
 The IANA has created a new subregistry for the KMPID parameter, with
 the following registration created initially:  "mikey".
 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 3830
 Note that this registration implies that the protocol identifier,
 KMPID, 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 with IANA.
 Note that the parameter name is case sensitive, and it is RECOMMENDED
 that the name be in lowercase 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 4567.

Arkko, et al. Standards Track [Page 26] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 New values MUST be registered with IANA.  Registrations SHALL include
 the following information:
  • Contact: the contact name and email address
  • Value name: the name of the value being registered (which MUST

comply with the KMPID as defined in Section 3)

  • 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 6 (and also

   complying to the specified requirements).

10. Acknowledgements

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

11. References

11.1. Normative References

 [MIKEY]    Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
            Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
            August 2004.
 [OAM]      Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
            with Session Description Protocol (SDP)", RFC 3264, June
            2002.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 2434,
            October 1998.
 [RFC3548]  Josefsson, S., "The Base16, Base32, and Base64 Data
            Encodings", RFC 3548, July 2003.
 [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66, RFC
            3986, January 2005.
 [RFC4234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", RFC 4234, October 2005.

Arkko, et al. Standards Track [Page 27] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

 [RTSP]     Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
            Streaming Protocol (RTSP)", RFC 2326, April 1998.
 [SDPnew]   Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
            Description Protocol", RFC 4566, July 2006.
 [SIP]      Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
            A., Peterson, J., Sparks, R., Handley, M., and E.
            Schooler, "SIP: Session Initiation Protocol", RFC 3261,
            June 2002.

11.2. Informative References

 [E2M]      Ono, K. and S. Tachimoto, "Requirements for End-to-Middle
            Security for the Session Initiation Protocol (SIP)", RFC
            4189, October 2005.
 [KERB]     Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
            Kerberos Network Authentication Service (V5)", RFC 4120,
            July 2005.
 [RFC3851]  Ramsdell, B., "Secure/Multipurpose Internet Mail
            Extensions (S/MIME) Version 3.1 Message Specification",
            RFC 3851, July 2004.
 [SDES]     Andreasen, F., Baugher, M., and D. Wing, "Session
            Description Protocol (SDP) Security Descriptions for Media
            Streams", RFC 4568, July 2006.
 [SPREC]    Andreasen, F., Baugher, M., and Wing, D., "Security
            Preconditions for Session Description Protocol Media
            Streams", Work in Progress, October 2005.
 [SRTP]     Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
            Norrman, "The Secure Real-time Transport Protocol (SRTP)",
            RFC 3711, March 2004.

Arkko, et al. Standards Track [Page 28] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

Authors' Addresses

 Jari Arkko
 Ericsson
 02420 Jorvas
 Finland
 Phone:  +358 40 5079256
 EMail:  jari.arkko@ericsson.com
 Elisabetta Carrara
 Royal Institute of Technology
 Stockholm
 Sweden
 EMail:  carrara@kth.se
 Fredrik Lindholm
 Ericsson
 SE-16480 Stockholm
 Sweden
 Phone:  +46 8 58531705
 EMail:  fredrik.lindholm@ericsson.com
 Mats Naslund
 Ericsson Research
 SE-16480 Stockholm
 Sweden
 Phone:  +46 8 58533739
 EMail:  mats.naslund@ericsson.com
 Karl Norrman
 Ericsson Research
 SE-16480 Stockholm
 Sweden
 Phone:  +46 8 4044502
 EMail:  karl.norrman@ericsson.com

Arkko, et al. Standards Track [Page 29] RFC 4567 Key Management Extensions for SDP and RTSP July 2006

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Arkko, et al. Standards Track [Page 30]

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