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Network Working Group                                           J. ArkkoRequest for Comments: 4567                                   F. LindholmCategory: Standards Track                                     M. Naslund                                                              K. Norrman                                                                Ericsson                                                              E. Carrara                                           Royal Institute of Technology                                                               July 2006Key Management Extensions for Session DescriptionProtocol (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 2006Table of Contents1. Introduction ....................................................31.1. Notational Conventions .....................................42. Applicability ...................................................43. Extensions to SDP and RTSP ......................................53.1. SDP Extensions .............................................53.2. RTSP Extensions ............................................64. Usage with SDP, SIP, RTSP, and SAP ..............................74.1. Use of SDP .................................................84.1.1. General Processing ..................................84.1.2. Use of SDP with Offer/Answer and SIP ...............104.1.3. Use of SDP with SAP ................................134.1.4. Bidding-Down Attack Prevention .....................134.2. RTSP Usage ................................................145. Example Scenarios ..............................................175.1. Example 1 (SIP/SDP) .......................................175.2. Example 2 (SDP) ...........................................185.3. Example 3 (RTSP) ..........................................185.4. Example 4 (RTSP) ..........................................206. Adding Further Key Management Protocols ........................217. Integration of MIKEY ...........................................227.1. MIKEY Interface ...........................................228. Security Considerations ........................................239. IANA Considerations ............................................259.1. SDP Attribute Registration ................................259.2. RTSP Registration .........................................269.3. Protocol Identifier Registration ..........................2610. Acknowledgements ..............................................2711. References ....................................................2711.1. Normative References .....................................2711.2. Informative References ...................................28Arkko, et al.               Standards Track                     [Page 2]

RFC 4567       Key Management Extensions for SDP and RTSP      July 20061.  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 20063.  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 toSection 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 inSection 3 of this memo, and base64 is as   defined in SDP [SDPnew].  Prtcl-id refers to the set of values   defined for KMPID inSection 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 inSection 3 of this memo, "base64" as   defined in [SDPnew], and "URI" as defined inSection 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 inSection 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 (seeSection 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 inSection 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 inSection 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 inSection4.1.4).   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; seeSection20.43 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 mediaArkko, 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 ofSection 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 20064.1.3. 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 (seeSection 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 inSection 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 inSection 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 inSection 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 (seeSection 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 20065.  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 (Section7).  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.comArkko, 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/1.0Arkko, 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/videoArkko, 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 inSection 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 toSection 9.   * The information that the key management needs from SDP and RTSP,     and vice versa, as described inSection 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 inSection 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 (seeSection 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 inSection 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 inSection 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; seeSection 9 for details.   The information that the key management needs from SDP and RTSP, and   vice versa, followsSection 4.  To avoid bidding-down attacks, the   directives inSection 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 inSection 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 (orArkko, 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 Considerations9.1.  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:            SeeRFC 4567, Section 3.        Reference:RFC 4567, Section 3.1        Values:             SeeRFC 4567, Sections3.1 and9.3.Arkko, et al.               Standards Track                    [Page 25]

RFC 4567       Key Management Extensions for SDP and RTSP      July 20069.2.  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:    seeRFC 4567, Section 3.2   Intended usage:   seeRFC 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:          seeRFC 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 inSection 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 inRFC 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 inSection 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 toSection 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.  References11.1.  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,RFC3986, 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)",RFC4189, 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 2006Authors' 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.comArkko, et al.               Standards Track                    [Page 29]

RFC 4567       Key Management Extensions for SDP and RTSP      July 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM 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.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   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; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Arkko, et al.               Standards Track                    [Page 30]