Internet Engineering Task Force J. Arkko MMUSIC Working Group E. Carrara INTERNET-DRAFT F. Lindholm Expires:
AprilAugust 2004 M. Naslund K. Norrman Ericsson October 2003February 2004 Key Management Extensions for Session Description Protocol (SDP) and Real Time Streaming Protocol (RTSP) <draft-ietf-mmusic-kmgmt-ext-09.txt><draft-ietf-mmusic-kmgmt-ext-10.txt> Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/lid-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright Notice Copyright (C) The Internet Society (2003).(2004). All Rights Reserved. Abstract This document defines general extensions for SDP and RTSP to carry messagesmessages, 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, itstheir use is meaningful only when it is completedcomplemented by thean appropriate key management protocol in use.protocol. General guidelines are also given on how the framework should be used together with SIP and RTSP. The usage with the MIKEY key management protocol is also defined. TABLE OF CONTENTS 1. Introduction.....................................................2 1.1. Notational Conventions.........................................3Conventions.........................................4 2. Extensions to SDP and RTSP.......................................4 2.1. SDP Extensions.................................................4 2.2. RTSP Extensions................................................5 3. Usage with SIPSDP, SIP, RTSP, and RTSP..........................................5SAP...............................6 3.1. Use of SDP.....................................................7 3.1.1 General processing............................................7 3.1.2 Use of SDP processing.........................................6 3.2. SIP usage......................................................7 3.3. RTSP usage.....................................................8 3.4.with offer/answer and SIP..........................8 3.1.3 Use of SDP with SAP..........................................10 3.1.4 Bidding-down attack prevention.................................9 3.5. Example scenarios.............................................10prevention...............................10 3.2. RTSP usage....................................................12 4. Example scenarios...............................................14 5. Adding further Key management protocols.........................13 5. Security Considerations.........................................13protocols.........................18 6. Integration of MIKEY............................................18 6.1 MIKEY Interface................................................19 7. Security Considerations.........................................20 8. IANA Considerations.............................................14 6.1.Considerations.............................................21 8.1. SDP Attribute Registration....................................14 6.2.Registration....................................21 8.2. RTSP Header Registration......................................15 6.3.Registration.............................................21 8.3. Protocol Identifier Registration..............................15 7. Acknowledgments.................................................16 8. Author's Addresses..............................................16Registration..............................22 9. References......................................................17 9.1.Acknowledgments.................................................23 10. Author's Addresses.............................................23 11. References.....................................................24 11.1. Normative References..........................................17 9.2.References.........................................24 11.2. Informative References........................................17References.......................................24 1. Introduction [Editor[RFC Editor remark] All instances of RFC xxxx should be replaced with the RFC number of this document, when published. Furthermore, all instances of RFC yyyy should be replaced with the RFC number of the MIKEY (Multimedia Internet KEYing) document [MIKEY], when published. There has recently been work to define a security frameworkprofile 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 protocolprotocol'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 algorithmalgorithms to be used. The key management protocol has similarities with, e.g., SIP [SIP] and RTSP [RTSP] in the sense that it negotiates necessary information in order to be able to setup the session. The focus in the following sections is to describe a new SDP attribute and RTSP header extension to support key management, and the integrationto show how these can be integrated within SIP and RTSP. A framework is therefore described in the following. ThisThe resulting framework is completed by one or more key management protocols, to describe how the framework is used, e.g.which is the data to be carried inuse the extensions.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 thesession establishment makes it easy to tie the key management to the multimedia sessions. * This approach may be more efficient than setting up the security later, as that approach might force extra roundtrips, possibly also a separate set-up for each stream, hence implying more delay to the actual setup of the media session. * The possibility to negotiate keying material end-to-end without applying end-to-end protection of the SDP (instead, hop-by-hop security mechanisms can be used which may be useful if intermediate proxies needs access to the SDP). Currently in SDP [SDPnew], there exists one field existsto transport keys, i.e.the "k=" field. However, this is not enough for a key management protocol as there are many more parameters that need to be transported.transported, and the "k=" field is not extendible. The approach hereused is to use andextend the SDP description tothrough 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. The document also defines the use of the described framework together with the key management protocol Multimedia Internet KEYing (MIKEY) [MIKEY]. 1.1. Notational Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Extensions to SDP and RTSP This section describes common attributes that are tocan be included in anSDP descriptionor in anRTSP headerwhen an integrated key management protocol is used. The attribute values MUSTfollow the general SDP orand RTSP guidelines (see [SDPnew] and [RTSP]). For both SDP and RTSP, the general method of adding the key management protocol is to introduce new attributes, one identifier to identify the specific key management protocol, and one data field where the key management protocol data is placed. The key management protocol data contains the necessary information to establish the security protocol, e.g., keys and cryptographic parameters. All parameters and keys are protected by the key management protocol. The key management data SHALL be base64 [RFC3548] encoded and comply with the base64 grammar as defined in [SDPnew]. The key management protocol identifier, KMID, is defined as below (where ALPHA and DIGIT are as definedin [RFC2234]).Augmented Backus- Naur Form grammar (ABNF) [RFC2234]. KMID = 1*(ALPHA/DIGIT)1*(ALPHA / DIGIT) Values for the identifier, KMID, are registered and defined in accordance to Section 6.8. Note that the KMID will be case sensitive and it is thereforeRECOMMENDED that values registered are lower case letters. 2.1. SDP Extensions This section provides an Augmented Backus-Naur Form (ABNF)ABNF grammar (as used in [SDPnew]) for the key management extensions to SDP. Note that the new definitions are compliant with the definition of an attribute field, i.e. attribute = (att-field ":" att-value) | att-field One new attributeThe att-field and att-value for SDP is defined: key-mgmtthe key management extensions are as follow: key-mgmt-att-field = "key-mgmt: ""key-mgmt" key-mgmt-att-value = 0*1SP prtcl-id SP keymgmt-data prtcl-id = KMID ; e.g. "mikey" keymgmt-data = textbase64 SP = 0x20 where KMID is as previously defined, "text"defined in Section 2 of this memo, base64 is as defined in SDP [SDPnew]. Prtcl-id refers to the set of values defined for KMID in Section 6. "text" is consistent with the requirement of base64- encoded data, and KMID is consistent with the standard definition of non-ws-string.7. The attribute mayMAY 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 33.1 describes in detail how the attributes are used and how the SDP is handled in different usage scenarios. 2.2. RTSP Extensions To support the needed attribute,key management attributes, the following RTSP header is defined: KeyMgmt = "keymgmt""KeyMgmt" ":" 1#key-mgmt-speckey-mgmt-spec 0*("," key-mgmt-spec) key-mgmt-spec = "prot" "=" KMID ";" ["uri" "=" <"> rtsp_URL <"> ";"] "data" "=" quoted-stringbase64 where KMID is as previouslydefined in Section 2 of this memo, "base64" as defined in [SDPnew], and "quoted-string""rtsp_URL" as defined in the RTSP specification[RTSP]. "quoted-string" is consistent withThe "uri" parameter identifies the requirement of base64-encoded data,context for which the key management data applies, and KMID is consistent withthe standard definitionRTSP URI SHALL match a (session or media) URI present in the description of token.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 shouldMAY be possible to useused in the messages and directions described in the table below. Method | Direction | Requirement --------------------------------------------- DESCRIBE C->S optionalresponse | S->C | RECOMMENDED SETUP | C->S required ANNOUNCE C->S,| REQUIRED SETUP Response | S->C optional (required: if re-key is supported)| REQUIRED (error) Note: Section 33.2 describes in detail how the RTSP extensions are used. We define one new RTSP status code to report error due to any failure during the key management processing (Section 3.2): Status-Code = "463" ; Key management failure A 463 response MAY contain a KeyMgmt header with a key management protocol message that further indicates the nature of the error. 3. Usage with SIPSDP, SIP, RTSP, and RTSPSAP This section gives rules and recommendations of how/when to include the defined key management attribute when SIP and/or RTSP are used together with SDP. When a key management protocol is integrated with SIP/SDP and RTSP, the following general requirements are placed on the key management: * It MUST be possible to execute the key management protocol in at most one roundtrip in case the answerer accepts the offer.request-response message exchange. * It MUST be possible from the SIP/SDP and RTSP application, using the key management API, to receive key management data, and information of whether a message is accepted or not. Today, the MIKEY protocol [MIKEY] has adopted the key management extensions to work together with SIP and RTSP. Other protocols MAY use the described attribute and header, e.g. Kerberos [KERB], however this is subject to future standardization. 3.1. General SDP processing When an SDP message is created, the following procedure SHALL be applied: *The identifiercontent of the key management protocol used MUST be placed inmessages depends on the prtcl-id field. The protocol identifier values are specified by IANA (see Section 6). * The list ofkey management protocol identifiersthat is provided byused. However, the SDP application to (each)content of such key management protocol, as defined in Section 3.4. (to defeat bidding-down attacks). * The keymgmt-data field MUSTmessages might be createdexpected to be roughly as follows.follow. The key management protocol MUST be used to createInitiator (e.g. the offerer) includes the key management message. This message SHALL be base64 encoded [RFC3548] by the SDP application and then encapsulateddata in a first message, containing the keymgmt-data attribute. Themedia description it should apply to. This data may e.g. be a MIKEY message (see [MIKEY], Section 7). A received SDP message that containsin general consists of the security parameters (including key management attributes SHALL be processed inmaterial) needed to secure the communication, together with the necessary authentication information (to assure that the message is authentic). At the Responder's side, the following manner: * Thekey management protocol is identified according tochecks the validity of the prtcl-id field. The protocol identifier values are specified by IANA (Section 6). * Thekey management data frommessage, together with the keymgmt-data field MUST be extracted, base64 decoded to reconstructavailability of the original message,parameters offered, and then passed toprovides the key management protocol. * The list of protocol identifiers is provided bydata to be included in the SDP applicationanswer. This answer may typically authenticate the Responder to the key management protocol, as defined in Section 3.4. Note that depending on key management protocol, some extra parameters mightInitiator, and also be requested by the specific API, such asstate if the source/destination network address/port(s) forinitial offer was accepted or not. Certain protocols might require the specified media (however, this will be implementation specific depending onResponder to include a selection of the actual API). The extrasecurity parameters that a key management protocol might need (other than the ones defined here) SHOULD be documented, describing their use, as well ashe is willing to support. Again, the interactionactual content of thatsuch response is dependent on the particular key management protocol with SDP and RTSP. * Ifprotocol. Section 6 describes a realization of the MIKEY protocol using these mechanisms. Procedures to be used when mapping new key management processing is successful, thenprotocols onto this framework are described in Section 5. 3.1. Use of SDP This section describes the answerer sends backprocessing rules for the answer. Otherwise, ifdifferent applications which use SDP for the key management rejectsmanagement. 3.1.1 General processing The processing when SDP is used is slightly different according to the offer, an errorway SDP is sent back ("606 Not Acceptable")transported, and if it uses an offer/answer or announcement. The processing can be divided into four different steps: 1) How to create the session is aborted. See Section 3.2 for further details. Noteinitial 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 key management attribute MAYlast two steps may not always be repeated more than once (e.g., one at session level and one at media level). Consequently, the process is repeatedapplicable, as there are cases where an answer can not or will not be sent back. The general processing for eachcreating an initial offer SHALL follow the following actions: * The identifier of the key management attribute detected. However,protocol used MUST be placed in casethe prtcl-id field of failureSDP. A table of thelegal protocols identifiers is maintained by IANA (see Section 8). * The keymgmt-data field MUST be created as follows. The key management (on either session or media level),protocol MUST be used to create the session setupkey management message. This message SHALL be aborted (see also Section 3.2 and Section 3.3 for more details). Inbase64 encoded [RFC3548] by the Offer/Answer case,SDP application and then encapsulated in general when therethe keymgmt-data attribute. Note though that the semantics of the encapsulated message is an answer, if more than onedependent on the key management protocol that is supported, multiple instances of the key management attribute MAY be included in the initial offer, each transportingused. The general processing for handling a differentreceived offer SHALL follow the following actions: * The key management data, thus indicating supported alternatives. Ifprotocol is identified according to the prtcl-id field. A table of legal protocols identifiers is maintained by IANA (Section 8). * The key management data from the keymgmt-data field MUST be extracted, base64 decoded to reconstruct the original message, and then passed to the sender includes more than onekey management protocol attribute at session level (analogousfor 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 level), these SHOULD(however, this will be listed in order of preference (the first beingimplementation specific depending on the preferred).actual API). The receiver selects theextra parameters that a key management protocol it wishes to use and includes only that attribute inmight need (other than the answer. Ifones defined here) SHOULD be documented, describing their use, as well as the receiver does not support anyinteraction of that key management protocol with SDP and RTSP. * If errors occur, or the sender's suggestedkey management protocols,offer is rejected, the receiver returns ansession SHALL be aborted. Possible error message (see section 3.2 and section 3.3), whereby the sender MUST abortmessages are dependent on the current setup procedure. Note thatspecific session establishment protocol. At this stage, the placement of multiplekey management offers inwill have either accepted or rejected the offered parameters. This MAY cause a singleresponse message has the disadvantage thatto be generated, depending on the message expandskey management protocol and the computational workload forapplication scenario. If an answer is to be generated, the offerer will increase drastically. Unless the guidelines of Section 3.4 are followed, multiple lines may open up for bidding-down attacks. Thefollowing Sections describe the specific use with SIP and RTSP respectively. There aregeneral actions SHALL be performed: * The identifier of course other cases where SDP is used, such as SAP and HTTP. If SDP is transported in an Offer-Answer model fashion, thenthe guidelines in Section 3.2 cankey management protocol used MUST be used. However, for one-way SDP distribution (i.e. without back channel),placed in the above guidelines canprtcl-id field. * The keymgmt-data field MUST be used though with certain restrictions. First, thecreated as follows. The key management protocol MUST support one-way messages, and secondly, only onebe used to create the key management protocolmessage. This message SHALL be offered (i.e. no negotiation will be possible). This document does NOT address one-to-many distribution scenarios, as this would require different types of key management protocols. The support for such scenarios is for future standardization. 3.2. SIP usage When used with SIPbase64 encoded [RFC3548] by the SDP application and then encapsulated in the offer/answer model,keymgmt-data attribute. The semantics of the offerer SHOULD includeencapsulated message is dependent on the key management data within an offerprotocol that contains the media description it should apply to. At the answerer's side,is used. The general processing for handling a received answer SHALL follow the following actions: * The key management protocol checks the validity ofis identified according to the prtcl-id field. * The key management message, together withdata from the availability ofkeymgmt-data field MUST be extracted, base64 decoded to reconstruct the offered attribute values,original message, and then providespassed to the key management data to be included in the answer.protocol for processing. * If errors occur, or the key management offer is not accepted,rejected, the answerer SHOULD return a "606 Not Acceptable" message, including one or more Warning headers (e.g. a 306 "Attribute not understood" when onesession SHALL be aborted. If possible an error message indicating the failure SHOULD be sent back. Otherwise, if all the steps are successful, the normal setup proceeds. 3.1.2 Use of SDP with offer/answer and SIP This section defines additional processing rules, to the parameters is not supported). The session is then abortedgeneral one defined in Section 3.1.1, applicable only to applications using SDP with the offer-answer model [OAM] (and itin particular SIP). When an initial offer is up to local policy or end user to decide how to continue). Re-keying cancreated, the following offer-answer specific procedure SHALL be handled as a new offer, i.e. a re-INVITE shouldapplied: * Before creating the key management data field, the list of protocol identifiers MUST be sent withprovided by the new proposed parameters. The answerer treats thisSDP application to (each) key management protocol, as defined in Section 3.1.4 (to defeat bidding-down attacks). For a newreceived SDP offer wherethat contains the key management isattributes, the issue of change. In general,following offer-answer specific procedure SHALL be applied: * Before, or in conjunction with, passing the re-INVITE (andkey management data to the key exchange) must be finalized beforemanagement protocol, the securitycomplete list of protocol can changeidentifier from the offer message is provided by the SDP application to the keys. The samekey management protocol used(as defined in Section 3.1.4). When an answer is created, the original INVITEfollowing offer-answer specific procedure SHALL alsobe used in the re-INVITE carrying re-keying.applied: * If the re-INVITE carrying re-keying fails (e.g.,key management rejects the authentication verification fails),offer, the answerer SHOULD sendreturn a "606 Not Acceptable" message,message and optionally also including one or more Warning headers (at least a 306). The offerer MUST then abort the security setup. 3.3. RTSP usage RTSP does(a 306 "Attribute not useunderstood" when one of the offer/answer model, as SIP does. This causes some problems, as itparameters is not possible (without abusing RTSP)supported, and a 399 "Miscellaneous warning" with arbitrary information to send back an answerbe presented to the server (as the server willa human user or logged, see Section 20.43 in most cases be the one initiating[SIP]). Further details about the security parameter exchange). To solve this, a new header has been introduced (Section 2.2). This also assumes thatcause of failure MAY be described in an included message from the key management also has some kind of bindingprotocol. The session is then aborted (and it is up to the media, solocal policy or end user to decide how to continue). Note that the responsekey management attribute (related to the server willsame key management protocol) MAY be processed as required. To obtain apresent both at session description, the client initially contacts the server via a DESCRIBE message (according to RTSP, alevel and at media description could alsolevel. Consequently, the process SHALL be obtained by other means e.g. using http). The initialrepeated for each such key management message from the RTSP server is sent to the client inattribute detected. In case the SDPkey management processing of any such attribute does not succeed (e.g. authentication failure, parameters not supported etc.), on either session or media level, the 200 OK in response to the DESCRIBE. When responding to this, the client usesentire session setup SHALL be aborted, including those parts of the new RTSP header to send back an answer (included insession which successfully completed their part of the SETUP message).key management. If a server receives a SETUP message in which it expects amore than one key management message, but noneprotocol is included, a 403 Forbidden SHOULD be returned to the client, whereby the current setup MUST be aborted. The processing of creating a key management header in RTSP SHALL be as follow: * The identifiersupported, multiple instances of the key management protocol used (e.g. MIKEY) MUSTattribute MAY be placedincluded in the "prot" field of the header. The prot values are specified by IANA (Section 6). * The list of protocol identifiers is sent byinitial offer when using the RTSP application to (each)offer-answer model, each transporting a different key management protocol as described in Section 3.4. (to defeat bidding-down attacks). * The keymgmt-data field MUST be created as follows. Theprotocol, thus indicating supported alternatives. If the offerer includes more than one key management protocol MUST be used to createattribute at session level (analogous for the key management message. This message SHALLmedia level), these SHOULD be base64 encoded by the SDP application and then encapsulatedlisted in the "data" fieldorder of preference (the first being the header.preferred). The data may e.g. be a MIKEY message (see [MIKEY], Section 7). A received key management header SHALL be processed inanswerer selects the following manner: * Thekey management protocol is identifiedit wishes to use, and processes only it, on either session or media level, or on both, according to where located. If the "prot" field. * Theanswerer does not support any of the offerer's suggested key management data from the "data" field MUST be extracted, base64 decoded to reconstructprotocols, the originalreceiver returns a "606 Not Acceptable" error message, and then passed towhereby the key management protocol.sender MUST abort the current setup procedure. Note that depending onthe placement of multiple key management protocol, some extra parameters might of course be requested byoffers in a single message has the specific API, such asdisadvantage that the source/destination network address/port(s)message expands and the computational workload for the specified media (however, thisofferer will be implementation specific depending on the actual API). * Depending onincrease drastically. Unless the outcomeguidelines of Section 3.1.4 are followed, multiple lines may open up bidding-down attacks. The offerer MUST include the key management processing (i.e. whether it was successful or not),data within an offer that contains the processing can proceed according to normal rules (see also below). The server MAY provide re-keying/updating facilities by sendingmedia description it applies to. Re-keying MUST be handled as a new key management message in an ANNOUNCE message. The ANNOUNCE message contains an SDP message includingoffer, with the key managementnew proposed parameters. The response message is put in theanswerer treats this as a new RTSP header in the response from the client to the server. Note thatoffer where the ANNOUNCE messages MUST be supported if this feature is to be used. 3.4. Bidding-down attack prevention The possibility to support multiplekey management protocols may, unless properly handled, introduce so-called bidding-down attacks. Specifically, a man-in-the-middle could "peel off" cryptographically strong offers (deleting key-mgmt lines from the message), leaving only weaker ones as the responderĘs choice. To avoid this,is the list of identifiersissue of the proposed key management protocols MUST be authenticated.change. The authenticationre-keying exchange MUST be done separately by each key managementfinalized before the security protocol (see e.g. Section 7.1 in [MIKEY]). Accordingly, it MUST be specified (incan change the keys. The same key management protocol specification itself orused in a companion document) howthe list of key management protocol identifiers can be processed tooriginal offer SHALL also be authenticated fromused in the offerer tonew offer carrying re-keying. If the new offer carrying re- keying fails (e.g., the authentication verification fails), the answerer bySHOULD send a "606 Not Acceptable" message, including one or more Warning headers (at least a 306). The offerer MUST then abort the specific key management protocol.session. Note that, in multicast scenarios, unlike unicast, there is only a single view of the stream [OAM], hence there MUST be a uniform agreement of the security parameters. 3.1.3 Use of SDP with SAP There are cases where SDP is used without conforming to the offer/answer model; instead it is a one-way SDP distribution (i.e. without back channel), such as when used with SAP and HTTP. The processing follows the two first steps of the general SDP processing (see Section 3.1.1). It can be noted that the processing in this case differs from the offer/answer case in the fact that even ifonly one key management protocol is used,SHALL be offered (i.e. no negotiation will be possible). This implies that still MUST authenticate its own protocol identifier.the bidding down attack is not an issue; therefore the countermeasure is not needed. The list ofkey management protocol identifiersused MUST then be givensupport one-way messages. 3.1.4 Bidding-down attack prevention The possibility to each of the selected (offered)support multiple key management protocols bymay, unless properly handled, introduce bidding-down attacks. Specifically, a man-in-the-middle could "peel off" cryptographically strong offers (deleting the application with ";" separated identifiers. Allkey management lines from the offered protocolmessage), leaving only weaker ones as the Responder's choice. To avoid this, the list of identifiers of the proposed key management protocols MUST be included, in the same order as they appear in the corresponding SDP description.authenticated. The protocol list can formallyauthentication MUST be described as prtcl-list = KMIDdone separately by each key management protocol. Accordingly, it MUST be specified (in the key management protocol specification itself or in a companion document) how the list of key management protocol identifiers can be processed to be authenticated from the offerer to the answerer by the specific key management protocol. Note that even if only one key management protocol is used, that still MUST authenticate its own protocol identifier. The list of protocol identifiers MUST then be given to each of the selected (offered) key management protocols by the application with ";" separated identifiers. All the offered protocol identifiers MUST be included, in the same order as they appear in the corresponding SDP description. The protocol list can formally be described as prtcl-list = KMID *(";" KMID) where KMID is as defineddefined in Section 2. For example, if the offered protocols are MIKEY and two yet-to-be- invented protocols KEYP1, KEYP2, the SDP is: v=0 o=alice 2891092738 2891092738 IN IP4 lost.example.com s=Secret discussion t=0 0 c=IN IP4 lost.example.com a=key-mgmt:mikey <data1> a=key-mgmt:keyp1 <data2> a=key-mgmt:keyp2 <data3> m=audio 39000 RTP/SAVP 98 a=rtpmap:98 AMR/8000 m=video 42000 RTP/SAVP 31 a=rtpmap:31 H261/90000 The protocol list, "mikey;keyp1;keyp2", would be generated from the SDP description and used as input to each specified key management protocol (together with the data for that protocol). Each of the three protocols includes this protocol identifier list in its authentication coverage (according to its protocol specification). If more than one protocol is supported by the offerer, it is RECOMMENDED that all acceptable protocols are included in the first offer, rather than making single, subsequent alternative offers in response to error messages, see "Security Considerations". 3.2. RTSP usage RTSP does not use the offer/answer model, as SIP does. This causes some problems, as it is not possible (without modifying RTSP) to send back an answer. To solve this, a new header has been introduced (Section 2.2). This also assumes that the key management also has some kind of binding to the media, so that the response to the server will be processed as required. The server SHALL be the Initiator of the key management exchange for sessions in PLAY mode, i.e. transporting media from server to client. The below text describes the behavior for PLAY mode. For any other mode the behavior is not defined in this specification. To obtain a session description, the client initially contacts the server via a DESCRIBE message (according to RTSP, a media description could also be obtained by other means e.g. using http). The initial key management message from the RTSP server is sent to the client in the SDP of the 200 OK in response to the DESCRIBE. Note that only one key management protocol SHALL be used per session / media level. A server MAY allow the SDP with key-management attribute(s) to be distributed to the client though other means than RTSP. The "uri" parameter of the KeyMgmt header is used to indicate for the key management protocol on what context the carried message applies. For key management messages on the SDP session level, the answer MUST contain the RTSP aggregated control URL to indicate this. For Key management messages initially on SDP media level, the key management response message in the KeyMgmt header MAY use the RTSP media level URL. For RTSP sessions not using aggregated control, i.e. no session level control URI is defined, the key management protocol SHALL only be invoked on individual media streams. In this case also, the key management response SHALL be on individual media streams (i.e. one RTSP key management header per media). When responding to the initial key management message, the client uses the new RTSP header (KeyMgmt) to send back an answer. How this is done depends on the usage context. * Key management protocol responses for the initial establishment of security parameters for an aggregated RTSP session SHALL be sent in the first SETUP of the session. This means that if the key management is declared for the whole session but is setup in non- aggregated fashion, i.e. one media per RTSP session, each SETUP MUST carry the same response for the session level context. When performing a setup of the second or any subsequent media in a RTSP session the same key management parameters as established for the first media also applies to these setups. * Key management responses for the initial establishment of security parameters for an individual media SHALL only be included in SETUP for the corresponding media stream. If a server receives a SETUP message in which it expects a key management message, but none is included, a 403 Forbidden SHOULD be returned to the client, whereby the current setup MUST be aborted. When the server creates an initial SDP message, the procedure SHALL be the same as described in Section 3.1.1. The client processing of the initial SDP message from the server SHALL follow the same procedures as described in Section 3.1.1, except that, if there is an error, the session is aborted (no error is sent back). The client SHALL create the response, using the key management header in RTSP, as follows: * The identifier of the key management protocol used (e.g. MIKEY) MUST be placed in the "prot" field of the header. The prot values are maintained by IANA (Section 8). * The keymgmt-data field MUST be created as follows. The key management protocol MUST be used to create the key management message. This message SHALL be base64 encoded by the RTSP application and then encapsulated in the "data" field of the header. The semantic of the encapsulated message is dependent on the key management protocol that is used. * Include if necessary the URL to indicate the context in the "uri" parameter. The server SHALL process a received key management header in RTSP as follow: * The key management protocol is identified according to the "prot" field. * The key management data from the "data" field MUST be extracted, base64 decoded to reconstruct the original message, and then passed to the key management protocol for processing. * If the key management protocol is successful, the processing can proceed according to normal rules. * Otherwise, if the key management fails (e.g. due to authentication failure or parameter not supported), an error is sent back as the SETUP response using RTSP error code 463 (see Section 2.2) and the session is aborted. It is up to the key management protocol to specify (within the RTSP status code message or through key management messages) details about the type of error that occurred. Re-keying within RTSP is for further study, given that media updating mechanisms within RTSP are unspecified at the time this document is written. 4. Example scenarios The following examples utilizes MIKEY [MIKEY] as key management protocol to be integrated into SDP and RTSP (see Section 5.1.). Example 1 (SIP/SDP) A SIP call is taking place between Alice and Bob. Alice sends an Invite message consisting of the following offer: v=0 o=alice 2891092738 2891092738 IN IP4 w-land.example.com s=Cool stuff email@example.com t=0 0 c=IN IP4 w-land.example.com a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD... m=audio 49000 RTP/SAVP 98 a=rtpmap:98 AMR/8000 m=video 52230 RTP/SAVP 31 a=rtpmap:31 H261/90000 i.e. Alice proposes to set up one audio stream and one video stream that run over SRTP (signaled by the use of the SAVP profile). She uses MIKEY to set up the security parameters for SRTP (Section 6). The MIKEY message contains the security parameters, together with the necessary key material. Note that MIKEY is exchanging the crypto suite for both streams, as it is placed at the session level. Also, MIKEY provides its own security, i.e. when Bob processes Alice's MIKEY message, he will also find the signaling of the security parameters used to secure the MIKEY exchange. Alice's authentication information is also carried within the MIKEY message, to prove that the message is authentic. Upon receiving the offer, Bob checks the validity of the received MIKEY message, and, in case of successful verification, he accepts the offer and sends an answer back to Alice (with his authentication information, and, if necessary, also some key material from his side): v=0 o=bob 2891092897 2891092897 IN IP4 foo.example.com s=Cool stuff firstname.lastname@example.org t=0 0 c=IN IP4 foo.example.com a=key-mgmt:mikey skaoqDeMkdwRW278HjKVB... m=audio 49030 RTP/SAVP 98 a=rtpmap:98 AMR/8000 m=video 52230 RTP/SAVP 31 a=rtpmap:31 H261/90000 Upon receiving the answer, Alice verifies the correctness of it. In case of success, at this point Alice and Bob share the security parameters and the keys needed for a secure RTP communication. Example 2 (SDP) This example shows how Alice would have done if she wished to protect only the audio stream. She would have placed the MIKEY line at media level for the audio stream only (also specifying the use of the SRTP profile there, SAVP). The semantic of the MIKEY messages is as in Section 2. For example, ifthe offered protocols are MIKEY and two yet-to-be- invented protocols KEYP1, KEYP2,previous case, but applies only to the SDP is:audio stream. v=0 o=alice 2891092738 2891092738 IN IP4 lost.example.com s=Secret discussionw-land.example.com s=Cool stuff email@example.com t=0 0 c=IN IP4 lost.example.com a=key-mgmt:mikey <data1> a=key-mgmt:keyp1 <data2> a=key-mgmt:keyp2 <data3>w-land.example.com m=audio 3900049000 RTP/SAVP 98 a=rtpmap:98 AMR/8000 a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD... m=video 42000 RTP/SAVP52230 RTP/AVP 31 a=rtpmap:31 H261/90000 The protocol list, "mikey;keyp1;keyp2",Bob would be generated from the SDP description and usedthen act as input to each specified key management protocol (together withdescribed in the dataprevious example, including the MIKEY answer at the media level for the audio stream (as Alice did). Note that protocol). Each ofeven if the three protocols includes this protocol identifier list in its authentication coverage (according to its protocol specification). If more than one protocol are supported bykey management attribute were specified at session level, the offerer, itvideo part would not be affected by this (as a security profile is RECOMMENDED that all acceptable protocols are included innot used, instead the first offer, rather than making single, subsequent alternative offers in response to error messages, see "Security Considerations". 3.5. Example scenariosRTP/AVP profile is signaled). Example 1 (SIP)3 (RTSP) A SIP call is taking place between Aliceclient wants to set up a streaming session and Bob. Alicerequests a media description from the streaming server. DESCRIBE rtsp://server.example.com/fizzle/foo RTSP/1.0 CSeq: 312 Accept: application/sdp From: firstname.lastname@example.org The server sends back an InviteOK message consistingincluding an SDP description, together with the MIKEY message. The MIKEY message contains the necessary security parameters that the server is willing of offering to the client, together with authentication information (to prove that the message is authentic) and the key material. The SAVP profile also signals the use of SRTP for securing the following offer: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=aliceo=actionmovie 2891092738 2891092738 IN IP4 w-land.example.com s=Cool stuff email@example.com s=Action Movie firstname.lastname@example.org t=0 0 c=IN IP4 w-land.example.commovie.example.com a=control:rtsp://movie.example.com/action a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD.. m=audio 490000 RTP/SAVP 98 a=rtpmap:98 AMR/8000 a=control:rtsp://movie.example.com/action/audio m=video 522300 RTP/SAVP 31 a=rtpmap:31 H261/90000 i.e. Alice proposesa=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 set up one audio stream and one video stream that run over SRTP. To set upthe security parameters for SRTP, she uses MIKEY. Noteserver, the client authentication information (to prove that MIKEY is negotiatingthe crypto suite for both streams (as itmessage is placedauthentic) and, if necessary, some key material. SETUP rtsp://movie.example.com/action/audio RTSP/1.0 CSeq: 313 Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057 keymgmt: prot=mikey; uri="rtsp://movie.example.com/action"; data="skaoqDeMkdwRW278HjKVB..." The server processes the request including checking the validity of the key management header. RTSP/1.0 200 OK CSeq: 313 Session: 12345678 Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057; server_port=5000-5001 Note than in this case the key management line was specified at the session level). Bob acceptslevel, the offer and sends an answer back to Alice: v=0 o=bob 2891092897 2891092897 IN IP4 foo.example.com s=Cool stuff email@example.com t=0 0 c=IN IP4 foo.example.com a=key-mgmt:mikey skaoqDeMkdwRW278HjKVB... m=audio 49030 RTP/SAVP 98 a=rtpmap:98 AMR/8000 m=video 52230 RTP/SAVP 31 a=rtpmap:31 H261/90000 Example 2 (SDP) This example shows how Alice would have done if she wished to protectkey management information only goes into the audioSETUP related to the first stream. v=0 o=alice 2891092738 2891092738 IN IP4 w-land.example.com s=Cool stuff firstname.lastname@example.org t=0 0 c=IN IP4 w-land.example.com m=audio 49000 RTP/SAVP 98 a=rtpmap:98 AMR/8000 a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD... m=video 52230 RTP/AVP 31 a=rtpmap:31 H261/90000 NoteThe "uri" indicates to the server that even ifthe key management attribute were specified atcontext is for the whole aggregated session level,the video part would not be affected by this (as a security profile is not used). Example 3 (RTSP) Akey management applies. The RTSP client wants to setthen proceeds setting up a streaming sessionthe second media (video) in aggregation with the audio. As the two media are run in aggregation and requests athe key context was established in the first exchange, no more key management messages are needed. Example 4 (RTSP) The use of the MIKEY message at the media description fromlevel would change the streaming server. DESCRIBE rtsp://server.example.com/fizzle/foo RTSP/1.0 CSeq: 312 Accept: application/sdp From: email@example.com example as follows. The server sends back an200 OK message including anwould contain the two distinct SDP description.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 firstname.lastname@example.org t=0 0 c=IN IP4 movie.example.com a=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...a=control:rtsp://movie.example.com/action m=audio 0 RTP/SAVP 98 a=rtpmap:98 AMR/8000 control:rtsp://movie.example.com/action/audioa=key-mgmt:mikey uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD.. a=control:rtsp://movie.example.com/action/audio m=video 0 RTP/SAVP 31 a=rtpmap:31 H261/90000 control:rtsp://movie.example.com/action/videoa=key-mgmt:mikey dhsoKkdOokdo7eWsnDSJDuiSDF9sdhs727ghsd/.. a=control:rtsp://movie.example.com/action/video Each RTSP header are inserted in the SETUP related to the audio and video separately: SETUP rtsp://movie.example.com/action/audio RTSP/1.0 CSeq: 313 Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057 keymgmt: prot=mikey; uri="rtsp://movie.example.com/action/audio"; data="skaoqDeMkdwRW278HjKVB..." and similarly for the video session: SETUP rtsp://movie.example.com/action/video RTSP/1.0 CSeq: 315 Transport: RTP/SAVP/UDP;unicast;client_port=3058-3059 keymgmt: prot=mikey; uri="rtsp://movie.example.com/action/video"; data="RW278HjKVBskaoqDeMkdw..." Note: The client is now ready"uri" parameter could be excluded from the two SETUP messages in this example. 5. Adding further Key management protocols This framework cannot be used with all key management protocols. The key management protocol needs to setupcomply with the requirements described in Section 3. In addition to this, the following needs to be defined: * The key management protocol identifier to be used as the protocol identifier should be registered at IANA according to Section 8. * The information that the key management needs from SDP and RTSP, and vice versa, as described in Section 3. The exact API is implementation specific, but it SHOULD at least support the sessions. It includesexchange of the specified information. * The key management data in the first message going backprotocol to be added MUST be such, that the server (i.e.processing in Section 3 (describing its interactions with SDP and RTSP) can be applied. Note in particular, Section 3.1.4 requires each key management protocol to specify how the SETUP message). SETUP rtsp://movie.example.com/action/audio RTSP/1.0 CSeq: 313 Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057 keymgmt: prot=mikey; data="skaoqDeMkdwRW278HjKVB..."list of protocol identifiers is authenticated inside that key management protocol. The server processes the request including checkingkey management MUST always be given the validityprotocol identifier(s) of the key management header. RTSP/1.0 200 OK CSeq: 313 Session: 12345678 Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057; server_port=5000-5001 The RTSP then proceeds as usual (with e.g. a SETUP message forprotocol(s) included in the video followedoffer in the correct order as they appear. Finally, it is obviously crucial to analyze possible security implications induced by the introduction of a PLAY message). 4. Adding further Key management protocols This framework cannot be used with allnew key management protocols. Theprotocol in the described framework. Today, the MIKEY protocol [MIKEY] has adopted the key management protocol needsextensions to complywork together with SIP and RTSP (see Section 6). Other protocols MAY use the described attribute and header, e.g. Kerberos [KERB], however this is subject to future standardization. 6. Integration of MIKEY [MIKEY] describes a key management protocol for real-time applications (both for peer-to-peer communication and group communication). MIKEY can be integrated within SDP and RTSP, following the rules and guidelines described in this document. MIKEY satisfies the requirements described in Section 3. In additionThe MIKEY message is formed as defined in [MIKEY], then passed from MIKEY to this,the following needs to be defined: *SDP application that base64 encodes it, and encapsulates it in the keymgmt-data attribute. The examples in Section 4 use MIKEY, where the semantic of the exchange is also briefly explained. The key management protocol identifier (KMID) to be used as the protocol identifier shouldSHALL be "mikey" and is registered at IANA according toIANA, see in detail Section 6 (e.g. "mikey" for MIKEY). *8. The information that the key management needs from SDP and RTSP, and vice versa, as described infollows Section 3. To avoid bidding-down attacks, the directives in Section 3.1.4 are followed. The exact APIlist of protocol identifiers is implementation specific, butauthenticated within MIKEY by placing such list in a General Extension Payload (of type "SDP IDs", [MIKEY]), which then automatically will be integrity protected/signed. The receiver SHALL then match the list in the General Extension Payload with the list included in SDP and SHOULD (according to policy) if they differ, or if integrity/signature verification fails, reject the offer. To signal the MIKEY identity of the client to the server in the DESCRIBE, it is RECOMMENDED to include the From header field in RTSP. 6.1 MIKEY Interface This subsection describes some aspects, which implementers SHOULD consider. If the MIKEY implementation is separate from the SDP/SIP/RTSP, an application programming interface (API) between MIKEY and those protocols is needed with certain functionality (however, exactly what it looks like is implementation dependent). Implementers of MIKEY are RECOMMENDED to consider providing at least supportthe following functionality: * the possibility for MIKEY to exchangereceive information about the specified information.sessions negotiated. This is to some extent implementation dependent. But it is RECOMMENDED that, in the case of SRTP streams, the number of SRTP streams is included (and the direction of these). It is also RECOMMENDED to provide the destination addresses and ports to MIKEY. When referring to streams described in SDP, MIKEY allocated two consecutive numbers for the related Crypto Session indexes (as each stream can be bi-directional). An example: if the SDP contains two m lines (specifying whatever direction of the streams), and MIKEY is at the session level, then MIKEY allocates e.g. the CS IDs '1' and '2' for the first m line, and '3' and '4' for the second m line. * The key management protocolthe 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 CSB ID (to later be added MUST be such, thatable to identify the processing in Section 3 (describing its interactions with SDPactive MIKEY session), and RTSP)the SSRCs and the ROC for SRTP usage. It is also RECOMMENDED that extra information about errors can be applied. Note in particular, Section 3.4 requires each key management protocolreceived. * the possibility for the SIP or RTSP application to specify howreceive outgoing MIKEY messages. * the list of protocol identifierspossibility to tear down a MIKEY CSB (e.g. if the SIP session is authenticated inside that key management protocol. The key management MUST always be givenclosed, the protocol identifier(s)CSB SHOULD also be closed). 7. Security Considerations The framework for transfer of thekey management protocol(s) included in the offer in the correct orderdata as they appear. Finally, itdescribed here is obviously crucialintended to analyze possibleprovide the security implications induced byparameters for the introductionend-to-end protection of a new key management protocol inthe described framework. 5. Security Considerations As a general practice, itmedia session. It is afurthermore good thing, not only to try to secure the session, but alsopractice to secure the session setup.setup (e.g. SDP, SIP, RTSP, SAP). However, it might be that the security of the session setup mightis not possible on an end-to-end basis, but the setup may requireto be protected on a hop-by-hop basis (this is generally the case for SIP/SDP whenachieve end-to-end, but only hop-by-hop. For example, SIP requires intermediate proxies needsto obtain information abouthave access to part of the sessions etc, c.f.SIP message, and sometimes also to the SDP description (c.f. [E2M]). In fact,General security considerations for the focus of thissession setup can be found in SDP [SDPnew], SIP [SIP], and RTSP [RTSP]. The framework defined in this memo is mainlyuseful when end-to- end protection ofthe session setup is not used,protected in an end-to-end fashion, but wherethe media streams needs to be end-to-end protected. General security considerations forprotected, hence the session setup can be found in SDP [SDPnew], SIP [SIP], and RTSP [RTSP].security parameters such as keys are not wanted revealed to intermediaries. The security will also depend on the encapsulated level of security the key management protocol offers. It follows that, under the assumption that the key management schemes are secure, the SDP can be passed along unprotected without affecting the key management as such, and the media streams will still be secure even if some attackers gained knowledge of the SDP contents. Further security considerations can be found for each key management protocol (for MIKEY these can be found in [MIKEY]). However, if the SDP messages are not sent authenticated between the parties, it is possible for an active attacker to change attributes without being detected. As the key management protocol may (indirectly) rely on some of the session information from SDP (e.g., address information), an attack on SDP may have indirect consequences on the key management. Even if the key management protocol does not rely on parameters of SDP and will not be affected by manipulation of these, different DoS attacks aimed at SDP (e.g. the SIMCAP extensions)may lead to undesired interruption in the setup. The use of multiple key management protocols in the same offer may open up the possibility of a bidding-down attack, as specified in Section 126.96.36.199.4. To exclude such possibility, the authentication of the protocol identifier list is used. Note though, that the security level of the authenticated protocol identifier will be as high (or low), as the "weakest" protocol. Therefore, it is discouraged to offer protocols with too different security levels. Note that it is impossible to assure the authenticity of a declined offer, since even if it comes from the true respondent, the fact that the answerer declines the offer usually means that he does not support the protocol(s) offered, and consequently cannot be expected to authenticate the response either. This means that if the initiatorInitiator is unsure of which protocol(s) the responderResponder supports, we RECOMMEND that the initiatorInitiator 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 initiatorInitiator eventually offers a protocol "to the liking" of the MITM. This is not really a security problem, but rather a mild form of denial of service that can be avoided by following the above recommendation. In the case that the response declines any security (therefore there is impossibility of authenticating it), the session setup SHALL be aborted. 6.8. IANA Considerations 188.8.131.52. SDP Attribute Registration A new SDP attribute needs to be registered for the purpose of key management protocol integration with SDP. Contact: Fredrik Lindholm mailto: email@example.com tel: +46 8 58531705 SDP Attribute Field ("att-field"): Name: key-mgmtkey-mgmt-att-field Long form: key management protocol attribute field Type of name: att-field Type of attribute: Media and session level Purpose: See RFC xxxx, Section 2. Reference: RFC xxxx, Section 2.1 Values: See RFC xxxx, Section 6.3 184.108.40.206 and 8.3. 8.2. RTSP HeaderRegistration A new RTSP Header needs to be registered 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 xxxx, Section 2.2 Intended usage: see RFC xxxx, Section 2.2 Proxy treatment: Proxies SHOULD forwardSHALL NOT add, change, or delete the headerheader. The proxy does not need to read this header. Purpose: see RFC xxxx, Section 2 6.3.The RTSP Status-Code "463" [RFC xxxx], with the default string "Key management failure", needs to be registered. 8.3. Protocol Identifier Registration This document defines one new name spacespace, the "SDP/RTSP key management protocol identifier", associated with the protocol identifier, KMID, defined in Section 2 to be used with the above registered key-mgmtattributes in SDP and RTSP. A new registry needs to be set up for the KMID parameter, with the following registration created initially: "mikey". Contact: Fredrik Lindholm mailto: firstname.lastname@example.org tel: +46 8 58531705 Value name: mikey Long name: Multimedia Internet KEYing Purpose: Usage of MIKEY with the key-mgmtkey-mgmt-att-field attribute and the keymgmt RTSP header Reference: Section 7 in RFC yyyy Note that this registration will imply that the protocol identifier, KMID, name space will be shared between SDP and RTSP. Further values may be registered according to the "Specification Required" policy as defined in [RFC2434]. Each new registration needs to indicate the parameter name, and register it within IANA. Note that the parameter name is case sensitive and it is recommendedRECOMMENDED that the name shouldto be in lower case letters. For each new registration, it is mandatory that a permanent, stable, and publicly accessible document exists that specifies the semantics of the registered parameter and the requested details of interaction between the key management protocol and SDP, as specified in RFC xxxx. The registration itself of new values should be sent to IANA. Registrations shouldSHALL 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 KMID as defined in Section 2) * Long Name: long-form name in English (optional)* Purpose: short explanation of the purpose of the registered name. * Reference: a reference to the specification (e.g. RFC number) of the draftproviding the usage guidelines in accordance to Section 45 (and also complying to the specified requirements). 7.9. Acknowledgments Thanks to:The authors would like to thank Joerg Ott, Rolf Blom andBlom, Magnus Westerlund.Brolin, Johan Bilien, Jon-Olov Vatn, and Erik Eliasson. A special thanks to Joerg Ott andColin Perkins. 8.Perkins and Magnus Westerlund, who contributed in many sections. 10. Author's Addresses Jari Arkko Ericsson 02420 Jorvas Phone: +358 40 5079256 Finland Email: email@example.com Elisabetta Carrara Ericsson Research SE-16480 Stockholm Phone: +46 8 50877040 Sweden EMail: firstname.lastname@example.org Fredrik Lindholm Ericsson Research SE-16480 Stockholm Phone: +46 8 58531705 Sweden EMail: email@example.com Mats Naslund Ericsson Research SE-16480 Stockholm Phone: +46 8 58533739 Sweden EMail: firstname.lastname@example.org Karl Norrman Ericsson Research SE-16480 Stockholm Phone: +46 8 4044502 Sweden EMail: email@example.com 9.11. References 220.127.116.11. Normative References [MIKEY] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and Norrman, K., "MIKEY: Multimedia Internet KEYing", IETF, RFC yyyy, [Internet Draft, <draft-ietf-msec-mikey-08.txt> ]. [OAM] Rosenberg, J. and Schulzrinne, H., "An Offer/Answer Model with the Session Description Protocol (SDP)", IETF, RFC 3264. [RTSP] Schulzrinne, H., Rao, A., and Lanphier, R., "Real Time Streaming Protocol (RTSP)", IETF, RFC 2326. [RFC2119] Bradner, S. "Key words for use in RFCs to Indicate Requirement Levels", IETF, RFC 2119. [SDPnew] Handley, M., Jacobson, V., and Perkins, C., "SDP: Session Description Protocol", Internet Draft, IETF, Work in progress (MMUSIC), draft-ietf-mmusic-sdp-new-13.txt.draft-ietf-mmusic-sdp- new-15.txt. [SIP] Handley, M., Schulzrinne, H., Schooler, E., and Rosenberg, J., "SIP: Session Initiation Protocol", IETF, RFC 3261. [RFC2234] Crocker, D. and Overell, P., "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [RFC2434] Narten, T. and Alvestrand, H., "Guidelines for Writing an IANA Considerations Section in RFCs", IETF, RFC 2434. [RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", IETF, RFC 3548. 18.104.22.168. Informative References [E2M] Ono, K. and Tachimoto, S., "End-to-middle security in the Session Initiation Protocol (SIP)", Internet Draft, IETF, Work in Progress.draft-ono- sipping-end2middle-security-00. [KERB] Kohl, J., Neuman, C., "The Kerberos Network Authentication Service (V5)", IETF, RFC 1510. [MIKEY] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and Norrman, K., "MIKEY: Multimedia Internet KEYing", IETF, RFC yyyy, [Internet Draft, Work in progress (MSEC)].[SRTP] Baugher, M., Blom, R., Carrara, E., McGrew, D., Naslund, M, Norrman, K., and Oran, D., "The Secure Real Time Transport Protocol", Internet Draft, IETF, Work<draft-ietf-avt-srtp-09.txt>. 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