MSEC S. Fries Internet-Draft Siemens Intended status: Informational D. Ignjatic Expires: May 20, 2007 Polycom November 16, 2006 On the applicability of various MIKEY modes and extensions draft-ietf-msec-mikey-applicability-03.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 20, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Fries & Ignjatic Expires May 20, 2007 [Page 1] Internet-Draft MIKEY modes applicability November 2006 Abstract Multimedia Internet Keying - MIKEY - is a key management protocol that can be used for real-time applications. In particular, it has been defined focusing on the support of the Secure Real-time Transport Protocol. MIKEY itself defines four key distribution methods. Moreover, it is defined to allow extensions of the protocol. As MIKEY becomes more and more accepted, extensions to the base protocol arose, especially in terms of additional key distribution methods, but also in terms of payload enhancements. This document provides an overview about MIKEY in general as well as the existing extensions in MIKEY, which have been defined or are in the process of definition. It is intended as additional source of information for developers or architects to provide more insight in use case scenarios and motivations as well as advantages and disadvantages for the different key distribution schemes. The use cases discussed in this document are strongly related to dedicated SIP call scenarios providing challenges for key management in general beyond them media before SDP answer, forking, and shared key conferencing. Fries & Ignjatic Expires May 20, 2007 [Page 2] Internet-Draft MIKEY modes applicability November 2006 Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 Terminology and Definitions . . . . . . . . . . . . . . . . . 6 3 MIKEY Overview . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1 Pre-shared key protected distribution . . . . . . . . . . . 8 3.2 Public Key encrypted key distribution . . . . . . . . . . . 9 3.3 Diffie-Hellman key agreement protected with digital signatures . . . . . . . . . . . . . . . . . . . . . . . . 9 3.4 Unprotected key distribution . . . . . . . . . . . . . . . 10 3.5 Diffie-Hellman key agreement protected with pre-shared secrets . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.6 SAML assisted DH-key agreement . . . . . . . . . . . . . . 11 3.7 Asymmetric key distribution with in-band certificate exchange . . . . . . . . . . . . . . . . . . . . . . . . . 13 4 Further MIKEY Extensions . . . . . . . . . . . . . . . . . . . 15 4.1 ECC algorithms support . . . . . . . . . . . . . . . . . . 15 4.1.1 Elliptic Curve Integrated Encryption Scheme application in MIKEY . . . . . . . . . . . . . . . . . 16 4.1.2 Elliptic Curve Menezes-Qu-Vanstone Scheme application in MIKEY . . . . . . . . . . . . . . . . . 16 4.2 New Payload for bootstrapping TESLA . . . . . . . . . . . . 16 4.3 MBMS extensions to the Key ID information type . . . . . . 17 4.4 OMA BCAST MIKEY General Extension Payload Specification . . 17 4.5 Supporting Integrity Transform carrying the Rollover Counter . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5 Selection and interworking of MIKEY modes . . . . . . . . . . 19 5.1 MIKEY and Early Media . . . . . . . . . . . . . . . . . . . 20 5.2 MIKEY and Forking . . . . . . . . . . . . . . . . . . . . . 21 5.3 MIKEY and Call Transfer/Redirect/Retarget . . . . . . . . . 22 5.4 MIKEY and Shared Key Conferencing . . . . . . . . . . . . . 22 6 Transport of MIKEY messages . . . . . . . . . . . . . . . . . 24 7 MIKEY alternatives for SRTP security parameter negotiation . . 25 8 Summary of MIKEY related IANA Registrations . . . . . . . . . 27 9 Security Considerations . . . . . . . . . . . . . . . . . . . 28 10 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 11 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31 12.1 Normative References . . . . . . . . . . . . . . . . . . . 31 12.2 Informative References . . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34 Intellectual Property and Copyright Statements . . . . . . . . . . 35 Fries & Ignjatic Expires May 20, 2007 [Page 3] Internet-Draft MIKEY modes applicability November 2006 1 Introduction Key distribution describes the process of delivering cryptographic keys to the required parties. MIKEY [RFC3830], the Multimedia Internet Keying, has been defined focusing on support for the establishment of security context for the Secure Real-time Transport Protocol [RFC3711]. Note that MIKEY is not restricted to be used for SRTP only, as it features a generic approach and allows for extensions to the key distribution schemes.Thus, it may also be used for security parameter negotiation for other protocols. For MIKEY meanwhile seven key distribution methods are described as there are: o Symmetric key distribution as defined in [RFC3830] (MIKEY-PSK) o Asymmetric key distribution as defined in [RFC3830] (MIKEY-RSA) o Diffie-Hellman key agreement protected by digital signatures as defined in [RFC3830] (MIKEY-DHSIGN) o Unprotected key distribution (MIKEY-NULL) o Diffie-Hellman key agreement protected by symmetric pre-shared keys as defined in [RFC4650] (MIKEY-DHHMAC) o SAML assisted Diffie-Hellman key agreement as defined [Reference to draft-moskowitz-MIKEY-SAML-DH] (MIKEY-DHSAML) o Asymmetric key distribution (based on asymmetric encryption) with in-band certificate provision as defined in [I-D.ietf-msec-mikey-rsa-r] (MIKEY-RSA-R) Note that the latter three modes are extensions to MIKEY as there have been scenarios where none of the first four modes defined in [RFC3830] fits perfectly. There are further extensions to MIKEY comprising algorithm enhancements and a new payload definition supporting other protocols than SRTP. Algorithm extensions are defined in the following document: o ECC algorithms for MIKEY as defined in [I-D.ietf-msec-mikey-ecc] Payload extensions are defined in the following documents: o Bootstrapping TESLA, defining a new payload for the Timed Efficient Stream Loss-tolerant Authentication protocol [RFC4082] as defined in [RFC4442] Fries & Ignjatic Expires May 20, 2007 [Page 4] Internet-Draft MIKEY modes applicability November 2006 o The Key ID information type for the general extension payload as defined in [RFC4563] o OMA BCAST MIKEY General Extension Payload Specification, as defined in [I-D.dondeti-msec-mikey-genext-oma] o Integrity Transform Carrying Roll-over Counter for SRTP, as defined in [I-D.lehtovirta-srtp-rcc]. Note that this is rather an extension to SRTP and requires MIKEY to carry a new parameter, but is stated here for completeness. This document provides an overview about MIKEY and the relations to the different extensions to provide a framework when using MIKEY. It is intended as additional source of information for developers or architects to provide more insight in use case scenarios and motivations as well as advantages and disadvantages for the different key distribution schemes. The use cases discussed in this document are strongly related to dedicated SIP call scenarios providing challenges for key management in general, as there are: o Early Media res. Media before SDP answer o Forking o Call Transfer/Redirect/Retarget o Shared Key Conferencing Fries & Ignjatic Expires May 20, 2007 [Page 5] Internet-Draft MIKEY modes applicability November 2006 2 Terminology and Definitions 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 RFC 2119 [RFC2119]. The following definitions have been taken from [RFC3830]: (Data) Security Protocol: the security protocol used to protect the actual data traffic. Examples of security protocols are IPsec and SRTP. Data Security Association (Data SA): information for the security protocol, including a TEK and a set of parameters/policies. Crypto Session (CS): uni- or bi-directional data stream(s), protected by a single instance of a security protocol. Crypto Session Bundle (CSB): collection of one or more Crypto Sessions, which can have common TGKs (see below) and security parameters. Crypto Session ID: unique identifier for the CS within a CSB. Crypto Session Bundle ID (CSB ID): unique identifier for the CSB. TEK Generation Key (TGK): a bit-string agreed upon by two or more parties, associated with CSB. From the TGK, Traffic-encrypting Keys can then be generated without needing further communication. Traffic-Encrypting Key (TEK): the key used by the security protocol to protect the CS (this key may be used directly by the security protocol or may be used to derive further keys depending on the security protocol). The TEKs are derived from the CSB's TGK. TGK re-keying: the process of re-negotiating/updating the TGK (and consequently future TEK(s)). Initiator: the initiator of the key management protocol, not necessarily the initiator of the communication. Responder: the responder in the key management protocol. Salting key: a random or pseudo-random (see [RAND, HAC]) string used to protect against some off-line pre-computation attacks on the underlying security protocol. HDR: denotes the protocol header Fries & Ignjatic Expires May 20, 2007 [Page 6] Internet-Draft MIKEY modes applicability November 2006 PRF(k,x): a keyed pseudo-random function E(k,m): encryption of m with the key k RAND: Random value T: Timestamp CERTx: the certificate of x SIGNx: the signature from x using the private key of x PKx: the public key of x IDx: the identity of x [] an optional piece of information {} denotes zero or more occurrences || concatenation | OR (selection operator) ^ exponentiation XOR exclusive or The following definitions have been added additionally to the ones from [RFC3830]: SSRC Synchronization Source Identifier Fries & Ignjatic Expires May 20, 2007 [Page 7] Internet-Draft MIKEY modes applicability November 2006 3 MIKEY Overview This section will provide an overview about MIKEY. The focus lies here on the key distribution methods as well as the discussion about advantages and disadvantages of the different schemes. Note that the MIKEY key distribution schemes rely on loosely synchronized clocks. A secure network clock synchronization protocol should realize this. MIKEY recommends the ISO time synchronization protocol [ISO_sec_time]. The format applied to the timestamps submitted in the MIKEY have to match the NTP format described in [RFC1305]. In other cases, such as of a SIP endpoint clock synchronization by deriving time from a trusted outbound proxy may be appropriate. If MIKEY is used for SRTP [RFC3711] bootstrapping, it also uses the SSRC to associate security policies with actual sessions. The SSRC identifies the synchronization source. The value is chosen randomly, with the intent that no two synchronization sources within the same SRTP session will have the same SSRC. Although the probability of multiple sources choosing the same identifier is low, all (S)RTP implementations must be prepared to detect and resolve collisions. Nevertheless in multimedia communication scenarios supporting forking Section 5.2, collisions may occur leading to so-called two-time pads, i.e., the same key is used for media streams to different destinations. Note that two time pads may also occur for media streams to the same destination. 3.1 Pre-shared key protected distribution This option of the key management uses a pre-shared secret key to derive key material for integrity protection and encryption to protect the actual exchange of key material. Note that the pre- shared secret is agreed upon before the session, e.g., by out-of-band means. The response message is optional and may be used for mutual authentication or error signaling. Initiator Responder I_MESSAGE = HDR, T, RAND, [IDi],[IDr], {SP}, KEMAC ---> R_MESSAGE = [<---] HDR, T, [IDr], V The advantages of this approach lay in the fact that there is no dependency on a PKI (Public Key Infrastructure), the solution consumes low bandwidth and enables high performance, and is all in all a simple straightforward master key provisioning. The disadvantages are that no perfect forward secrecy is provided and key Fries & Ignjatic Expires May 20, 2007 [Page 8] Internet-Draft MIKEY modes applicability November 2006 generation is just performed by the initiator. Furthermore, the approach is not scalable to larger configurations but is acceptable in small-sized groups. Note that according to [RFC3830] this option is mandatory to implement. 3.2 Public Key encrypted key distribution Using the asymmetric option of the key management, the initiator generates the key material (TGK's) to be transmitted and sends it encrypted with a so-called envelope key, which in turn is encrypted with the receiver's public key. The envelope key, env-key, which is a random number, is used to derive the auth-key and the enc-key. Moreover, the envelope key may be used as a pre-shared key to establish further crypto sessions. The response message is optional and may be used for mutual authentication or error signaling. Initiator Responder I_MESSAGE = HDR, T, RAND, [IDi|CERTi], [IDr], {SP}, KEMAC, [CHASH], PKE, SIGNi ---> R_MESSAGE = [<---] HDR, T, [IDr], V An advantage of this approach are that the usage of self-signed certificates can avoid PKI. Note that using self-signed certificates may result in limited scalability. The disadvantages comprise the necessity of a PKI for fully scalability, the performance of the key generation just by the initiator, and no provision of perfect forward secrecy. Additionally, the responder certificate needs to be available in advance at the sender's side. Furthermore, the verification of certificates may not be done in real-time. This could be the case in scenarios where the revocation status of certificates is checked through a further component. Note, according to [RFC3830] this option is mandatory to implement. 3.3 Diffie-Hellman key agreement protected with digital signatures The Diffie-Hellman option of the key management enables a shared secret establishment between initiator and responder in a way where both parties contribute to the shared secret. The Diffie-Hellman key agreement is authenticated (and integrity protected) using digital signatures. Fries & Ignjatic Expires May 20, 2007 [Page 9] Internet-Draft MIKEY modes applicability November 2006 Initiator Responder I_MESSAGE = HDR, T, RAND, [IDi|CERTi], [IDr], {SP}, DHi, SIGNi ---> R_MESSAGE = <--- HDR, T, [IDr|CERTr], IDi, DHr, DHi, SIGNr [RFC3830] does mandate the support of RSA as specific asymmetric algorithm for the signature generation. Additionally the algorithm used for signature or public key encryption is defined by, and dependent on the certificate used. Besides the use of X.509v3 certificates it is mandatory to support the Diffie-Hellmann group "OAKLEY5" [RFC2412]. The advantages of this approach are a fair, mutual key agreement (both parties provide to the key), perfect forward secrecy, and the absence of the need to fetch a certificate in advance as needed for the MIKEY-RSA method depicted above. Moreover, it provides also the option to use self-signed certificates to avoid PKI (would result in limited scalability and more complex provisioning). Note that, depending on the security policy, self- signed certificates may not be suitable for every use case. Negatively to remark is that this approach scales mainly to point-to- point groups and depends on PKI for full scalability. Multiparty conferencing is not supported using just MIKEY-DHSIGN. Nevertheless, the established Diffie-Hellman-Secret may serve as a pre-shared key to bootstrap group-related security parameter. Furthermore, as for the MIKEY-RSA mode described above, the verification of certificates may not be necessarily done in real-time. This could be the case in scenarios where the revocation status of certificates is checked through a further component. 3.4 Unprotected key distribution MIKEY also supports a mode to provide a key in an unprotected manner (MIKEY-NULL). This is based on the symmetric key encryption option depicted in Section 3.1 but is used with the NULL encryption and the NULL authentication algorithm. It may be compared with the plain approach in sdescriptions [RFC4568]. MIKEY-NULL completely relies on the security of the underlying layer, e.g., provided by TLS. This option should be used with caution as it does not protect the key management. 3.5 Diffie-Hellman key agreement protected with pre-shared secrets This is an additional option which has been defined in [RFC4650]. In contrast to the method described in Section 3.3 here the Diffie- Hellmann key agreement is authenticated (and integrity protected) Fries & Ignjatic Expires May 20, 2007 [Page 10] Internet-Draft MIKEY modes applicability November 2006 using a pre-shared secret and keyed hash function. Initiator Responder I_MESSAGE = 3D HDR, T, RAND, [IDi], IDr, {SP}, DHi, KEMAC ---> R_MESSAGE = <--- 3D HDR, T,[IDr], IDi, DHr, DHi, KEMAC TGK =3D g^(xi * yi) TGK =3D g^(xi * yi) For the integrity protection of the Diffie-Hellman key agreement [RFC4650] mandates the use of HMAC SHA-1. Regarding Diffie-Hellman groups [RFC3830] is referenced. Thus, it is mandatory to support the Diffie-Hellman group "OAKLEY5" [RFC2412]. This option has also several advantages, as there are the fair mutual key agreement, the perfect forward secrecy, and no dependency on a PKI and PKI standards. Moreover, this scheme has a sound performance and reduced bandwidth requirements and provides a simple and straightforward master key provisioning. The scalability of this approach comprising only point-to-point communication is a disadvantage. This mode of operation provides an efficient scheme in deployments where there is a central trusted server that is provisioned with shared secrets for many clients. Such setups could for example be enterprise PBXs, service provider proxies, etc. In contrast to the plain pre-shared key encryption based mode, described in Section 3.1, this mode offers perfect forward secrecy. 3.6 SAML assisted DH-key agreement There has been a longer discussion during meetings and the MSEC mailing about a SAML assisted DH approach, which have not been submitted as a draft.[Reference to draft-moskowitz-MIKEY-SAML-DH]. Nevertheless, the discussed is targeted to fulfill general requirements on key management approaches and is therefore stated here: 1. Mutual authentication of involved parties 2. Both parties involved contribute to the session key generation 3. Provide perfect forward secrecy 4. Support distribution of group session keys Fries & Ignjatic Expires May 20, 2007 [Page 11] Internet-Draft MIKEY modes applicability November 2006 5. Provide liveliness tests when involved parties do not have a reliable clock 6. Support of limited parties involved To fulfill all of the requirements, the document proposes the use of a classic Diffie-Hellman key agreement protocol for key establishment in conjunction with UA's SIP server signed element authenticating the Diffie-Hellman key and the ID using the SAML (Security Association Markup Language, [SAML_overview]) approach. Here the client's public Diffie-Hellman-credentials are signed by the server to form a SAML assertion [CRED], which may be used for later sessions with other clients. This assertion needs at least to convey the ID, public DH key, expiry, and the signature from the server. This provides the involved clients with mutual authentication and message integrity of the key management messages exchanged. Initiator Responder I_MESSAGE = HDR, T, RAND1, [CREDi], IDr, {SP} ---> R_MESSAGE = <--- HDR, T, [CREDr], IDi, DHr, RAND2, (SP) TGK = HMACx(RAND1|RAND2), where x = g^(xi * xr). Additionally the document proposes a second roundtrip to avoid the dependence on synchronized clocks and provide liveliness checks. This is achieved by exchanging nonces, protected with the session key. This second roundtrip can also be used for distribution of group keys or for the leverage of a weak DH key for a stronger session key. The trigger for the second round trip would be handled via SP, the Security Policy communicated via MIKEY. Initiator Responder I_MESSAGE = HDR, SIGN(ENC(RAND3)) ---> R_MESSAGE = <--- SIGN(ENC(RAND4)) Note if group keys are to be provided RAND would be substituted by that group key. With the second roundtrip, this approach also provides an option for all of the other key distribution methods, when liveliness checks are needed. The drawback of the second roundtrip is that these messages Fries & Ignjatic Expires May 20, 2007 [Page 12] Internet-Draft MIKEY modes applicability November 2006 need to be integrated into the call flow of the signaling protocol. In straight forward call one roundtrip may be enough to setup a session. Thus this second roundtrip would require additional messages to be exchanged. 3.7 Asymmetric key distribution with in-band certificate exchange This is an additional option which has been defined in [I-D.ietf-msec-mikey-rsa-r]. It describes the asymmetric key distribution with optional in-band certificate exchange. Initiator Responder I_MESSAGE = HDR, T, [IDi|CERTi], [IDr], {SP}, [RAND], SIGNi ---> R_MESSAGE = <--- HDR, [GenExt(CSB-ID)], T, RAND, [IDr|CERTr], [SP], KEMAC, SIGNr This option has some advantages compared to the asymmetric key distribution stated in Section 3.2. Here, the sender and receiver do not need to know the certificate of the other peer in advance as it may be sent in the MIKEY initiator message. Thus, the receiver of this message can utilize the received key material to encrypt the session parameter and send them back as part of the MIKEY response message. The certificate check may be done depending on the signing authority. If the certificate is signed by an publicly accepted authority the certificate validation is done on the common base. In the other case additional steps may be necessary. The disadvantage is that no perfect forward secrecy is provided. This mode is meant to provide an easy option for certificate provisioning when PKI is present and/or required. Specifically in SIP, session invitations can be retargeted or forked. MIKEY modes that require the Initiator to target a single well known Responder may be impractical here as they may require multiple roundtrips to do key negotiation. By allowing the Responder to generate secret material used for key derivation this mode allows for an efficient key delivery scheme. Note that the Initiator can contribute to the material the key is derived from through CSB-ID and RAND payloads in unicast use cases. This mode is also useful in multicast scenarios where multiple clients are contacting a known server and are downloading the key. Server workload is significantly reduced in these scenarios compared to MIKEY in public key mode. Examples of deployments where this mode can be used are enterprises with PKI, service provider setups where the service provider decides to Fries & Ignjatic Expires May 20, 2007 [Page 13] Internet-Draft MIKEY modes applicability November 2006 provision certificates to its users, etc. Fries & Ignjatic Expires May 20, 2007 [Page 14] Internet-Draft MIKEY modes applicability November 2006 4 Further MIKEY Extensions This section will provide an overview about further MIKEY extensions for crypto algorithms, generic payload enhancements, as well as enhancements to support the negotiation of security parameters for other security protocols than SRTP. These extensions have been defined in several additional documents. 4.1 ECC algorithms support [I-D.ietf-msec-mikey-ecc] proposes extensions to the authentication, encryption and digital signature methods described for use in MIKEY, employing elliptic-curve cryptography (ECC). These extensions are defined to align MIKEY with other ECC implementations and standards. The motivation for supporting ECC within the MIKEY stems from the following advantages: o ECC support is generally added to security protocols o ECC support requires considerably smaller keys by keeping the same security level compared to other asymmetric techniques (like RSA). Elliptic curve algorithms are capable of providing security consistent with AES keys of 128, 192, and 256 bits without extensive growth in asymmetric key sizes. o As stated in [I-D.ietf-msec-mikey-ecc] implementations have shown that elliptic curve algorithms can significantly improve performance and security-per-bit over other recommended algorithms. These advantages make the usage of ECC especially interesting for embedded devices, which may have only limited performance and storage capabilities. [I-D.ietf-msec-mikey-ecc] proposes several ECC based mechanisms to enhance the MIKEY key distribution schemes, as there are: o Use of ECC methods extending the Diffie-Hellman key exchange: MIKEY-DHSIGN with ECDSA o Use of ECC methods extending the Diffie-Hellman key exchange: MIKEY-DHSIGN with ECDH o Use of Elliptic Curve Integrated Encryption Scheme (MIKEY-ECIES) o Use of Elliptic Curve Scheme Menezes-Qu-Vanstone (MIKEY-ECMQV) Fries & Ignjatic Expires May 20, 2007 [Page 15] Internet-Draft MIKEY modes applicability November 2006 The following subsections will provide more detailed information about the message exchanges for MIKEY-ECIES and MIKEY-ECMQV. 4.1.1 Elliptic Curve Integrated Encryption Scheme application in MIKEY The following figure shows the message exchange for the MIKEY-ECIES scheme: Initiator Responder I_MESSAGE = HDR, T, RAND, [IDi|CERTi], [IDr], {SP}, ECCPT, KEMAC, [CHASH], SIGNi ---> R_MESSAGE = [<---] HDR, T, [IDr], V 4.1.2 Elliptic Curve Menezes-Qu-Vanstone Scheme application in MIKEY The following figure shows the message exchange for the MIKEY-ECMQV scheme: Initiator Responder I_MESSAGE = HDR, T, RAND, [IDi|CERTi], [IDr], {SP}, ECCPT, KEMAC, [CHASH], SIGNi ---> R_MESSAGE = [<---] HDR, T, [IDr], V 4.2 New Payload for bootstrapping TESLA TESLA [RFC4082] is a protocol for providing source authentication in multicast scenarios. TESLA is an efficient protocol with low communication and computation overhead, which scales to large numbers of receivers, and also tolerates packet loss. TESLA is based on loose time synchronization between the sender and the receivers. Source authentication is realized in TESLA by using Message Authentication Code (MAC) chaining. The use of TESLA within the Secure Real-time Transport Protocol (SRTP) has been published in [RFC4383] targeting multicast authentication in scenarios, where SRTP is applied to protect the multimedia data. This solution assumes that TESLA parameters are made available by out-of-band mechanisms. [RFC4442] specifies payloads for MIKEY to bootstrap TESLA for source authentication of secure group communications using SRTP. TESLA may be bootstrapped using one of the MIKEY key management approaches Fries & Ignjatic Expires May 20, 2007 [Page 16] Internet-Draft MIKEY modes applicability November 2006 described above by sending the MIKEY message via unicast, multicast or broadcast. This approach provides the necessary parameter payload extensions for the usage of TESLA in SRTP. Nevertheless, if the parameter set is also sufficient for other TESLA use cases, it can be applied as well. 4.3 MBMS extensions to the Key ID information type This extension specifies a new Type (the Key ID Information Type) for the General Extension Payload. This is used in, e.g., the Multimedia Broadcast/Multicast Service (MBMS) specified in the 3rd Generation Partnership Project (3GPP). MBMS requires the use of MIKEY to convey the keys and related security parameters needed to secure the multimedia that is multicast or broadcast. One of the requirements that MBMS puts on security is the ability to perform frequent updates of the keys. The rationale behind this is that it will be costly for subscribers to re-distribute the decryption keys to non-subscribers. The cost for re-distributing the keys using the unicast channel should be higher than the cost of purchasing the keys for this scheme to have an effect. To achieve this, MBMS uses a three-level key management, to distribute group keys to the clients, and be able to re-key by pushing down a new group key. MBMS has the need to identify, which types of keys are involved in the MIKEY message and their identity. [RFC4563] specifies a new Type for the General Extension Payload in MIKEY, to identify the type and identity of involved keys. Moreover, as MBMS uses MIKEY both as a registration protocol and a re-key protocol, this RFC specifies the necessary additions that allow MIKEY to function both as a unicast and multicast re-key protocol in the MBMS setting. 4.4 OMA BCAST MIKEY General Extension Payload Specification The document [I-D.dondeti-msec-mikey-genext-oma] specifies a new general extension payload type for use in the Open Mobile Alliance's (OMA) Browser and Content Broadcast (BCAST) group. OMA BCAST's service and content protection specification uses short term key message and long term key message payloads that in certain broadcast distribution systems are carried in MIKEY. The document defines a general extensions payload to allow possible extensions to MIKEY without defining a new payload. The general extension payload can be used in any MIKEY message and is part of the authenticated or signed data part. Note, that only a parameter description is included, but no key information. Fries & Ignjatic Expires May 20, 2007 [Page 17] Internet-Draft MIKEY modes applicability November 2006 4.5 Supporting Integrity Transform carrying the Rollover Counter The document [I-D.lehtovirta-srtp-rcc] defines a new integrity transform for SRTP [RFC3711] providing the option to also transmit the Roll Over Counter (ROC) as part of dedicated SRTP packets. This extension has been defined for the use in the 3GPP multicast/ broadcast service. While the communicating parties did agree on a starting ROC, in some cases the receiver will not be able to synchronize his ROC with the one used by the sender even if it is signaled to him out of band. Here the new extension provides the possibility for the receiver to re-synchronize to the sender's ROC. To signal the use of the new integrity transform new definitions for certain MIKEY payloads need to be done. These MIKEY new definition comprise the integrity transform s and new integrity transform parameter. Moreover, the document specifies integrity parameter, to enable the usage of different integrity transforms for SRTP and SRTCP. Fries & Ignjatic Expires May 20, 2007 [Page 18] Internet-Draft MIKEY modes applicability November 2006 5 Selection and interworking of MIKEY modes While MIKEY and its extensions provide plenty of choice in terms of modes of operation an implementation may choose to simplify its behavior. This can be achieved by operating in a single mode of operation when in Initiator's role. Where PKI is available and/or required an implementation may choose for example to start all sessions in RSA-R mode but it would be trivial for it to act as a Responder in public key mode. If envelope keys are cached it can then also choose to do re-keying in shared key mode. In general, modes of operation where the Initiator generates keying material are useful when two peers are aware of each other before the MIKEY communication takes place. If an implementation chooses not to operate in shared key mode its behavior may be identical to a peer that does but lacks the shared key. Similarly, if a peer chooses not to operate in the public key mode it may reject the certificate of the Initiator. The same applies to peers that choose to operate in one of the DH modes exclusively. Forward MIKEY modes like public key or shared key mode when used in SIP/SDP may lead to complications in some calls scenarios, for example forking scenarios were key derivation material gets distributed to multiple parties. As mentioned earlier this may be impractical as some of the destinations may not have the resources to validate the message and may cause the initiator to drop the session invitation. Even in the case all parties involved have all the prerequisites for interpreting the MIKEY message received there is a possible problem with multiple responders starting media sessions using the same key. While the SSRCs will be different in most of the cases they are only sixteen bits long and there is a high probability of a two-time pad problem. As suggested earlier forward modes are most useful when the two peers are aware of each other before the communication takes place (as is the case in key renewal scenarios when costly public key operations can be avoided by using the envelope key). The following list may give an idea, how the different MIKEY modes may be used or combined, depending on available key material at the initiator side. 1. If the Initiator has a PSK with the Responder, it uses the PSK mode. 2. If the Initiator has a PSK with the Responder, but needs PFS or knows that the responder has a policy that both parties should provide entropy to the key, then it uses the DH-HMAC mode. Fries & Ignjatic Expires May 20, 2007 [Page 19] Internet-Draft MIKEY modes applicability November 2006 3. If the Initiator has the RSA key of the Responder, it uses the RSA mode to establish the TGK. Note that the TGK may be used as PSK together with Option 1 in the future. 4. The Initiator uses RSA-R when he does expect the receiver not having his certificate. Using RSA-R he can provide his certificate information in-band to the receiver. Moreover, the initiator may also provide a random number which can be used by the receiver for key generation. Thus both parties can be involved in the key management. But as the inclusion of the random number cannot be forced by the initiator, true PFS cannot be provided. Note that in this mode, after establishing the TGK, it may be used as PSK with other MIKEY options. 5. The Initiator uses DH-SIGN when PFS is required by his policy and he knows that the responder has a policy that both parties should provide entropy. Note that also in this mode, after establishing the TGK, it may be used as PSK with other MIKEY options. 6. If no PSK or certificate is available at the initiators side (and likewise at the receivers side) but lower level security (like TLS ot IPSec) is in place the user may use the unprotected mode of MIKEY. Besides the available key material choosing between the different modes of MIKEY depends strongly on the use case. This document will discuss further scenarios to argue for preferred modes. The following call scenarios provide a list of potential call scenarios and are matter of discussion: o Early Media o Forking o Call Transfer/Redirect/Retarget o Shared key conferencing 5.1 MIKEY and Early Media In early media scenarios, SRTP data may be received before the answer over the SIP signaling arrives. The two MIKEY modes, which only require one message to be transported (Section 3.1 and Section 3.2), work nicely in early media situations, as both, sender and receiver have all the necessary parameters in place before actually sending/ receiving encrypted data. The other modes, featuring either Diffie- Hellman key agreement (Section 3.3, Section 3.5, and Section 3.6) or the enhanced asymmetric variant (Section 3.7) suffer from the Fries & Ignjatic Expires May 20, 2007 [Page 20] Internet-Draft MIKEY modes applicability November 2006 requirements that the initiator has to wait for the response before being able to decrypt the incoming SRTP media. In fact, even if early media is not used, in other words if media is not sent before the SDP answer a similar problem may arise from the fact that SIP/SDP signaling has to traverse multiple proxies on its way back and media may arrive before the SDP answer. It is expected that this delay would be significantly shorter than in the case of early media though. It is worth mentioning here that security descriptions ([RFC4568]) have the same problem as the initiating end needs the SDP answer before it can start decrypting SRTP media. To cope with the early media problem there are further approaches to describe security preconditions [I-D.ietf-mmusic-securityprecondition], i.e., certain preconditions need to be met to enable voice data encryption. One example is for instance that a scenario where a provisional response, containing the required MIKEY parameter, is sent before encrypted media is processed. 5.2 MIKEY and Forking In SIP forking scenarios a SIP proxy server sends an INVITE request to more than one location. This means that also the MIKEY payload, which is part of the SDP is sent to several (different) locations. MIKEY modes supporting signatures may be used in forking scenarios (Section 3.3 and Section 3.7) as here the receiver can validate the signature. There are limitations with the symmetric key encryption as well as the asymmetric key encryption modes (Section 3.1 and Section 3.2). This is due to the fact that in symmetric encryption the recipient needs to possess the symmetric key before handling the MIKEY data. For asymmetric MIKEY modes, if the sender is aware of the forking he may not know in advance to which location the INVITE is forked and thus may not use the right receiver certificate to encrypt the MIKEY envelope key. Note, the sender may include several MIKEY containers into the same INVITE message to cope with forking, but this requires the knowledge of all forking targets in advance and also requires the possession of the target certificates. It is out of the scope of MIKEY to specify behavior in such a case. DH modes or the Section 3.7 do not have this problem. In scenarios, where the sender is not aware of forking, only the intended receiver is able to decrypt the MIKEY container. If forking is combined with early media the situation gets aggravated. If MIKEY modes requiring full roundtrip are used, like the signed Diffie-Hellman, multiple responses may overload the end device. An example is forking to 30 destinations (group pickup), Fries & Ignjatic Expires May 20, 2007 [Page 21] Internet-Draft MIKEY modes applicability November 2006 while MIKEY is used with the signed Diffie-Hellman mode together with security preconditions. Here, every target would answer with a provisional response, leading to 30 signature validations and Diffie- Hellman calculations at the senders site. This may lead to a prolonged media setup delay. Moreover, depending on the MIKEY mode chosen, a two-time pad may occur in dependence of the negotiated key material and the SSRC. For the non Diffie-Hellman modes, a two-time pad may occur when multiple receivers pick the same SSRC. For the MIKEY Diffie-Hellman modes this can only happen, when multiple receiver pick the same SSRC and the same Diffie-Hellman half key. 5.3 MIKEY and Call Transfer/Redirect/Retarget In a SIP environment MIKEY exchange is tied to SDP offer/answer and irrespective of the implementation model used for call transfer the same properties and limitations of MIKEY modes apply as in a normal call setup scenarios. In certain SIP scenarios the functionality of redirect is supported. In redirect scenarios the call initiator gets a response that the called party for instance has temporarily moved and may be reached at a different destination. The caller can now perform a call establishment with the new destination. Depending on the originally chosen MIKEY mode, the caller may not be able to perform this mode with the new destination. To be more precise MIKEY-PSK, and MIKEY- DHHMAC require a pre-shared secret in advance. MIKEY-RSA requires the knowledge about the target's certificate. Thus, these modes may influence the ability of the caller to initiate a session. Another functionality, which may be supported in SIP is retargeting. In contrast to redirect, the call initiator does not get a response about the different target. The SIP proxy sends the request to a different target about receiving a redirect response from the originally called target. This most likely will lead to problems when using MIKEY modes requiring a pre-shared key (MIKEY-PSK, MIKEY- DHHMAC) or were the caller used asymmetric key encryption (MIKEY-RSA) because the key management was originally targeted to a different destination. 5.4 MIKEY and Shared Key Conferencing First of all, not all modes of MIKEY support shared key conferencing. Mainly the Diffie Hellman modes cannot be used straight forward for conferencing as this mechanism results in a pairwise shared secret key. All other modes can be applied in conferencing scenarios by obeying the initiator and responder role, i.e., the half roundtrip Fries & Ignjatic Expires May 20, 2007 [Page 22] Internet-Draft MIKEY modes applicability November 2006 modes need to be initiated by the conferencing unit, to be able to distribute the conferencing key. The remaining full roundtrip mode, MIKEY RSA-R will be initiated by the client, while the conferencing unit provides the conferencing key based on the received certificate. An example conferencing architecture is defined in the IETF's XCON WG. The scope of this working group relates to mechanism for membership and authorization control, a mechanism to manipulate and describe media "mixing" or "topology" for multiple media types (audio, video, text), a mechanism for notification of conference related events/changes (for example a floor change), and a basic floor control protocol. A docuemnt describing possible use case scenarios is available in [I-D.ietf-xcon-conference-scenarios]. Fries & Ignjatic Expires May 20, 2007 [Page 23] Internet-Draft MIKEY modes applicability November 2006 6 Transport of MIKEY messages MIKEY defines message formats to transport key information and security policies between communicating entities. It does not define the embedding of these messages into the used signaling protocol. This definition is provided in separate documents, depending on the used signaling protocol. Nevertheless, MIKEY can also be transported over plain UDP or TCP to port 2269. Several IETF defined protocols utilize the Session Description Protocol (SDP, [RFC2327]) to transport the session parameters. Examples are the Session Initiation Protocol (SIP, [RFC3261] or the Gateway Control Protocol (GCP, [RFC3525]). The transport of MIKEY messages as part of SDP is described in [RFC4567]. Here, the complete MIKEY message is base64 encoded and transmitted as part of the SDP part of the signaling protocol message. Note, as several key distribution messages may be transported within one SDP container, [RFC4567] also comprises an integrity protection regarding all supplied key distribution attempts. Thus, bidding down attacks will be recognized. MIKEY is also applied in ITU-T protocols like H.323, which is used to establish communication sessions similar to SIP. For H.323 a security framework exists, which is defined in H.235. Within this framework H.235.7 [H.235.7] describes the usage of MIKEY and SRTP in the context of H.323. In contrast to SIP H.323 uses ASN.1 (Abstract Syntax Notation). Thus there is no need to encode the MIKEY container as base64. Within H.323 the MIKEY container is binary encoded. Fries & Ignjatic Expires May 20, 2007 [Page 24] Internet-Draft MIKEY modes applicability November 2006 7 MIKEY alternatives for SRTP security parameter negotiation Besides MIKEY there exists several approaches to handle the security parameter establishment. This is due to the fact, that some limitations in certain scenarios have been seen. Examples are early media and forking situations as described in Section 5. The following list provides a short summary about possible alternatives: o sdescription - [RFC4568] describes a key management scheme, which uses SDP for transport and completely relies on underlying protocol security. For transport the documents defines a SDP attribute transmitting all necessary SRTP parameter in clear. For security it references TLS and S/MIME.In contrast to MIKEY in the message from the initiator to the responder the SRTP parameter for the direction initiator to responder is sent rather than vice versa. This may lead to problems in early media scenarios. o sdescription with early media support - [I-D.wing-mmusic-sdes-early-media] enhances the above scheme with the possibility to also be usable in early media scenarios, when security preconditions is not used. o Encrypted Key Transport for Secure RTP - [I-D.mcgrew-srtp-ekt] is an extension to SRTP that provides for the secure transport of SRTP master keys, Rollover Counters, and other information, within SRTCP. This facility enables SRTP to work for decentralized conferences with minimal control, and to handle situations caused by SIP forking and early media. o Diffie Hellman support in SDP - [I-D.baugher-mmusic-sdp-dh] defines a new SDP attribute for exchanging Diffie-Hellman public keys. The attribute is an SDP session-level attribute for describing DH keys, and there is a new media-level parameter for describing public keying material for SRTP key generation. o DTLS/SRTP compatibility mode - is described as part of [I-D.tschofenig-avt-rtp-dtls] and provides for using DTLS as key management approach in conjunction with partial encryption targeted for low bandwidth connections. o SRTP extensions for DTLS - [Reference to I-D.mcgrew-dtls-srtp] describes a method of using DTLS key management for SRTP by using a new extension that indicates that SRTP is to be used for data protection, and which establishes SRTP keys. o ZRTP - [I-D.zimmermann-avt-zrtp] This document defines ZRTP as RTP header extensions for a Diffie-Hellman exchange to agree on a session key and parameters for establishing SRTP sessions. The Fries & Ignjatic Expires May 20, 2007 [Page 25] Internet-Draft MIKEY modes applicability November 2006 ZRTP protocol is completely self-contained in RTP and does not require support in the signaling protocol or assume a PKI. Fries & Ignjatic Expires May 20, 2007 [Page 26] Internet-Draft MIKEY modes applicability November 2006 8 Summary of MIKEY related IANA Registrations For MIKEY and the extensions to MIKEY IANA registrations have been made. Here only a link to the appropriate IANA registration is provided to avoid inconsistencies. The IANA registrations for MIKEY payloads can be found under http://www.iana.org/assignments/mikey-payloads These registrations comprise the MIKEY base registrations as well as registrations made by MIKEY extensions regarding the payload. The IANA registrations for MIKEY port numbers can be found under http://www.iana.org/assignments/port-numbers (search for MIKEY). Fries & Ignjatic Expires May 20, 2007 [Page 27] Internet-Draft MIKEY modes applicability November 2006 9 Security Considerations This document does not define extensions to existing protocols. It rather provides an overview about the set of MIKEY and available extensions. Thus, the reader is referred to the original documents defining the base protocol and the extensions for the security considerations. Fries & Ignjatic Expires May 20, 2007 [Page 28] Internet-Draft MIKEY modes applicability November 2006 10 IANA Considerations This document does not require any IANA registration. Fries & Ignjatic Expires May 20, 2007 [Page 29] Internet-Draft MIKEY modes applicability November 2006 11 Acknowledgments The authors would like to thank Lakshminath Dondeti for his document reviews and for his guidance. Fries & Ignjatic Expires May 20, 2007 [Page 30] Internet-Draft MIKEY modes applicability November 2006 12. References 12.1. Normative References [RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K. Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830, August 2004. 12.2. Informative References [H.235.7] ""ITU-T Recommendation H.235.7: Usage of the MIKEY Key Management Protocol for the Secure Real Time Transport Protocol (SRTP) within H.235"", 2005. [I-D.baugher-mmusic-sdp-dh] Baugher, M. and D. McGrew, "Diffie-Hellman Exchanges for Multimedia Sessions", draft-baugher-mmusic-sdp-dh-00 (work in progress), February 2006. [I-D.dondeti-msec-mikey-genext-oma] Dondeti, L., "OMA BCAST MIKEY General Extension Payload Specification", draft-dondeti-msec-mikey-genext-oma-02 (work in progress), September 2006. [I-D.ietf-mmusic-securityprecondition] Andreasen, F. and D. Wing, "Security Preconditions for Session Description Protocol (SDP) Media Streams", draft-ietf-mmusic-securityprecondition-03 (work in progress), October 2006. [I-D.ietf-msec-mikey-ecc] Milne, A., "ECC Algorithms for MIKEY", draft-ietf-msec-mikey-ecc-01 (work in progress), October 2006. [I-D.ietf-msec-mikey-rsa-r] Ignjatic, D., "An additional mode of key distribution in MIKEY: MIKEY-RSA-R", draft-ietf-msec-mikey-rsa-r-07 (work in progress), August 2006. [I-D.ietf-xcon-conference-scenarios] Even, R. and N. Ismail, "Conferencing Scenarios", draft-ietf-xcon-conference-scenarios-05 (work in progress), September 2005. [I-D.lehtovirta-srtp-rcc] Lehtovirta, V., "Integrity Transform Carrying Roll-over Counter", draft-lehtovirta-srtp-rcc-06 (work in progress), Fries & Ignjatic Expires May 20, 2007 [Page 31] Internet-Draft MIKEY modes applicability November 2006 October 2006. [I-D.mcgrew-srtp-ekt] McGrew, D., "Encrypted Key Transport for Secure RTP", draft-mcgrew-srtp-ekt-01 (work in progress), June 2006. [I-D.tschofenig-avt-rtp-dtls] Tschofenig, H. and E. Rescorla, "Real-Time Transport Protocol (RTP) over Datagram Transport Layer Security (DTLS)", draft-tschofenig-avt-rtp-dtls-00 (work in progress), March 2006. [I-D.wing-mmusic-sdes-early-media] Raymond, R. and D. Wing, "Security Descriptions Extension for Early Media", draft-wing-mmusic-sdes-early-media-00 (work in progress), October 2005. [I-D.zimmermann-avt-zrtp] Zimmermann, P., "ZRTP: Extensions to RTP for Diffie- Hellman Key Agreement for SRTP", draft-zimmermann-avt-zrtp-02 (work in progress), October 2006. [ISO_sec_time] ""ISO/IEC 18014 Information technology - Security techniques - Time-stamping services, Part 1-3."", 2002. [RFC1305] Mills, D., "Network Time Protocol (Version 3) Specification, Implementation", RFC 1305, March 1992. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. [RFC2412] Orman, H., "The OAKLEY Key Determination Protocol", RFC 2412, November 1998. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC3261] 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. Fries & Ignjatic Expires May 20, 2007 [Page 32] Internet-Draft MIKEY modes applicability November 2006 [RFC3525] Groves, C., Pantaleo, M., Anderson, T., and T. Taylor, "Gateway Control Protocol Version 1", RFC 3525, June 2003. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004. [RFC4082] Perrig, A., Song, D., Canetti, R., Tygar, J., and B. Briscoe, "Timed Efficient Stream Loss-Tolerant Authentication (TESLA): Multicast Source Authentication Transform Introduction", RFC 4082, June 2005. [RFC4383] Baugher, M. and E. Carrara, "The Use of Timed Efficient Stream Loss-Tolerant Authentication (TESLA) in the Secure Real-time Transport Protocol (SRTP)", RFC 4383, February 2006. [RFC4442] Fries, S. and H. Tschofenig, "Bootstrapping Timed Efficient Stream Loss-Tolerant Authentication (TESLA)", RFC 4442, March 2006. [RFC4563] Carrara, E., Lehtovirta, V., and K. Norrman, "The Key ID Information Type for the General Extension Payload in Multimedia Internet KEYing (MIKEY)", RFC 4563, June 2006. [RFC4567] Arkko, J., Lindholm, F., Naslund, M., Norrman, K., and E. Carrara, "Key Management Extensions for Session Description Protocol (SDP) and Real Time Streaming Protocol (RTSP)", RFC 4567, July 2006. [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session Description Protocol (SDP) Security Descriptions for Media Streams", RFC 4568, July 2006. [RFC4650] Euchner, M., "HMAC-Authenticated Diffie-Hellman for Multimedia Internet KEYing (MIKEY)", RFC 4650, September 2006. [SAML_overview] Huges, J. and E. Maler, ""Security Assertion Markup Language (SAML) 2.0 Technical Overview, Working Draft"", 2005. Fries & Ignjatic Expires May 20, 2007 [Page 33] Internet-Draft MIKEY modes applicability November 2006 Authors' Addresses Steffen Fries Siemens Otto-Hahn-Ring 6 Munich, Bavaria 81739 Germany Email: steffen.fries@siemens.com Dragan Ignjatic Polycom 1000 W. 14th Street North Vancouver, BC V7P 3P3 Canada Email: dignjatic@polycom.com Fries & Ignjatic Expires May 20, 2007 [Page 34] Internet-Draft MIKEY modes applicability November 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 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 in BCP 78 and BCP 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 at http://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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Fries & Ignjatic Expires May 20, 2007 [Page 35]