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Network Working Group                                         M. EuchnerRequest for Comments: 4650                                September 2006Category: Standards TrackHMAC-Authenticated Diffie-Hellmanfor Multimedia Internet KEYing (MIKEY)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).Abstract   This document describes a lightweight point-to-point key management   protocol variant for the multimedia Internet keying (MIKEY) protocol   MIKEY, as defined inRFC 3830.  In particular, this variant deploys   the classic Diffie-Hellman key agreement protocol for key   establishment featuring perfect forward secrecy in conjunction with a   keyed hash message authentication code for achieving mutual   authentication and message integrity of the key management messages   exchanged.  This protocol addresses the security and performance   constraints of multimedia key management in MIKEY.Euchner                     Standards Track                     [Page 1]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006Table of Contents1. Introduction ....................................................21.1. Definitions ................................................51.2. Abbreviations ..............................................61.3. Conventions Used in This Document ..........................72. Scenario ........................................................72.1. Applicability ..............................................72.2. Relation to GKMARCH ........................................83. DHHMAC Security Protocol ........................................83.1. TGK Re-keying .............................................104. DHHMAC Payload Formats .........................................104.1.  Common Header Payload (HDR) ..............................114.2. Key Data Transport Payload (KEMAC) ........................124.3. ID Payload (ID) ...........................................124.4. General Extension Payload .................................125. Security Considerations ........................................135.1. Security Environment ......................................135.2. Threat Model ..............................................135.3. Security Features and Properties ..........................155.4. Assumptions ...............................................195.5. Residual Risk .............................................205.6. Authorization and Trust Model .............................216. Acknowledgments ................................................217. IANA Considerations ............................................228. References .....................................................228.1. Normative References ......................................228.2. Informative References ....................................22Appendix A. Usage of MIKEY-DHHMAC in H.235 ........................251.  Introduction   There is work done in IETF to develop key management schemes.  For   example, IKE [12] is a widely accepted unicast scheme for IPsec, and   the MSEC WG is developing other schemes, addressed to group   communication [17], [18].  For reasons discussed below, there is,   however, a need for a scheme with low latency, suitable for demanding   cases such as real-time data over heterogeneous networks and small   interactive groups.   As pointed out in MIKEY (see [2]), secure real-time multimedia   applications demand a particular adequate lightweight key management   scheme that takes care to establish dynamic session keys securely and   efficiently in a conversational multimedia scenario.   In general, MIKEY scenarios cover peer-to-peer, simple one-to-many,   and small-sized groups.  MIKEY in particular describes three keyEuchner                     Standards Track                     [Page 2]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   management schemes for the peer-to-peer case that all finish their   task within one roundtrip:   -  a symmetric key distribution protocol (MIKEY-PS) based on pre-      shared master keys   -  a public-key encryption-based key distribution protocol (MIKEY-PK      and reverse-mode MIKEY-RSA-R [33]) assuming a public-key      infrastructure with RSA-based (Rivest, Shamir and Adleman)      private/public keys and digital certificates   -  a Diffie-Hellman key agreement protocol (MIKEY-DHSIGN) deploying      digital signatures and certificates.   All of these three key management protocols are designed so that they   complete their work within just one roundtrip.  This requires   depending on loosely synchronized clocks and deploying timestamps   within the key management protocols.   However, it is known [6] that each of the three key management   schemes has its subtle constraints and limitations:   -  The symmetric key distribution protocol (MIKEY-PS) is simple to      implement; however, it was not intended to scale to support any      configurations beyond peer-to-peer, simple one-to-many, and      small-size (interactive) groups, due to the need for mutually      pre-assigned shared master secrets.      Moreover, the security provided does not achieve the property of      perfect forward secrecy; i.e., compromise of the shared master      secret would render past and even future session keys susceptible      to compromise.      Further, the generation of the session key happens just at the      initiator.  Thus, the responder has to fully trust the initiator      to choose a good and secure session secret; the responder is able      neither to participate in the key generation nor to influence that      process.  This is considered a specific limitation in less trusted      environments.   -  The public-key encryption scheme (MIKEY-PK and MIKEY-RSA-R [33])      depends upon a public-key infrastructure that certifies the      private-public keys by issuing and maintaining digital      certificates.  While such key management schemes provide full      scalability in large networked configurations, public-key      infrastructures are still not widely available, and, in general,      implementations are significantly more complex.Euchner                     Standards Track                     [Page 3]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006      Further, additional roundtrips and computational processing might      be necessary for each end system in order to ascertain      verification of the digital certificates.  For example, typical      operations in the context of a public-key infrastructure may      involve extra network communication handshakes with the public-key      infrastructure and with certification authorities and may      typically involve additional processing steps in the end systems.      These operations would include validating digital certificates      (RFC 3029, [24]), ascertaining the revocation status of digital      certificates (RFC 2560, [23]), asserting certificate policies,      construction of certification path(s) ([26]), requesting and      obtaining necessary certificates (RFC 2511, [25]), and management      of certificates for such purposes ([22]).  Such steps and tasks      all result in further delay of the key agreement or key      establishment phase among the end systems, which negatively      affects setup time.  Any extra PKI handshakes and processing are      not in the scope of MIKEY, and since this document only deploys      symmetric security mechanisms, aspects of PKI, digital      certificates, and related processing are not further covered in      this document.      Finally, as in the symmetric case, the responder depends      completely upon the initiator's choosing good and secure session      keys.   -  The third MIKEY-DHSIGN key management protocol deploys the      Diffie-Hellman key agreement scheme and authenticates the exchange      of the Diffie-Hellman half-keys in each direction by using a      digital signature.  This approach has the same advantages and      deficiencies as described in the previous section in terms of a      public-key infrastructure.      However, the Diffie-Hellman key agreement protocol is known for      its subtle security strengths in that it is able to provide full      perfect forward secrecy (PFS) and further have to both parties      actively involved in session key generation.  This special      security property (despite the somewhat higher computational      costs) makes Diffie-Hellman techniques attractive in practice.   In order to overcome some of the limitations as outlined above, a   special need has been recognized for another efficient key agreement   protocol variant in MIKEY.  This protocol variant aims to provide the   capability of perfect forward secrecy as part of a key agreement with   low latency without dependency on a public-key infrastructure.Euchner                     Standards Track                     [Page 4]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   This document describes a fourth lightweight key management scheme   for MIKEY that could somehow be seen as a synergetic optimization   between the pre-shared key distribution scheme and the Diffie-Hellman   key agreement.   The idea of the protocol in this document is to apply the Diffie-   Hellman key agreement, but rather than deploy a digital signature for   authenticity of the exchanged keying material, it instead uses a   keyed-hash for symmetrically pre-assigned shared secrets.  This   combination of security mechanisms is called the HMAC-authenticated   Diffie-Hellman (DH) key agreement for MIKEY (DHHMAC).   The DHHMAC variant closely follows the design and philosophy of MIKEY   and reuses MIKEY protocol payload components and MIKEY mechanisms to   its maximum benefit and for best compatibility.   Like the MIKEY Diffie-Hellman protocol, DHHMAC does not scale beyond   a point-to-point constellation; thus, both MIKEY Diffie-Hellman   protocols do not support group-based keying for any group size larger   than two entities.1.1.  Definitions   The definitions and notations in this document are aligned with   MIKEY; see [2] sections1.3 -1.4.   All large integer computations in this document should be understood   as being mod p within some fixed group G for some large prime p; see   [2]section 3.3.  However, the DHHMAC protocol is also applicable   generally to other appropriate finite, cyclical groups as well.   It is assumed that a pre-shared key s is known by both entities   (initiator and responder).  The authentication key auth_key is   derived from the pre-shared secret s using the pseudo-random function   PRF; see [2] sections4.1.3 and4.1.5.   In this text, [X] represents an optional piece of information.   Generally throughout the text, X SHOULD be present unless certain   circumstances MAY allow X to be optional and not to be present,   thereby potentially resulting in weaker security.  Likewise, [X, Y]   represents an optional compound piece of information where the pieces   X and Y either SHOULD both be present or MAY optionally both be   absent.  {X} denotes zero or more occurrences of X.Euchner                     Standards Track                     [Page 5]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 20061.2.  Abbreviations   auth_key        Pre-shared authentication key, PRF-derived from                   pre-shared key s.   DH              Diffie-Hellman   DHi             Public Diffie-Hellman half key g^(xi) of the                   Initiator   DHr             Public Diffie-Hellman half key g^(xr) of the                   Responder   DHHMAC          HMAC-authenticated Diffie-Hellman   DoS             Denial-of-service   G               Diffie-Hellman group   HDR             MIKEY common header payload   HMAC            Keyed Hash Message Authentication Code   HMAC-SHA1       HMAC using SHA1 as hash function (160-bit result)   IDi             Identity of initiator   IDr             Identity of receiver   IKE             Internet Key Exchange   IPsec           Internet Protocol Security   MIKEY           Multimedia Internet KEYing   MIKEY-DHHMAC    MIKEY Diffie-Hellman key management protocol using                   HMAC   MIKEY-DHSIGN    MIKEY Diffie-Hellman key agreement protocol   MIKEY-PK        MIKEY public-key encryption-based key distribution                   protocol   MIKEY-PS        MIKEY pre-shared key distribution protocol   p               Diffie-Hellman prime modulus   PKI             Public-key Infrastructure   PRF             MIKEY pseudo-random function (see [2]section4.1.3)   RSA             Rivest, Shamir, and Adleman   s               Pre-shared key   SDP             Session Description Protocol   SOI             Son-of-IKE, IKEv2   SP              MIKEY Security Policy (Parameter) Payload   T               Timestamp   TEK             Traffic Encryption Key   TGK             MIKEY TEK Generation Key, as the common Diffie-                   Hellman shared secret   TLS             Transport Layer Security   xi              Secret, (pseudo) random Diffie-Hellman key of the                   Initiator   xr              Secret, (pseudo) random Diffie-Hellman key of the                   ResponderEuchner                     Standards Track                     [Page 6]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 20061.3.  Conventions Used in This Document   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 inRFC 2119 [1].2.  Scenario   The HMAC-authenticated Diffie-Hellman key agreement protocol (DHHMAC)   for MIKEY addresses the same scenarios and scope as the other three   key management schemes in MIKEY address.   DHHMAC is applicable in a peer-to-peer group where no access to a   public-key infrastructure can be assumed to be available.  Rather,   pre- shared master secrets are assumed to be available among the   entities in such an environment.   In a pair-wise group, it is assumed that each client will be setting   up a session key for its outgoing links with its peer using the DH-   MAC key agreement protocol.   As is the case for the other three MIKEY key management protocols,   DHHMAC assumes, at least, loosely synchronized clocks among the   entities in the small group.   To synchronize the clocks in a secure manner, some operational or   procedural means are recommended.  MIKEY-DHHMAC does not define any   secure time synchronization measures; however, sections5.4 and9.3   of [2] provide implementation guidance on clock synchronization and   timestamps.2.1.  Applicability   MIKEY-DHHMAC and the other MIKEY key management protocols are   intended for application-level key management and are optimized for   multimedia applications with real-time session setup and session   management constraints.   As the MIKEY-DHHMAC key management protocol terminates in one   roundtrip, DHHMAC is applicable for integration into two-way   handshake session or call signaling protocols such as   a) SIP [13] and SDP, where the encoded MIKEY messages are      encapsulated and transported in SDP containers of the SDP      offer/answer seeRFC 3264 [27]) handshake, as described in [4];      andEuchner                     Standards Track                     [Page 7]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   b) H.323 (see [15]), where the encoded MIKEY messages are transported      in the H.225.0 fast start call signaling handshake.Appendix A      outlines the usage of MIKEY-DHHMAC within H.235.   MIKEY-DHHMAC is offered as an option to the other MIKEY key   management variants (MIKEY-pre-shared, MIKEY-public-key and MIKEY-   DH-SIGN) for all those cases where DHHMAC has its particular   strengths (seesection 5).2.2.  Relation to GKMARCH   The Group key management architecture (GKMARCH) [19] describes a   generic architecture for multicast security group key management   protocols.  In the context of this architecture, MIKEY-DHHMAC may   operate as a registration protocol; see also [2]section 2.4.  The   main entities involved in the architecture are a group controller/key   server (GCKS), the receiver(s), and the sender(s).  Due to the pair-   wise nature of the Diffie-Hellman operation and the 1-roundtrip   constraint, usage of MIKEY-DHHMAC rules out any deployment as a group   key management protocol with more than two group entities.  Only the   degenerate case with two peers is possible where, for example, the   responder acts as the group controller.   Note that MIKEY does not provide re-keying in the GKMARCH sense, only   updating of the keys by normal unicast messages.3.  DHHMAC Security Protocol   The following figure defines the security protocol for DHHMAC:               Initiator                        Responder   I_message = HDR, T, RAND, [IDi], IDr,               {SP}, DHi, KEMAC                    ----------------------->   R_message = HDR, T,                                                [IDr], IDi, DHr,                                                DHi, KEMAC                    <----------------------      Figure 1: HMAC-authenticated Diffie-Hellman key-based exchange,        where xi and xr are (pseudo) randomly chosen, respectively,                    by the initiator and the responder.   The DHHMAC key exchange SHALL be done according to Figure 1.  The   initiator chooses a (pseudo) random value, xi, and sends an HMACed   message including g^(xi) and a timestamp to the responder.  It is   recommended that the initiator SHOULD always include the identityEuchner                     Standards Track                     [Page 8]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   payloads IDi and IDr within the I_message; unless the receiver can   defer the initiator's identity by some other means, IDi MAY   optionally be omitted.  The initiator SHALL always include the   recipient's identity.   The group parameters (e.g., the group G) are a set of parameters   chosen by the initiator.  Note that like in the MIKEY protocol, both   sender and receiver explicitly transmit the Diffie-Hellman group G   within the Diffie-Hellman payload DHi or DHr through an encoding   (e.g., OAKLEY group numbering; see [2]section 6.4).  The actual   group parameters g and p, however, are not explicitly transmitted but   can be deduced from the Diffie-Hellman group G.  The responder   chooses a (pseudo) random positive integer, xr, and sends an HMACed   message including g^(xr) and the timestamp to the initiator.  The   responder SHALL always include the initiator's identity IDi   regardless of whether the I_message conveyed any IDi.  It is   RECOMMENDED that the responder SHOULD always include the identity   payload IDr within the R_message; unless the initiator can defer the   responder's identity by some other means, IDr MAY optionally be left   out.   Both parties then calculate the TGK as g^(xi * xr).   The HMAC authentication provides authentication of the DH half-keys   and is necessary to avoid man-in-the-middle attacks.   This approach is less expensive than digitally signed Diffie-Hellman   in that both sides compute one exponentiation and one HMAC first,   then one HMAC verification, and finally another Diffie-Hellman   exponentiation.   With off-line pre-computation, the initial Diffie-Hellman half-key   MAY be computed before the key management transaction and thereby MAY   further reduce the overall roundtrip delay, as well as the risk of   denial-of-service attacks.   Processing of the TGK SHALL be accomplished as described in MIKEY [2]section 4.   The computed HMAC result SHALL be conveyed in the KEMAC payload field   where the MAC fields holds the HMAC result.  The HMAC SHALL be   computed over the entire message, excluding the MAC field using   auth_key; see alsosection 4.2.Euchner                     Standards Track                     [Page 9]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 20063.1.  TGK Re-keying   TGK re-keying for DHHMAC generally proceeds as described in [2]section 4.5.  Specifically, Figure 2 provides the message exchange   for the DHHMAC update message.               Initiator                        Responder   I_message = HDR, T, [IDi], IDr,               {SP}, [DHi], KEMAC                    ----------------------->   R_message = HDR, T,                                                [IDr], IDi,                                                [DHr, DHi], KEMAC                    <----------------------                      Figure 2: DHHMAC update message   TGK re-keying supports two procedures:   a) True re-keying by exchanging new and fresh Diffie-Hellman half-      keys.  For this, the initiator SHALL provide a new, fresh DHi, and      the responder SHALL respond with a new, fresh DHr and the received      DHi.   b) Non-key related information update without including any Diffie-      Hellman half-keys in the exchange.  Such a transaction does not      change the actual TGK but updates other information such as      security policy parameters.  To update the non-key related      information only, [DHi] and [DHr, DHi] SHALL be left out.4.  DHHMAC Payload Formats   This section specifies the payload formats and data type values for   DHHMAC; see also [2]section 6, for a definition of the MIKEY   payloads.   This document does not define new payload formats but re-uses MIKEY   payloads for DHHMAC as referenced:   * Common header payload (HDR); seesection 4.1 and [2]section 6.1.   * SRTP ID sub-payload; see [2]section 6.1.1.   * Key data transport payload (KEMAC); seesection 4.2 and [2]section6.2.   * DH data payload; see [2]section 6.4.Euchner                     Standards Track                    [Page 10]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   * Timestamp payload; see [2]section 6.6.   * ID payload; [2]section 6.7.   * Security Policy payload (SP); see [2]section 6.10.   * RAND payload (RAND); see [2]section 6.11.   * Error payload (ERR); see [2]section 6.12.   * General Extension Payload; see [2]section 6.15.4.1.  Common Header Payload (HDR)   Referring to [2]section 6.1, the following data types SHALL be used   for DHHMAC:      Data type     | Value | Comment   -------------------------------------------------------------      DHHMAC init   |     7 | Initiator's DHHMAC exchange message      DHHMAC resp   |     8 | Responder's DHHMAC exchange message      Error         |     6 | Error message; see [2]section 6.12                                Table 4.1.a   Note: A responder is able to recognize the MIKEY DHHMAC protocol by   evaluating the data type field as 7 or 8.  This is how the responder   can differentiate between MIKEY and MIKEY DHHMAC.   The next payload field SHALL be one of the following values:   Next payload| Value |       Section   ----------------------------------------------------------------   Last payload|     0 | -   KEMAC       |     1 |section 4.2 and [2]section 6.2   DH          |     3 | [2]section 6.4   T           |     5 | [2]section 6.6   ID          |     6 | [2]section 6.7   SP          |    10 | [2]section 6.10   RAND        |    11 | [2]section 6.11   ERR         |    12 | [2]section 6.12   General Ext.|    21 | [2]section 6.15                                Table 4.1.b   Other defined next payload values defined in [2] SHALL not be applied   to DHHMAC.Euchner                     Standards Track                    [Page 11]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   In case of a decoding error or of a failed HMAC authentication   verification, the responder SHALL apply the Error payload data type.4.2.  Key Data Transport Payload (KEMAC)   DHHMAC SHALL apply this payload for conveying the HMAC result along   with the indicated authentication algorithm.  When used in   conjunction with DHHMAC, KEMAC SHALL not convey any encrypted data;   thus, Encr alg SHALL be set to 2 (NULL), Encr data len SHALL be set   to 0, and Encr data SHALL be left empty.  The AES key wrap method   (see [16]) SHALL not be applied for DHHMAC.   For DHHMAC, this key data transport payload SHALL be the last payload   in the message.  Note that the Next payload field SHALL be set to   Last payload.  The HMAC is then calculated over the entire MIKEY   message, excluding the MAC field using auth_key as described in [2]section 5.2, and then stored within the MAC field.      MAC alg       | Value |           Comments   ------------------------------------------------------------------      HMAC-SHA-1    |     0 | Mandatory, Default (see [3])      NULL          |     1 | Very restricted use; see                            | [2]section 4.2.4                                Table 4.2.a   HMAC-SHA-1 is the default hash function that MUST be implemented as   part of the DHHMAC.  The length of the HMAC-SHA-1 result is 160 bits.4.3.  ID Payload (ID)   For DHHMAC, this payload SHALL only hold a non-certificate-based   identity.4.4.  General Extension Payload   For DHHMAC, to avoid bidding-down attacks, this payload SHALL list   all key management protocol identifiers of a surrounding   encapsulation protocol, such as SDP [4].  The General Extension   Payload SHALL be integrity protected with the HMAC using the shared   secret.   Type      | Value | Comments   SDP IDs   |     1 | List of SDP key management IDs (allocated for                       use in [4]); see also [2]section 6.15.                                Table 4.4.aEuchner                     Standards Track                    [Page 12]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 20065.  Security Considerations   This document addresses key management security issues throughout.   For a comprehensive explanation of MIKEY security considerations,   please refer to MIKEY [2]section 9.   In addition, this document addresses security issues according to   [7], where the following security considerations apply in particular   to this document:5.1.  Security Environment   The DHHMAC security protocol described in this document focuses   primarily on communication security; i.e., the security issues   concerned with the MIKEY DHHMAC protocol.  Nevertheless, some system   security issues are also of interest that are not explicitly defined   by the DHHMAC protocol, but that should be provided locally in   practice.   The system that runs the DHHMAC protocol entity SHALL provide the   capability to generate (pseudo) random numbers as input to the   Diffie-Hellman operation (see [8]).  Furthermore, the system SHALL be   capable of storing the generated (pseudo) random data, secret data,   keys, and other secret security parameters securely (i.e.,   confidential and safe from unauthorized tampering).5.2.  Threat Model   The threat model, to which this document adheres, covers the issues   of end-to-end security in the Internet generally, without ruling out   the possibility that MIKEY DHHMAC can be deployed in a corporate,   closed IP environment.  This also includes the possibility that MIKEY   DHHMAC can be deployed on a hop-by-hop basis with some intermediate   trusted "MIKEY DHHMAC proxies" involved.   Since DHHMAC is a key management protocol, the following security   threats are of concern:   * Unauthorized interception of plain TGKs: For DHHMAC, this threat     does not occur since the TGK is not actually transmitted on the     wire (not even in encrypted fashion).   * Eavesdropping of other, transmitted keying information: DHHMAC     protocol does not explicitly transmit the TGK at all.  Instead, by     using the Diffie-Hellman "encryption" operation, which conceals the     secret (pseudo) random values, only partial information (i.e., the     DH half-key) for construction of the TGK is transmitted.  It is     fundamentally assumed that availability of such Diffie-HellmanEuchner                     Standards Track                    [Page 13]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006     half-keys to an eavesdropper does not result in any substantial     security risk; see 5.4.  Furthermore, the DHHMAC carries other data     such as timestamps, (pseudo) random values, identification     information or security policy parameters; eavesdropping of any     such data is not considered to yield any significant security risk.   * Masquerade of either entity: This security threat must be avoided,     and if a masquerade attack would be attempted, appropriate     detection means must be in place.  DHHMAC addresses this threat by     providing mutual peer entity authentication.   * Man-in-the-middle attacks: Such attacks threaten the security of     exchanged, non-authenticated messages.  Man-in-the-middle attacks     usually come with masquerade and or loss of message integrity (see     below).  Man-in-the-middle attacks must be avoided and, if present     or attempted, must be detected appropriately.  DHHMAC addresses     this threat by providing mutual peer entity authentication and     message integrity.   * Loss of integrity: This security threat relates to unauthorized     replay, deletion, insertion, and manipulation of messages.     Although any such attacks cannot be avoided, they must at least be     detected.  DHHMAC addresses this threat by providing message     integrity.   * Bidding-down attacks: When multiple key management protocols, each     of a distinct security level, are offered (such as those made     possible by SDP [4]), avoiding bidding-down attacks is of concern.     DHHMAC addresses this threat by reusing the MIKEY General Extension     Payload mechanism, where all key management protocol identifiers     are to be listed within the MIKEY General Extension Payload.   Some potential threats are not within the scope of this threat model:   * Passive and off-line cryptanalysis of the Diffie-Hellman algorithm:     Under certain reasonable assumptions (see 5.4, below), it is widely     believed that DHHMAC is sufficiently secure and that such attacks     are infeasible, although the possibility of a successful attack     cannot be ruled out.   * Non-repudiation of the receipt or of the origin of the message:     These are not requirements within the context of DHHMAC in this     environment, and thus related countermeasures are not provided at     all.Euchner                     Standards Track                    [Page 14]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   * Denial-of-service or distributed denial-of-service attacks: Some     considerations are given on some of those attacks, but DHHMAC does     not claim to provide full countermeasure against any of those     attacks.  For example, stressing the availability of the entities     is not thwarted by means of the key management protocol; some other     local countermeasures should be applied.  Further, some DoS attacks     are not countered, such as interception of a valid DH- request and     its massive instant duplication.  Such attacks might at least be     countered partially by some local means that are outside the scope     of this document.   * Identity protection: Like MIKEY, identity protection is not a major     design requirement for MIKEY-DHHMAC, either; see [2].  No security     protocol is known so far that is able to provide the objectives of     DHHMAC as stated insection 5.3, including identity protection     within just a single roundtrip.  MIKEY-DHHMAC trades identity     protection for better security for the keying material and shorter     roundtrip time.  Thus, MIKEY-DHHMAC does not provide identity     protection on its own but may inherit such property from a security     protocol underneath that actually features identity protection.     The DHHMAC security protocol (seesection 3) and the TGK re-keying     security protocol (seesection 3.1) provide the option not to     supply identity information.  This option is only applicable if     some other means are available to supply trustworthy identity     information; e.g., by relying on secured links underneath MIKEY     that supply trustworthy identity information some other way.     However, it is understood that without identity information, the     MIKEY key management security protocols might be subject to     security weaknesses such as masquerade, impersonation, and     reflection attacks, particularly in end-to-end scenarios where no     other secure means of assured identity information are provided.     Leaving identity fields optional (if doing so is possible) thus     should not be seen as a privacy method, either, but rather as a     protocol optimization feature.5.3.  Security Features and Properties   With the security threats in mind, this document provides the   following security features and yields the following properties:   * Secure key agreement with the establishment of a TGK at both peers:     This is achieved using an authenticated Diffie-Hellman key     management protocol.Euchner                     Standards Track                    [Page 15]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   * Peer-entity authentication (mutual): This authentication     corroborates that the host/user is authentic in that possession of     a pre-assigned secret key is proven using keyed HMAC.     Authentication occurs on the request and on the response message;     thus authentication is mutual.     The HMAC computation corroborates for authentication and message     integrity of the exchanged Diffie-Hellman half-keys and associated     messages.  The authentication is absolutely necessary in order to     avoid man-in-the-middle attacks on the exchanged messages in     transit and, in particular, on the otherwise non-authenticated     exchanged Diffie-Hellman half-keys.     Note: This document does not address issues regarding     authorization; this feature is not provided explicitly.  However,     DHHMAC authentication means support and facilitate realization of     authorization means (local issue).   * Cryptographic integrity check: The cryptographic integrity check is     achieved using a message digest (keyed HMAC).  It includes the     exchanged Diffie-Hellman half-keys but covers the other parts of     the exchanged message as well.  Both mutual peer entity     authentication and message integrity provide effective     countermeasures against man-in-the-middle attacks.     The initiator may deploy a local timer that fires when the awaited     response message did not arrive in a timely manner.  This is     intended to detect deletion of entire messages.   * Replay protection of the messages is achieved using embedded     timestamps: In order to detect replayed messages, it is essential     that the clocks among initiator and sender be roughly synchronized.     The reader is referred to [2]section 5.4, and [2]section 9.3,     which provide further considerations and give guidance on clock     synchronization and timestamp usage.  Should the clock     synchronization be lost, end systems cannot detect replayed     messages anymore, and the end systems cannot securely establish     keying material.  This may result in a denial-of-service; see [2]section 9.5.   * Limited DoS protection: Rapid checking of the message digest allows     verifying the authenticity and integrity of a message before     launching CPU intensive Diffie-Hellman operations or starting other     resource consuming tasks.  This protects against some denial-of-     service attacks: malicious modification of messages and spam     attacks with (replayed or masqueraded) messages.  DHHMAC probably     does not explicitly counter sophisticated distributed, large-scale     denial-of-service attacks that compromise system availability, forEuchner                     Standards Track                    [Page 16]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006     example.  Some DoS protection is provided by inclusion of the     initiator's identity payload in the I_message.  This allows the     recipient to filter out those (replayed) I_messages that are not     targeted for him and to avoid creating unnecessary MIKEY sessions.   * Perfect-forward secrecy (PFS): Other than the MIKEY pre-shared and     public-key-based key distribution protocols, the Diffie-Hellman key     agreement protocol features a security property called perfect     forward secrecy.  That is, even if the long-term pre-shared key is     compromised at some point in time, this does not compromise past or     future session keys.     Neither the MIKEY pre-shared nor the MIKEY public-key protocol     variants are able to provide the security property of perfect-     forward secrecy.  Thus, none of the other MIKEY protocols is able     to substitute the Diffie-Hellman PFS property.     As such, DHHMAC and digitally signed DH provide a far superior     security level to that of the pre-shared or public-key-based key     distribution protocol in that respect.   * Fair, mutual key contribution: The Diffie-Hellman key management     protocol is not a strict key distribution protocol per se, in which     the initiator distributes a key to its peers.  Actually, both     parties involved in the protocol exchange are able to contribute to     the common Diffie-Hellman TEK traffic generating key equally.  This     reduces the risk of either party cheating or unintentionally     generating a weak session key.  This makes the DHHMAC a fair key     agreement protocol.  One may view this property as an additional     distributed security measure that increases security robustness     over that of the case where all the security depends just on the     proper implementation of a single entity.     For Diffie-Hellman key agreement to be secure, each party SHALL     generate its xi or xr values using a strong, unpredictable pseudo-     random generator if a source of true randomness is not available.     Further, these values xi or xr SHALL be kept private.  It is     RECOMMENDED that these secret values be destroyed once the common     Diffie-Hellman shared secret key has been established.   * Efficiency and performance: Like the MIKEY-public key protocol, the     MIKEY DHHMAC key agreement protocol securely establishes a TGK     within just one roundtrip.  Other existing key management     techniques, such as IPsec-IKE [12], IPsec-IKEv2 [14], TLS [11], and     other schemes, are not deemed adequate in addressing those real-     time and security requirements sufficiently; they all use more than     a single roundtrip.  All the MIKEY key management protocols are     able to complete their task of security policy parameterEuchner                     Standards Track                    [Page 17]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006     negotiation, including key-agreement or key distribution, in one     roundtrip.  However, the MIKEY pre-shared and MIKEY public-key     protocol are both able to complete their task even in a half-     roundtrip when the confirmation messages are omitted.     Using HMAC in conjunction with a strong one-way hash function (such     as SHA1) may be achieved more efficiently in software than     expensive public-key operations.  This yields a particular     performance benefit of DHHMAC over signed DH or the public-key     encryption protocol.     If a very high security level is desired for long-term secrecy of     the negotiated Diffie-Hellman shared secret, longer hash values may     be deployed, such as SHA256, SHA384, or SHA512 provide, possibly in     conjunction with stronger Diffie-Hellman groups.  This is left as     for further study.     For the sake of improved performance and reduced roundtrip delay,     either party may  pre-compute its public Diffie-Hellman half-key     off-line.     On the other side and under reasonable conditions, DHHMAC consumes     more CPU cycles than the MIKEY pre-shared key distribution     protocol.  The same might hold true quite likely for the MIKEY     public-key distribution protocol (depending on choice of the     private and public key lengths).  As such, it can be said that     DHHMAC provides sound performance when compared with the other     MIKEY protocol variants.     The use of optional identity information (with the constraints     stated insection 5.2) and optional Diffie-Hellman half-key fields     provides a means to increase performance and shorten the consumed     network bandwidth.   * Security infrastructure: This document describes the HMAC-     authenticated Diffie-Hellman key agreement protocol, which     completely avoids digital signatures and the associated public-key     infrastructure, as would be necessary for the X.509 RSA public-     key-based key distribution protocol or the digitally signed     Diffie-Hellman key agreement protocol as described in MIKEY.     Public-key infrastructures may not always be available in certain     environments, nor may they be deemed adequate for real-time     multimedia applications when additional steps are taken for     certificate validation and certificate revocation methods with     additional roundtrips into account.Euchner                     Standards Track                    [Page 18]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006     DHHMAC does not depend on PKI, nor do implementations require PKI     standards.  Thus, it is believed to be much simpler than the more     complex PKI facilities.     DHHMAC is particularly attractive in those environments where     provisioning of a pre-shared key has already been accomplished.   * NAT-friendliness: DHHMAC is able to operate smoothly through     firewall/NAT devices as long as the protected identity information     of the end entity is not an IP/transport address.   * Scalability: Like the MIKEY signed Diffie-Hellman protocol, DHHMAC     does not scale to any larger configurations beyond peer-to-peer     groups.5.4.  Assumptions   This document states a couple of assumptions upon which the security   of DHHMAC significantly depends.  The following conditions are   assumed:   * The parameters xi, xr, s, and auth_key are to be kept secret.   * The pre-shared key s has sufficient entropy and cannot be     effectively guessed.   * The pseudo-random function (PRF) is secure, yields the pseudo-     random property, and maintains the entropy.   * A sufficiently large and secure Diffie-Hellman group is applied.   * The Diffie-Hellman assumption holds saying basically that even with     knowledge of the exchanged Diffie-Hellman half-keys and knowledge     of the Diffie-Hellman group, it is infeasible to compute the TGK or     to derive the secret parameters xi or xr.  The latter is also     called the discrete logarithm assumption.  Please see [6], [9], or     [10] for more background information regarding the Diffie-Hellman     problem and its computational complexity assumptions.   * The hash function (SHA1) is secure; i.e., it is computationally     infeasible to find a message that corresponds to a given message     digest, or to find two different messages that produce the same     message digest.   * The HMAC algorithm is secure and does not leak the auth_key.  In     particular, the security depends on the message authentication     property of the compression function of the hash function H when it     is applied to single blocks (see [5]).Euchner                     Standards Track                    [Page 19]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   * A source capable of producing sufficiently many bits of (pseudo)     randomness is available.   * The system upon which DHHMAC runs is sufficiently secure.5.5.  Residual Risk   Although these detailed assumptions are non-negligible, security   experts generally believe that all these assumptions are reasonable   and that the assumptions made can be fulfilled in practice with   little or no expenses.   The mathematical and cryptographic assumptions of the properties of   the PRF, the Diffie-Hellman algorithm (discrete log-assumption), the   HMAC algorithm, and the SHA1 algorithms have been neither proven nor   disproven at this time.   Thus, a certain residual risk remains, which might threaten the   overall security at some unforeseeable time in the future.   The DHHMAC would be compromised as soon as any of the listed   assumptions no longer hold.   The Diffie-Hellman mechanism is a generic security technique that is   not only applicable to groups of prime order or of characteristic   two.  This is because of the fundamental mathematical assumption that   the discrete logarithm problem is also a very hard one in general   groups.  This enables Diffie-Hellman to be deployed also for GF(p)*,   for sub-groups of sufficient size, and for groups upon elliptic   curves.  RSA does not allow such generalization, as the core   mathematical problem is a different one (large integer   factorization).   RSA asymmetric keys tend to become increasingly lengthy (1536 bits   and more) and thus very computationally intensive.  Nevertheless,   Elliptic Curve Diffie-Hellman (ECDH) allows key lengths to be cut   down substantially (say 170 bits or more) while maintaining at least   the security level and providing even more significant performance   benefits in practice.  Moreover, it is believed that elliptic-curve   techniques provide much better protection against side channel   attacks due to the inherent redundancy in the projective coordinates.   For all these reasons, one may view elliptic-curve-based Diffie-   Hellman as being more "future-proof" and robust against potential   threats than RSA is.  Note that Elliptic Curve Diffie-Hellman   variants of MIKEY are defined in [31].Euchner                     Standards Track                    [Page 20]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   HMAC-SHA1 is a key security mechanism within DHHMAC on which the   overall security of MIKEY DHHMAC depends.  MIKEY DHHMAC uses HMAC-   SHA1 in combination with the classic Diffie-Hellman key agreement   scheme.  HMAC-SHA1 is a keyed one-way hash function that involves a   secret in its computation.  DHHMAC applies HMAC-SHA1 for protection   of the MIKEY payload.  Likewise, the pseudo-random function PRF   within MIKEY [2] uses the HMAC-SHA1 mechanism as a key derivation   function.  While certain attacks have been reported against SHA1 and   MD5 (see [29]), with current knowledge (see [29], [30]), no attacks   have been reported against the HMAC-SHA1 security mechanism.  In   fact, [32] proves that HMAC possesses the property of a pseudo-random   function PRF assuming solely that the (SHA1) hash function is a   pseudo-random function. [32] also provides evidence that HMAC is   robust against collision attacks on the underlying hash function.  It   is believed that MIKEY DHHMAC should be considered secure enough for   the time being.  Thus, there is no need to change the underlying   security mechanism within the MIKEY DHHMAC protocol.   It is not recommended to deploy DHHMAC for any other use than that   depicted insection 2.  Any misapplication might lead to unknown,   undefined properties.5.6.  Authorization and Trust Model   Basically, similar remarks on authorization as those stated in [2]section 4.3.2 hold also for DHHMAC.  However, as noted before, this   key management protocol does not serve full groups.   One may view the pre-established shared secret as yielding some pre-   established trust relationship between the initiator and the   responder.  This results in a much simpler trust model for DHHMAC   than would be the case for some generic group key management protocol   and potential group entities without any pre-defined trust   relationship.  In conjunction with the assumption of a shared key,   the common group controller simplifies the communication setup of the   entities.   One may view the pre-established trust relationship through the pre-   shared secret as some means for pre-granted, implied authorization.   This document does not define any particular authorization means but   leaves this subject to the application.6.  Acknowledgments   This document incorporates kindly, valuable review feedback from   Steffen Fries, Hannes Tschofenig, Fredrick Lindholm, Mary Barnes, and   Russell Housley and general feedback by the MSEC WG.Euchner                     Standards Track                    [Page 21]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 20067.  IANA Considerations   This document does not define its own new name spaces for DHHMAC,   beyond the IANA name spaces that have been assigned for MIKEY; see   [2] sections10 and10.1 and IANA MIKEY payload name spaces [37].   In order to align Table 4.1.a with Table 6.1.a in [2], IANA is   requested to add the following entries to their MIKEY Payload Name   Space:   Data Type        Value  Reference   ---------------  -----  ---------   DHHMAC init          7RFC 4650   DHHMAC resp          8RFC 46508.  References8.1.  Normative References   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement         Levels",BCP 14,RFC 2119, March 1997.   [2]   Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.         Norrman, "MIKEY: Multimedia Internet KEYing",RFC 3830, August         2004.   [3]   NIST, FIBS-PUB 180-2, "Secure Hash Standard", April 1995,http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf.   [4]   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)",RFC4567, July 2006.   [5]   Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing         for Message Authentication",RFC 2104, February 1997.8.2.  Informative References   [6]   A.J. Menezes, P. van Oorschot, S. A. Vanstone: "Handbook of         Applied Cryptography", CRC Press 1996.   [7]   Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on         Security Considerations",BCP 72,RFC 3552, July 2003.   [8]   Eastlake 3rd, D., Crocker, S., and J. Schiller, "Randomness         Recommendations for Security",RFC 1750, December 1994.Euchner                     Standards Track                    [Page 22]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   [9]   Ueli M. Maurer, S. Wolf: "The Diffie-Hellman Protocol",         Designs, Codes, and Cryptography, Special Issue Public Key         Cryptography, Kluwer Academic Publishers, vol. 19, pp. 147-171,         2000.ftp://ftp.inf.ethz.ch/pub/crypto/publications/MauWol00c.ps.   [10]  Discrete Logarithms and the Diffie-Hellman Protocol,http://www.crypto.ethz.ch/research/ntc/dldh/.   [11]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)         Protocol Version 1.1",RFC 4346, April 2006.   [12]  Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",RFC 2409, November 1998.   [13]  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.   [14]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",RFC4306, December 2005.   [15]  ITU-T Recommendation H.235.7: " H.323 Security framework: Usage         of the MIKEY Key Management Protocol for the Secure Real Time         Transport Protocol (SRTP) within H.235"; 9/2005.   [16]  Schaad, J. and R. Housley, "Advanced Encryption Standard (AES)         Key Wrap Algorithm",RFC 3394, September 2002.   [17]  Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The Group         Domain of Interpretation",RFC 3547, July 2003.   [18]  Harney, H., Meth, U., Colegrove, A., and G. Gross, "GSAKMP:         Group Secure Association Key Management Protocol",RFC 4535,         June 2006.   [19]  Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,         "Multicast Security (MSEC) Group Key Management Architecture",RFC 4046, April 2005.   [20]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.         Norrman, "The Secure Real-time Transport Protocol (SRTP)",RFC3711, March 2004.   [21]  ITU-T Recommendation H.235.0, " H.323 Security framework:         Security framework for H-series (H.323 and other H.245 based)         multimedia systems", (09/2005).Euchner                     Standards Track                    [Page 23]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006   [22]  Adams, C., Farrell, S., Kause, T., and T. Mononen, "Internet         X.509 Public Key Infrastructure Certificate Management Protocol         (CMP)",RFC 4210, September 2005.   [23]  Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams,         "X.509 Internet Public Key Infrastructure Online Certificate         Status Protocol - OCSP",RFC 2560, June 1999.   [24]  Adams, C., Sylvester, P., Zolotarev, M., and R. Zuccherato,         "Internet X.509 Public Key Infrastructure Data Validation and         Certification Server Protocols",RFC 3029, February 2001.   [25]  Schaad, J., "Internet X.509 Public Key Infrastructure         Certificate Request Message Format (CRMF)",RFC 4211, September         2005.   [26]  Cooper, M., Dzambasow, Y., Hesse, P., Joseph, S., and R.         Nicholas, "Internet X.509 Public Key Infrastructure:         Certification Path Building",RFC 4158, September 2005.   [27]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with         Session Description Protocol (SDP)",RFC 3264, June 2002.   [37]  IANA MIKEY Payload Name Spaces perRFC 3830, seehttp://www.iana.org/assignments/mikey-payloads.   [29]  Hoffman, P. and B. Schneier, "Attacks on Cryptographic Hashes         in Internet Protocols",RFC 4270, November 2005.   [30]  Bellovin, S.M. and E.K. Rescorla: "Deploying a New Hash         Algorithm", October 2005,http://www.cs.columbia.edu/~smb/papers/new-hash.pdf.   [31]  Milne, A., Blaser, M., Brown, D., and L. Dondetti, "ECC         Algorithms For MIKEY", Work in Progress, June 2005.   [32]  Bellare, M.: "New Proofs for NMAC and HMAC: Security Without         Collision-Resistance",http://eprint.iacr.org/2006/043.pdf,         November 2005.   [33]  Ignjatic, D., Dondeti, L., Audet, F., and P. Lin, "An         additional mode of key Distribution in MIKEY: MIKEY-RSA-R",         Work in Progress, August 2006.Euchner                     Standards Track                    [Page 24]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006Appendix A.  Usage of MIKEY-DHHMAC in H.235   This appendix provides informative overview how MIKEY-DHHMAC can be   applied in some H.323-based multimedia environments.  Generally,   MIKEY is applicable for multimedia applications including IP   telephony.  [15] describes various use cases of the MIKEY key   management protocols (MIKEY-PS, MIKEY-PK, MIKEY-DHSIGN and MIKEY-   DHHMAC) with the purpose to establish TGK keying material among H.323   endpoints.  The TGKs are then used for media encryption by applying   SRTP [20].  Addressed scenarios include point-to-point with one or   more intermediate gatekeepers (trusted or partially trusted) in   between.   One particular use case addresses MIKEY-DHHMAC to establish a media   connection from an endpoint B calling (through a gatekeeper) to   another endpoint A that is located within that same gatekeeper zone.   While EP-A and EP-B typically do not share any auth_key a priori,   some separate protocol exchange means are achieved outside the actual   call setup procedure to establish an auth_key for the time while   endpoints are being registered with the gatekeeper; such protocols   exist [15] but are not shown in this document.  The auth_key between   the endpoints is being used to authenticate and integrity protect the   MIKEY-DHHMAC messages.   To establish a call, it is assumed that endpoint B has obtained   permission from the gatekeeper (not shown).  Endpoint B as the caller   builds the MIKEY-DHHMAC I_message (seesection 3) and sends the   I_message encapsulated within the H.323-SETUP to endpoint A.  A   routing gatekeeper (GK) would forward this message to endpoint B; in   case of a non-routing gatekeeper, endpoint B sends the SETUP directly   to endpoint A.  In either case, H.323 inherent security mechanisms   [21] are applied to protect the (encapsulation) message during   transfer.  This is not depicted here.  The receiving endpoint A is   able to verify the conveyed I_message and can compute a TGK.   Assuming that endpoint A would accept the call, EP-A then builds the   MIKEY-DHHMAC R_message and sends the response as part of the   CallProceeding-to-Connect message back to the calling endpoint B   (possibly through a routing gatekeeper).  Endpoint B processes the   conveyed R_message to compute the same TGK as the called endpoint A.   1.) EP-B -> (GK) -> EP-A: SETUP(I_fwd_message [, I_rev_message])   2.) EP-A -> (GK) -> EP-B: CallProceeding-to-CONNECT(R_fwd_message       [, R_rev_message])   Notes: If it is necessary to establish directional TGKs for full-          duplex links in both directions B->A and A->B, then the          calling endpoint B instantiates the DHHMAC protocol twice:          once in the direction B->A using I_fwd_message and another runEuchner                     Standards Track                    [Page 25]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006          in parallel in the direction A->B using I_rev_message.  In          that case, two MIKEY-DHHMAC I_messages are encapsulated within          SETUP (I_fwd_message and I_rev_message) and two MIKEY-DHHMAC          R_messages (R_fwd_message and R_rev_message) are encapsulated          within CallProceeding-to-CONNECT.  The I_rev_message          corresponds with the I_fwd_message.  Alternatively, the called          endpoint A may instantiate the DHHMAC protocol in a separate          run with endpoint B (not shown); however, this requires a          third handshake to complete.          For more details on how the MIKEY protocols may be deployed          with H.235, please refer to [15].Author's Address   Martin Euchner   Hofmannstr. 51   81359 Munich, Germany   Phone: +49 89 722 55790   Fax:   +49 89 722 62366   EMail: martin_euchner@hotmail.comEuchner                     Standards Track                    [Page 26]

RFC 4650      HMAC-Authenticated Diffie-Hellman for MIKEY September 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Euchner                     Standards Track                    [Page 27]