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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 2627 ** Downref: Normative reference to an Informational RFC: RFC 3740 ** Downref: Normative reference to an Informational RFC: RFC 4046 == Outdated reference: A later version (-11) exists of draft-ietf-ipsecme-qr-ikev2-04 -- Obsolete informational reference (is this intentional?): RFC 2409 (Obsoleted by RFC 4306) Summary: 3 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group B. Weis 3 Internet-Draft Cisco Systems 4 Obsoletes: 6407 (if approved) V. Smyslov 5 Intended status: Standards Track ELVIS-PLUS 6 Expires: January 3, 2019 July 2, 2018 8 Group Key Management using IKEv2 9 draft-yeung-g-ikev2-14 11 Abstract 13 This document presents a set of IKEv2 exchanges that comprise a group 14 key management protocol. The protocol is in conformance with the 15 Multicast Security (MSEC) key management architecture, which contains 16 two components: member registration and group rekeying. Both 17 components require a Group Controller/Key Server to download IPsec 18 group security associations to authorized members of a group. The 19 group members then exchange IP multicast or other group traffic as 20 IPsec packets. This document obsoletes RFC 6407. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on January 3, 2019. 39 Copyright Notice 41 Copyright (c) 2018 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (https://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3 57 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 58 1.2. G-IKEv2 Payloads . . . . . . . . . . . . . . . . . . . . 5 59 2. G-IKEv2 integration into IKEv2 protocol . . . . . . . . . . . 6 60 2.1. UDP port . . . . . . . . . . . . . . . . . . . . . . . . 6 61 3. G-IKEv2 Protocol . . . . . . . . . . . . . . . . . . . . . . 6 62 3.1. G-IKEv2 member registration and secure channel 63 establishment . . . . . . . . . . . . . . . . . . . . . . 6 64 3.1.1. GSA_AUTH exchange . . . . . . . . . . . . . . . . . . 7 65 3.1.2. GSA_REGISTRATION Exchange . . . . . . . . . . . . . . 8 66 3.1.3. IKEv2 Header Initialization . . . . . . . . . . . . . 9 67 3.1.4. GM Registration Operations . . . . . . . . . . . . . 9 68 3.1.5. GCKS Registration Operations . . . . . . . . . . . . 10 69 3.1.6. Interaction with IKEv2 protocols . . . . . . . . . . 12 70 3.2. Group Maintenance Channel . . . . . . . . . . . . . . . . 12 71 3.2.1. GSA_REKEY exchange . . . . . . . . . . . . . . . . . 12 72 3.2.2. GSA_INBAND_REKEY exchange . . . . . . . . . . . . . . 16 73 3.2.3. Deletion of SAs . . . . . . . . . . . . . . . . . . . 17 74 3.3. Counter-based modes of operation . . . . . . . . . . . . 18 75 4. Header and Payload Formats . . . . . . . . . . . . . . . . . 19 76 4.1. The G-IKEv2 Header . . . . . . . . . . . . . . . . . . . 19 77 4.2. Group Identification (IDg) Payload . . . . . . . . . . . 20 78 4.3. Security Association - GM Supported Transforms (SAg) . . 20 79 4.4. Group Security Association Payload . . . . . . . . . . . 20 80 4.4.1. GSA Policy . . . . . . . . . . . . . . . . . . . . . 21 81 4.5. KEK Policy . . . . . . . . . . . . . . . . . . . . . . . 22 82 4.5.1. KEK Attributes . . . . . . . . . . . . . . . . . . . 23 83 4.6. GSA TEK Policy . . . . . . . . . . . . . . . . . . . . . 26 84 4.6.1. TEK ESP and AH Protocol-Specific Policy . . . . . . . 27 85 4.7. GSA Group Associated Policy . . . . . . . . . . . . . . . 28 86 4.7.1. ACTIVATION_TIME_DELAY/DEACTIVATION_TIME_DELAY . . . . 29 87 4.8. Key Download Payload . . . . . . . . . . . . . . . . . . 30 88 4.8.1. TEK Download Type . . . . . . . . . . . . . . . . . . 31 89 4.8.2. KEK Download Type . . . . . . . . . . . . . . . . . . 32 90 4.8.3. LKH Download Type . . . . . . . . . . . . . . . . . . 33 91 4.8.4. SID Download Type . . . . . . . . . . . . . . . . . . 36 92 4.9. Delete Payload . . . . . . . . . . . . . . . . . . . . . 37 93 4.10. Notify Payload . . . . . . . . . . . . . . . . . . . . . 38 94 4.11. Authentication Payload . . . . . . . . . . . . . . . . . 39 95 5. Security Considerations . . . . . . . . . . . . . . . . . . . 39 96 5.1. GSA registration and secure channel . . . . . . . . . . . 39 97 5.2. GSA maintenance channel . . . . . . . . . . . . . . . . . 39 98 5.2.1. Authentication/Authorization . . . . . . . . . . . . 39 99 5.2.2. Confidentiality . . . . . . . . . . . . . . . . . . . 39 100 5.2.3. Man-in-the-Middle Attack Protection . . . . . . . . . 39 101 5.2.4. Replay/Reflection Attack Protection . . . . . . . . . 39 102 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 103 6.1. New registries . . . . . . . . . . . . . . . . . . . . . 40 104 6.2. New payload and exchange types added to the existing 105 IKEv2 registry . . . . . . . . . . . . . . . . . . . . . 40 106 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41 107 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 41 108 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 42 109 9.1. Normative References . . . . . . . . . . . . . . . . . . 42 110 9.2. Informative References . . . . . . . . . . . . . . . . . 43 111 Appendix A. Use of LKH in G-IKEv2 . . . . . . . . . . . . . . . 44 112 A.1. Group Creation . . . . . . . . . . . . . . . . . . . . . 44 113 A.2. Group Member Exclusion . . . . . . . . . . . . . . . . . 45 114 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 116 1. Introduction and Overview 118 A group key management protocol provides IPsec keys and policy to a 119 set of IPsec devices which are authorized to communicate using a 120 Group Security Association (GSA) defined in [RFC3740]. The data 121 communications within the group (e.g., IP multicast packets) are 122 protected by a key pushed to the group members (GMs) by the Group 123 Controller/Key Server (GCKS). This document presents a set of IKEv2 124 [RFC7296] exchanges that comprise a group key management protocol. 126 A GM begins a "registration" exchange when it first joins the group. 127 With G-IKEv2, the GCKS authenticates and authorizes GMs, then pushes 128 policy and keys used by the group to the GM. G-IKEv2 includes two 129 "registration" exchanges. The first is the GSA_AUTH exchange ( 130 Section 3.1.1), which follows an IKE_SA_INIT exchange. The second is 131 the GSA_REGISTRATION exchange ( Section 3.1.2), which a GM can use 132 within an established IKE SA. Group rekeys are accomplished using 133 either the GSA_REKEY exchange (a single message distributed to all 134 GMs, usually as a multicast message), or as a GSA_INBAND_REKEY 135 exchange delivered individually to group members using existing IKE 136 SAs). 138 Large and small groups may used different sets of these protocols. 139 When a large group of devices are communicating, the GCKS is likely 140 to use the GSA_REKEY message for efficiency. This is shown in 141 Figure 1. (Note: For clarity, IKE_SA_INIT is omitted from the 142 figure.) 143 +--------+ 144 +------------->| GCKS |<-------------+ 145 | +--------+ | 146 | | ^ | 147 | | | | 148 | | GSA_AUTH | 149 | | or | 150 | | GSA_REGISTRATION | 151 | | | | 152 GSA_AUTH | | GSA_AUTH 153 or GSA_REKEY | or 154 GSA_REGISTRATION | | GSA_REGISTRATION 155 | | | | 156 | +------------+-----------------+ | 157 | | | | | | 158 v v v v v v 159 +-------+ +--------+ +-------+ 160 | GM | ... | GM | ... | GM | 161 +-------+ +--------+ +-------+ 162 ^ ^ ^ 163 | | | 164 +-------ESP-------+-------ESP------+ 166 Figure 1: G-IKEv2 used in large groups 168 Alternatively, a small group may simply use the GSA_AUTH as a 169 registration protocol, where he GCKS issues rekeys using the 170 GSA_INBAND_REKEY within the same IKEv2 SA. The GCKS is also likely 171 to be a GM in a small group (as shown in Figure 2.) 172 GSA_AUTH, GSA_INBAND_REKEY 173 +-----------------------------------------------+ 174 | | 175 | GSA_AUTH, GSA_INBAND_REKEY | 176 | +-----------------------------+ | 177 | | | | 178 | | GSA_AUTH, GSA_INBAND_REKEY | | 179 | | +--------+ | | 180 v v v v v v 181 +---------+ +----+ +----+ +----+ 182 | GCKS/GM | | GM | | GM | | GM | 183 +---------+ +----+ +----+ +----+ 184 ^ ^ ^ ^ 185 | | | | 186 +----ESP-----+------ESP-------+-----ESP-----+ 188 Figure 2: G-IKEv2 used in small groups 190 IKEv2 message semantics are preserved in that all communications 191 consists of message request-response pairs. The exception to this 192 rule is the GSA_REKEY exchange, which is a single message delivering 193 group updates to the GMs. 195 G-IKEv2 conforms with the The Multicast Group (MEC) Security 196 Architecture [RFC3740], and the Multicast Security (MSEC) Group Key 197 Management Architecture [RFC4046]. G-IKEv2 replaces GDOI [RFC6407], 198 which defines a similar group key management protocol using IKEv1 199 [RFC2409] (since deprecated by IKEv2). When G-IKEv2 is used, group 200 key management use cases can benefit from the simplicity, increased 201 robustness and cryptographic improvements of IKEv2 (see Appendix A of 202 [RFC7296]. 204 1.1. Requirements Language 206 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 207 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 208 "OPTIONAL" in this document are to be interpreted as described in BCP 209 14 [RFC2119] [RFC8174] when, and only when, they appear in all 210 capitals, as shown here. 212 1.2. G-IKEv2 Payloads 214 1. IDg (group ID) - The GM requests the GCKS for membership into the 215 group by sending its IDg payload. 217 2. GSA (Group Security Association) - The GCKS sends the group 218 policy to the GM using this payload. 220 3. KD (Key Download) - The GCKS sends the control and data keys to 221 the GM using the KD payload. 223 2. G-IKEv2 integration into IKEv2 protocol 225 G-IKEv2 uses the security mechanisms of IKEv2 (peer authentication, 226 confidentiality, message integrity) to ensure that only authenticated 227 devices have access to the group policy and keys. The G-IKEv2 228 exchange further provides group authorization, and secure policy and 229 key download from the GCKS to GMs. 231 It is assumed that readers are familiar with the IKEv2 protocol, so 232 this document skips many details that are described in [RFC7296]. 234 2.1. UDP port 236 G-IKEv2 SHOULD use port 848, the same as GDOI [RFC6407], because they 237 serve a similar function. They can use the same ports, just as IKEv1 238 and IKEv2 can share port 500. The version number in the IKEv2 header 239 distinguishes the G-IKEv2 protocol from GDOI protocol [RFC6407]. 240 G-IKEv2 MAY also use port the IKEv2 ports (500, 4500), which would 241 provide a better integration with IKEv2. 243 3. G-IKEv2 Protocol 245 3.1. G-IKEv2 member registration and secure channel establishment 247 The registration protocol consists of a minimum of two message 248 exchanges, IKE_SA_INIT and GSA_AUTH; member registration may have a 249 few more messages exchanged if the EAP method, cookie challenge (for 250 DoS protection) or negotiation of Diffie-Hellman group is included. 251 Each exchange consists of request/response pairs. The first exchange 252 IKE_SA_INIT is defined in IKEv2 [RFC7296]. This exchange negotiates 253 cryptographic algorithms, exchanges nonces and does a Diffie-Hellman 254 exchange between the group member (GM) and the Group Controller/Key 255 Server (GCKS). 257 The second exchange GSA_AUTH authenticates the previous messages, 258 exchanges identities and certificates. These messages are encrypted 259 and integrity protected with keys established through the IKE_SA_INIT 260 exchange, so the identities are hidden from eavesdroppers and all 261 fields in all the messages are authenticated. The GCKS SHOULD 262 authorize group members to be allowed into the group as part of the 263 GSA_AUTH exchange. Once the GCKS accepts a group member to join a 264 group it will download the data security keys (TEKs) and/or group key 265 encrypting key (KEK) or KEK array as part of the GSA_AUTH response 266 message. In the following descriptions, the payloads contained in 267 the message are indicated by names as listed below. Payloads defined 268 as part of other IKEv2 extensions MAY also be included in these 269 exchanges. 271 Notation Payload 272 ------------------------------------------------------------ 273 AUTH Authentication 274 CERT Certificate 275 CERTREQ Certificate Request 276 GSA Group Security Association 277 HDR IKEv2 Header 278 IDg Identification - Group 279 IDi Identification - Initiator 280 IDr Identification - Responder 281 KD Key Download 282 KE Key Exchange 283 Ni, Nr Nonce 284 SA Security Association 285 SAg Security Association - GM Supported Transforms 287 The details of the contents of each payload are described in 288 Section 4. Payloads that may optionally appear will be shown in 289 brackets, such as [ CERTREQ ], to indicate that a certificate request 290 payload can optionally be included. 292 3.1.1. GSA_AUTH exchange 294 After the group member and GCKS use the IKE_SA_INIT exchange to 295 negotiate cryptographic algorithms, exchange nonces, and perform a 296 Diffie-Hellman exchange as defined in IKEv2 [RFC7296], the GSA_AUTH 297 exchange MUST complete before any other exchanges can be done. The 298 security properties of the GSA_AUTH exchange are the same as the 299 properties of the IKE_AUTH exchange. It is used to authenticate the 300 IKE_SA_INIT messages, exchange identities and certificates. G-IKEv2 301 also uses this exchange for group member registration and 302 authorization. Even though the IKE_AUTH does contain the SA2, TSi, 303 and TSr payload the GSA_AUTH does not. They are not needed because 304 policy is not negotiated between the group member and the GCKS, but 305 instead downloaded from the GCKS to the group member. 307 Initiator (Member) Responder (GCKS) 308 -------------------- ------------------ 309 HDR, SK { IDi, [CERT,] [CERTREQ, ] [IDr, ] 310 AUTH, IDg, [SAg, ] [N ] } --> 312 After the IKE_SA_INIT exchange completes, the group member initiates 313 a GSA_AUTH request to join a group indicated by the IDg payload. The 314 GM MAY include an SAg payload declaring which Transforms that it is 315 willing to accept, and also MAY include the Notify payload status 316 type SENDER_ID_REQUEST to request SIDs for a Counter-based cipher 317 from the GCKS. 319 <-- HDR, SK { IDr, [CERT, ] AUTH, [ GSA, KD, ] [D, ] } 321 The GCKS responds with IDr, optional CERT, and AUTH material as if it 322 were an IKE_AUTH. It also informs the group member of the 323 cryptographic policies of the group in the GSA payload and the key 324 material in the KD payload. The GCKS can also include a Delete (D) 325 payload instructing the group member to delete existing SAs it might 326 have as the result of a previous group member registration. 328 In addition to the IKEv2 error handling, the GCKS can reject the 329 registration request when the IDg is invalid or authorization fails, 330 etc. In these cases, see Section 4.10, the GSA_AUTH response will 331 not include the GSA and KD, but will include a Notify payload 332 indicating errors. If the group member included an SAg payload, and 333 the GCKS chooses to evaluate it, and it detects that that group 334 member cannot support the security policy defined for the group, then 335 the GCKS SHOULD return a NO_PROPOSAL_CHOSEN. When the GCKS indicates 336 errors, and the group member cannot resolve the errors, the group 337 member MUST delete the registration IKE SA. 339 Initiator (Member) Responder (GCKS) 340 -------------------- ------------------ 341 <-- HDR, SK { N } 343 If the group member finds the policy sent by the GCKS is 344 unacceptable, the member SHOULD notify the GCKS by sending IDg and 345 the Notify type NO_PROPOSAL_CHOSEN as shown below. 347 Initiator (Member) Responder (GCKS) 348 -------------------- ------------------ 349 HDR, SK {IDg [N,]} --> 351 <-- HDR, SK {} 353 3.1.2. GSA_REGISTRATION Exchange 355 When a secure channel is already established between a GM and the 356 GCKS, the GM registration for a group can reuse the established 357 secure channel. In this scenario the GM will use the 358 GSA_REGISTRATION exchange by including the desired group ID (IDg) to 359 request data security keys (TEKs) and/or group key encrypting keys 360 (KEKs) from the GCKS. If the group member includes an SAg payload, 361 and the GCKS chooses to evaluate it, and it detects that group member 362 cannot support the security policy defined for the group, then the 363 GCKS SHOULD return a NO_PROPOSAL_CHOSEN. The GM MAY also include the 364 Notify payload status type SENDER_ID_REQUEST to request SIDs for a 365 Counter-based cipher from the GCKS. The GCKS response payloads are 366 created and processed as in the GSA_AUTH reply. 368 Initiator (Member) Responder (GCKS) 369 -------------------- ------------------ 370 HDR, SK {IDg, [SAg, ][N ] } --> 372 <-- HDR, SK { GSA, KD, [D ] } 374 This exchange can also be used if the group member finds the policy 375 sent by the GCKS is unacceptable. The group member SHOULD notify the 376 GCKS by sending IDg and the Notify type NO_PROPOSAL_CHOSEN, as shown 377 below. The GCKS MUST unregister the group member. 379 Initiator (Member) Responder (GCKS) 380 -------------------- ------------------ 381 HDR, SK {IDg [N,]} --> 383 <-- HDR, SK {} 385 3.1.3. IKEv2 Header Initialization 387 The Major Version is (2) and Minor Version is (0) according to IKEv2 388 [RFC7296], and maintained in this document. The G-IKEv2 IKE_SA_INIT, 389 GSA_AUTH and GSA_REGISTRATION use the IKE SPI according to IKEv2 390 [RFC7296], section 2.6. 392 3.1.4. GM Registration Operations 394 A G-IKEv2 Initiator (GM) requesting registration contacts the GCKS 395 using the IKE_SA_INIT exchange and receives the response from the 396 GCKS. This exchange is unchanged from the IKE_SA_INIT in IKEv2 397 protocol. 399 Upon completion of parsing and verifying the IKE_SA_INIT response, 400 the GM sends the GSA_AUTH message with the IKEv2 payloads from 401 IKE_AUTH (without the SAi2, TSi and TSr payloads) along with the 402 Group ID informing the GCKS of the group the initiator wishes to 403 join. The initiator MAY specify how many Sender-ID values it would 404 like to receive in the Notify payload status type, SENDER_ID_REQUEST, 405 in case the Data Security SA supports a counter mode cipher (see 406 Section 3.3). 408 An initiator may be limited in the types of Transforms that it is 409 able or willing to use, and may find it useful to inform the GCKS 410 which Transforms that it is willing to accept. It can OPTIONALLY 411 include an SAg payload, which can include ESP and/or AH Proposals. 413 Each Proposal contains a list of Transforms that it is willing to 414 support for that protocol. A Proposal of type ESP can include ENCR, 415 INTEG, and ESN Transforms. A Proposal of type AH can include INTEG, 416 and ESN Transforms. The SPI length of each Proposal in an SAg MUST 417 be zero, and the SPI field is null. Generally, a single Proposal of 418 each type will suffice, because the group member is not negotiating 419 Transform sets, simply alerting the GCKS to restrictions it may have. 421 Upon receiving the GSA_AUTH response, the initiator parses the 422 response from the GCKS authenticating the exchange using the IKEv2 423 method, then processes the GSA and KD. 425 The GSA payload contains the security policy and cryptographic 426 protocols used by the group. This policy describes the Rekey SA 427 (KEK), if present, Data-security SAs (TEK), and other group policy 428 (GAP). If the policy in the GSA payload is not acceptable to the GM, 429 it SHOULD notify the GCKS with a NO_PROPOSAL_CHOSEN Notify payload 430 (see Section 3.1.1 and Section 3.1.2). Finally the KD is parsed 431 providing the keying material for the TEK and/or KEK. The GM 432 interprets the KD key packets, where each key packet includes the 433 keying material for SAs distributed in the GSA payload. Keying 434 material is matched by comparing the SPIs in the key packets to SPIs 435 previously included in the GSA payloads. Once TEK keys and policy 436 are matched, the GM provides them to the data security subsystem, and 437 it is ready to send or receive packets matching the TEK policy. 439 The GSA KEK policy MUST include KEK attribute KEK_MESSAGE_ID with a 440 Message ID. The Message ID in the KEK_MESSAGE_ID attribute MUST be 441 checked against any previously received Message ID for this group. 442 If it is less than the previously received number, it should be 443 considered stale and ignored. This could happen if two GSA_AUTH 444 exchanges happened in parallel, and the Message ID changed. This 445 KEK_MESSAGE_ID is used by the GM to prevent GSA_REKEY message replay 446 attacks. The first GSA_REKEY message that the GM receives from the 447 GCKS must have a Message ID greater or equal to the Message ID 448 received in the KEK_MESSAGE_ID attribute. 450 3.1.5. GCKS Registration Operations 452 A G-IKEv2 GCKS passively listens for incoming requests from group 453 members. When the GCKS receives an IKE_SA_INIT request, it selects 454 an IKE proposal and generates a nonce and DH to include them in the 455 IKE_SA_INIT response. 457 Upon receiving the GSA_AUTH request, the GCKS authenticates the group 458 member using the same procedures as in the IKEv2 IKE_AUTH. The GCKS 459 then authorizes the group member according to group policy before 460 preparing to send the GSA_AUTH response. If the GCKS fails to 461 authorize the GM, it will respond with an AUTHORIZATION_FAILED notify 462 message. 464 The GSA_AUTH response will include the group policy in the GSA 465 payload and keys in the KD payload. If the GCKS policy includes a 466 group rekey option, this policy is constructed in the GSA KEK and the 467 key is constructed in the KD KEK. The GSA KEK MUST include the 468 KEK_MESSAGE_ID attribute, specifying the starting Message ID the GCKS 469 will use when sending the GSA_REKEY message to the group member. 470 This Message ID is used to prevent GSA_REKEY message replay attacks 471 and will be increased each time a GSA_REKEY message is sent to the 472 group. The GCKS data traffic policy is included in the GSA TEK and 473 keys are included in the KD TEK. The GSA GAP MAY also be included to 474 provide the ATD and/or DTD (Section 4.7.1) specifying activation and 475 deactivation delays for SAs generated from the TEKs. If one or more 476 Data Security SAs distributed in the GSA payload included a counter 477 mode of operation, the GCKS includes at least one SID value in the KD 478 payload, and possibly more depending on the request received in the 479 Notify payload status type SENDER_ID_REQUEST requesting the number of 480 SIDs from the group member. 482 If the GCKS receives a GSA_REGISTRATION exchange with a request to 483 register a GM to a group, the GCKS will need to authorize the GM with 484 the new group (IDg) and respond with the corresponding group policy 485 and keys. If the GCKS fails to authorize the GM, it will respond 486 with the AUTHORIZATION_FAILED notification. 488 If a group member includes an SAg in its GSA_AUTH or GSA_REGISTRATION 489 request, the GCKS MAY evaluate it according to an implementation 490 specific policy. 492 o The GCKS could evaluate the list of Transforms and compare it to 493 its current policy for the group. If the group member did not 494 include all of the ESP or AH Transforms in its current policy, 495 then it could return a NO_PROPOSAL_CHOSEN Notification. 497 o The GCKS could store the list of Transforms, with the goal of 498 migrating the group policy to a different Transform when all of 499 the group members indicate that they can support that Transform. 501 o The GCKS could store the list of Transforms and adjust the current 502 group policy based on the capabilities of the devices as long as 503 they fall within the acceptable security policy of the GCKS. 505 3.1.6. Interaction with IKEv2 protocols 507 3.1.6.1. Session Resumption 509 G-IKEv2 is compatible with and can use IKEv2 Session Resumption 510 [RFC5723] except that a GM would include the initial ticket request 511 in a GSA_AUTH exchange instead of an IKE_AUTH exchange. 513 3.1.6.2. Postquantum Preshared Keys for IKEv2 515 G-IKEv2 can take advantage of the protection provided by Postquantum 516 Preshared Keys (PPK) for IKEv2 [I-D.ietf-ipsecme-qr-ikev2]. However, 517 the current PPK draft leaves the initial IKE SA susceptible to 518 quantum computer (QC) attacks. It suggests that for applications 519 using IKEv2 to be QC-secure, an immediate IKE SA rekey should take 520 place followed by a GSA_REGISTRATION exchange. 522 3.2. Group Maintenance Channel 524 The GCKS is responsible for rekeying the secure group per the group 525 policy. Rekeying is an operation whereby the GCKS provides 526 replacement TEKs and KEK, deleting TEKs, and/or excluding group 527 members. The GCKS may initiate a rekey message if group membership 528 and/or policy has changed, or if the keys are about to expire. Two 529 forms of group maintenance channels are provided in G-IKEv2 to push 530 new policy to group members. 532 GSA_REKEY The GSA_REKEY exchange is an exchange initiated by the 533 GCKS, where the rekey policy is usually delivered to group members 534 using IP multicast as a transport. This is valuable for large and 535 dynamic groups, and where policy may change frequently and an 536 scalable rekeying method is required. When the GSA_REKEY exchange 537 is used, the IKEv2 SA protecting the member registration exchanges 538 is terminated, and group members await policy changes from the 539 GCKS via the GSA_REKEY exchange. 541 GSA_INBAND_REKEY The GSA_INBAND_REKEY exchange is a rekey method 542 using the IKEv2 SA that was setup to protecting the member 543 registration exchange. This exchange allows the GCKS to rekey 544 without using an independent GSA_REKEY exchange. The 545 GSA_INBAND_REKEY exchange is useful when G-IKEv2 is used with a 546 small group of cooperating devices. 548 3.2.1. GSA_REKEY exchange 550 The GCKS initiates the G-IKEv2 Rekey securely, usually using IP 551 multicast. Since this rekey does not require a response and it sends 552 to multiple GMs, G-IKEv2 rekeying MUST NOT support IKE SA windowing. 554 The GCKS rekey message replaces the rekey GSA KEK or KEK array, and/ 555 or creates a new Data-Security GSA TEK. The SID Download attribute 556 in the Key Download payload (defined in Section 4.8.4) MUST NOT be 557 part of the Rekey Exchange as this is sender specific information and 558 the Rekey Exchange is group specific. The GCKS initiates the 559 GSA_REKEY exchange as following: 561 Members (Responder) GCKS (Initiator) 562 -------------------- ------------------ 563 <-- HDR, SK { GSA, KD, [D,] AUTH } 565 HDR is defined in Section 4.1. The Message ID in this message will 566 start with the same value the GCKS sent to the group members in the 567 KEK attribute KEK_MESSAGE_ID during registration; this Message ID 568 will be increased each time a new GSA_REKEY message is sent to the 569 group members. 571 The GSA payload contains the current rekey and data security SAs. 572 The GSA may contain a new rekey SA and/or a new data security SA, 573 which, optionally contains an LKH rekey SA, Section 4.4. 575 The KD payload contains the keys for the policy included in the GSA. 576 If the data security SA is being refreshed in this rekey message, the 577 IPsec keys are updated in the KD, and/or if the rekey SA is being 578 refreshed in this rekey message, the rekey Key or the LKH KEK array 579 is updated in the KD payload. 581 A Delete payload MAY be included to instruct the GM to delete 582 existing SAs. 584 The AUTH payload is included to authenticate the GSA_REKEY message 585 using a method defined in the IKEv2 Authentication Method IANA 586 registry [IKEV2-IANA]. The method SHOULD be a digital signature 587 authentication scheme to ensure that the message was originated from 588 an authorized GCKS. A Shared Key Integrity Code SHOULD NOT be used 589 as it doesn't provide source origin authentication (although a small 590 group may not require source origin authentication). During group 591 member registration, the GCKS sends the authentication key in the GSA 592 KEK payload, KEK_AUTH_KEY attribute, which the group member uses to 593 authenticate the key server. Before the current Authentication Key 594 expires, the GCKS will send a new KEK_AUTH_KEY to the group members 595 in a GSA_REKEY message. The AUTH key that is used in the rekey 596 message may not be the same as the authentication key used in 597 GSA_AUTH. Typically a rekey message is sent as multicast and 598 received by all group members, therefore the same AUTH key is 599 distributed to all group members. 601 After adding the AUTH payload to the rekey message, the current KEK 602 encryption key is used to encrypt all of the payloads following the 603 HDR. 605 3.2.1.1. GSA_REKEY GCKS Operations 607 The GCKS builds the rekey message with a Message ID value that is one 608 greater than the value included in the previous rekey. If the 609 message is using a new KEK attribute, the Message ID is reset to 1 in 610 this message. The GSA, KD, and D payloads follow with the same 611 characteristics as in the GSA Registration exchange. The AUTH 612 payload is the final payload added to the message. It is created by 613 hashing the string "G-IKEv2" and the message created so far, and then 614 is digitally signed. Finally, the content of the Encrypted payload 615 is encrypted and authenticated using the current KEK keys. 617 Because GSA_REKEY messages are not acknowledged and could be 618 discarded by the network, one or more GMs may not receive the 619 message. To mitigate such lost messages, during a rekey event the 620 GCKS SHOULD transmit several GSA_REKEY messages with the new policy. 621 When re-transmitting a GSA_REKEY a GCKS needs to ensure that TEK and 622 KEK time-to-live lifetimes are still the correct values. If the 623 lifetimes in a re-transmitted message are stale, they will represent 624 an artificially lengthened lifetime, possibly resulting in GMs with 625 unsynchronized TEK and KEK lifetimes. 627 3.2.1.2. GSA_REKEY GM Operations 629 When a group member receives the Rekey Message from the GCKS it 630 decrypts the message using the current KEK, validates the signature 631 using the public key retrieved in a previous G-IKEv2 exchange, 632 verifies the Message ID, and processes the GSA and KD payloads. The 633 group member then downloads the new data security SA and/or new Rekey 634 GSA. The parsing of the payloads is identical to the parsing done in 635 the registration exchange. 637 Replay protection is achieved by a group member rejecting a GSA_REKEY 638 message which has a Message ID smaller than the current Message ID 639 that the GM is expecting. The GM expects the Message ID in the first 640 GSA_REKEY message it receives to be equal or greater than the message 641 id it receives in the KEK_MESSAGE_ID attribute. The GM expects the 642 message ID in subsequent GSA_REKEY messages to be greater than the 643 last valid GSA_REKEY message ID it received. 645 If the GSA payload includes a Data-Security SA including a counter- 646 modes of operation and the receiving group member is a sender for 647 that SA, the group member uses its current SID value with the Data- 648 Security SAs to create counter-mode nonces. If it is a sender and 649 does not hold a current SID value, it MUST NOT install the Data- 650 Security SAs. It MAY initiate a GSA_REGISTRATION exchange to the 651 GCKS in order to obtain an SID value (along with current group 652 policy). 654 If the GM receives a notification that a Data-Security SA is about to 655 expire (such as a "soft lifetime" expiration as described in 656 Section 4.4.2.1 of [RFC4301]), it SHOULD initiate a registration to 657 the GCKS. This registration serves as a request for current SAs, and 658 will result in the download of replacement SAs, assuming the GCKS 659 policy has created them. 661 3.2.1.3. Forward and Backward Access Control 663 Through the G-IKEv2 rekey, G-IKEv2 supports algorithms such as LKH 664 that have the property of denying access to a new group key by a 665 member removed from the group (forward access control) and to an old 666 group key by a member added to the group (backward access control). 667 An unrelated notion to PFS, "forward access control" and "backward 668 access control" have been called "perfect forward security" and 669 "perfect backward security" in the literature [RFC2627]. 671 Group management algorithms providing forward and backward access 672 control other than LKH have been proposed in the literature, 673 including OFT [OFT] and Subset Difference [NNL]. These algorithms 674 could be used with G-IKEv2, but are not specified as a part of this 675 document. 677 Support for group management algorithms are supported via the 678 KEY_MANAGEMENT_ALGORITHM attribute which is sent in the GSA KEK 679 policy. G-IKEv2 specifies one method by which LKH can be used for 680 forward and backward access control. Other methods of using LKH, as 681 well as other group management algorithms such as OFT or Subset 682 Difference may be added to G-IKEv2 as part of a later document. 684 3.2.1.3.1. Forward Access Control Requirements 686 When group membership is altered using a group management algorithm 687 new GSA TEKs (and their associated keys) are usually also needed. 688 New GSAs and keys ensure that members who were denied access can no 689 longer participate in the group. 691 If forward access control is a desired property of the group, new GSA 692 TEKs and the associated key packets in the KD payload MUST NOT be 693 included in a G-IKEv2 rekey message which changes group membership. 694 This is required because the GSA TEK policy and the associated key 695 packets in the KD payload are not protected with the new KEK. A 696 second G-IKEv2 rekey message can deliver the new GSA TEKS and their 697 associated key packets because it will be protected with the new KEK, 698 and thus will not be visible to the members who were denied access. 700 If forward access control policy for the group includes keeping group 701 policy changes from members that are denied access to the group, then 702 two sequential G-IKEv2 rekey messages changing the group KEK MUST be 703 sent by the GCKS. The first G-IKEv2 rekey message creates a new KEK 704 for the group. Group members, which are denied access, will not be 705 able to access the new KEK, but will see the group policy since the 706 G-IKEv2 rekey message is protected under the current KEK. A 707 subsequent G-IKEv2 rekey message containing the changed group policy 708 and again changing the KEK allows complete forward access control. A 709 G-IKEv2 rekey message MUST NOT change the policy without creating a 710 new KEK. 712 If other methods of using LKH or other group management algorithms 713 are added to G-IKEv2, those methods MAY remove the above restrictions 714 requiring multiple G-IKEv2 rekey messages, providing those methods 715 specify how the forward access control policy is maintained within a 716 single G-IKEv2 rekey message. 718 3.2.1.4. Fragmentation 720 IKE fragmentation [RFC7383] can be used to perform fragmentation of 721 large GSA_REKEY messages, however when the GSA_REKEY message is 722 emitted as an IP multicast packet there is a lack of response from 723 the GMs. This has the following implications. 725 o Policy regarding the use of IKE fragmentation is implicit. If a 726 GCKS detects that all GMs have negotiated support of IKE 727 fragmentation in IKE_SA_INIT, then it MAY use IKE fragmentation on 728 large GSA_REKEY exchange messages. 730 o The GCKS must always use IKE fragmentation based on a known 731 fragmentation threshold (unspecified in this memo), as there is no 732 way to check if fragmentation is needed by first sending 733 unfragmented messages and waiting for response. 735 o PMTU probing cannot be performed due to lack of GSA_REKEY response 736 message. 738 3.2.2. GSA_INBAND_REKEY exchange 740 When the IKEv2 SA protecting the member registration exchange is 741 maintained while group member participates in the group, the GCKS can 742 use the GSA_INBAND_REKEY exchange to individually provide policy 743 updates to the group member. 745 Member (Responder) GCKS (Initiator) 746 -------------------- ------------------ 747 <-- HDR, SK { GSA, KD, [D,] } 749 HDR, SK {} --> 751 Because this is an IKEv2 exchange, the HDR is treated as defined in 752 [RFC7296]. 754 3.2.2.1. GSA_INBAND_REKEY GCKS Operations 756 The GSA, KD, and D payloads are built in the same manner as in a 757 registration exchange. 759 3.2.2.2. GSA_INBAND_REKEY GM Operations 761 The GM processes the GSA, KD, and D payloads in the same manner as if 762 they were received in a registration exchange. 764 3.2.3. Deletion of SAs 766 There are occasions when the GCKS may want to signal to group members 767 to delete policy at the end of a broadcast, or if group policy has 768 changed. Deletion of keys MAY be accomplished by sending the G-IKEv2 769 Delete Payload [RFC7296], section 3.11 as part of the GSA_REKEY 770 Exchange as shown below. 772 Members (Responder) GCKS (Initiator) 773 -------------------- ------------------ 774 <-- HDR, SK { 775 [GSA ], [KD ], [D, ] AUTH } 777 The GSA MAY specify the remaining active time of the remaining policy 778 by using the DTD attribute in the GSA GAP. If a GCKS has no further 779 SAs to send to group members, the GSA and KD payloads MUST be omitted 780 from the message. There may be circumstances where the GCKS may want 781 to start over with a clean slate. If the administrator is no longer 782 confident in the integrity of the group, the GCKS can signal deletion 783 of all the policies of a particular TEK protocol by sending a TEK 784 with a SPI value equal to zero in the delete payload. For example, 785 if the GCKS wishes to remove all the KEKs and all the TEKs in the 786 group, the GCKS SHOULD send a Delete payload with a SPI of zero and a 787 protocol_id of a TEK protocol_id value defined in Section 4.6, 788 followed by another Delete payload with a SPI of zero and protocol_id 789 of zero, indicating that the KEK SA should be deleted. 791 3.3. Counter-based modes of operation 793 Several new counter-based modes of operation have been specified for 794 ESP (e.g., AES-CTR [RFC3686], AES-GCM [RFC4106], AES-CCM [RFC4309], 795 AES-GMAC [RFC4543]) and AH (e.g., AES-GMAC [RFC4543]). These 796 counter-based modes require that no two senders in the group ever 797 send a packet with the same Initialization Vector (IV) using the same 798 cipher key and mode. This requirement is met in G-IKEv2 when the 799 following requirements are met: 801 o The GCKS distributes a unique key for each Data-Security SA. 803 o The GCKS uses the method described in [RFC6054], which assigns each 804 sender a portion of the IV space by provisioning each sender with one 805 or more unique SID values. 807 When at least one Data-Security SA included in the group policy 808 includes a counter-based mode of operation, the GCKS automatically 809 allocates and distributes one SID to each group member acting in the 810 role of sender on the Data-Security SA. The SID value is used 811 exclusively by the group member to which it was allocated. The group 812 member uses the same SID for each Data-Security SA specifying the use 813 of a counter-based mode of operation. A GCKS MUST distribute unique 814 keys for each Data-Security SA including a counter-based mode of 815 operation in order to maintain unique key and nonce usage. 817 During registration, the group member can choose to request one or 818 more SID values. Requesting a value of 1 is not necessary since the 819 GCKS will automatically allocate exactly one to the group member. A 820 group member MUST request as many SIDs matching the number of 821 encryption modules in which it will be installing the TEKs in the 822 outbound direction. Alternatively, a group member MAY request more 823 than one SID and use them serially. This could be useful when it is 824 anticipated that the group member will exhaust their range of Data- 825 Security SA nonces using a single SID too quickly (e.g., before the 826 time-based policy in the TEK expires). 828 When the group policy includes a counter-based mode of operation, a 829 GCKS SHOULD use the following method to allocate SID values, which 830 ensures that each SID will be allocated to just one group member. 832 1. A GCKS maintains an SID-counter, which records the SIDs that have 833 been allocated. SIDs are allocated sequentially, with zero as the 834 first allocated SID. 836 2. Each time an SID is allocated, the current value of the counter 837 is saved and allocated to the group member. The SID-counter is then 838 incremented in preparation for the next allocation. 840 3. When the GCKS specifies a counter-based mode of operation in the 841 Data Security SA a group member may request a count of SIDs during 842 registration in a Notify payload information of type SEND_ID_REQUEST. 843 When the GCKS receives this request, it increments the SID-counter 844 once for each requested SID, and distributes each SID value to the 845 group member. 847 4. A GCKS allocates new SID values for each GSA_REGISTRATION 848 exchange originated by a sender, regardless of whether a group member 849 had previously contacted the GCKS. In this way, the GCKS is not 850 required to maintaining a record of which SID values it had 851 previously allocated to each group member. More importantly, since 852 the GCKS cannot reliably detect whether the group member had sent 853 data on the current group Data-Security SAs it does not know what 854 Data-Security counter-mode nonce values that a group member has used. 855 By distributing new SID values, the key server ensures that each time 856 a conforming group member installs a Data-Security SA it will use a 857 unique set of counter-based mode nonces. 859 5. When the SID-counter maintained by the GCKS reaches its final SID 860 value, no more SID values can be distributed. Before distributing 861 any new SID values, the GCKS MUST delete the Data-Security SAs for 862 the group, followed by creation of new Data-Security SAs, and 863 resetting the SID-counter to its initial value. 865 6. The GCKS SHOULD send a GSA_REKEY message deleting all Data- 866 Security SAs and the Rekey SA for the group. This will result in the 867 group members initiating a new GSA_REGISTRATION exchange, in which 868 they will receive both new SID values and new Data-Security SAs. The 869 new SID values can safely be used because they are only used with the 870 new Data-Security SAs. Note that deletion of the Rekey SA is 871 necessary to ensure that group members receiving a GSA_REKEY exchange 872 before the re-register do not inadvertently use their old SIDs with 873 the new Data-Security SAs. Using the method above, at no time can 874 two group members use the same IV values with the same Data-Security 875 SA key. 877 4. Header and Payload Formats 879 Refer to IKEv2 [RFC7296] for existing payloads. Some payloads used 880 in G-IKEv2 exchanges are not aligned to 4-octet boundaries, which is 881 also the case for some IKEv2 payloads (see Section 3.2 of [RFC7296]). 883 4.1. The G-IKEv2 Header 885 G-IKEv2 uses the same IKE header format as specified in RFC 7296 886 section 3.1. 888 Several new payload formats are required in the group security 889 exchanges. 891 Next Payload Type Value 892 ----------------- ----- 893 Group Identification (IDg) 50 894 Group Security Association (GSA) 51 895 Key Download (KD) 52 897 New exchange types GSA_AUTH, GSA_REGISTRATION and GSA_REKEY are added 898 to the IKEv2 [RFC7296] protocol. 900 Exchange Type Value 901 -------------- ----- 902 GSA_AUTH 39 903 GSA_REGISTRATION 40 904 GSA_REKEY 41 905 GSA_INBAND_REKEY TBD 907 Major Version is 2 and Minor Version is 0 as in IKEv2 [RFC7296]. IKE 908 SA Initiator's SPI, IKE SA Responder's SPI, Flags, Message ID, and 909 Length are as specified in [RFC7296]. 911 4.2. Group Identification (IDg) Payload 913 The IDg Payload allows the group member to indicate which group it 914 wants to join. The payload is constructed by using the IKEv2 915 Identification Payload (section 3.5 of [RFC7296]). ID type ID_KEY_ID 916 MUST be supported. ID types ID_IPV4_ADDR, ID_FQDN, ID_RFC822_ADDR, 917 ID_IPV6_ADDR SHOULD be supported. ID types ID_DER_ASN1_DN and 918 ID_DER_ASN1_GN are not expected to be used. 920 4.3. Security Association - GM Supported Transforms (SAg) 922 The SAg payload declares which Transforms a GM is willing to accept. 923 The payload is constructed using the format of the IKEv2 Security 924 Association payload (section 3.3 of [RFC7296]). The Payload Type for 925 SAg is identical to the SA Payload Type. 927 4.4. Group Security Association Payload 929 The Group Security Association payload is used by the GCKS to assert 930 security attributes for both Rekey and Data-security SAs. 932 0 1 2 3 933 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 934 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 935 | Next Payload |C| RESERVED | Payload Length | 936 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 938 The Security Association Payload fields are defined as follows: 940 o Next Payload (1 octet) -- Identifies the next payload type for the 941 G-IKEv2 registration or the G-IKEv2 rekey message. 943 o Critical (1 bit) -- Set according to [RFC7296]. 945 o RESERVED (7 bits) -- Must be zero. 947 o Payload Length (2 octets) -- Is the octet length of the current 948 payload including the generic header and all TEK and KEK policies. 950 4.4.1. GSA Policy 952 Following the GSA generic payload header are GSA policies for group 953 rekeying (KEK), data traffic SAs (TEK) and/or Group Associated Policy 954 (GAP). There may be zero or one GSA KEK policy, zero or one GAP 955 policies, and zero or more GSA TEK policies, where either one GSA KEK 956 or GSA TEK payload MUST be present. 958 This latitude allows various group policies to be accommodated. For 959 example if the group policy does not require the use of a Rekey SA, 960 the GCKS would not need to send a GSA KEK attribute to the group 961 member since all SA updates would be performed using the Registration 962 SA. Alternatively, group policy might use a Rekey SA but choose to 963 download a KEK to the group member only as part of the Registration 964 SA. Therefore, the GSA KEK policy would not be necessary as part of 965 the GSA_REKEY message. 967 Specifying multiple GSA TEKs allows multiple related data streams 968 (e.g., video, audio, and text) to be associated with a session, but 969 each protected with an individual security association policy. 971 A GAP payload allows for the distribution of group-wise policy, such 972 as instructions for when to activate and de-activate SAs. 974 Policies following the GSA payload use the following common header. 976 0 1 2 3 977 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 979 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 980 | Type | RESERVED | Length | 981 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 983 Type is defined as follows: 985 ID Class Value 986 -------- ----- 987 RESERVED 0 988 KEK 1 989 GAP 2 990 TEK 3 991 Expert Review 4-127 992 Private Use 128-255 994 4.5. KEK Policy 996 The GSA KEK policy contains security attributes for the KEK method 997 for a group and parameters specific to the G-IKEv2 registration 998 operation. The source and destination traffic selectors describe the 999 network identities used for the rekey messages. 1001 0 1 2 3 1002 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1003 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1004 | Type = 1 ! RESERVED ! Length | 1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1006 | | 1007 ~ SPI ~ 1008 | | 1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1010 | | 1011 ~ ~ 1012 | | 1013 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1014 | | 1015 ~ ~ 1016 | | 1017 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1018 | | 1019 ~ ~ 1020 | | 1021 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1022 ~ KEK Attributes ~ 1023 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1025 The GSA KEK Payload fields are defined as follows: 1027 o Type = 1 (1 octet) -- Identifies the GSA payload type as KEK in 1028 the G-IKEv2 registration or the G-IKEv2 rekey message. 1030 o RESERVED (1 octet) -- Must be zero. 1032 o Length (2 octets) -- Length of this structure including KEK 1033 attributes. 1035 o SPI (16 octets) -- Security Parameter Index for the rekey message. 1036 The SPI must be the IKEv2 Header SPI pair where the first 8 octets 1037 become the "Initiator's SPI" field in the G-IKEv2 rekey message 1038 IKEv2 HDR, and the second 8 octets become the "Responder's SPI" in 1039 the same HDR. As described above, these SPIs are assigned by the 1040 GCKS. 1042 o Source & Destination Traffic Selectors - Substructures describing 1043 the source and destination of the network identities. These 1044 identities refer to the source and destination of the next KEK 1045 rekey SA. Defined format and values are specified by IKEv2 1046 [RFC7296], section 3.13.1. 1048 o Transform Substructure List -- A list of Transform Substructures 1049 specifies the transform information. The format is defined in 1050 IKEv2 [RFC7296], section 3.3.2, and values are described in the 1051 IKEv2 registries [IKEV2-IANA]. Valid Transform Types are ENCR, 1052 INTEG. The Last Substruc value in each Transform Substructure 1053 will be set to 3 except for the last one in the list, which is set 1054 to 0. 1056 o KEK Attributes -- Contains KEK policy attributes associated with 1057 the group. The following sections describe the possible 1058 attributes. Any or all attributes may be optional, depending on 1059 the group policy. 1061 4.5.1. KEK Attributes 1063 The following attributes may be present in a GSA KEK policy. The 1064 attributes must follow the format defined in the IKEv2 [RFC7296] 1065 section 3.3.5. In the table, attributes that are defined as TV are 1066 marked as Basic (B); attributes that are defined as TLV are marked as 1067 Variable (V). The terms Reserved, Unassigned, and Private Use are to 1068 be applied as defined in [RFC8126]. The registration procedure is 1069 Expert Review. 1071 ID Class Value Type 1072 -------- ----- ---- 1073 Reserved 0 1074 KEK_MANAGEMENT_ALGORITHM 1 B 1075 Reserved 2 1076 Reserved 3 1077 KEK_KEY_LIFETIME 4 V 1078 Reserved 5 1079 KEK_AUTH_METHOD 6 B 1080 KEK_AUTH_HASH 7 B 1081 KEK_MESSAGE_ID 8 V 1082 Unassigned 9-16383 1083 Private Use 16384-32767 1085 The following attributes may only be included in a G-IKEv2 1086 registration message: KEK_MANAGEMENT_ALGORITHM. 1088 Minimum attributes that must be sent as part of an GSA KEK: 1089 KEK_ENCR_ALGORITHM, KEK_KEY_LENGTH (if the cipher definition includes 1090 a variable length key), KEK_MESSAGE_ID, KEK_KEY_LIFETIME, 1091 KEK_INTEGRITY_ALGORITHM, KEK_AUTH_METHOD, and KEK_AUTH_HASH (except 1092 for DSA based algorithms). 1094 4.5.1.1. KEK_MANAGEMENT_ALGORITHM 1096 The KEK_MANAGEMENT_ALGORITHM attribute specifies the group KEK 1097 management algorithm used to provide forward or backward access 1098 control (i.e., used to exclude group members). Defined values are 1099 specified in the following table. The terms Reserved, Unassigned, 1100 and Private Use are to be applied as defined in [RFC8126]. The 1101 registration procedure is Expert Review. 1103 KEK Management Type Value 1104 ------------------- ----- 1105 Reserved 0 1106 LKH 1 1107 Unassigned 2-16383 1108 Private Use 16384-32767 1110 4.5.1.2. KEK_ENCR_ALGORITHM 1112 The KEK_ENCR_ALGORITHM attribute specifies the encryption algorithm 1113 used with the KEK. This value is a value from the IKEv2 Transform 1114 Type 1 - Encryption Algorithm Transform IDs registry[IKEV2-IANA]. If 1115 a KEK_MANAGEMENT_ALGORITHM is defined which defines multiple keys 1116 (e.g., LKH), and if the management algorithm does not specify the 1117 algorithm for those keys, then the algorithm defined by the 1118 KEK_ENCR_ALGORITHM attribute MUST be used for all keys which are 1119 included as part of this KEK management. 1121 4.5.1.3. KEK_KEY_LENGTH 1123 The KEK_KEY_LENGTH attribute specifies the KEK Algorithm key length 1124 (in bits). 1126 The Group Controller/Key Server (GCKS) adds the KEK_KEY_LENGTH 1127 attribute to the GSA payload when distributing KEK policy to group 1128 members. The group member verifies whether or not it has the 1129 capability of using a cipher key of that size. If the cipher 1130 definition includes a fixed key length, the group member can make its 1131 decision solely using the KEK_ENCR_ALGORITHM attribute and does not 1132 need the KEK_KEY_LENGTH attribute. Sending the KEK_KEY_LENGTH 1133 attribute in the GSA payload is OPTIONAL if the KEK cipher has a 1134 fixed key length. 1136 4.5.1.4. KEK_KEY_LIFETIME 1138 The KEK_KEY_LIFETIME attribute specifies the maximum time for which 1139 the KEK is valid. The GCKS may refresh the KEK at any time before 1140 the end of the valid period. The value is a four (4) octet number 1141 defining a valid time period in seconds. 1143 4.5.1.5. KEK_INTEGRITY_ALGORITHM 1145 The KEK_INTEGRITY attribute specifies the integrity algorithm used to 1146 protect the rekey message. This integrity algorithm is a value from 1147 the IKEv2 Transform Type 3 - Integrity Algorithm Transform IDs 1148 registry [IKEV2-IANA]. 1150 4.5.1.6. KEK_AUTH_METHOD 1152 The KEK_AUTH_METHOD attribute specifies the method of authentication 1153 used. This value is from the IKEv2 Authentication Method registry 1154 [IKEV2-IANA]. 1156 4.5.1.7. KEK_AUTH_HASH 1158 The KEK_AUTH_HASH attribute specifies the hash algorithm used to 1159 generate the AUTH key to authenticate GSA_REKEY messages. Hash 1160 algorithms are defined in IANA registry IKEv2 Hash Algorithms 1161 [IKEV2-IANA]. This attribute can be used by a group member to 1162 determine in advance if it supports the algorithm used in the rekey 1163 message. 1165 4.5.1.8. KEK_MESSAGE_ID 1167 The KEK_MESSAGE_ID attribute defines the initial Message ID to be 1168 used by the GCKS in the GSA_REKEY messages. The Message ID is a 4 1169 octet unsigned integer in network byte order. 1171 4.6. GSA TEK Policy 1173 The GSA TEK policy contains security attributes for a single TEK 1174 associated with a group. 1176 0 1 2 3 1177 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1179 | Type = 3 | RESERVED | Length | 1180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1181 | Protocol-ID | TEK Protocol-Specific Payload | 1182 +-+-+-+-+-+-+-+-+ ~ 1183 ~ | 1184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1186 The GSA TEK Payload fields are defined as follows: 1188 o Type = 3 (1 octet) -- Identifies the GSA payload type as TEK in 1189 the G-IKEv2 registration or the G-IKEv2 rekey message. 1191 o RESERVED (1 octet) -- Must be zero. 1193 o Length (2 octets) -- Length of this structure, including the TEK 1194 Protocol-Specific Payload. 1196 o Protocol-ID (1 octet) -- Value specifying the Security Protocol. 1197 The following table defines values for the Security Protocol. 1198 Support for the GSA_PROTO_IPSEC_AH GSA TEK is OPTIONAL. The terms 1199 Reserved, Unassigned, and Private Use are to be applied as defined 1200 in [RFC8126]. The registration procedure is Expert Review. 1202 Protocol ID Value 1203 ----------- ----- 1204 Reserved 0 1205 GSA_PROTO_IPSEC_ESP 1 1206 GSA_PROTO_IPSEC_AH 2 1207 Unassigned 3-127 1208 Private Use 128-255 1210 o TEK Protocol-Specific Payload (variable) -- Payload which 1211 describes the attributes specific for the Protocol-ID. 1213 4.6.1. TEK ESP and AH Protocol-Specific Policy 1215 The TEK Protocol-Specific policy contains two traffic selectors one 1216 for the source and one for the destination of the protected traffic, 1217 SPI, Transforms, and Attributes. 1219 The TEK Protocol-Specific policy for ESP and AH is as follows: 1221 0 1 2 3 1222 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1224 | SPI | 1225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1226 | | 1227 ~ ~ 1228 | | 1229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1230 | | 1231 ~ ~ 1232 | | 1233 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1234 | | 1235 ~ ~ 1236 | | 1237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1238 ~ TEK Attributes ~ 1239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1241 The GSA TEK Policy fields are defined as follows: 1243 o SPI (4 octets) -- Security Parameter Index. 1245 o Source & Destination Traffic Selectors - The traffic selectors 1246 describe the source and the destination of the protected traffic. 1247 The format and values are defined in IKEv2 [RFC7296], section 1248 3.13.1. 1250 o Transform Substructure List -- A list of Transform Substructures 1251 specifies the transform information. The format is defined in 1252 IKEv2 [RFC7296], section 3.3.2, and values are described in the 1253 IKEv2 registries [IKEV2-IANA]. Valid Transform Types for ESP are 1254 ENCR, INTEG, and ESN. Valid Transform Types for AH are INTEG and 1255 ESN. The Last Substruc value in each Transform Substructure will 1256 be set to 3 except for the last one in the list, which is set to 1257 0. A Transform Substructure with attributes (e.g, the ENCR Key 1258 Length), they are included within the Transform Substructure as 1259 usual. 1261 o TEK Attributes -- Contains the TEK policy attributes associated 1262 with the group, in the format defined in Section 3.3.5 of 1263 [RFC7296]. All attributes are optional, depending on the group 1264 policy. 1266 Attribute Types are as follows. The terms Reserved, Unassigned, and 1267 Private Use are to be applied as defined in [RFC8126]. The 1268 registration procedure is Expert Review. 1270 ID Class Value Type 1271 -------- ----- ---- 1272 Reserved 0 1273 TEK_KEY_LIFETIME 1 V 1274 TEK_MODE 2 B 1275 Unassigned 3-16383 1276 Private Use 16384-32767 1278 It is NOT RECOMMENDED that the GCKS distribute both ESP and AH 1279 Protocol-Specific Policies for the same set of Traffic Selectors. 1281 4.6.1.1. TEK_KEY_LIFETIME 1283 The TEK_KEY_LIFETIME attribute specifies the maximum time for which 1284 the TEK is valid. When the TEK expires, the AH or ESP security 1285 association and all keys downloaded under the security association 1286 are discarded. The GCKS may refresh the TEK at any time before the 1287 end of the valid period. 1289 The value is a four (4) octet number defining a valid time period in 1290 seconds. If unspecified the default value of 28800 seconds (8 hours) 1291 shall be assumed. 1293 4.6.1.2. TEK_MODE 1295 The value of 0 is used for tunnel mode and 1 for transport mode. In 1296 the absence of this attribute tunnel mode will be used. 1298 4.7. GSA Group Associated Policy 1300 Group specific policy that does not belong to rekey policy (GSA KEK) 1301 or traffic encryption policy (GSA TEK) can be distributed to all 1302 group member using GSA GAP (Group Associated Policy). 1304 The GSA GAP payload is defined as follows: 1306 0 1 2 3 1307 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1309 | Type = 2 ! RESERVED ! Length | 1310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1311 ~ Group Associated Policy Attributes ~ 1312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1314 The GSA GAP payload fields are defined as follows: 1316 o Type = 2 (1 octet) -- Identifies the GSA payload type as GAP in 1317 the G-IKEv2 registration or the G-IKEv2 rekey message. 1319 o RESERVED (1 octet) -- Must be zero. 1321 o Length (2 octets) -- Length of this structure, including the GSA 1322 GAP header and Attributes. 1324 o Group Associated Policy Attributes (variable) -- Contains 1325 attributes following the format defined in Section 3.3.5 of 1326 [RFC7296]. 1328 Attribute Types are as follows. The terms Reserved, Unassigned, and 1329 Private Use are to be applied as defined in [RFC8126]. The 1330 registration procedure is Expert Review. 1332 Attribute Type Value Type 1333 -------------- ----- ---- 1334 Reserved 0 1335 ACTIVATION_TIME_DELAY 1 B 1336 DEACTIVATION_TIME_DELAY 2 B 1337 Unassigned 3-16383 1338 Private Use 16384-32767 1340 4.7.1. ACTIVATION_TIME_DELAY/DEACTIVATION_TIME_DELAY 1342 Section 4.2.1 of RFC 5374 specifies a key rollover method that 1343 requires two values be provided to group members. The 1344 ACTIVATION_TIME_DELAY attribute allows a GCKS to set the Activation 1345 Time Delay (ATD) for SAs generated from TEKs. The ATD defines how 1346 long after receiving new SAs that they are to be activated by the GM. 1347 The ATD value is in seconds. 1349 The DEACTIVATION_TIME_DELAY allows the GCKS to set the Deactivation 1350 Time Delay (DTD) for previously distributed SAs. The DTD defines how 1351 long after receiving new SAs it should deactivate SAs that are 1352 destroyed by the rekey event. The value is in seconds. 1354 The values of ATD and DTD are independent. However, the DTD value 1355 should be larger, which allows new SAs to be activated before older 1356 SAs are deactivated. Such a policy ensures that protected group 1357 traffic will always flow without interruption. 1359 4.8. Key Download Payload 1361 The Key Download Payload contains the group keys for the group 1362 specified in the GSA Payload. These key download payloads can have 1363 several security attributes applied to them based upon the security 1364 policy of the group as defined by the associated GSA Payload. 1366 0 1 2 3 1367 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1369 | Next Payload |C| RESERVED | Length | 1370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1371 | Number of Key Packets | RESERVED2 | 1372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-! 1373 ~ Key Packets ~ 1374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1376 The Key Download Payload fields are defined as follows: 1378 o Next Payload (1 octet) -- Identifier for the payload type of the 1379 next payload in the message. If the current payload is the last 1380 in the message, then this field will be zero. 1382 o Critical (1 bit) -- Set according to [RFC7296]. 1384 o RESERVED (7 bits) -- Unused, set to zero. 1386 o Payload Length (2 octets) -- Length in octets of the current 1387 payload, including the generic payload header. 1389 o Number of Key Packets (2 octets) -- Contains the total number of 1390 Key Packets passed in this data block. 1392 o Key Packets (variable) -- Contains Key Packets. Several types of 1393 key packets are defined. Each Key Packet has the following 1394 format. 1396 0 1 2 3 1397 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1399 | KD Type | RESERVED | KD Length | 1400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1401 | SPI Size | SPI (variable) ~ 1402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1403 ~ Key Packet Attributes ~ 1404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1406 o Key Download (KD) Type (1 octet) -- Identifier for the Key Data 1407 field of this Key Packet. In the following table the terms 1408 Reserved, Unassigned, and Private Use are to be applied as defined 1409 in [RFC8126]. The registration procedure is Expert Review. 1411 Key Download Type Value 1412 ----------------- ----- 1413 Reserved 0 1414 TEK 1 1415 KEK 2 1416 LKH 3 1417 SID 4 1418 Unassigned 5-127 1419 Private Use 128-255 1421 o RESERVED (1 octet) -- Unused, set to zero. 1423 o Key Download Length (2 octets) -- Length in octets of the Key 1424 Packet data, including the Key Packet header. 1426 o SPI Size (1 octet) -- Value specifying the length in octets of the 1427 SPI as defined by the Protocol-Id. 1429 o SPI (variable length) -- Security Parameter Index which matches a 1430 SPI previously sent in an GSA KEK or GSA TEK Payload. 1432 o Key Packet Attributes (variable length) -- Contains Key 1433 information. The format of this field is specific to the value of 1434 the KD Type field. The following sections describe the format of 1435 each KD Type. 1437 4.8.1. TEK Download Type 1439 The following attributes may be present in a TEK Download Type. 1440 Exactly one attribute matching each type sent in the GSA TEK payload 1441 MUST be present. The attributes must follow the format defined in 1442 IKEv2 (Section 3.3.5 of [RFC7296]). In the table, attributes defined 1443 as TV are marked as Basic (B); attributes defined as TLV are marked 1444 as Variable (V). The terms Reserved, Unassigned, and Private Use are 1445 to be applied as defined in [RFC8126]. The registration procedure is 1446 Expert Review. 1448 TEK Class Value Type 1449 --------- ----- ---- 1450 Reserved 0 1451 TEK_ALGORITHM_KEY 1 V 1452 TEK_INTEGRITY_KEY 2 V 1453 Unassigned 3-16383 1454 Private Use 16384-32767 1456 It is possible that the GCKS will send no TEK key packets in a 1457 Registration KD payload (as well as no corresponding GSA TEK payloads 1458 in the GSA payload), after which the TEK payloads will be sent in a 1459 rekey message. At least one TEK MUST be included in each Rekey KD 1460 payload. 1462 4.8.1.1. TEK_ALGORITHM_KEY 1464 The TEK_ALGORITHM_KEY class contains encryption keying material for 1465 the corresponding SPI. This keying material will be used with the 1466 encryption algorithm specified in the GSA TEK payload, and according 1467 to the IPsec transform describing that encryption algorithm. The 1468 keying material is treated equivalent to IKEv2 KEYMAT derived for 1469 that IPsec transform. If the encryption algorithm requires a nonce 1470 (e.g., AES-GCM), the nonce is chosen as shown in Section 3.2. 1472 4.8.1.2. TEK_INTEGRITY_KEY 1474 The TEK_INTEGRITY_KEY class declares that the integrity key for the 1475 corresponding SPI is contained in the Key Packet Attribute. Readers 1476 should refer to [IKEV2-IANA] for the latest values. 1478 4.8.2. KEK Download Type 1480 The following attributes may be present in a KEK Download Type. 1481 Exactly one attribute matching each type sent in the GSA KEK payload 1482 MUST be present. The attributes must follow the format defined in 1483 IKEv2 (Section 3.3.5 of [RFC7296]). In the table, attributes defined 1484 as TV are marked as Basic (B); attributes defined as TLV are marked 1485 as Variable (V). The terms Reserved, Unassigned, and Private Use are 1486 to be applied as defined in [RFC8126]. The registration procedure is 1487 Expert Review. 1489 KEK Class Value Type 1490 --------- ----- ---- 1491 Reserved 0 1492 KEK_ENCR_KEY 1 V 1493 KEK_INTEGRITY_KEY 2 V 1494 KEK_AUTH_KEY 3 V 1495 Unassigned 4-16383 1496 Private Use 16384-32767 1498 If the KEK Key Packet is included, there MUST be only one present in 1499 the KD payload. 1501 4.8.2.1. KEK_ENCR_KEY 1503 The KEK_ENCR_KEY class declares that the encryption key for the 1504 corresponding SPI is contained in the Key Packet Attribute. The 1505 encryption algorithm that will use this key was specified in the GSA 1506 KEK payload. 1508 If the mode of operation for the algorithm requires an Initialization 1509 Vector (IV), an explicit IV MUST be included in the KEK_ENCR_KEY 1510 before the actual key. 1512 4.8.2.2. KEK_INTEGRITY_KEY 1514 The KEK_INTEGRITY_KEY class declares the integrity key for this SPI 1515 is contained in the Key Packet Attribute. The integrity algorithm 1516 that will use this key was specified in the GSA KEK payload. 1518 4.8.2.3. KEK_AUTH_KEY 1520 The KEK_AUTH_KEY class declares that the authentication key for this 1521 SPI is contained in the Key Packet Attribute. The signature 1522 algorithm that will use this key was specified in the GSA KEK 1523 payload. An RSA public key format is defined in RFC 3447, 1524 Section A.1.1. DSS public key format is defined in RFC 3279 1525 Section 2.3.2. For ECDSA Public keys, use format described in RFC 1526 5480 Section 2.2. 1528 4.8.3. LKH Download Type 1530 The LKH key packet is comprised of attributes representing different 1531 leaves in the LKH key tree. 1533 The following attributes are used to pass an LKH KEK array in the KD 1534 payload. The attributes must follow the format defined in IKEv2 1535 (Section 3.3.5 of [RFC7296]). In the table, attributes defined as TV 1536 are marked as Basic (B); attributes defined as TLV are marked as 1537 Variable (V). The terms Reserved, Unassigned, and Private Use are to 1538 be applied as defined in [RFC8126]. The registration procedure is 1539 Expert Review. 1541 LKH Download Class Value Type 1542 ------------------ ----- ---- 1543 Reserved 0 1544 LKH_DOWNLOAD_ARRAY 1 V 1545 LKH_UPDATE_ARRAY 2 V 1546 Unassigned 3-16383 1547 Private Use 16384-32767 1549 If an LKH key packet is included in the KD payload, there MUST be 1550 only one present. 1552 4.8.3.1. LKH_DOWNLOAD_ARRAY 1554 The LKH_DOWNLOAD_ARRAY class is used to download a set of LKH keys to 1555 a group member. It MUST NOT be included in a IKEv2 rekey message KD 1556 payload if the IKEv2 rekey is sent to more than one group member. If 1557 an LKH_DOWNLOAD_ARRAY attribute is included in a KD payload, there 1558 MUST be only one present. 1560 This attribute consists of a header block, followed by one or more 1561 LKH keys. 1563 0 1 2 3 1564 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1565 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1566 | # of LKH Keys | RESERVED | 1567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1568 ~ LKH Keys ~ 1569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1571 The KEK_LKH attribute fields are defined as follows: 1573 o Number of LKH Keys (2 octets) -- This value is the number of 1574 distinct LKH keys in this sequence. 1576 o RESERVED (1 octet) -- Unused, set to zero. 1578 Each LKH Key is defined as follows: 1580 0 1 2 3 1581 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1583 ! LKH ID | Encr Alg | 1584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1585 | Key Handle | 1586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1587 ~ Key Data ~ 1588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1590 o LKH ID (2 octets) -- This is the position of this key in the 1591 binary tree structure used by LKH. 1593 o Encr Alg (2 octets) -- This is the encryption algorithm for which 1594 this key data is to be used. This value is specified in 1595 Section 4.5.1.2. 1597 o RESERVED (1 octet) -- Unused, set to zero. 1599 o Key Handle (4 octets) -- This is a randomly generated value to 1600 uniquely identify a key within an LKH ID. 1602 o Key Data (variable length) -- This is the actual encryption key 1603 data, which is dependent on the Encr Alg algorithm for its format. 1604 If the mode of operation for the algorithm requires an 1605 Initialization Vector (IV), an explicit IV MUST be included in the 1606 Key Data field before the actual key. 1608 The first LKH Key structure in an LKH_DOWNLOAD_ARRAY attribute 1609 contains the Leaf identifier and key for the group member. The rest 1610 of the LKH Key structures contain keys along the path of the key tree 1611 in the order starting from the leaf, culminating in the group KEK. 1613 4.8.3.2. LKH_UPDATE_ARRAY 1615 The LKH_UPDATE_ARRAY class is used to update the LKH keys for a 1616 group. It is most likely to be included in a G-IKEv2 rekey message 1617 KD payload to rekey the entire group. This attribute consists of a 1618 header block, followed by one or more LKH keys, as defined in 1619 Section 4.8.3.1. 1621 There may be any number of LKH_UPDATE_ARRAY attributes included in a 1622 KD payload. 1624 0 1 2 3 1625 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1626 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1627 | # of LKH Keys | LKH ID | 1628 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1629 | Key Handle | 1630 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1631 ~ LKH Keys ~ 1632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1634 o Number of LKH Keys (2 octets) -- This value is the number of 1635 distinct LKH keys in this sequence. 1637 o LKH ID (2 octets) -- This is the node identifier associated with 1638 the key used to encrypt the first LKH Key. 1640 o Key Handle (4 octets) -- This is the value that uniquely 1641 identifies the key within the LKH ID which was used to encrypt the 1642 first LKH key. 1644 The LKH Keys are as defined in Section 4.8.3.1. The LKH Key 1645 structures contain keys along the path of the key tree in the order 1646 from the LKH ID found in the LKH_UPDATE_ARRAY header, culminating in 1647 the group KEK. The Key Data field of each LKH Key is encrypted with 1648 the LKH key preceding it in the LKH_UPDATE_ARRAY attribute. The 1649 first LKH Key is encrypted under the key defined by the LKH ID and 1650 Key Handle found in the LKH_UPDATE_ARRAY header. 1652 4.8.4. SID Download Type 1654 The SID attribute is used to download one or more Sender-ID (SID) 1655 values for the exclusive use of a group member. The terms Reserved, 1656 Unassigned, and Private Use are to be applied as defined in 1657 [RFC8126]. The registration procedure is Expert Review. 1659 SID Download Class Value Type 1660 ------------------ ----- ---- 1661 Reserved 0 1662 NUMBER_OF_SID_BITS 1 B 1663 SID_VALUE 2 V 1664 Unassigned 3-16383 1665 Private Use 16384-32767 1667 Because a SID value is intended for a single group member, the SID 1668 Download type MUST NOT be distributed in a GSA_REKEY message 1669 distributed to multiple group members. 1671 4.8.4.1. NUMBER_OF_SID_BITS 1673 The NUMBER_OF_SID_BITS class declares how many bits of the cipher 1674 nonce in which to represent an SID value. This value is applied to 1675 each SID value distributed in the SID Download. 1677 4.8.4.2. SID_VALUE 1679 The SID_VALUE class declares a single SID value for the exclusive use 1680 of this group member. Multiple SID_VALUE attributes MAY be included 1681 in a SID Download. 1683 4.8.4.3. GM Semantics 1685 The SID_VALUE attribute value distributed to the group member MUST be 1686 used by that group member as the SID field portion of the IV for all 1687 Data-Security SAs including a counter-based mode of operation 1688 distributed by the GCKS as a part of this group. When the Sender- 1689 Specific IV (SSIV) field for any Data-Security SA is exhausted, the 1690 group member MUST NOT act as a sender on that SA using its active 1691 SID. The group member SHOULD re-register, at which time the GCKS 1692 will issue a new SID to the group member, along with either the same 1693 Data-Security SAs or replacement ones. The new SID replaces the 1694 existing SID used by this group member, and also resets the SSIV 1695 value to its starting value. A group member MAY re-register prior to 1696 the actual exhaustion of the SSIV field to avoid dropping data 1697 packets due to the exhaustion of available SSIV values combined with 1698 a particular SID value. 1700 A group member MUST ignore an SID Download Type KD payload present in 1701 a GSA-REKEY message, otherwise more than one GM may end up using the 1702 same SID. 1704 4.8.4.4. GCKS Semantics 1706 If any KD payload includes keying material that is associated with a 1707 counter-mode of operation, an SID Download Type KD payload containing 1708 at least one SID_VALUE attribute MUST be included. The GCKS MUST NOT 1709 send the SID Download Type KD payload as part of a GSA_REKEY message, 1710 because distributing the same sender-specific policy to more than one 1711 group member will reduce the security of the group. 1713 4.9. Delete Payload 1715 There are occasions when the GCKS may want to signal to group members 1716 to delete policy at the end of a broadcast, or if policy has changed. 1717 Deletion of keys MAY be accomplished by sending an IKEv2 Delete 1718 Payload, section 3.11 of [RFC7296] as part of the GSA_AUTH or 1719 GSA_REKEY Exchange. One or more Delete payloads MAY be placed 1720 following the HDR payload in the GSA_AUTH or GSA_REKEY Exchange. 1722 The Protocol ID MUST be 41 for GSA_REKEY Exchange, 2 for AH or 3 for 1723 ESP. Note that only one protocol id value can be defined in a Delete 1724 payload. If a TEK and a KEK SA for GSA_REKEY Exchange must be 1725 deleted, they must be sent in different Delete payloads. Similarly, 1726 if a TEK specifying ESP and a TEK specifying AH need to be deleted, 1727 they must be sent in different Delete payloads. 1729 There may be circumstances where the GCKS may want to reset the 1730 policy and keying material for the group. The GCKS can signal 1731 deletion of all policy of a particular TEK by sending a TEK with a 1732 SPI value equal to zero in the delete payload. In the event that the 1733 administrator is no longer confident in the integrity of the group 1734 they may wish to remove all KEK and all the TEKs in the group. This 1735 is done by having the GCKS send a delete payload with a SPI of zero 1736 and a Protocol-ID of AH or ESP to delete all TEKs, followed by 1737 another delete payload with a SPI value of zero and Protocol-ID of 1738 KEK SA to delete the KEK SA. 1740 4.10. Notify Payload 1742 G-IKEv2 uses the same Notify payload as specified in [RFC7296], 1743 section 3.10. 1745 There are additional Notify Message types introduced by G-IKEv2 to 1746 communicate error conditions and status. 1748 NOTIFY messages - error types Value 1749 ------------------------------------------------------------------- 1750 INVALID_GROUP_ID - 45 1751 Indicates the group id sent during the registration process is 1752 invalid. 1754 AUTHORIZATION_FAILED - 46 1755 Sent in the response to a GSA_AUTH message when authorization failed. 1757 NOTIFY messages - status types Value 1758 ------------------------------------------------------------------- 1759 SENDER_ID_REQUEST - 16429 1760 Sent in GSA_AUTH or GSA_REGISTRATION to request SIDs from the GCKS. 1761 The data includes a count of how many SID values it desires. 1763 4.11. Authentication Payload 1765 G-IKEv2 uses the same Authentication payload as specified in 1766 [RFC7296], section 3.8, to sign the rekey message. 1768 5. Security Considerations 1770 5.1. GSA registration and secure channel 1772 G-IKEv2 registration exchange uses IKEv2 IKE_SA_INIT protocols, 1773 inheriting all the security considerations documented in [RFC7296] 1774 section 5 Security Considerations, including authentication, 1775 confidentiality, protection against man-in-the-middle, protection 1776 against replay/reflection attacks, and denial of service protection. 1777 The GSA_AUTH and GSA_REGISTRATION exchanges also take advantage of 1778 those protections. In addition, G-IKEv2 brings in the capability to 1779 authorize a particular group member regardless of whether they have 1780 the IKEv2 credentials. 1782 5.2. GSA maintenance channel 1784 The GSA maintenance channel is cryptographically and integrity 1785 protected using the cryptographic algorithm and key negotiated in the 1786 GSA member registration exchanged. 1788 5.2.1. Authentication/Authorization 1790 Authentication is implicit, the public key of the identity is 1791 distributed during the registration, and the receiver of the rekey 1792 message uses that public key and identity to verify the message came 1793 from the authorized GCKS. 1795 5.2.2. Confidentiality 1797 Confidentiality is provided by distributing a confidentiality key as 1798 part of the GSA member registration exchange. 1800 5.2.3. Man-in-the-Middle Attack Protection 1802 GSA maintenance channel is integrity protected by using a digital 1803 signature. 1805 5.2.4. Replay/Reflection Attack Protection 1807 The GSA_REKEY message includes a monotonically increasing sequence 1808 number to protect against replay and reflection attacks. A group 1809 member will recognize a replayed message by comparing the Message ID 1810 number to that of the last received rekey message, any rekey message 1811 containing a Message ID number less than or equal to the last 1812 received value MUST be discarded. Implementations should keep a 1813 record of recently received GSA rekey messages for this comparison. 1815 6. IANA Considerations 1817 6.1. New registries 1819 A new set of registries should be created for G-IKEv2, on a new page 1820 titled Group Key Management using IKEv2 (G-IKEv2) Parameters. The 1821 following registries should be placed on that page. The terms 1822 Reserved, Expert Review and Private Use are to be applied as defined 1823 in [RFC8126]. 1825 GSA Policy Type Registry, see Section 4.4.1 1827 KEK Attributes Registry, see Section 4.5.1 1829 KEK Management Algorithm Registry, see Section 4.5.1.1 1831 GSA TEK Payload Protocol ID Type Registry, see Section 4.6 1833 TEK Attributes Registry, see Section 4.6 1835 Key Download Type Registry, see Section 4.8 1837 TEK Download Type Attributes Registry, see Section 4.8.1 1839 KEK Download Type Attributes Registry, see Section 4.8.2 1841 LKH Download Type Attributes Registry, see Section 4.8.3 1843 SID Download Type Attributes Registry, see Section 4.8.4 1845 6.2. New payload and exchange types added to the existing IKEv2 1846 registry 1848 The following new payloads and exchange types specified in this memo 1849 have already been allocated by IANA and require no further action, 1850 other than replacing the draft name with an RFC number. 1852 The present document describes new IKEv2 Next Payload types, see 1853 Section 4.1 1855 The present document describes new IKEv2 Exchanges types, see 1856 Section 4.1 1857 The present document describes new IKEv2 notification types, see 1858 Section 4.10 1860 7. Acknowledgements 1862 The authors thank Lakshminath Dondeti and Jing Xiang for first 1863 exploring the use of IKEv2 for group key management and providing the 1864 basis behind the protocol. Mike Sullenberger and Amjad Inamdar were 1865 instrumental in helping resolve many issues in several versions of 1866 the document. 1868 8. Contributors 1870 The following individuals made substantial contributions to early 1871 versions of this memo. 1873 Sheela Rowles 1874 Cisco Systems 1875 170 W. Tasman Drive 1876 San Jose, California 95134-1706 1877 USA 1879 Phone: +1-408-527-7677 1880 Email: sheela@cisco.com 1882 Aldous Yeung 1883 Cisco Systems 1884 170 W. Tasman Drive 1885 San Jose, California 95134-1706 1886 USA 1888 Phone: +1-408-853-2032 1889 Email: cyyeung@cisco.com 1891 Paulina Tran 1892 Cisco Systems 1893 170 W. Tasman Drive 1894 San Jose, California 95134-1706 1895 USA 1897 Phone: +1-408-526-8902 1898 Email: ptran@cisco.com 1899 Yoav Nir 1900 Dell EMC 1901 9 Andrei Sakharov St 1902 Haifa 3190500 1903 Israel 1905 Email: ynir.ietf@gmail.com 1907 9. References 1909 9.1. Normative References 1911 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1912 Requirement Levels", BCP 14, RFC 2119, 1913 DOI 10.17487/RFC2119, March 1997, 1914 . 1916 [RFC2627] Wallner, D., Harder, E., and R. Agee, "Key Management for 1917 Multicast: Issues and Architectures", RFC 2627, 1918 DOI 10.17487/RFC2627, June 1999, 1919 . 1921 [RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security 1922 Architecture", RFC 3740, DOI 10.17487/RFC3740, March 2004, 1923 . 1925 [RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm, 1926 "Multicast Security (MSEC) Group Key Management 1927 Architecture", RFC 4046, DOI 10.17487/RFC4046, April 2005, 1928 . 1930 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1931 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 1932 December 2005, . 1934 [RFC6054] McGrew, D. and B. Weis, "Using Counter Modes with 1935 Encapsulating Security Payload (ESP) and Authentication 1936 Header (AH) to Protect Group Traffic", RFC 6054, 1937 DOI 10.17487/RFC6054, November 2010, 1938 . 1940 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 1941 Kivinen, "Internet Key Exchange Protocol Version 2 1942 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 1943 2014, . 1945 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1946 Writing an IANA Considerations Section in RFCs", BCP 26, 1947 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1948 . 1950 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1951 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1952 May 2017, . 1954 9.2. Informative References 1956 [I-D.ietf-ipsecme-qr-ikev2] 1957 Fluhrer, S., McGrew, D., Kampanakis, P., and V. Smyslov, 1958 "Postquantum Preshared Keys for IKEv2", draft-ietf- 1959 ipsecme-qr-ikev2-04 (work in progress), July 2018. 1961 [IKEV2-IANA] 1962 IANA, "Internet Key Exchange Version 2 (IKEv2) 1963 Parameters", February 2016, 1964 . 1967 [NNL] Naor, D., Noal, M., and J. Lotspiech, "Revocation and 1968 Tracing Schemes for Stateless Receivers", Advances in 1969 Cryptology, Crypto '01, Springer-Verlag LNCS 2139, 2001, 1970 pp. 41-62, 2001, 1971 . 1973 [OFT] McGrew, D. and A. Sherman, "Key Establishment in Large 1974 Dynamic Groups Using One-Way Function Trees", Manuscript, 1975 submitted to IEEE Transactions on Software Engineering, 1976 1998, . 1979 [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange 1980 (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998, 1981 . 1983 [RFC3686] Housley, R., "Using Advanced Encryption Standard (AES) 1984 Counter Mode With IPsec Encapsulating Security Payload 1985 (ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004, 1986 . 1988 [RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode 1989 (GCM) in IPsec Encapsulating Security Payload (ESP)", 1990 RFC 4106, DOI 10.17487/RFC4106, June 2005, 1991 . 1993 [RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM 1994 Mode with IPsec Encapsulating Security Payload (ESP)", 1995 RFC 4309, DOI 10.17487/RFC4309, December 2005, 1996 . 1998 [RFC4543] McGrew, D. and J. Viega, "The Use of Galois Message 1999 Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543, 2000 DOI 10.17487/RFC4543, May 2006, 2001 . 2003 [RFC5723] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange 2004 Protocol Version 2 (IKEv2) Session Resumption", RFC 5723, 2005 DOI 10.17487/RFC5723, January 2010, 2006 . 2008 [RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain 2009 of Interpretation", RFC 6407, DOI 10.17487/RFC6407, 2010 October 2011, . 2012 [RFC7383] Smyslov, V., "Internet Key Exchange Protocol Version 2 2013 (IKEv2) Message Fragmentation", RFC 7383, 2014 DOI 10.17487/RFC7383, November 2014, 2015 . 2017 Appendix A. Use of LKH in G-IKEv2 2019 Section 5.4 of [RFC2627] describes the LKH architecture, and how a 2020 GCKS uses LKH to exclude group members. This section clarifies how 2021 the LKH architecture is used with G-IKEv2. 2023 A.1. Group Creation 2025 When a GCKS forms a group, it creates a key tree as shown in the 2026 figure below. The key tree contains logical keys (represented as 2027 numbers in the figure) and a private key shared with only a single GM 2028 (represented as letters in the figure). Note that the use of numbers 2029 and letters is used for explanatory purposes; in fact, each key would 2030 have an LKH ID, which is two-octet identifier chosen by the GCKS. 2031 The GCKS may create a complete tree as shown, or a partial tree which 2032 is created on demand as members join the group. The top of the key 2033 tree (i.e., "1" in Figure 3) is used as the KEK for the group. 2035 1 2036 +------------------------------+ 2037 2 3 2038 +---------------+ +---------------+ 2039 4 5 6 7 2040 +-------+ +-------+ +--------+ +--------+ 2041 A B C D E F G H 2043 Figure 3: Initial LKH tree 2045 When GM "A" joins the group, the GCKS provides an LKH_DOWNLOAD_ARRAY 2046 in the KD payload of the GSA_AUTH or GSA_REGISTRATION exchange. 2047 Given the tree shown in figure above, the LKH_DOWNLOAD_ARRAY will 2048 contain four LKH Key payloads, each containing an LKH ID and Key 2049 Data. If the LKH ID values were chosen as shown in the figure, four 2050 LKH Keys would be provided to GM "A", in the following order: A, 4, 2051 2, 1. When GM "B" joins the group, it would also be given four LKH 2052 Keys in the following order: B, 4, 2, 1. And so on, until GM "H" 2053 joins the group and is given H, 7, 3, 1. 2055 A.2. Group Member Exclusion 2057 If the GKCS has reason to believe that a GM should be excluded, then 2058 it can do so by sending a GSA_REKEY exchange that includes a set of 2059 LKH_UPDATE_ARRAY attributes in the KD payload. Each LKH_UPDATE_ARRAY 2060 contains a set of LKH Key payloads, in which every GM other than the 2061 excluded GM will be able to determine a set of new logical keys, 2062 which culminate in a new key "1". The excluded GM will observe the 2063 set of LKH_UPDATE_ARRAY attributes, but cannot determine the new 2064 logical keys because each of the "Key Data" fields is encrypted with 2065 a key held by other GMs. The GM will hold no keys to properly 2066 decrypt any of the "Key Data" fields, including key "1" (i.e., the 2067 new KEK). When a subsequent GSA_REKEY exchange is delivered by the 2068 GCKS and protected by the new KEK, the excluded GM will no longer be 2069 able to see the contents of the GSA_REKEY, including new TEKs that 2070 will be delivered to replace existing TEKs. At this point, the GM 2071 will no longer be able to participate in the group. 2073 In the example below, new keys are represented as the number followed 2074 by a "prime" symbol (e.g., "1" becomes "1'"). Each key is encrypted 2075 by another key. This is represented as "{key1}key2", where key2 2076 encrypts key1. For example, "{1'}2' states that a new key "1'" is 2077 encrypted with a new key "2'". 2079 If GM "B" is to be excluded, the GCKS will need to include three 2080 LKH_UPDATE_ARRAY attributes in the GSA_REKEY message. The order of 2081 the attributes does not matter; only the order of the keys within 2082 each attribute. 2084 o One will provide GM "A" with new logical keys that are shared with 2085 B: {4'}A, {2'}4', {1'}2' 2087 o One will provide all GMs holding key "5" with new logical keys: 2088 {2'}5, {1'}2' 2090 o One will provide all GMs holding key "3" with a new KEK: {1'}3 2092 Each GM will look at each LKH_UPDATE_ARRAY attribute and observe an 2093 LKH ID which is present in an LKH Key delivered to them in the 2094 LKH_DOWNLOAD_ARRAY they were given. If they find a matching LKH ID, 2095 then they will decrypt the new key with the logical key immediately 2096 preceding that LKH Key, and so on until they have received the new 1' 2097 key. 2099 The resulting key tree from this rekey event would would be shown in 2100 Figure 4. 2102 1' 2103 +------------------------------+ 2104 2' 3 2105 +---------------+ +---------------+ 2106 4' 5 6 7 2107 +---+ +-------+ +--------+ +--------+ 2108 A B C D E F G H 2110 Figure 4: LKH tree after B has been excluded 2112 Authors' Addresses 2114 Brian Weis 2115 Cisco Systems 2116 170 W. Tasman Drive 2117 San Jose, California 95134-1706 2118 USA 2120 Phone: +1-408-526-4796 2121 Email: bew@cisco.com 2123 Valery Smyslov 2124 ELVIS-PLUS 2125 PO Box 81 2126 Moscow (Zelenograd) 124460 2127 Russian Federation 2129 Phone: +7 495 276 0211 2130 Email: svan@elvis.ru