Network Working Group B. Weis Internet-Draft Independent Obsoletes: 6407 (if approved) V. Smyslov Intended status: Standards Track ELVIS-PLUS Expires: July 12, 2020 January 9, 2020 Group Key Management using IKEv2 draft-ietf-ipsecme-g-ikev2-00 Abstract This document presents a set of IKEv2 exchanges that comprise a group key management protocol. The protocol is in conformance with the Multicast Security (MSEC) key management architecture, which contains two components: member registration and group rekeying. Both components require a Group Controller/Key Server to download IPsec group security associations to authorized members of a group. The group members then exchange IP multicast or other group traffic as IPsec packets. This document obsoletes RFC 6407. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 12, 2020. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect Weis & Smyslov Expires July 12, 2020 [Page 1] Internet-Draft G-IKEv2 January 2020 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 1.2. G-IKEv2 Integration into IKEv2 Protocol . . . . . . . . . 5 1.2.1. G-IKEv2 Transport and Port . . . . . . . . . . . . . 5 1.2.2. IKEv2 Header Initialization . . . . . . . . . . . . . 6 1.3. G-IKEv2 Protocol . . . . . . . . . . . . . . . . . . . . 6 1.3.1. G-IKEv2 Payloads . . . . . . . . . . . . . . . . . . 6 1.4. G-IKEv2 Member Registration and Secure Channel Establishment . . . . . . . . . . . . . . . . . . . . . . 7 1.4.1. GSA_AUTH exchange . . . . . . . . . . . . . . . . . . 7 1.4.2. GSA_REGISTRATION Exchange . . . . . . . . . . . . . . 9 1.4.3. GM Registration Operations . . . . . . . . . . . . . 10 1.4.4. GCKS Registration Operations . . . . . . . . . . . . 11 1.4.5. Group Maintenance Channel . . . . . . . . . . . . . . 12 1.4.6. Counter-based modes of operation . . . . . . . . . . 19 1.5. Interaction with IKEv2 Protocol Extensions . . . . . . . 21 1.5.1. Postquantum Preshared Keys for IKEv2 . . . . . . . . 21 2. Header and Payload Formats . . . . . . . . . . . . . . . . . 23 2.1. The G-IKEv2 Header . . . . . . . . . . . . . . . . . . . 23 2.2. Group Identification (IDg) Payload . . . . . . . . . . . 24 2.3. Security Association - GM Supported Transforms (SAg) . . 24 2.4. Group Security Association Payload . . . . . . . . . . . 24 2.4.1. GSA Policy . . . . . . . . . . . . . . . . . . . . . 25 2.4.2. KEK Policy . . . . . . . . . . . . . . . . . . . . . 26 2.4.3. GSA TEK Policy . . . . . . . . . . . . . . . . . . . 30 2.4.4. GSA Group Associated Policy . . . . . . . . . . . . . 33 2.5. Key Download Payload . . . . . . . . . . . . . . . . . . 34 2.5.1. TEK Download Type . . . . . . . . . . . . . . . . . . 36 2.5.2. KEK Download Type . . . . . . . . . . . . . . . . . . 37 2.5.3. LKH Download Type . . . . . . . . . . . . . . . . . . 38 2.5.4. SID Download Type . . . . . . . . . . . . . . . . . . 40 2.6. Delete Payload . . . . . . . . . . . . . . . . . . . . . 42 2.7. Notify Payload . . . . . . . . . . . . . . . . . . . . . 42 2.8. Authentication Payload . . . . . . . . . . . . . . . . . 43 3. Security Considerations . . . . . . . . . . . . . . . . . . . 43 3.1. GSA Registration and Secure Channel . . . . . . . . . . . 43 3.2. GSA Maintenance Channel . . . . . . . . . . . . . . . . . 44 3.2.1. Authentication/Authorization . . . . . . . . . . . . 44 3.2.2. Confidentiality . . . . . . . . . . . . . . . . . . . 44 3.2.3. Man-in-the-Middle Attack Protection . . . . . . . . . 44 3.2.4. Replay/Reflection Attack Protection . . . . . . . . . 44 Weis & Smyslov Expires July 12, 2020 [Page 2] Internet-Draft G-IKEv2 January 2020 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 4.1. New Registries . . . . . . . . . . . . . . . . . . . . . 44 4.2. New Payload and Exchange Types Added to the Existing IKEv2 Registry . . . . . . . . . . . . . . . . . . . . . 45 4.3. Changes to Previous Allocations . . . . . . . . . . . . . 45 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 45 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 46 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 7.1. Normative References . . . . . . . . . . . . . . . . . . 47 7.2. Informative References . . . . . . . . . . . . . . . . . 48 Appendix A. Use of LKH in G-IKEv2 . . . . . . . . . . . . . . . 50 A.1. Group Creation . . . . . . . . . . . . . . . . . . . . . 50 A.2. Group Member Exclusion . . . . . . . . . . . . . . . . . 51 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52 1. Introduction and Overview A group key management protocol provides IPsec keys and policy to a set of IPsec devices which are authorized to communicate using a Group Security Association (GSA) defined in [RFC3740]. The data communications within the group (e.g., IP multicast packets) are protected by a key pushed to the group members (GMs) by the Group Controller/Key Server (GCKS). This document presents a set of IKEv2 [RFC7296] exchanges that comprise a group key management protocol. A GM begins a "registration" exchange when it first joins the group. With G-IKEv2, the GCKS authenticates and authorizes GMs, then pushes policy and keys used by the group to the GM. G-IKEv2 includes two "registration" exchanges. The first is the GSA_AUTH exchange ( Section 1.4.1), which follows an IKE_SA_INIT exchange. The second is the GSA_REGISTRATION exchange ( Section 1.4.2), which a GM can use within an established IKE SA. Group rekeys are accomplished using either the GSA_REKEY exchange (a single message distributed to all GMs, usually as a multicast message), or as a GSA_INBAND_REKEY exchange delivered individually to group members using existing IKE SAs). Large and small groups may use different sets of these protocols. When a large group of devices are communicating, the GCKS is likely to use the GSA_REKEY message for efficiency. This is shown in Figure 1. (Note: For clarity, IKE_SA_INIT is omitted from the figure.) Weis & Smyslov Expires July 12, 2020 [Page 3] Internet-Draft G-IKEv2 January 2020 +--------+ +------------->| GCKS |<-------------+ | +--------+ | | | ^ | | | | | | | GSA_AUTH | | | or | | | GSA_REGISTRATION | | | | | GSA_AUTH | | GSA_AUTH or GSA_REKEY | or GSA_REGISTRATION | | GSA_REGISTRATION | | | | | +------------+-----------------+ | | | | | | | v v v v v v +-------+ +--------+ +-------+ | GM | ... | GM | ... | GM | +-------+ +--------+ +-------+ ^ ^ ^ | | | +-------ESP-------+-------ESP------+ Figure 1: G-IKEv2 used in large groups Alternatively, a small group may simply use the GSA_AUTH as a registration protocol, where the GCKS issues rekeys using the GSA_INBAND_REKEY within the same IKEv2 SA. The GCKS is also likely to be a GM in a small group (as shown in Figure 2.) GSA_AUTH, GSA_INBAND_REKEY +-----------------------------------------------+ | | | GSA_AUTH, GSA_INBAND_REKEY | | +-----------------------------+ | | | | | | | GSA_AUTH, GSA_INBAND_REKEY | | | | +--------+ | | v v v v v v +---------+ +----+ +----+ +----+ | GCKS/GM | | GM | | GM | | GM | +---------+ +----+ +----+ +----+ ^ ^ ^ ^ | | | | +----ESP-----+------ESP-------+-----ESP-----+ Figure 2: G-IKEv2 used in small groups Weis & Smyslov Expires July 12, 2020 [Page 4] Internet-Draft G-IKEv2 January 2020 IKEv2 message semantics are preserved in that all communications consists of message request-response pairs. The exception to this rule is the GSA_REKEY exchange, which is a single message delivering group updates to the GMs. G-IKEv2 conforms with the Multicast Group Security Architecture [RFC3740], and the Multicast Security (MSEC) Group Key Management Architecture [RFC4046]. G-IKEv2 replaces GDOI [RFC6407], which defines a similar group key management protocol using IKEv1 [RFC2409] (since deprecated by IKEv2). When G-IKEv2 is used, group key management use cases can benefit from the simplicity, increased robustness and cryptographic improvements of IKEv2 (see Appendix A of [RFC7296]. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 1.2. G-IKEv2 Integration into IKEv2 Protocol G-IKEv2 uses the security mechanisms of IKEv2 (peer authentication, confidentiality, message integrity) to ensure that only authenticated devices have access to the group policy and keys. The G-IKEv2 exchange further provides group authorization, and secure policy and key download from the GCKS to GMs. Some IKEv2 extensions require special handling if used with G-IKEv2. See Section 1.5 for more details. It is assumed that readers are familiar with the IKEv2 protocol, so this document skips many details that are described in [RFC7296]. 1.2.1. G-IKEv2 Transport and Port G-IKEv2 SHOULD use UDP port 848, the same as GDOI [RFC6407], because they serve a similar function. They can use the same ports, just as IKEv1 and IKEv2 can share port 500. The version number in the IKE header distinguishes the G-IKEv2 protocol from GDOI protocol [RFC6407]. G-IKEv2 MAY also use the IKEv2 ports (500, 4500), which would provide a better integration with IKEv2. G-IKEv2 MAY also use TCP transport for registration (unicast) IKE SA, as defined in [RFC8229]. Weis & Smyslov Expires July 12, 2020 [Page 5] Internet-Draft G-IKEv2 January 2020 1.2.2. IKEv2 Header Initialization The Major Version is (2) and Minor Version is (0) according to IKEv2 [RFC7296], and maintained in this document. The G-IKEv2 IKE_SA_INIT, GSA_AUTH, GSA_REGISTRATION and GSA_INBAND_REKEY use the IKE SPI according to IKEv2 [RFC7296], section 2.6. 1.3. G-IKEv2 Protocol 1.3.1. G-IKEv2 Payloads In the following descriptions, the payloads contained in the G-IKEv2 messages are indicated by names as listed below. Notation Payload ------------------------------------------------------------ AUTH Authentication CERT Certificate CERTREQ Certificate Request GSA Group Security Association HDR IKEv2 Header IDg Identification - Group IDi Identification - Initiator IDr Identification - Responder KD Key Download KE Key Exchange Ni, Nr Nonce SA Security Association SAg Security Association - GM Supported Transforms Payloads defined as part of other IKEv2 extensions MAY also be included in these messages. Payloads that may optionally appear will be shown in brackets, such as [ CERTREQ ], to indicate that a certificate request payload can optionally be included. G-IKEv2 defines several new payloads not used in IKEv2: o IDg (Group ID) - The GM requests the GCKS for membership into the group by sending its IDg payload. o GSA (Group Security Association) - The GCKS sends the group policy to the GM using this payload. o KD (Key Download) - The GCKS sends the control and data keys to the GM using the KD payload. Weis & Smyslov Expires July 12, 2020 [Page 6] Internet-Draft G-IKEv2 January 2020 o SAg (Security Association - GM Supported Transforms) - the GM sends supported transforms, so that GCKS may select a policy appropriate for all members of the group. The details of the contents of each payload are described in Section 2. 1.4. G-IKEv2 Member Registration and Secure Channel Establishment The registration protocol consists of a minimum of two messages exchanges, IKE_SA_INIT and GSA_AUTH; member registration may have a few more messages exchanged if the EAP method, cookie challenge (for DoS protection) or negotiation of Diffie-Hellman group is included. Each exchange consists of request/response pairs. The first exchange IKE_SA_INIT is defined in IKEv2 [RFC7296]. This exchange negotiates cryptographic algorithms, exchanges nonces and does a Diffie-Hellman exchange between the group member (GM) and the Group Controller/Key Server (GCKS). The second exchange GSA_AUTH authenticates the previous messages, exchanges identities and certificates. These messages are encrypted and integrity protected with keys established through the IKE_SA_INIT exchange, so the identities are hidden from eavesdroppers and all fields in all the messages are authenticated. The GCKS SHOULD authorize group members to be allowed into the group as part of the GSA_AUTH exchange. Once the GCKS accepts a group member to join a group it will download the data security keys (TEKs) and/or group key encrypting key (KEK) or KEK array as part of the GSA_AUTH response message. 1.4.1. GSA_AUTH exchange After the group member and GCKS use the IKE_SA_INIT exchange to negotiate cryptographic algorithms, exchange nonces, and perform a Diffie-Hellman exchange as defined in IKEv2 [RFC7296], the GSA_AUTH exchange MUST complete before any other exchanges can be done. The security properties of the GSA_AUTH exchange are the same as the properties of the IKE_AUTH exchange. It is used to authenticate the IKE_SA_INIT messages, exchange identities and certificates. G-IKEv2 also uses this exchange for group member registration and authorization. Even though the IKE_AUTH does contain the SA2, TSi, and TSr payload the GSA_AUTH does not. They are not needed because policy is not negotiated between the group member and the GCKS, but instead downloaded from the GCKS to the group member. Weis & Smyslov Expires July 12, 2020 [Page 7] Internet-Draft G-IKEv2 January 2020 Initiator (Member) Responder (GCKS) -------------------- ------------------ HDR, SK { IDi, [CERT,] [CERTREQ, ] [IDr, ] AUTH, IDg, [SAg, ] [N ] } --> Figure 3: GSA_AUTH Request After the IKE_SA_INIT exchange completes, the group member initiates a GSA_AUTH request to join a group indicated by the IDg payload. The GM MAY include an SAg payload declaring which Transforms that it is willing to accept. A GM that intends to emit data packets SHOULD include a Notify payload status type of SENDER, which enables the GCKS to provide any additional policy necessary by group senders. Initiator (Member) Responder (GCKS) -------------------- ------------------ <-- HDR, SK { IDr, [CERT, ] AUTH, [ GSA, KD, ] [D, ] } Figure 4: GSA_AUTH Normal Response The GCKS responds with IDr, optional CERT, and AUTH material as if it were an IKE_AUTH. It also informs the group member of the cryptographic policies of the group in the GSA payload and the key material in the KD payload. The GCKS can also include a Delete (D) payload instructing the group member to delete existing SAs it might have as the result of a previous group member registration. Note, that since the GCKS generally doesn't know which SAs the GM has, the SPI field in the Delete payload(s) SHOULD be set to zero in this case. (See more discussion on the Delete payload in Section 2.6.) In addition to the IKEv2 error handling, the GCKS can reject the registration request when the IDg is invalid or authorization fails, etc. In these cases, see Section 2.7, the GSA_AUTH response will not include the GSA and KD, but will include a Notify payload indicating errors. If the group member included an SAg payload, and the GCKS chooses to evaluate it, and it detects that that group member cannot support the security policy defined for the group, then the GCKS SHOULD return a NO_PROPOSAL_CHOSEN. Other types of notifications can be AUTHORIZATION_FAILED or REGISTRATION_FAILED. Initiator (Member) Responder (GCKS) -------------------- ------------------ <-- HDR, SK { IDr, [CERT, ] AUTH, N } Figure 5: GSA_AUTH Error Response Weis & Smyslov Expires July 12, 2020 [Page 8] Internet-Draft G-IKEv2 January 2020 If the group member finds the policy sent by the GCKS is unacceptable, the member SHOULD initiate GSA_REGISTRATION exchange sending IDg and the Notify NO_PROPOSAL_CHOSEN (see Section 1.4.2)). 1.4.2. GSA_REGISTRATION Exchange When a secure channel is already established between a GM and the GCKS, the GM registration for a group can reuse the established secure channel. In this scenario the GM will use the GSA_REGISTRATION exchange. Payloads in the exchange are generated and processed as defined in Section 1.4.1. Initiator (Member) Responder (GCKS) -------------------- ------------------ HDR, SK {IDg, [SAg, ][N ] } --> <-- HDR, SK { GSA, KD, [D ] } Figure 6: GSA_REGISTRATION Normal Exchange As with GSA_AUTH exchange, the GCKS can reject the registration request when the IDg is invalid or authorization fails, or GM cannot support the security policy defined for the group (which can be concluded by GCKS by evaluation of SAg payload). In this case the GCKS returns an appropriate error notification as described in Section 1.4.1. Initiator (Member) Responder (GCKS) -------------------- ------------------ HDR, SK {IDg, [SAg, ][N ] } --> <-- HDR, SK { N } Figure 7: GSA_REGISTRATION Error Exchange This exchange can also be used if the group member finds the policy sent by the GCKS is unacceptable or for some reason wants to unregister itself from the group. The group member SHOULD notify the GCKS by sending IDg and the Notify type NO_PROPOSAL_CHOSEN or REGISTRATION_FAILED, as shown below. The GCKS MUST unregister the group member. Initiator (Member) Responder (GCKS) -------------------- ------------------ HDR, SK {IDg, N } --> <-- HDR, SK {} Figure 8: GM Reporting Errors in GSA_REGISTRATION Exchange Weis & Smyslov Expires July 12, 2020 [Page 9] Internet-Draft G-IKEv2 January 2020 1.4.3. GM Registration Operations A G-IKEv2 Initiator (GM) requesting registration contacts the GCKS using the IKE_SA_INIT exchange and receives the response from the GCKS. This exchange is unchanged from the IKE_SA_INIT in IKEv2 protocol. Upon completion of parsing and verifying the IKE_SA_INIT response, the GM sends the GSA_AUTH message with the IKEv2 payloads from IKE_AUTH (without the SAi2, TSi and TSr payloads) along with the Group ID informing the GCKS of the group the initiator wishes to join. An initiator intending to emit data traffic SHOULD send a SENDER Notify payload status. The SENDER not only signifies that it is a sender, but provides the initiator the ability to request Sender-ID values, in case the Data Security SA supports a counter mode cipher. Section 1.4.6) includes guidance on requesting Sender- ID values. An initiator may be limited in the types of Transforms that it is able or willing to use, and may find it useful to inform the GCKS which Transforms that it is willing to accept. It can OPTIONALLY include an SAg payload, which can include ESP and/or AH Proposals. Each Proposal contains a list of Transforms that it is willing to support for that protocol. A Proposal of type ESP can include ENCR, INTEG, and ESN Transforms. A Proposal of type AH can include INTEG, and ESN Transforms. The SPI length of each Proposal in an SAg is set to zero, and thus the SPI field is null. The GCKS MUST ignore SPI field in the SAg payload. Generally, a single Proposal of each type will suffice, because the group member is not negotiating Transform sets, simply alerting the GCKS to restrictions it may have, however if the GM has restrictions on combination of algorithms, this can be expressed by sending several proposals. Upon receiving the GSA_AUTH response, the initiator parses the response from the GCKS authenticating the exchange using the IKEv2 method, then processes the GSA and KD. The GSA payload contains the security policy and cryptographic protocols used by the group. This policy describes the Rekey SA (KEK), if present, Data-security SAs (TEK), and other group policy (GAP). If the policy in the GSA payload is not acceptable to the GM, it SHOULD notify the GCKS by initiating a GSA_REGISTRATION exchange with a NO_PROPOSAL_CHOSEN Notify payload (see Section 1.4.2). Note, that this should normally not happen if the GM includes SAg payload in the GSA_AUTH request and the GCKS takes it into account. Finally the KD is parsed providing the keying material for the TEK and/or KEK. The GM interprets the KD key packets, where each key packet includes the keying material for SAs distributed in the GSA payload. Weis & Smyslov Expires July 12, 2020 [Page 10] Internet-Draft G-IKEv2 January 2020 Keying material is matched by comparing the SPIs in the key packets to SPIs previously included in the GSA payloads. Once TEK keys and policy are matched, the GM provides them to the data security subsystem, and it is ready to send or receive packets matching the TEK policy. The GSA KEK policy MUST include KEK attribute KEK_MESSAGE_ID with a Message ID. The Message ID in the KEK_MESSAGE_ID attribute MUST be checked against any previously received Message ID for this group. If it is less than the previously received number, it should be considered stale and ignored. This could happen if two GSA_AUTH exchanges happened in parallel, and the Message ID changed. This KEK_MESSAGE_ID is used by the GM to prevent GSA_REKEY message replay attacks. The first GSA_REKEY message that the GM receives from the GCKS must have a Message ID greater or equal to the Message ID received in the KEK_MESSAGE_ID attribute. Once a GM has received GSA_REKEY policy during a registration the IKE SA may be closed. However, the GM SHOULD NOT close IKE SA, it is the GCKS who makes the decision whether to close or keep it, because depending on the policy the IKE SA may be used for inband rekeying for small groups. 1.4.4. GCKS Registration Operations A G-IKEv2 GCKS passively listens for incoming requests from group members. When the GCKS receives an IKE_SA_INIT request, it selects an IKE proposal and generates a nonce and DH to include them in the IKE_SA_INIT response. Upon receiving the GSA_AUTH request, the GCKS authenticates the group member using the same procedures as in the IKEv2 IKE_AUTH. The GCKS then authorizes the group member according to group policy before preparing to send the GSA_AUTH response. If the GCKS fails to authorize the GM, it will respond with an AUTHORIZATION_FAILED notify message. The GSA_AUTH response will include the group policy in the GSA payload and keys in the KD payload. If the GCKS policy includes a group rekey option, this policy is constructed in the GSA KEK and the key is constructed in the KD KEK. The GSA KEK MUST include the KEK_MESSAGE_ID attribute, specifying the starting Message ID the GCKS will use when sending the GSA_REKEY message to the group member. This Message ID is used to prevent GSA_REKEY message replay attacks and will be increased each time a GSA_REKEY message is sent to the group. The GCKS data traffic policy is included in the GSA TEK and keys are included in the KD TEK. The GSA GAP MAY also be included to provide the ATD and/or DTD (Section 2.4.4.1) specifying activation Weis & Smyslov Expires July 12, 2020 [Page 11] Internet-Draft G-IKEv2 January 2020 and deactivation delays for SAs generated from the TEKs. If the group member has indicated that it is a sender of data traffic and one or more Data Security SAs distributed in the GSA payload included a counter mode of operation, the GCKS responds with one or more SIDs (see Section 1.4.6). If the GCKS receives a GSA_REGISTRATION exchange with a request to register a GM to a group, the GCKS will need to authorize the GM with the new group (IDg) and respond with the corresponding group policy and keys. If the GCKS fails to authorize the GM, it will respond with the AUTHORIZATION_FAILED notification. If a group member includes an SAg in its GSA_AUTH or GSA_REGISTRATION request, the GCKS MAY evaluate it according to an implementation specific policy. o The GCKS could evaluate the list of Transforms and compare it to its current policy for the group. If the group member did not include all of the ESP or AH Transforms in its current policy, then it could return a NO_PROPOSAL_CHOSEN Notification. o The GCKS could store the list of Transforms, with the goal of migrating the group policy to a different Transform when all of the group members indicate that they can support that Transform. o The GCKS could store the list of Transforms and adjust the current group policy based on the capabilities of the devices as long as they fall within the acceptable security policy of the GCKS. Depending on its policy, the GCKS may have no need for the IKE SA (e.g., it does not plan to initiate an GSA_INBAND_REKEY exchange). If the GM does not initiate another registration exchange or Notify (e.g., NO_PROPOSAL_CHOSEN), and also does not close the IKE SA and the GCKS is not intended to use the SA, then after a short period of time the GCKS SHOULD close the IKEv2 SA. The delay before closing provides for receipt of a GM's error notification in the event of packet loss. 1.4.5. Group Maintenance Channel The GCKS is responsible for rekeying the secure group per the group policy. Rekeying is an operation whereby the GCKS provides replacement TEKs and KEK, deleting TEKs, and/or excluding group members. The GCKS may initiate a rekey message if group membership and/or policy has changed, or if the keys are about to expire. Two forms of group maintenance channels are provided in G-IKEv2 to push new policy to group members. Weis & Smyslov Expires July 12, 2020 [Page 12] Internet-Draft G-IKEv2 January 2020 GSA_REKEY The GSA_REKEY exchange is an exchange initiated by the GCKS, where the rekey policy is usually delivered to group members using IP multicast as a transport. This is valuable for large and dynamic groups, and where policy may change frequently and an scalable rekeying method is required. When the GSA_REKEY exchange is used, the IKEv2 SA protecting the member registration exchanges is terminated, and group members await policy changes from the GCKS via the GSA_REKEY exchange. GSA_INBAND_REKEY The GSA_INBAND_REKEY exchange is a rekey method using the IKEv2 SA that was setup to protecting the member registration exchange. This exchange allows the GCKS to rekey without using an independent GSA_REKEY exchange. The GSA_INBAND_REKEY exchange is useful when G-IKEv2 is used with a small group of cooperating devices. 1.4.5.1. GSA_REKEY Exchange The GCKS initiates the G-IKEv2 Rekey securely, usually using IP multicast. Since this rekey does not require a response and it sends to multiple GMs, G-IKEv2 rekeying MUST NOT support IKE SA windowing. The GCKS rekey message replaces the rekey GSA KEK or KEK array, and/ or creates a new Data-Security GSA TEK. The SID Download attribute in the Key Download payload (defined in Section 2.5.4) MUST NOT be part of the Rekey Exchange as this is sender specific information and the Rekey Exchange is group specific. The GCKS initiates the GSA_REKEY exchange as following: Members (Responder) GCKS (Initiator) -------------------- ------------------ <-- HDR, SK { GSA, KD, [D,] [AUTH] } Figure 9: GSA_REKEY Exchange HDR is defined in Section 2.1. The Message ID in this message will start with the same value the GCKS sent to the group members in the KEK attribute KEK_MESSAGE_ID during registration; this Message ID will be increased each time a new GSA_REKEY message is sent to the group members. The GSA payload contains the current rekey and data security SAs. The GSA may contain a new rekey SA and/or a new data security SA, which, optionally contains an LKH rekey SA, Section 2.4. The KD payload contains the keys for the policy included in the GSA. If the data security SA is being refreshed in this rekey message, the IPsec keys are updated in the KD, and/or if the rekey SA is being Weis & Smyslov Expires July 12, 2020 [Page 13] Internet-Draft G-IKEv2 January 2020 refreshed in this rekey message, the rekey Key or the LKH KEK array is updated in the KD payload. A Delete payload MAY be included to instruct the GM to delete existing SAs. The AUTH payload MUST be included to authenticate the GSA_REKEY message if the authentication method is based on public key signatures and MUST NOT be included if it is based on shared secret. In a latter case, the fact that a GM can decrypt the GSA_REKEY message and verify its ICV proves that the sender of this message knows the current KEK, thus authenticating that the sender is a member of the group. Shared secret authentication doesen't provide source origin authentication. For this reason using it as authentication method for multicast Rekey is NOT RECOMMENDED unless source origin authentication is not required (for example, in a small group of highly trusted GMs). If AUTH payload is included then the Auth Method field MUST be one specifying using digital signatures. During group member registration, the GCKS sends the authentication key in the GSA KEK payload, KEK_AUTH_KEY attribute, which the group member uses to authenticate the key server. Before the current Authentication Key expires, the GCKS will send a new KEK_AUTH_KEY to the group members in a GSA_REKEY message. The AUTH key that is used in the rekey message may be not the same as the authentication key used in GSA_AUTH. 1.4.5.1.1. GSA_REKEY GCKS Operations The GCKS builds the rekey message with a Message ID value that is one greater than the value included in the previous rekey. If the message is using a new KEK attribute, the Message ID is reset to 1 in this message. The GSA, KD, and D payloads follow with the same characteristics as in the GSA Registration exchange. If present the AUTH payload is created as follows. First the message is prepared, all payloads are formed and included in the message, but the content of the Encrypted payload is not yet encrypted. However, the Encrypted payload must be fully formed, including correct values in IV, Padding and Pad Length and fields. The AUTH payload is included in the message with the correct values in the Payload Header (including Next Payload, Payload Length and Auth Method fields). The Authentication Data field is zeroed for the purposes of signature calculation, but if Digiatal Signature authentication method is in use, then the ASN.1 Length and the AlgorithmIdentifier fields must be properly filled in, see [RFC7427]. The signature is computed using the signature algorithm from the KEK_AUTH_METHOD attribute (along with the KEK_AUTH_HASH if KEK_AUTH_METHOD is not Digital Signature) Weis & Smyslov Expires July 12, 2020 [Page 14] Internet-Draft G-IKEv2 January 2020 and the private key corresponding to the public key from the KEK_AUTH_KEY attribute. It is computed over the block of data starting from the first octet of IKE Header (but non including non- ESP marker if it is present) to the last octet of the (not yet encrypted) Encrypted Payload (i.e. up to and including Pad Length field). Then the signature is placed into the Signature Value of the AUTH payload, the content of the Encrypted payload is encrypted and the ICV is computed using current KEK keys. Because GSA_REKEY messages are not acknowledged and could be discarded by the network, one or more GMs may not receive the message. To mitigate such lost messages, during a rekey event the GCKS may transmit several GSA_REKEY messages with the new policy. The retransmitted messages MUST be bitwise identical and SHOULD be sent within a short time interval (a few seconds) to ensure that time-to-live would not not substantially skewed for the GMs that would receive different copies of the messages. GCKS may also include one or several KEK_NEXT_SPI/TEK_NEXT_SPI attributes specifying SPIs for the prospected rekeys, so that listening GMs are able to detect lost rekey messages and recover from this situation. See Sections Section 2.4.2.1.6 and Section 2.4.3.1.4 for more detail. 1.4.5.1.2. GSA_REKEY GM Operations When a group member receives the Rekey Message from the GCKS it decrypts the message using the current KEK, validates the signature using the public key retrieved in a previous G-IKEv2 exchange if AUTH payload is present, verifies the Message ID, and processes the GSA and KD payloads. The group member then downloads the new data security SA and/or new Rekey SA. The parsing of the payloads is identical to the parsing done in the registration exchange. Replay protection is achieved by a group member rejecting a GSA_REKEY message which has a Message ID smaller than the current Message ID that the GM is expecting. The GM expects the Message ID in the first GSA_REKEY message it receives to be equal or greater than the message id it receives in the KEK_MESSAGE_ID attribute. The GM expects the message ID in subsequent GSA_REKEY messages to be greater than the last valid GSA_REKEY message ID it received. If the GSA payload includes a Data-Security SA including a counter- modes of operation and the receiving group member is a sender for that SA, the group member uses its current SID value with the Data- Security SAs to create counter-mode nonces. If it is a sender and does not hold a current SID value, it MUST NOT install the Data- Security SAs. It MAY initiate a GSA_REGISTRATION exchange to the Weis & Smyslov Expires July 12, 2020 [Page 15] Internet-Draft G-IKEv2 January 2020 GCKS in order to obtain an SID value (along with current group policy). Once a new Rekey SA is installed as a result of GSA_REKEY message, the current Rekey SA (over which the message was received) MUST be silently deleted after waiting DEACTIVATION_TIME_DELAY interval regardless of its expiration time. If the GSA TEK payload includes TEK_REKEY_SPI attribute then after installing a new Data-Security SA the old one, identified by the SPI in this attribute, MUST be silently deleted after waiting DEACTIVATION_TIME_DELAY interval regardless of its expiration time. If a Data-Security SA is not rekeyed yet and is about to expire (a "soft lifetime" expiration is described in Section 4.4.2.1 of [RFC4301]), the GM SHOULD initiate a registration to the GCKS. This registration serves as a request for current SAs, and will result in the download of replacement SAs, assuming the GCKS policy has created them. A GM SHOULD also initiate a registration request if a Rekey SA is about to expire and not yet replaced with a new one. 1.4.5.1.3. Forward and Backward Access Control Through the G-IKEv2 rekey, G-IKEv2 supports algorithms such as LKH that have the property of denying access to a new group key by a member removed from the group (forward access control) and to an old group key by a member added to the group (backward access control). An unrelated notion to PFS, "forward access control" and "backward access control" have been called "perfect forward security" and "perfect backward security" in the literature [RFC2627]. Group management algorithms providing forward and backward access control other than LKH have been proposed in the literature, including OFT [OFT] and Subset Difference [NNL]. These algorithms could be used with G-IKEv2, but are not specified as a part of this document. Support for group management algorithms are supported via the KEY_MANAGEMENT_ALGORITHM attribute which is sent in the GSA KEK policy. G-IKEv2 specifies one method by which LKH can be used for forward and backward access control. Other methods of using LKH, as well as other group management algorithms such as OFT or Subset Difference may be added to G-IKEv2 as part of a later document. 1.4.5.1.3.1. Forward Access Control Requirements When group membership is altered using a group management algorithm new GSA TEKs (and their associated keys) are usually also needed. Weis & Smyslov Expires July 12, 2020 [Page 16] Internet-Draft G-IKEv2 January 2020 New GSAs and keys ensure that members who were denied access can no longer participate in the group. If forward access control is a desired property of the group, new GSA TEKs and the associated key packets in the KD payload MUST NOT be included in a G-IKEv2 rekey message which changes group membership. This is required because the GSA TEK policy and the associated key packets in the KD payload are not protected with the new KEK. A second G-IKEv2 rekey message can deliver the new GSA TEKS and their associated key packets because it will be protected with the new KEK, and thus will not be visible to the members who were denied access. If forward access control policy for the group includes keeping group policy changes from members that are denied access to the group, then two sequential G-IKEv2 rekey messages changing the group KEK MUST be sent by the GCKS. The first G-IKEv2 rekey message creates a new KEK for the group. Group members, which are denied access, will not be able to access the new KEK, but will see the group policy since the G-IKEv2 rekey message is protected under the current KEK. A subsequent G-IKEv2 rekey message containing the changed group policy and again changing the KEK allows complete forward access control. A G-IKEv2 rekey message MUST NOT change the policy without creating a new KEK. If other methods of using LKH or other group management algorithms are added to G-IKEv2, those methods MAY remove the above restrictions requiring multiple G-IKEv2 rekey messages, providing those methods specify how the forward access control policy is maintained within a single G-IKEv2 rekey message. 1.4.5.1.4. Fragmentation IKE fragmentation [RFC7383] can be used to perform fragmentation of large GSA_REKEY messages, however when the GSA_REKEY message is emitted as an IP multicast packet there is a lack of response from the GMs. This has the following implications. o Policy regarding the use of IKE fragmentation is implicit. If a GCKS detects that all GMs have negotiated support of IKE fragmentation in IKE_SA_INIT, then it MAY use IKE fragmentation on large GSA_REKEY exchange messages. o The GCKS must always use IKE fragmentation based on a known fragmentation threshold (unspecified in this memo), as there is no way to check if fragmentation is needed by first sending unfragmented messages and waiting for response. Weis & Smyslov Expires July 12, 2020 [Page 17] Internet-Draft G-IKEv2 January 2020 o PMTU probing cannot be performed due to lack of GSA_REKEY response message. 1.4.5.2. GSA_INBAND_REKEY Exchange When the IKEv2 SA protecting the member registration exchange is maintained while group member participates in the group, the GCKS can use the GSA_INBAND_REKEY exchange to individually provide policy updates to the group member. Member (Responder) GCKS (Initiator) -------------------- ------------------ <-- HDR, SK { GSA, KD, [D,] } HDR, SK {} --> Figure 10: GSA_INBAND_REKEY Exchange Because this is an IKEv2 exchange, the HDR is treated as defined in [RFC7296]. 1.4.5.2.1. GSA_INBAND_REKEY GCKS Operations The GSA, KD, and D payloads are built in the same manner as in a registration exchange. 1.4.5.2.2. GSA_INBAND_REKEY GM Operations The GM processes the GSA, KD, and D payloads in the same manner as if they were received in a registration exchange. 1.4.5.3. Deletion of SAs There are occasions when the GCKS may want to signal to group members to delete policy at the end of a broadcast, or if group policy has changed. Deletion of keys MAY be accomplished by sending the G-IKEv2 Delete Payload [RFC7296], section 3.11 as part of the GSA_REKEY Exchange as shown below. Members (Responder) GCKS (Initiator) -------------------- ------------------ <-- HDR, SK { [GSA ], [KD ], [D, ] [AUTH ] } Figure 11: SA Deletion in GSA_REKEY The GSA MAY specify the remaining active time of the remaining policy by using the DTD attribute in the GSA GAP. If a GCKS has no further SAs to send to group members, the GSA and KD payloads MUST be omitted from the message. There may be circumstances where the GCKS may want Weis & Smyslov Expires July 12, 2020 [Page 18] Internet-Draft G-IKEv2 January 2020 to start over with a clean slate. If the administrator is no longer confident in the integrity of the group, the GCKS can signal deletion of all the policies of a particular TEK protocol by sending a TEK with a SPI value equal to zero in the delete payload. For example, if the GCKS wishes to remove all the KEKs and all the TEKs in the group, the GCKS SHOULD send a Delete payload with a SPI of zero and a protocol_id of a TEK protocol_id value defined in Section 2.4.3, followed by another Delete payload with a SPI of zero and protocol_id of zero, indicating that the KEK SA should be deleted. 1.4.6. Counter-based modes of operation Several new counter-based modes of operation have been specified for ESP (e.g., AES-CTR [RFC3686], AES-GCM [RFC4106], AES-CCM [RFC4309], AES-GMAC [RFC4543]) and AH (e.g., AES-GMAC [RFC4543]). These counter-based modes require that no two senders in the group ever send a packet with the same Initialization Vector (IV) using the same cipher key and mode. This requirement is met in G-IKEv2 when the following requirements are met: o The GCKS distributes a unique key for each Data-Security SA. o The GCKS uses the method described in [RFC6054], which assigns each sender a portion of the IV space by provisioning each sender with one or more unique SID values. 1.4.6.1. Allocation of SIDs When at least one Data-Security SA included in the group policy includes a counter-based mode of operation, the GCKS automatically allocates and distributes one SID to each group member acting in the role of sender on the Data-Security SA. The SID value is used exclusively by the group member to which it was allocated. The group member uses the same SID for each Data-Security SA specifying the use of a counter-based mode of operation. A GCKS MUST distribute unique keys for each Data-Security SA including a counter-based mode of operation in order to maintain unique key and nonce usage. During registration, the group member can choose to request one or more SID values. Requesting a value of 1 is not necessary since the GCKS will automatically allocate exactly one to the group member. A group member MUST request as many SIDs matching the number of encryption modules in which it will be installing the TEKs in the outbound direction. Alternatively, a group member MAY request more than one SID and use them serially. This could be useful when it is anticipated that the group member will exhaust their range of Data- Security SA nonces using a single SID too quickly (e.g., before the time-based policy in the TEK expires). Weis & Smyslov Expires July 12, 2020 [Page 19] Internet-Draft G-IKEv2 January 2020 When the group policy includes a counter-based mode of operation, a GCKS SHOULD use the following method to allocate SID values, which ensures that each SID will be allocated to just one group member. 1. A GCKS maintains an SID-counter, which records the SIDs that have been allocated. SIDs are allocated sequentially, with zero as the first allocated SID. 2. Each time an SID is allocated, the current value of the counter is saved and allocated to the group member. The SID-counter is then incremented in preparation for the next allocation. 3. When the GCKS specifies a counter-based mode of operation in the Data Security SA a group member may request a count of SIDs during registration in a Notify payload information of type SENDER. When the GCKS receives this request, it increments the SID-counter once for each requested SID, and distributes each SID value to the group member. The GCKS SHOULD have a policy-defined upper bound for the number of SIDs that it will return irrespective of the number requested by the GM. 4. A GCKS allocates new SID values for each GSA_REGISTRATION exchange originated by a sender, regardless of whether a group member had previously contacted the GCKS. In this way, the GCKS is not required to maintaining a record of which SID values it had previously allocated to each group member. More importantly, since the GCKS cannot reliably detect whether the group member had sent data on the current group Data-Security SAs it does not know what Data-Security counter-mode nonce values that a group member has used. By distributing new SID values, the key server ensures that each time a conforming group member installs a Data-Security SA it will use a unique set of counter-based mode nonces. 5. When the SID-counter maintained by the GCKS reaches its final SID value, no more SID values can be distributed. Before distributing any new SID values, the GCKS MUST delete the Data-Security SAs for the group, followed by creation of new Data-Security SAs, and resetting the SID-counter to its initial value. 6. The GCKS SHOULD send a GSA_REKEY message deleting all Data- Security SAs and the Rekey SA for the group. This will result in the group members initiating a new GSA_REGISTRATION exchange, in which they will receive both new SID values and new Data-Security SAs. The new SID values can safely be used because they are only used with the new Data-Security SAs. Note that deletion of the Rekey SA is necessary to ensure that group members receiving a GSA_REKEY exchange before the re-register do not inadvertently use their old SIDs with the new Data-Security SAs. Using the method above, at no time can Weis & Smyslov Expires July 12, 2020 [Page 20] Internet-Draft G-IKEv2 January 2020 two group members use the same IV values with the same Data-Security SA key. 1.4.6.2. GM Usage of SIDs A GM applies the SID to Data Security SA as follows. 1. The most significant bits NUMBER_OF_SID_BITS of the IV are taken to be the SID field of the IV. 2. The SID is placed in the least significant bits of the SID field, where any unused most significant bits are set to zero. If the SID value doesn't fit into the NUMBER_OF_SID_BITS bits, then the GM MUST treat this as a fatal error and re-register to the group. 1.5. Interaction with IKEv2 Protocol Extensions IKEv2 defines a number of extensions that can be used to extend protocol functionality. G-IKEv2 is compatible with most of such extensions. In particular, EAP authentication defined in [RFC7296] can be used to establish registration IKE SA, as well as Secure Password authentication ([RFC6467]). G-IKEv2 is compatible with and can use IKEv2 Session Resumption [RFC5723] except that a GM would include the initial ticket request in a GSA_AUTH exchange instead of an IKE_AUTH exchange. G-IKEv2 is also compatible with Quantum Safe Key Exchange framework, defined in [I-D.tjhai-ipsecme-hybrid-qske-ikev2]. Some IKEv2 extensions however require special handling if used in G-IKEv2. 1.5.1. Postquantum Preshared Keys for IKEv2 G-IKEv2 can take advantage of the protection provided by Postquantum Preshared Keys (PPK) for IKEv2 [I-D.ietf-ipsecme-qr-ikev2]. However, the use of PPK leaves the initial IKE SA susceptible to quantum computer (QC) attacks. For this reason an alternative approach for using PPK in IKEv2 defined in [I-D.smyslov-ipsecme-ikev2-qr-alt] SHOULD be used. If the alternative approach is not supported by the peers, then the GCKS MUST NOT send GSA and KD payloads in the GSA_AUTH response message. Instead, the GCKS MUST return a new notification REKEY_IS_NEEDED. Upon receiving this notification in the GSA_AUTH response the GM MUST perform an IKE SA rekey and then initiate a new GSA_REGISTRATION request for the same group. Below are possible scenarios involving using PPK. Weis & Smyslov Expires July 12, 2020 [Page 21] Internet-Draft G-IKEv2 January 2020 GM begins IKE_SA_INIT requesting PPK, and GCKS responds with willingness to do it, or aborts according to its "mandatory_or_not" flag: Initiator (Member) Responder (GCKS) -------------------- ------------------ HDR, SAi1, KEi, Ni, N(USE_PPK) ---> <--- HDR, SAr1, KEr, Nr, [CERTREQ], N(USE_PPK) Figure 12: IKE_SA_INIT Exchange requesting using PPK GM begins GSA_AUTH with PPK_ID; if using PPK is not mandatory for the GM, N(NO_PPK_AUTH) is included too: Initiator (Member) Responder (GCKS) -------------------- ------------------ HDR, SK {IDi, AUTH, IDg, N(PPK_IDENTITY), N(NO_PPK_AUTH) } ---> Figure 13: GSA_AUTH Request using PPK If GCKS has no such PPK and using PPK is not mandatory for it and N(NO_PPK_AUTH) is included, then the GCKS continues w/o PPK; in this case no rekey is needed: Initiator (Member) Responder (GCKS) -------------------- ------------------ <--- HDR, SK { IDr, AUTH, GSA, KD } Figure 14: GSA_AUTH Response using no PPK If GCKS has no such PPK and either N(NO_PPK_AUTH) is missing or using PPK is mandatory for GCKS, the GCKS aborts the exchange: Initiator (Member) Responder (GCKS) -------------------- ------------------ <--- HDR, SK { N(AUTHENTICATION_FAILED) } Figure 15: GSA_AUTH Error Response Assuming GCKS has a proper PPK the GCKS continues with request to GM to immediately perform a rekey: Weis & Smyslov Expires July 12, 2020 [Page 22] Internet-Draft G-IKEv2 January 2020 Initiator (Member) Responder (GCKS) -------------------- ------------------ <--- HDR, SK{IDr, AUTH, N(PPK_IDENTITY), N(REKEY_IS_NEEDED) } Figure 16: GSA_AUTH Response using PPK GM initiates CREATE_CHILD_SA to rekey IKE SA and then makes a new registration request for the same group over the new IKE SA: Initiator (Member) Responder (GCKS) -------------------- ------------------ HDR, SK {SA, Ni, KEi } ---> <--- HDR, SK {SA, Nr, KEr } HDR, SK {IDg } ---> <--- HDR, SK { GSA, KD } Figure 17: Rekeying IKE SA followed by GSA_REGISTRATION Exchange 2. Header and Payload Formats Refer to IKEv2 [RFC7296] for existing payloads. Some payloads used in G-IKEv2 exchanges are not aligned to 4-octet boundaries, which is also the case for some IKEv2 payloads (see Section 3.2 of [RFC7296]). 2.1. The G-IKEv2 Header G-IKEv2 uses the same IKE header format as specified in [RFC7296] section 3.1. Several new payload formats are required in the group security exchanges. Next Payload Type Value ----------------- ----- Group Identification (IDg) 50 Group Security Association (GSA) 51 Key Download (KD) 52 New exchange types GSA_AUTH, GSA_REGISTRATION and GSA_REKEY are added to the IKEv2 [RFC7296] protocol. Exchange Type Value -------------- ----- GSA_AUTH 39 GSA_REGISTRATION 40 GSA_REKEY 41 GSA_INBAND_REKEY TBD Weis & Smyslov Expires July 12, 2020 [Page 23] Internet-Draft G-IKEv2 January 2020 Major Version is 2 and Minor Version is 0 as in IKEv2 [RFC7296]. IKE SA Initiator's SPI, IKE SA Responder's SPI, Flags, Message ID, and Length are as specified in [RFC7296]. 2.2. Group Identification (IDg) Payload The IDg Payload allows the group member to indicate which group it wants to join. The payload is constructed by using the IKEv2 Identification Payload (section 3.5 of [RFC7296]). ID type ID_KEY_ID MUST be supported. ID types ID_IPV4_ADDR, ID_FQDN, ID_RFC822_ADDR, ID_IPV6_ADDR SHOULD be supported. ID types ID_DER_ASN1_DN and ID_DER_ASN1_GN are not expected to be used. 2.3. Security Association - GM Supported Transforms (SAg) The SAg payload declares which Transforms a GM is willing to accept. The payload is constructed using the format of the IKEv2 Security Association payload (section 3.3 of [RFC7296]). The Payload Type for SAg is identical to the SA Payload Type (33). 2.4. Group Security Association Payload The Group Security Association payload is used by the GCKS to assert security attributes for both Rekey and Data-security SAs. 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload |C| RESERVED | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 18: GSA Payload Format The Security Association Payload fields are defined as follows: o Next Payload (1 octet) -- Identifies the next payload type for the G-IKEv2 registration or the G-IKEv2 rekey message. o Critical (1 bit) -- Set according to [RFC7296]. o RESERVED (7 bits) -- Must be zero. o Payload Length (2 octets) -- Is the octet length of the current payload including the generic header and all TEK and KEK policies. Weis & Smyslov Expires July 12, 2020 [Page 24] Internet-Draft G-IKEv2 January 2020 2.4.1. GSA Policy Following the GSA generic payload header are GSA policies for group rekeying (KEK), data traffic SAs (TEK) and/or Group Associated Policy (GAP). There may be zero or one GSA KEK policy, zero or one GAP policies, and zero or more GSA TEK policies, where either one GSA KEK or GSA TEK payload MUST be present. This latitude allows various group policies to be accommodated. For example if the group policy does not require the use of a Rekey SA, the GCKS would not need to send a GSA KEK attribute to the group member since all SA updates would be performed using the Registration SA. Alternatively, group policy might use a Rekey SA but choose to download a KEK to the group member only as part of the Registration SA. Therefore, the GSA KEK policy would not be necessary as part of the GSA_REKEY message. Specifying multiple GSA TEKs allows multiple related data streams (e.g., video, audio, and text) to be associated with a session, but each protected with an individual security association policy. A GAP payload allows for the distribution of group-wise policy, such as instructions for when to activate and de-activate SAs. Policies are distributed in substructures to the GSA payload, and include the following header. 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | RESERVED | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 19: GSA Policy Generic Header Format The payload fields are defined as follows: o Type (1 octet) -- Identifies the substructure type. In the following table the terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. Weis & Smyslov Expires July 12, 2020 [Page 25] Internet-Draft G-IKEv2 January 2020 Type Value -------- ----- Reserved 0 KEK 1 GAP 2 TEK 3 Unassigned 4-127 Private Use 128-255 o RESERVED (1 octet) -- Unused, set to zero. o Length (2 octets) -- Length in octets of the substructure, including its header. 2.4.2. KEK Policy The GSA KEK policy contains security attributes for the KEK method for a group and parameters specific to the G-IKEv2 registration operation. The source and destination traffic selectors describe the network identities used for the rekey messages. 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 1 | RESERVED | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ SPI ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ KEK Attributes ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 20: KEK Policy Format The GSA KEK Payload fields are defined as follows: Weis & Smyslov Expires July 12, 2020 [Page 26] Internet-Draft G-IKEv2 January 2020 o Type = 1 (1 octet) -- Identifies the GSA payload type as KEK in the G-IKEv2 registration or the G-IKEv2 rekey message. o RESERVED (1 octet) -- Must be zero. o Length (2 octets) -- Length of this structure including KEK attributes. o SPI (16 octets) -- Security Parameter Index for the rekey message. The SPI must be the IKEv2 Header SPI pair where the first 8 octets become the "Initiator's SPI" field in the G-IKEv2 rekey message IKEv2 HDR, and the second 8 octets become the "Responder's SPI" in the same HDR. As described above, these SPIs are assigned by the GCKS. When selecting SPI the GCKS MUST make sure that the sole first 8 octets (corresponding to "Initiator's SPI" field in the IKEv2 header) uniquely identify the Rekey SA. o Source & Destination Traffic Selectors - Substructures describing the source and destination of the network identities. These identities refer to the source and destination of the next KEK rekey SA. Defined format and values are specified by IKEv2 [RFC7296], section 3.13.1. o Transform Substructure List -- A list of Transform Substructures specifies the transform information. The format is defined in IKEv2 [RFC7296], section 3.3.2, and values are described in the IKEv2 registries [IKEV2-IANA]. Valid Transform Types are ENCR, INTEG. The Last Substruc value in each Transform Substructure will be set to 3 except for the last one in the list, which is set to 0. o KEK Attributes -- Contains KEK policy attributes associated with the group. The following sections describe the possible attributes. Any or all attributes may be optional, depending on the group policy. 2.4.2.1. KEK Attributes The following attributes may be present in a GSA KEK policy. The attributes must follow the format defined in the IKEv2 [RFC7296] section 3.3.5. In the table, attributes that are defined as TV are marked as Basic (B); attributes that are defined as TLV are marked as Variable (V). The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. Weis & Smyslov Expires July 12, 2020 [Page 27] Internet-Draft G-IKEv2 January 2020 KEK Attributes Value Type Mandatory -------------- ----- ---- --------- Reserved 0 KEK_MANAGEMENT_ALGORITHM 1 B N Reserved 2 Reserved 3 KEK_KEY_LIFETIME 4 V Y Reserved 5 KEK_AUTH_METHOD 6 B Y KEK_AUTH_HASH 7 B N KEK_MESSAGE_ID 8 V Y (*) KEK_NEXT_SPI 9 V N Unassigned 10-16383 Private Use 16384-32767 (*) the KEK_MESSAGE_ID MUST be included in a G-IKEv2 registration message and MUST NOT be included in rekey messages. The following attributes may only be included in a G-IKEv2 registration message: KEK_MANAGEMENT_ALGORITHM, KEK_MESSAGE_ID. 2.4.2.1.1. KEK_MANAGEMENT_ALGORITHM The KEK_MANAGEMENT_ALGORITHM attribute specifies the group KEK management algorithm used to provide forward or backward access control (i.e., used to exclude group members). Defined values are specified in the following table. The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. KEK Management Type Value ------------------- ----- Reserved 0 LKH 1 Unassigned 2-16383 Private Use 16384-32767 2.4.2.1.2. KEK_KEY_LIFETIME The KEK_KEY_LIFETIME attribute specifies the maximum time for which the KEK is valid. The GCKS may refresh the KEK at any time before the end of the valid period. The value is a four (4) octet number defining a valid time period in seconds. Weis & Smyslov Expires July 12, 2020 [Page 28] Internet-Draft G-IKEv2 January 2020 2.4.2.1.3. KEK_AUTH_METHOD The KEK_AUTH_METHOD attribute specifies the method of authentication used. This value is from the IKEv2 Authentication Method registry [IKEV2-IANA]. The method must either specify using some public key signatures or Shared Key Message Integrity Code. Other authentication methods MUST NOT be used. 2.4.2.1.4. KEK_AUTH_HASH The KEK_AUTH_HASH attribute specifies the hash algorithm used to generate the AUTH key to authenticate GSA_REKEY messages. Hash algorithms are defined in IANA registry IKEv2 Hash Algorithms [IKEV2-IANA]. This attribute SHOULD NOT be sent if the KEK_AUTH_METHOD implies a particular hash algorithm (e.g., for DSA-based algorithms). Furthermore, it is not necessary for the GCKS to send it if the GM is known to support the algorithm because it declared it in a SIGNATURE_HASH_ALGORITHMS notification during registration (see [RFC7427]). 2.4.2.1.5. KEK_MESSAGE_ID The KEK_MESSAGE_ID attribute defines the initial Message ID to be used by the GCKS in the GSA_REKEY messages. The Message ID is a 4 octet unsigned integer in network byte order. 2.4.2.1.6. KEK_NEXT_SPI The KEK_NEXT_SPI attribute may optionally be included by GCKS in GSA_REKEY message, indicating what IKE SPIs are intended be used for the next rekey SA. The attribute data MUST be 16 octets in length specifying the pair of IKE SPIs as they appear in the IKE header. Multiple attributes of this type MAY be included, meaning that any of the supplied SPIs can be used for the next rekey. The GM may save these values and if later the GM starts receiving IKE messages with one of these SPIs without seeing a rekey message over the current rekey SA, this may be used as an indication, that the rekey message was lost on its way to this GM. In this case the GM SHOULD re-register to the group. Note, that this method of detecting missed rekeys can only be used by passive GMs, i.e. those, that only listen and don't send data. It's also no point to include this attribute in the GSA_INBAND_REKEY messages, since they use reliable transport. Note also, that the GCKS is free to forget its promises and not to use the SPIs it sent Weis & Smyslov Expires July 12, 2020 [Page 29] Internet-Draft G-IKEv2 January 2020 in the KEK_NEXT_SPI attributes before (e.g. in case of GCKS reboot), so the GM must only treat these information as a "best effort" made by GCKS to prepare for future rekeys. 2.4.3. GSA TEK Policy The GSA TEK policy contains security attributes for a single TEK associated with a group. 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 3 | RESERVED | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol-ID | TEK Protocol-Specific Payload | +-+-+-+-+-+-+-+-+ ~ ~ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 21: TEK Policy Generic Header Format The GSA TEK Payload fields are defined as follows: o Type = 3 (1 octet) -- Identifies the GSA payload type as TEK in the G-IKEv2 registration or the G-IKEv2 rekey message. o RESERVED (1 octet) -- Must be zero. o Length (2 octets) -- Length of this structure, including the TEK Protocol-Specific Payload. o Protocol-ID (1 octet) -- Value specifying the Security Protocol. The following table defines values for the Security Protocol. Support for the GSA_PROTO_IPSEC_AH GSA TEK is OPTIONAL. The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. Protocol ID Value ----------- ----- Reserved 0 GSA_PROTO_IPSEC_ESP 1 GSA_PROTO_IPSEC_AH 2 Unassigned 3-127 Private Use 128-255 o TEK Protocol-Specific Payload (variable) -- Payload which describes the attributes specific for the Protocol-ID. Weis & Smyslov Expires July 12, 2020 [Page 30] Internet-Draft G-IKEv2 January 2020 2.4.3.1. TEK ESP and AH Protocol-Specific Policy The TEK Protocol-Specific policy contains two traffic selectors one for the source and one for the destination of the protected traffic, SPI, Transforms, and Attributes. The TEK Protocol-Specific policy for ESP and AH is as follows: 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SPI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ TEK Attributes ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 22: AH and ESP TEK Policy Format The GSA TEK Policy fields are defined as follows: o SPI (4 octets) -- Security Parameter Index. o Source & Destination Traffic Selectors - The traffic selectors describe the source and the destination of the protected traffic. The format and values are defined in IKEv2 [RFC7296], section 3.13.1. o Transform Substructure List -- A list of Transform Substructures specifies the transform information. The format is defined in IKEv2 [RFC7296], section 3.3.2, and values are described in the IKEv2 registries [IKEV2-IANA]. Valid Transform Types for ESP are ENCR, INTEG, and ESN. Valid Transform Types for AH are INTEG and ESN. The Last Substruc value in each Transform Substructure will be set to 3 except for the last one in the list, which is set to 0. A Transform Substructure with attributes (e.g., the ENCR Key Weis & Smyslov Expires July 12, 2020 [Page 31] Internet-Draft G-IKEv2 January 2020 Length), they are included within the Transform Substructure as usual. o TEK Attributes -- Contains the TEK policy attributes associated with the group, in the format defined in Section 3.3.5 of [RFC7296]. All attributes are optional, depending on the group policy. Attribute Types are as follows. The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. TEK Attributes Value Type Mandatory -------------- ----- ---- --------- Reserved 0 TEK_KEY_LIFETIME 1 V N TEK_MODE 2 B Y TEK_REKEY_SPI 3 V N TEK_NEXT_SPI 4 V N Unassigned 5-16383 Private Use 16384-32767 It is NOT RECOMMENDED that the GCKS distribute both ESP and AH Protocol-Specific Policies for the same set of Traffic Selectors. 2.4.3.1.1. TEK_KEY_LIFETIME The TEK_KEY_LIFETIME attribute specifies the maximum time for which the TEK is valid. When the TEK expires, the AH or ESP security association and all keys downloaded under the security association are discarded. The GCKS may refresh the TEK at any time before the end of the valid period. The value is a four (4) octet number defining a valid time period in seconds. If unspecified the default value of 28800 seconds (8 hours) shall be assumed. 2.4.3.1.2. TEK_MODE The value of 0 is used for tunnel mode and 1 for transport mode. In the absence of this attribute tunnel mode will be used. 2.4.3.1.3. TEK_REKEY_SPI This attribute contains an SPI for the SA that is being rekeyed. The size of SPI depends on the protocol, for ESP and AH it is 4 octets, so the size of the data MUST be 4 octets for AH and ESP. Weis & Smyslov Expires July 12, 2020 [Page 32] Internet-Draft G-IKEv2 January 2020 If this attribute is included in the rekey message, the GM SHOULD delete the SA corresponding to this SPI once the new SA is installed and regardless of the expiration time of the SA to be deleted (but after waiting DEACTIVATION_TIME_DELAY time period). 2.4.3.1.4. TEK_NEXT_SPI This attribute contains an SPI that the GCKS reserved for the next rekey. The size of SPI depends on the protocol, for ESP and AH it is 4 octets, so the size of the data MUST be 4 octets for AH and ESP. Multiple attributes of this type MAY be included, which means that any of the provided SPIs can be used in the next rekey. The GM may save these values and if later the GM starts receiving IPsec messages with one of these SPIs without seeing a rekey message for it, this may be used as an indication, that the rekey message was lost on its way to this GM. In this case the GM SHOULD re-register to the group. Note, that this method of detecting missed rekey messages can only be used by passive GMs, i.e. those, that only listen and don't send data. It's also no point to include this attribute in the GSA_INBAND_REKEY messages, since they use reliable transport. Note also, that the GCKS is free to forget its promises and not to use the SPIs it sent in the TEK_NEXT_SPI attributes before (e.g. in case of GCKS reboot), so the GM must only treat these information as a "best effort" made by GCKS to prepare for future rekeys. 2.4.4. GSA Group Associated Policy Group specific policy that does not belong to rekey policy (GSA KEK) or traffic encryption policy (GSA TEK) can be distributed to all group member using GSA GAP (Group Associated Policy). The GSA GAP payload is defined as follows: 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 2 | RESERVED | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Group Associated Policy Attributes ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 23: GAP Policy Format The GSA GAP payload fields are defined as follows: Weis & Smyslov Expires July 12, 2020 [Page 33] Internet-Draft G-IKEv2 January 2020 o Type = 2 (1 octet) -- Identifies the GSA payload type as GAP in the G-IKEv2 registration or the G-IKEv2 rekey message. o RESERVED (1 octet) -- Must be zero. o Length (2 octets) -- Length of this structure, including the GSA GAP header and Attributes. o Group Associated Policy Attributes (variable) -- Contains attributes following the format defined in Section 3.3.5 of [RFC7296]. Attribute Types are as follows. The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. Attribute Type Value Type -------------- ----- ---- Reserved 0 ACTIVATION_TIME_DELAY 1 B DEACTIVATION_TIME_DELAY 2 B Unassigned 3-16383 Private Use 16384-32767 2.4.4.1. ACTIVATION_TIME_DELAY/DEACTIVATION_TIME_DELAY Section 4.2.1 of [RFC5374] specifies a key rollover method that requires two values be provided to group members. The ACTIVATION_TIME_DELAY attribute allows a GCKS to set the Activation Time Delay (ATD) for SAs generated from TEKs. The ATD defines how long after receiving new SAs that they are to be activated by the GM. The ATD value is in seconds. The DEACTIVATION_TIME_DELAY allows the GCKS to set the Deactivation Time Delay (DTD) for previously distributed SAs. The DTD defines how long after receiving new SAs it should deactivate SAs that are destroyed by the rekey event. The value is in seconds. The values of ATD and DTD are independent. However, the DTD value should be larger, which allows new SAs to be activated before older SAs are deactivated. Such a policy ensures that protected group traffic will always flow without interruption. 2.5. Key Download Payload The Key Download Payload contains the group keys for the group specified in the GSA Payload. These key download payloads can have Weis & Smyslov Expires July 12, 2020 [Page 34] Internet-Draft G-IKEv2 January 2020 several security attributes applied to them based upon the security policy of the group as defined by the associated GSA Payload. 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload |C| RESERVED | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Key Packets ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 24: Key Download Payload Format The Key Download Payload fields are defined as follows: o Next Payload (1 octet) -- Identifier for the payload type of the next payload in the message. If the current payload is the last in the message, then this field will be zero. o Critical (1 bit) -- Set according to [RFC7296]. o RESERVED (7 bits) -- Unused, set to zero. o Payload Length (2 octets) -- Length in octets of the current payload, including the generic payload header. o Key Packets (variable) -- Contains Key Packets. Several types of key packets are defined. Each Key Packet has the following format. 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | KD Type | RESERVED | KD Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SPI Size | SPI (variable) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Key Packet Attributes ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 25: Key Packet Format o Key Download (KD) Type (1 octet) -- Identifier for the Key Data field of this Key Packet. In the following table the terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. Weis & Smyslov Expires July 12, 2020 [Page 35] Internet-Draft G-IKEv2 January 2020 Key Download Type Value ----------------- ----- Reserved 0 TEK 1 KEK 2 LKH 3 SID 4 Unassigned 5-127 Private Use 128-255 o RESERVED (1 octet) -- Unused, set to zero. o Key Download Length (2 octets) -- Length in octets of the Key Packet data, including the Key Packet header. o SPI Size (1 octet) -- Value specifying the length in octets of the SPI as defined by the Protocol-Id. o SPI (variable length) -- Security Parameter Index which matches a SPI previously sent in an GSA KEK or GSA TEK Payload. o Key Packet Attributes (variable length) -- Contains Key information. The format of this field is specific to the value of the KD Type field. The following sections describe the format of each KD Type. 2.5.1. TEK Download Type The following attributes may be present in a TEK Download Type. Exactly one attribute matching each type sent in the GSA TEK payload MUST be present. The attributes must follow the format defined in IKEv2 (Section 3.3.5 of [RFC7296]). In the table, attributes defined as TV are marked as Basic (B); attributes defined as TLV are marked as Variable (V). The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. TEK KD Attributes Value Type Mandatory ----------------- ----- ---- --------- Reserved 0-2 TEK_KEYMAT 3 V Y Unassigned 4-16383 Private Use 16384-32767 It is possible that the GCKS will send no TEK key packets in a Registration KD payload (as well as no corresponding GSA TEK payloads in the GSA payload), after which the TEK payloads will be sent in a rekey message. Weis & Smyslov Expires July 12, 2020 [Page 36] Internet-Draft G-IKEv2 January 2020 2.5.1.1. TEK_KEYMAT The TEK_KEYMAT attribute contains keying material for the corresponding SPI. This keying material will be used with the transform specified in the GSA TEK payload. The keying material is treated equivalent to IKEv2 KEYMAT derived for that IPsec transform. 2.5.2. KEK Download Type The following attributes may be present in a KEK Download Type. Exactly one attribute matching each type sent in the GSA KEK payload MUST be present. The attributes must follow the format defined in IKEv2 (Section 3.3.5 of [RFC7296]). In the table, attributes defined as TV are marked as Basic (B); attributes defined as TLV are marked as Variable (V). The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. KEK KD Attributes Value Type Mandatory ----------------- ----- ---- --------- Reserved 0 KEK_ENCR_KEY 1 V Y KEK_INTEGRITY_KEY 2 V N KEK_AUTH_KEY 3 V N Unassigned 4-16383 Private Use 16384-32767 If the KEK Key Packet is included, there MUST be only one present in the KD payload. 2.5.2.1. KEK_ENCR_KEY The KEK_ENCR_KEY attribute type declares that the encryption key for the corresponding SPI is contained in the Key Packet Attribute. The encryption algorithm that will use this key was specified in the GSA KEK payload. 2.5.2.2. KEK_INTEGRITY_KEY The KEK_INTEGRITY_KEY attribute type declares the integrity key for this SPI is contained in the Key Packet Attribute. The integrity algorithm that will use this key was specified in the GSA KEK payload. Weis & Smyslov Expires July 12, 2020 [Page 37] Internet-Draft G-IKEv2 January 2020 2.5.2.3. KEK_AUTH_KEY The KEK_AUTH_KEY attribute type declares that the authentication key for this SPI is contained in the Key Packet Attribute. The signature algorithm that will use this key was specified in the GSA KEK payload. An RSA public key format is defined in [RFC3447], Section A.1.1. DSS public key format is defined in [RFC3279] Section 2.3.2. For ECDSA Public keys, use format described in [RFC5480] Section 2.2. Other algorithms added to the IKEv2 Authentication Method registry are also expected to include a format of the public key included in the algorithm specification. 2.5.3. LKH Download Type The LKH key packet is comprised of attributes representing different leaves in the LKH key tree. The following attributes are used to pass an LKH KEK array in the KD payload. The attributes must follow the format defined in IKEv2 (Section 3.3.5 of [RFC7296]). In the table, attributes defined as TV are marked as Basic (B); attributes defined as TLV are marked as Variable (V). The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. LKH KD Attributes Value Type ----------------- ----- ---- Reserved 0 LKH_DOWNLOAD_ARRAY 1 V LKH_UPDATE_ARRAY 2 V Unassigned 3-16383 Private Use 16384-32767 If an LKH key packet is included in the KD payload, there MUST be only one present. 2.5.3.1. LKH_DOWNLOAD_ARRAY The LKH_DOWNLOAD_ARRAY attribute type is used to download a set of LKH keys to a group member. It MUST NOT be included in a IKEv2 rekey message KD payload if the IKEv2 rekey is sent to more than one group member. If an LKH_DOWNLOAD_ARRAY attribute is included in a KD payload, there MUST be only one present. This attribute consists of a header block, followed by one or more LKH keys. Weis & Smyslov Expires July 12, 2020 [Page 38] Internet-Draft G-IKEv2 January 2020 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | # of LKH Keys | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ LKH Keys ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 26: LKH_DOWNLOAD_ARRAY Format The KEK_LKH attribute fields are defined as follows: o Number of LKH Keys (2 octets) -- This value is the number of distinct LKH keys in this sequence. o RESERVED (2 octets) -- Unused, set to zero. Each LKH Key is defined as follows: 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LKH ID | Encr Alg | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Handle | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Key Data ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 27: LKH Key Format o LKH ID (2 octets) -- This is the position of this key in the binary tree structure used by LKH. o Encr Alg (2 octets) -- This is the encryption algorithm for which this key data is to be used. This value is specified in the ENCR transform in the GSA payload. o Key Handle (4 octets) -- This is a randomly generated value to uniquely identify a key within an LKH ID. o Key Data (variable length) -- This is the actual encryption key data, which is dependent on the Encr Alg algorithm for its format. The first LKH Key structure in an LKH_DOWNLOAD_ARRAY attribute contains the Leaf identifier and key for the group member. The rest of the LKH Key structures contain keys along the path of the key tree in the order starting from the leaf, culminating in the group KEK. Weis & Smyslov Expires July 12, 2020 [Page 39] Internet-Draft G-IKEv2 January 2020 2.5.3.2. LKH_UPDATE_ARRAY The LKH_UPDATE_ARRAY attribute type is used to update the LKH keys for a group. It is most likely to be included in a G-IKEv2 rekey message KD payload to rekey the entire group. This attribute consists of a header block, followed by one or more LKH keys, as defined in Section 2.5.3.1. There may be any number of LKH_UPDATE_ARRAY attributes included in a KD payload. 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | # of LKH Keys | LKH ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Handle | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ LKH Keys ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 28: LKH_UPDATE_ARRAY Format o Number of LKH Keys (2 octets) -- This value is the number of distinct LKH keys in this sequence. o LKH ID (2 octets) -- This is the node identifier associated with the key used to encrypt the first LKH Key. o Key Handle (4 octets) -- This is the value that uniquely identifies the key within the LKH ID which was used to encrypt the first LKH key. The LKH Keys are as defined in Section 2.5.3.1. The LKH Key structures contain keys along the path of the key tree in the order from the LKH ID found in the LKH_UPDATE_ARRAY header, culminating in the group KEK. The Key Data field of each LKH Key is encrypted with the LKH key preceding it in the LKH_UPDATE_ARRAY attribute. The first LKH Key is encrypted under the key defined by the LKH ID and Key Handle found in the LKH_UPDATE_ARRAY header. 2.5.4. SID Download Type The SID attribute is used to download one or more Sender-ID (SID) values for the exclusive use of a group member. The terms Reserved, Unassigned, and Private Use are to be applied as defined in [RFC8126]. The registration procedure is Expert Review. Weis & Smyslov Expires July 12, 2020 [Page 40] Internet-Draft G-IKEv2 January 2020 SID KD Attributes Value Type ----------------- ----- ---- Reserved 0 NUMBER_OF_SID_BITS 1 B SID_VALUE 2 V Unassigned 3-16383 Private Use 16384-32767 Because a SID value is intended for a single group member, the SID Download type MUST NOT be distributed in a GSA_REKEY message distributed to multiple group members. 2.5.4.1. NUMBER_OF_SID_BITS The NUMBER_OF_SID_BITS attribute type declares how many bits of the cipher nonce in which to represent an SID value. The bits are applied as the most significant bits of the IV, as shown in Figure 1 of [RFC6054] and specified in Section 1.4.6.2. Guidance for a GCKS choosing the NUMBER_OF_SID_BITS is provided in Section 3 of [RFC6054]. This value is applied to each SID value distributed in the SID Download. 2.5.4.2. SID_VALUE The SID_VALUE attribute type declares a single SID value for the exclusive use of this group member. Multiple SID_VALUE attributes MAY be included in a SID Download. 2.5.4.3. GM Semantics The SID_VALUE attribute value distributed to the group member MUST be used by that group member as the SID field portion of the IV for all Data-Security SAs including a counter-based mode of operation distributed by the GCKS as a part of this group. When the Sender- Specific IV (SSIV) field for any Data-Security SA is exhausted, the group member MUST NOT act as a sender on that SA using its active SID. The group member SHOULD re-register, at which time the GCKS will issue a new SID to the group member, along with either the same Data-Security SAs or replacement ones. The new SID replaces the existing SID used by this group member, and also resets the SSIV value to its starting value. A group member MAY re-register prior to the actual exhaustion of the SSIV field to avoid dropping data packets due to the exhaustion of available SSIV values combined with a particular SID value. Weis & Smyslov Expires July 12, 2020 [Page 41] Internet-Draft G-IKEv2 January 2020 A group member MUST ignore an SID Download Type KD payload present in a GSA-REKEY message, otherwise more than one GM may end up using the same SID. 2.5.4.4. GCKS Semantics If any KD payload includes keying material that is associated with a counter-mode of operation, an SID Download Type KD payload containing at least one SID_VALUE attribute MUST be included. The GCKS MUST NOT send the SID Download Type KD payload as part of a GSA_REKEY message, because distributing the same sender-specific policy to more than one group member will reduce the security of the group. 2.6. Delete Payload There are occasions when the GCKS may want to signal to group members to delete policy at the end of a broadcast, if group policy has changed, or the GCKS needs to reset the policy and keying material for the group due to an emergency. Deletion of keys MAY be accomplished by sending an IKEv2 Delete Payload, section 3.11 of [RFC7296] as part of a registration or rekey Exchange. Whenever an SA is to be deleted, the GKCS SHOULD send the Delete Payload in both registration and rekey exchanges, because GMs with previous group policy may contact the GCKS using either exchange. The Protocol ID MUST be 41 for GSA_REKEY Exchange, 2 for AH or 3 for ESP. Note that only one protocol id value can be defined in a Delete payload. If a TEK and a KEK SA for GSA_REKEY Exchange must be deleted, they must be sent in different Delete payloads. Similarly, if a TEK specifying ESP and a TEK specifying AH need to be deleted, they must be sent in different Delete payloads. There may be circumstances where the GCKS may want to reset the policy and keying material for the group. The GCKS can signal deletion of all policy of a particular TEK by sending a TEK with a SPI value equal to zero in the delete payload. In the event that the administrator is no longer confident in the integrity of the group they may wish to remove all KEK and all the TEKs in the group. This is done by having the GCKS send a delete payload with a SPI of zero and a Protocol-ID of AH or ESP to delete all TEKs, followed by another delete payload with a SPI value of zero and Protocol-ID of KEK SA to delete the KEK SA. 2.7. Notify Payload G-IKEv2 uses the same Notify payload as specified in [RFC7296], section 3.10. Weis & Smyslov Expires July 12, 2020 [Page 42] Internet-Draft G-IKEv2 January 2020 There are additional Notify Message types introduced by G-IKEv2 to communicate error conditions and status. NOTIFY messages - error types Value ------------------------------------------------------------------- INVALID_GROUP_ID - 45 AUTHORIZATION_FAILED - 46 REGISTRATION_FAILED - TBD INVALID_GROUP_ID indicates the group id sent during the registration process is invalid. AUTHORIZATION_FAILED is sent in the response to a GSA_AUTH message when authorization failed. REGISTRATION_FAILED is sent by the GCKS when the GM registration request cannot be satisfied. NOTIFY messages - status types Value ------------------------------------------------------------------- SENDER - 16429 REKEY_IS_NEEDED - TBD SENDER notification is sent in GSA_AUTH or GSA_REGISTRATION to indicate that the GM intends to be sender of data traffic. The data includes a count of how many SID values the GM desires. The count MUST be 4 octets long and contain the big endian representation of the number of requested SIDs. REKEY_IS_NEEDED is sent in GSA_AUTH response message to indicate that the GM must perform an immediate rekey of IKE SA to make it secure against quantum computers and then start a registration request over. 2.8. Authentication Payload G-IKEv2 uses the same Authentication payload as specified in [RFC7296], section 3.8, to sign the rekey message. 3. Security Considerations 3.1. GSA Registration and Secure Channel G-IKEv2 registration exchange uses IKEv2 IKE_SA_INIT protocols, inheriting all the security considerations documented in [RFC7296] section 5 Security Considerations, including authentication, confidentiality, protection against man-in-the-middle, protection against replay/reflection attacks, and denial of service protection. The GSA_AUTH and GSA_REGISTRATION exchanges also take advantage of Weis & Smyslov Expires July 12, 2020 [Page 43] Internet-Draft G-IKEv2 January 2020 those protections. In addition, G-IKEv2 brings in the capability to authorize a particular group member regardless of whether they have the IKEv2 credentials. 3.2. GSA Maintenance Channel The GSA maintenance channel is cryptographically and integrity protected using the cryptographic algorithm and key negotiated in the GSA member registration exchanged. 3.2.1. Authentication/Authorization Authentication is implicit, the public key of the identity is distributed during the registration, and the receiver of the rekey message uses that public key and identity to verify the message came from the authorized GCKS. 3.2.2. Confidentiality Confidentiality is provided by distributing a confidentiality key as part of the GSA member registration exchange. 3.2.3. Man-in-the-Middle Attack Protection GSA maintenance channel is integrity protected by using a digital signature. 3.2.4. Replay/Reflection Attack Protection The GSA_REKEY message includes a monotonically increasing sequence number to protect against replay and reflection attacks. A group member will recognize a replayed message by comparing the Message ID number to that of the last received rekey message, any rekey message containing a Message ID number less than or equal to the last received value MUST be discarded. Implementations should keep a record of recently received GSA rekey messages for this comparison. 4. IANA Considerations 4.1. New Registries A new set of registries should be created for G-IKEv2, on a new page titled Group Key Management using IKEv2 (G-IKEv2) Parameters. The following registries should be placed on that page. The terms Reserved, Expert Review and Private Use are to be applied as defined in [RFC8126]. GSA Policy Type Registry, see Section 2.4.1 Weis & Smyslov Expires July 12, 2020 [Page 44] Internet-Draft G-IKEv2 January 2020 KEK Attributes Registry, see Section 2.4.2.1 KEK Management Algorithm Registry, see Section 2.4.2.1.1 GSA TEK Payload Protocol ID Type Registry, see Section 2.4.3 TEK Attributes Registry, see Section 2.4.3 Key Download Type Registry, see Section 2.5 TEK Download Type Attributes Registry, see Section 2.5.1 KEK Download Type Attributes Registry, see Section 2.5.2 LKH Download Type Attributes Registry, see Section 2.5.3 SID Download Type Attributes Registry, see Section 2.5.4 4.2. New Payload and Exchange Types Added to the Existing IKEv2 Registry The following new payloads and exchange types specified in this memo have already been allocated by IANA and require no further action, other than replacing the draft name with an RFC number. The present document describes new IKEv2 Next Payload types, see Section 2.1 The present document describes new IKEv2 Exchanges types, see Section 2.1 The present document describes new IKEv2 notification types, see Section 2.7 4.3. Changes to Previous Allocations Section 4.7 indicates an allocation in the IKEv2 Notify Message Types - Status Types registry has been made. This NOTIFY type was allocated earlier in the development of G-IKEv2. The number is 16429, and was allocated with the name SENDER_REQUEST_ID. The name should be changed to SENDER. 5. Acknowledgements The authors thank Lakshminath Dondeti and Jing Xiang for first exploring the use of IKEv2 for group key management and providing the basis behind the protocol. Mike Sullenberger and Amjad Inamdar were Weis & Smyslov Expires July 12, 2020 [Page 45] Internet-Draft G-IKEv2 January 2020 instrumental in helping resolve many issues in several versions of the document. 6. Contributors The following individuals made substantial contributions to early versions of this memo. Sheela Rowles Cisco Systems 170 W. Tasman Drive San Jose, California 95134-1706 USA Phone: +1-408-527-7677 Email: sheela@cisco.com Aldous Yeung Cisco Systems 170 W. Tasman Drive San Jose, California 95134-1706 USA Phone: +1-408-853-2032 Email: cyyeung@cisco.com Paulina Tran Cisco Systems 170 W. Tasman Drive San Jose, California 95134-1706 USA Phone: +1-408-526-8902 Email: ptran@cisco.com Yoav Nir Dell EMC 9 Andrei Sakharov St Haifa 3190500 Israel Email: ynir.ietf@gmail.com 7. References Weis & Smyslov Expires July 12, 2020 [Page 46] Internet-Draft G-IKEv2 January 2020 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2627] Wallner, D., Harder, E., and R. Agee, "Key Management for Multicast: Issues and Architectures", RFC 2627, DOI 10.17487/RFC2627, June 1999, . [RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security Architecture", RFC 3740, DOI 10.17487/RFC3740, March 2004, . [RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm, "Multicast Security (MSEC) Group Key Management Architecture", RFC 4046, DOI 10.17487/RFC4046, April 2005, . [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005, . [RFC6054] McGrew, D. and B. Weis, "Using Counter Modes with Encapsulating Security Payload (ESP) and Authentication Header (AH) to Protect Group Traffic", RFC 6054, DOI 10.17487/RFC6054, November 2010, . [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014, . [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Weis & Smyslov Expires July 12, 2020 [Page 47] Internet-Draft G-IKEv2 January 2020 7.2. Informative References [I-D.ietf-ipsecme-qr-ikev2] Fluhrer, S., McGrew, D., Kampanakis, P., and V. Smyslov, "Mixing Preshared Keys in IKEv2 for Post-quantum Resistance", draft-ietf-ipsecme-qr-ikev2-10 (work in progress), December 2019. [I-D.smyslov-ipsecme-ikev2-qr-alt] Smyslov, V., "An Alternative Approach for Postquantum Preshared Keys in IKEv2", draft-smyslov-ipsecme-ikev2-qr- alt-00 (work in progress), October 2019. [I-D.tjhai-ipsecme-hybrid-qske-ikev2] Tjhai, C., Tomlinson, M., grbartle@cisco.com, g., Fluhrer, S., Geest, D., Garcia-Morchon, O., and V. Smyslov, "Framework to Integrate Post-quantum Key Exchanges into Internet Key Exchange Protocol Version 2 (IKEv2)", draft- tjhai-ipsecme-hybrid-qske-ikev2-04 (work in progress), July 2019. [IKEV2-IANA] IANA, "Internet Key Exchange Version 2 (IKEv2) Parameters", . [NNL] Naor, D., Noal, M., and J. Lotspiech, "Revocation and Tracing Schemes for Stateless Receivers", Advances in Cryptology, Crypto '01, Springer-Verlag LNCS 2139, 2001, pp. 41-62, 2001, . [OFT] McGrew, D. and A. Sherman, "Key Establishment in Large Dynamic Groups Using One-Way Function Trees", Manuscript, submitted to IEEE Transactions on Software Engineering, 1998, . [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998, . [RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April 2002, . Weis & Smyslov Expires July 12, 2020 [Page 48] Internet-Draft G-IKEv2 January 2020 [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC 3447, DOI 10.17487/RFC3447, February 2003, . [RFC3686] Housley, R., "Using Advanced Encryption Standard (AES) Counter Mode With IPsec Encapsulating Security Payload (ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004, . [RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode (GCM) in IPsec Encapsulating Security Payload (ESP)", RFC 4106, DOI 10.17487/RFC4106, June 2005, . [RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM Mode with IPsec Encapsulating Security Payload (ESP)", RFC 4309, DOI 10.17487/RFC4309, December 2005, . [RFC4543] McGrew, D. and J. Viega, "The Use of Galois Message Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543, DOI 10.17487/RFC4543, May 2006, . [RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast Extensions to the Security Architecture for the Internet Protocol", RFC 5374, DOI 10.17487/RFC5374, November 2008, . [RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk, "Elliptic Curve Cryptography Subject Public Key Information", RFC 5480, DOI 10.17487/RFC5480, March 2009, . [RFC5723] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange Protocol Version 2 (IKEv2) Session Resumption", RFC 5723, DOI 10.17487/RFC5723, January 2010, . [RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain of Interpretation", RFC 6407, DOI 10.17487/RFC6407, October 2011, . [RFC6467] Kivinen, T., "Secure Password Framework for Internet Key Exchange Version 2 (IKEv2)", RFC 6467, DOI 10.17487/RFC6467, December 2011, . Weis & Smyslov Expires July 12, 2020 [Page 49] Internet-Draft G-IKEv2 January 2020 [RFC7383] Smyslov, V., "Internet Key Exchange Protocol Version 2 (IKEv2) Message Fragmentation", RFC 7383, DOI 10.17487/RFC7383, November 2014, . [RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in the Internet Key Exchange Version 2 (IKEv2)", RFC 7427, DOI 10.17487/RFC7427, January 2015, . [RFC8229] Pauly, T., Touati, S., and R. Mantha, "TCP Encapsulation of IKE and IPsec Packets", RFC 8229, DOI 10.17487/RFC8229, August 2017, . Appendix A. Use of LKH in G-IKEv2 Section 5.4 of [RFC2627] describes the LKH architecture, and how a GCKS uses LKH to exclude group members. This section clarifies how the LKH architecture is used with G-IKEv2. A.1. Group Creation When a GCKS forms a group, it creates a key tree as shown in the figure below. The key tree contains logical keys (represented as numbers in the figure) and a private key shared with only a single GM (represented as letters in the figure). Note that the use of numbers and letters is used for explanatory purposes; in fact, each key would have an LKH ID, which is two-octet identifier chosen by the GCKS. The GCKS may create a complete tree as shown, or a partial tree which is created on demand as members join the group. The top of the key tree (i.e., "1" in Figure 29) is used as the KEK for the group. 1 +------------------------------+ 2 3 +---------------+ +---------------+ 4 5 6 7 +-------+ +-------+ +--------+ +--------+ A B C D E F G H Figure 29: Initial LKH tree When GM "A" joins the group, the GCKS provides an LKH_DOWNLOAD_ARRAY in the KD payload of the GSA_AUTH or GSA_REGISTRATION exchange. Given the tree shown in figure above, the LKH_DOWNLOAD_ARRAY will contain four LKH Key payloads, each containing an LKH ID and Key Data. If the LKH ID values were chosen as shown in the figure, four LKH Keys would be provided to GM "A", in the following order: A, 4, Weis & Smyslov Expires July 12, 2020 [Page 50] Internet-Draft G-IKEv2 January 2020 2, 1. When GM "B" joins the group, it would also be given four LKH Keys in the following order: B, 4, 2, 1. And so on, until GM "H" joins the group and is given H, 7, 3, 1. A.2. Group Member Exclusion If the GKCS has reason to believe that a GM should be excluded, then it can do so by sending a GSA_REKEY exchange that includes a set of LKH_UPDATE_ARRAY attributes in the KD payload. Each LKH_UPDATE_ARRAY contains a set of LKH Key payloads, in which every GM other than the excluded GM will be able to determine a set of new logical keys, which culminate in a new key "1". The excluded GM will observe the set of LKH_UPDATE_ARRAY attributes, but cannot determine the new logical keys because each of the "Key Data" fields is encrypted with a key held by other GMs. The GM will hold no keys to properly decrypt any of the "Key Data" fields, including key "1" (i.e., the new KEK). When a subsequent GSA_REKEY exchange is delivered by the GCKS and protected by the new KEK, the excluded GM will no longer be able to see the contents of the GSA_REKEY, including new TEKs that will be delivered to replace existing TEKs. At this point, the GM will no longer be able to participate in the group. In the example below, new keys are represented as the number followed by a "prime" symbol (e.g., "1" becomes "1'"). Each key is encrypted by another key. This is represented as "{key1}key2", where key2 encrypts key1. For example, "{1'}2' states that a new key "1'" is encrypted with a new key "2'". If GM "B" is to be excluded, the GCKS will need to include three LKH_UPDATE_ARRAY attributes in the GSA_REKEY message. The order of the attributes does not matter; only the order of the keys within each attribute. o One will provide GM "A" with new logical keys that are shared with B: {4'}A, {2'}4', {1'}2' o One will provide all GMs holding key "5" with new logical keys: {2'}5, {1'}2' o One will provide all GMs holding key "3" with a new KEK: {1'}3 Each GM will look at each LKH_UPDATE_ARRAY attribute and observe an LKH ID which is present in an LKH Key delivered to them in the LKH_DOWNLOAD_ARRAY they were given. If they find a matching LKH ID, then they will decrypt the new key with the logical key immediately preceding that LKH Key, and so on until they have received the new 1' key. Weis & Smyslov Expires July 12, 2020 [Page 51] Internet-Draft G-IKEv2 January 2020 The resulting key tree from this rekey event would would be shown in Figure 30. 1' +------------------------------+ 2' 3 +---------------+ +---------------+ 4' 5 6 7 +---+ +-------+ +--------+ +--------+ A B C D E F G H Figure 30: LKH tree after B has been excluded Authors' Addresses Brian Weis Independent USA Email: bew.stds@gmail.com Valery Smyslov ELVIS-PLUS PO Box 81 Moscow (Zelenograd) 124460 Russian Federation Phone: +7 495 276 0211 Email: svan@elvis.ru Weis & Smyslov Expires July 12, 2020 [Page 52]