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Huawei Technologies

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Mavenir Systems Pvt Ltd

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China Mobile

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Security IPSECME Working Group Internet-Draft This document describes a method for reducing the size of the Internet Key Exchange version 2 (IKEv2) exchanges at time of rekeying IKE SAs and Child SAs by removing or making optional of SA & TS payloads. Reducing size of IKEv2 exchanges is desirable for low power consumption battery powered devices. It also helps to avoid IP fragmentation of IKEv2 messages.

The Internet Key Exchange protocol version 2 (IKEv2) specified in is used in the IP Security (IPsec) architecture for the purposes of Security Association (SA) parameters negotiation and authenticated key exchange. The protocol uses UDP as the transport for its messages, which size varies from less than one hundred bytes to several kilobytes. According to , the secret keys used by IKE/IPSec SAs should be used only for a limited amount of time and to protect a limited amount of data. When the lifetime of an SA expires or is about to expire, the peers can rekey the SA to reestablish a new SA to take the place of the old one. For security gateways/ePDG in 4G networks and cRAN/Cloud in 5G networks, they will support more than 100,000 IKE/IPSEC tunnels. So on an average, for every second there may be hundreds or thousands of IKE SAs and Child SAs that are rekeying. This takes huge amount of bandwidth, packet fragmentation and more processing resources. For these devices, these problems can be solved by introducing the solution described in this document. This is also useful in Internet of Things (IoT) devices which utilizing lower power consumption technology. The appendix A of gives some estimate data. For these devices, reducing the length of IKE/Child SA rekeying messages can save the bandwidth consumption. At the same time, it can also save the computing processes by less payload are included. Most devices don’t prefer to change cryptographic suites frequently. By taking this advantage the SA and TS payloads can be made optional at the time of rekeying IKE SAs and Child SAs. In such situation, only a new SPI value is needed to create the new IKE SA and Child SA. So a new Notify payload which contains the needed SPI value can be sent instead of the SA and TS payloads. In case of rekeying IKE SAs, the SA payloads can be optimized if there is no change of cryptographic suites. In case of rekeying Child SAs, the SA and TS payloads can be optimized if there is no change of cryptographic suites and ACL configuration.

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 when, and only when, they appear in all capitals, as shown here.

This section provides protocol details and contains the normative parts. Before using this new optimization, the IPSec implementation who supports it has to know that the peer also supports it. Without the support on both sides, the optimized rekeying messages sent by one peer may be unrecognizable for the other peer. To prevent this failure from happening, the first step is to negotiate the support of this optimization between the two peers. There are two specific rekeying SAs cases: rekeying IKE SAs and rekeying Child SAs. After the negotiation, the initiator can optimize the rekeying message payloads in both cases. In other words, once the negotiation of support for optimizing payloads at rekeying IKE SAs and Child SAs is complete, both IKE SAs and Child SAs rekeying are supported by the two sides. The responder can react based on the received rekeying message.

The initiator indicates its support for optimizing optional payloads at rekeying IKE SAs and Child SAs by including a Notify payload of type MINIMAL_REKEY_SUPPORTED in the IKE_AUTH request message. By observing the MINIMAL_REKEY_SUPPORTED notification in the received message, the responder can deduce the initiator’s support of this extension. If the responder also supports this extension, it includes the MINIMAL_REKEY_SUPPORTED notification in the corresponding response message. After receiving the response message, the initiator can also know the support of this extension of the responder side. The IKE_AUTH message exchange in this case is shown below:

<-- HDR, SK {IDr, [CERT,] AUTH, SAr2, TSi, TSr, N(MINIMAL_REKEY_SUPPORTED)} ]]>

If the responder doesn’t support this extension, it MUST ignore the MINIMAL_REKEY_SUPPORTED notification sent by the initiator and MUST NOT respond error to the initiator. With no MINIMAL_REKEY_SUPPORTED notification in the response message, the initiator can deduce that the responder doesn’t support this extension. In this case, the IKE SAs and Child SAs rekeyings happen as the usual way without the optimizations defined in this document. The IKE_AUTH message exchange in this case is shown below:

<-- HDR, SK {IDr, [CERT,] AUTH, SAr2, TSi, TSr} ]]>

The payload optimization at rekeying IKE SAs MUST NOT be used unless both peers have indicated their support of this extension by using the negotiation method described in . If the initiator decides to optimize the payloads at the time of rekeying IKE SAs, then it includes the SA_UNCHANGED notification in its CREATE_CHILD_SA exchange message. If the initiator decides not to do the optimization, then it just sends the rekeying request message as the original way, the rekeying is conducted as defined. If the initiator and responder decides to do the optimization, then the IKE SA rekeying uses PFS by default.

At the time of rekeying an IKE SA, when the initiator determines there is no change on its cryptographic suites since this IKE SA was created or last rekeyed, it MAY send the SA_UNCHANGED notification payload instead of the SA payloads in the rekeying request message. In this SA_UNCHANGED notification, it contains the initiator’s new Security Parameter Index (SPI) used for creating the new IKE SA. After receiving the initiator’s rekeying request message with the SA_UNCHANGED notification and no SA payloads, the responder knows that the initiator wants to optimize the rekeying payload. Then when it determines that there is also no change in its cryptographic suites, the responder MAY send the rekeying respond message to the initiator with the SA_UNCHANGED notification payload instead of the SA payloads. In this SA_UNCHANGED notification, it contains the responder’s new SPI used for creating the new IKE SA. According to the initiator’s new SPI and the responder’s new SPI, the initiator and the responder can rekey the IKE SA on both sides. The CREATE_CHILD_SA message exchange in this case is shown below:

<-- HDR, SK {N(SA_UNCHANGED), Nr, KEr} ]]>

The initiator sends a SA_UNCHANGED notification payload, a Nonce payload and a Diffie-Hellman value in the KEi payload. A new initiator SPI is supplied in the SPI field of the SA_UNCHANGED notification payload. These messages also follow the original PFS with the signature and encryption algorithms used as last message. The responder replies (using the same Message ID to respond) with a SA_UNCHANGED notification payload, a Nonce payload and a Diffie-Hellman value in the KEr payload. A new responder SPI is supplied in the SPI field of the SA_UNCHANGED notification payload. This SA_UNCHANGED notification MUST be included in a CREATE_CHILD_SA exchange message when there is no SA payloads included. When the SA_UNCHANGED notification payload is included, the SA payload MUST NOT be included.

At the time of or before rekeying IKE SAs, the responder’s cryptographic suites may be changed while there is no change of initiator’s cryptographic suites. New cryptographic suites may be added to the responder, or some outdated cryptographic suites may be deleted from the responder. In this situation, the initiator MAY send the SA_UNCHANGED notification payload instead of the SA payloads in the CREATE_CHILD_SA request message at the time of rekeying IKE SAs. If the responder decides to continue using the previously negotiated cryptographic suite to rekey the IKE SA, it MAY send the SA_UNCHANGED notification payload in the CREATE_CHILD_SA response message, then the rekeying is conducted like the way described in . If the responder decides to re-negotiate the cryptographic suite, it MUST send NO_PROPOSAL_CHOSEN notification payload in the CREATE_CHILD_SA response message. After receiving this error notification, the initiator MUST retry the CREATE_CHILD_SA exchange with the SA payloads. Then the rekeying is conducted in the original way defined in . The CREATE_CHILD_SA message exchange in this case is shown below:

<-- HDR, SK {N(NO_PROPOSAL_CHOSEN), Nr, KEr} HDR, SK {SA, Ni, KEi} --> <-- HDR, SK {SA, Ni, KEi} ]]>

Besides, if the responder only supports the Child SA rekeying optimization and doesn’t support the IKE SA rekeying optimization, it can also follow the way described above, i.e., it MUST send NO_PROPOSAL_CHOSEN notification payload in the CREATE_CHILD_SA response message when receiving the SA_UNCHANGED notification at the time of rekeying IKE SAs.

The payload optimization at rekeying Child SAs MUST NOT be used unless both peers have indicated their support of this extension by using the negotiation method described in . If the initiator decides to optimize the payloads at the time of rekeying Child SAs, then it includes the SA_TS_UNCHANGED notification in its CREATE_CHILD_SA exchange message. If the initiator decides not to do the optimization, then it just sends the rekeying request message as the original way, the rekeying is conducted as defined. This SA_TS_UNCHANGED notification MUST be included in a CREATE_CHILD_SA exchange message when there is no SA and TS payloads included. The new Child SA is created with the SPI value in the SA_TS_UNCHANGED notification.

At the time of rekeying Child SAs, the initiator MAY send the SA_TS_UNCHANGED notification payload instead of the SA and TS payloads when there is no change in its cryptographic suites and ACL configuration since last negotiation. After receiving the initiator’s request message with the SA_TS_UNCHANGED notification, the responder MAY respond to the initiator with the SA_TS_UNCHANGED notification payload instead of the SA and TS payloads if there is also no change in its cryptographic suites and ACL configuration since last negotiation. At the time of rekeying a Child SA, when the initiator determines there is no change in its cryptographic suites and ACL configuration since this Child SA was created or last rekeyed, it MAY send the SA_TS_UNCHANGED notification payload instead of the SA and TS payloads in the rekeying request message. In this SA_TS_UNCHANGED notification, it contains the initiator’s new Security Parameter Index (SPI) used for creating the new Child SA. After receiving the initiator’s rekeying request message with the SA_TS_UNCHANGED notification and no SA and TS payloads, the responder knows that the initiator wants to optimize the rekeying payload. Then when it determines that there is also no change in its cryptographic suites and ACL configuration, the responder MAY send the rekeying respond message to the initiator with the SA_TS_UNCHANGED notification payload instead of the SA and TS payloads. In this SA_TS_UNCHANGED notification, it contains the responder’s new SPI used for creating the new Child SA. According to the initiator’s new SPI and the responder’s new SPI, the initiator and the responder can rekey the Child SA on both sides. The CREATE_CHILD_SA message exchange in this case is shown below:

<-- HDR, SK {N(SA_TS_UNCHANGED), Nr, [KEr,]} ]]>

This SA_TS_UNCHANGED notification MUST be included in a CREATE_CHILD_SA exchange message when there is no SA and TS payloads included at the time of rekeying Child SAs. When the SA_TS_UNCHANGED notification payload is included, the SA and TS payloads MUST NOT be included.

At the time of or before rekeying Child SAs, the responder’s cryptographic suites or ACL configuration may be changed while there is no change of initiator’s cryptographic suites and ACL configuration. In this situation, the initiator MAY send the SA_TS_UNCHANGED notification payload instead of the SA and TS payloads in the CREATE_CHILD_SA request message at the time of rekeying Child SAs. If the responder decides to continue using the previously negotiated cryptographic suite and Traffic Selectors to rekey the Child SA, it MAY send the SA_TS_UNCHANGED notification payload in the CREATE_CHILD_SA response message, then the rekeying is conducted like . If the responder decides to re-negotiate the cryptographic suite or Traffic Selectors, it MUST send NO_PROPOSAL_CHOSEN notification payload in the CREATE_CHILD_SA response message. After receiving this error notification, the initiator MUST retry the CREATE_CHILD_SA exchange with the SA and TS payloads. Then the rekeying is conducted in the original way defined in . The CREATE_CHILD_SA message exchange in this case is shown below:

<-- HDR, SK {N(NO_PROPOSAL_CHOSEN), Nr, KEr} HDR, SK {N(REKEY_SA), SA, Ni, [KEi,] TSi, TSr} --> <-- HDR, SK {SA, Nr, [KEr,] TSi, TSr} ]]>

Besides, if the responder only supports the IKE SA rekeying optimization and doesn’t support the Child SA rekeying optimization, it can also follow the way described above, i.e., it MUST send NO_PROPOSAL_CHOSEN notification payload in the CREATE_CHILD_SA response message when receiving the SA_TS_UNCHANGED notification at the time of rekeying Child SAs.

The MINIMAL_REKEY_SUPPORTED notification is used by the initiator and responder to inform their ability of optimizing optional payload at the time of rekeying IKE SAs and Child SAs to the peers. It is formatted as follows:

Protocol ID (1 octet) - MUST be 0. SPI Size (1 octet) - MUST be 0, meaning no SPI is present. Notify Message Type (2 octets) - MUST be <Need to get value from IANA>, the value assigned for the MINIMAL_REKEY_SUPPORTED notification. This notification contains no data.

The SA_UNCHANGED notification is used to replace the SA payloads at the time of rekeying IKE SAs when there is no change of cryptographic suites in initiator or responder. It is formatted as follows:

Protocol ID (1 octet) - MUST be 1. SPI Size (1 octet) - MUST be 8. Notify Message Type (2 octets) - MUST be <Need to get value from IANA>, the value assigned for the SA_UNCHANGED notification. SPI (8 octets) - Security Parameter Index. The initiator sends initiator SPI. The responder sends responder SPI.

The SA_TS_UNCHANGED notification is used to replace the SA payloads and TS payloads at the time of rekeying Child SAs when there is no change of cryptographic suites and ACL configuration in initiator or responder. The SPI of the new Child SA is included in this payload, and the SPI of the old Child SA is in the REKEY_SA notification payload. The SA_TS_UNCHANGED notification is formatted as follows:

Protocol ID (1 octet) - MUST be either (2) to indicate AH or (3) to indicate ESP. SPI Size (1 octet) - MUST be 4. Notify Message Type (2 octets) - MUST be <Need to get value from IANA>, the value assigned for the SA_TS_UNCHANGED notification. SPI (4 octets) - Security Parameter Index. The initiator sends initiator SPI. The responder sends responder SPI.

This document defines two new Notify Message Types in the “IKEv2 Notify Message Types - Status Types” registry. IANA is requested to assign codepoints in this registry.

TBD

In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document describes version 2 of the Internet Key Exchange (IKE) protocol. IKE is a component of IPsec used for performing mutual authentication and establishing and maintaining Security Associations (SAs). This document obsoletes RFC 5996, and includes all of the errata for it. It advances IKEv2 to be an Internet Standard. IPsec/ESP is used to secure end-to-end communications. This document lists the requirements Diet-ESP should meet to design IPsec/ESP for IoT.