RFC 7402
Using the Encapsulating Security Payload (ESP) Transport Format with the Host Identity Protocol (HIP)
Internet Engineering Task Force (IETF) P. Jokela Request for Comments: 7402 Ericsson Research NomadicLab Obsoletes: 5202 R. Moskowitz Category: Standards Track HTT Consulting ISSN: 2070-1721 J. Melen Ericsson Research NomadicLab April 2015 Using the Encapsulating Security Payload (ESP) Transport Format with the Host Identity Protocol (HIP)Abstract
This memo specifies an Encapsulating Security Payload (ESP) based mechanism for transmission of user data packets, to be used with the Host Identity Protocol (HIP). This document obsoletes RFC 5202. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7402. Copyright Notice Copyright (c) 2015 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 (http://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 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 ....................................................3 2. Conventions Used in This Document ...............................4 3. Using ESP with HIP ..............................................4 3.1. ESP Packet Format ..........................................5 3.2. Conceptual ESP Packet Processing ...........................5 3.2.1. Semantics of the Security Parameter Index (SPI) .....6 3.3. Security Association Establishment and Maintenance .........6 3.3.1. ESP Security Associations ...........................6 3.3.2. Rekeying ............................................7 3.3.3. Security Association Management .....................8 3.3.4. Security Parameter Index (SPI) ......................8 3.3.5. Supported Ciphers ...................................8 3.3.6. Sequence Number .....................................9 3.3.7. Lifetimes and Timers ................................9 3.4. IPsec and HIP ESP Implementation Considerations ............9 3.4.1. Data Packet Processing Considerations ..............10 3.4.2. HIP Signaling Packet Considerations ................10 4. The Protocol ...................................................11 4.1. ESP in HIP ................................................11 4.1.1. IPsec ESP Transport Format Type ....................11 4.1.2. Setting Up an ESP Security Association .............11 4.1.3. Updating an Existing ESP SA ........................12 5. Parameter and Packet Formats ...................................13 5.1. New Parameters ............................................13 5.1.1. ESP_INFO ...........................................13 5.1.2. ESP_TRANSFORM ......................................15 5.1.3. NOTIFICATION Parameter .............................16 5.2. HIP ESP Security Association Setup ........................17 5.2.1. Setup during Base Exchange .........................17 5.3. HIP ESP Rekeying ..........................................18 5.3.1. Initializing Rekeying ..............................19 5.3.2. Responding to the Rekeying Initialization ..........19 5.4. ICMP Messages .............................................20 5.4.1. Unknown SPI ........................................20 6. Packet Processing ..............................................20 6.1. Processing Outgoing Application Data ......................20 6.2. Processing Incoming Application Data ......................21 6.3. HMAC and SIGNATURE Calculation and Verification ...........21 6.4. Processing Incoming ESP SA Initialization (R1) ............22 6.5. Processing Incoming Initialization Reply (I2) .............22 6.6. Processing Incoming ESP SA Setup Finalization (R2) ........23 6.7. Dropping HIP Associations .................................23 6.8. Initiating ESP SA Rekeying ................................23
6.9. Processing Incoming UPDATE Packets ........................24
6.9.1. Processing UPDATE Packet: No Outstanding
Rekeying Request ...................................25
6.10. Finalizing Rekeying ......................................26
6.11. Processing NOTIFY Packets ................................26
7. Keying Material ................................................27
8. Security Considerations ........................................27
9. IANA Considerations ............................................28
10. References ....................................................29
10.1. Normative References .....................................29
10.2. Informative References ...................................30
Appendix A. A Note on Implementation Options ......................32
Appendix B. Bound End-to-End Tunnel Mode for ESP ..................32
B.1. Protocol Definition ........................................33
B.1.1. Changes to Security Association Data Structures .....33
B.1.2. Packet Format .......................................34
B.1.3. Cryptographic Processing ............................36
B.1.4. IP Header Processing ................................36
B.1.5. Handling of Outgoing Packets ........................37
B.1.6. Handling of Incoming Packets ........................38
B.1.7. Handling of IPv4 Options ............................39
Acknowledgments ...................................................40
Authors' Addresses ................................................40
1. Introduction
In the Host Identity Protocol Architecture [HIP-ARCH], hosts are
identified with public keys. The Host Identity Protocol (HIP)
[RFC7401] base exchange allows any two HIP-supporting hosts to
authenticate each other and to create a HIP association between
themselves. During the base exchange, the hosts generate a piece of
shared keying material using an authenticated Diffie-Hellman
exchange.
The HIP base exchange specification [RFC7401] does not describe any
transport formats or methods for user data to be used during the
actual communication; it only defines that it is mandatory to
implement the Encapsulating Security Payload (ESP) [RFC4303] based
transport format and method. This document specifies how ESP is used
with HIP to carry actual user data.
To be more specific, this document specifies a set of HIP protocol
extensions and their handling. Using these extensions, a pair of ESP
Security Associations (SAs) is created between the hosts during the
base exchange. The resulting ESP Security Associations use keys
drawn from the keying material (KEYMAT) generated during the base
exchange. After the HIP association and required ESP SAs have been
established between the hosts, the user data communication is protected using ESP. In addition, this document specifies methods to update an existing ESP Security Association. It should be noted that representations of Host Identity are not carried explicitly in the headers of user data packets. Instead, the ESP Security Parameter Index (SPI) is used to indicate the right host context. The SPIs are selected during the HIP ESP setup exchange. For user data packets, ESP SPIs (in possible combination with IP addresses) are used indirectly to identify the host context, thereby avoiding any additional explicit protocol headers. HIP and ESP traffic have known issues with middlebox traversal (RFC 5207 [RFC5207]). Other specifications exist for operating HIP and ESP over UDP. (RFC 5770 [RFC5770] is an experimental specification, and others are being developed.) Middlebox traversal is out of scope for this document. This document obsoletes RFC 5202.2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].3. Using ESP with HIP
The HIP base exchange is used to set up a HIP association between two hosts. The base exchange provides two-way host authentication and key material generation, but it does not provide any means for protecting data communication between the hosts. In this document, we specify the use of ESP for protecting user data traffic after the HIP base exchange. Note that this use of ESP is intended only for host-to-host traffic; security gateways are not supported. To support ESP use, the HIP base exchange messages require some minor additions to the parameters transported. In the R1 packet, the Responder adds the possible ESP transforms in an ESP_TRANSFORM parameter before sending it to the Initiator. The Initiator gets the proposed transforms, selects one of those proposed transforms, and adds it to the I2 packet in an ESP_TRANSFORM parameter. In this I2 packet, the Initiator also sends the SPI value that it wants to be used for ESP traffic flowing from the Responder to the Initiator. This information is carried using the ESP_INFO parameter. When finalizing the ESP SA setup, the Responder sends its SPI value to the Initiator in the R2 packet, again using ESP_INFO.
3.1. ESP Packet Format
The ESP specification [RFC4303] defines the ESP packet format for IPsec. The HIP ESP packet looks exactly the same as the IPsec ESP transport format packet. The semantics, however, are a bit different and are described in more detail in the next subsection.3.2. Conceptual ESP Packet Processing
ESP packet processing can be implemented in different ways in HIP. It is possible to implement it in a way that a standards compliant, unmodified IPsec implementation [RFC4303] can be used in conjunction with some additional transport checksum processing above it, and if IP addresses are used as indexes to the right host context. When a standards compliant IPsec implementation that uses IP addresses in the Security Policy Database (SPD) and Security Association Database (SAD) is used, the packet processing may take the following steps. For outgoing packets, assuming that the upper-layer pseudo header has been built using IP addresses, the implementation recalculates upper-layer checksums using Host Identity Tags (HITs) and, after that, changes the packet source and destination addresses back to corresponding IP addresses. The packet is sent to the IPsec ESP for transport mode handling, and from there the encrypted packet is sent to the network. When an ESP packet is received, the packet is first put through the IPsec ESP transport mode handling, and after decryption, the source and destination IP addresses are replaced with HITs, and finally, upper-layer checksums are verified before passing the packet to the upper layer. An alternative way to implement packet processing is the BEET (Bound End-to-End Tunnel) mode (see Appendix B). In BEET mode, the ESP packet is formatted as a transport mode packet, but the semantics of the connection are the same as for tunnel mode. The "outer" addresses of the packet are the IP addresses, and the "inner" addresses are the HITs. For outgoing traffic, after the packet has been encrypted, the packet's IP header is changed to a new one that contains IP addresses instead of HITs, and the packet is sent to the network. When the ESP packet is received, the SPI value, together with the integrity protection, allow the packet to be securely associated with the right HIT pair. The packet header is replaced with a new header containing HITs, and the packet is decrypted. BEET mode is completely internal for a host and doesn't require that the corresponding host implement it; instead, the corresponding host can have ESP transport mode and do HIT IP conversions outside ESP.
3.2.1. Semantics of the Security Parameter Index (SPI)
SPIs are used in ESP to find the right Security Association for received packets. The ESP SPIs have added significance when used with HIP; they are a compressed representation of a pair of HITs. Thus, SPIs MAY be used by intermediary systems in providing services like address mapping. Note that since the SPI has significance at the receiver, only the < DST, SPI >, where DST is a destination IP address, uniquely identifies the receiver HIT at any given point of time. The same SPI value may be used by several hosts. A single < DST, SPI > value may denote different hosts and contexts at different points of time, depending on the host that is currently reachable at the DST. Each host selects for itself the SPI it wants to see in packets received from its peer. This allows it to select different SPIs for different peers. The SPI selection SHOULD be random; the rules of Section 2.1 of the ESP specification [RFC4303] must be followed. A different SPI SHOULD be used for each HIP exchange with a particular host; this is to avoid a replay attack. Additionally, when a host rekeys, the SPI MUST be changed. Furthermore, if a host changes over to use a different IP address, it MAY change the SPI. One method for SPI creation that meets the above criteria would be to concatenate the HIT with a 32-bit random or sequential number, hash this (using SHA1), and then use the high-order 32 bits as the SPI. The selected SPI is communicated to the peer in the third (I2) and fourth (R2) packets of the base HIP exchange. Changes in SPI are signaled with ESP_INFO parameters.3.3. Security Association Establishment and Maintenance
3.3.1. ESP Security Associations
In HIP, ESP Security Associations are set up between the HIP nodes during the base exchange [RFC7401]. Existing ESP SAs can be updated later using UPDATE messages. The reason for updating the ESP SA later can be, for example, a need for rekeying the SA because of sequence number rollover. Upon setting up a HIP association, each association is linked to two ESP SAs, one for incoming packets and one for outgoing packets. The Initiator's incoming SA corresponds with the Responder's outgoing one, and vice versa. The Initiator defines the SPI for its incoming association, as defined in Section 3.2.1. This SA is herein called
SA-RI, and the corresponding SPI is called SPI-RI. Respectively, the Responder's incoming SA corresponds with the Initiator's outgoing SA and is called SA-IR, with the SPI being called SPI-IR. The Initiator creates SA-RI as a part of R1 processing, before sending out the I2, as explained in Section 6.4. The keys are derived from KEYMAT, as defined in Section 7. The Responder creates SA-RI as a part of I2 processing; see Section 6.5. The Responder creates SA-IR as a part of I2 processing, before sending out R2; see Section 6.5. The Initiator creates SA-IR when processing R2; see Section 6.6. The initial session keys are drawn from the generated keying material, KEYMAT, after the HIP keys have been drawn as specified in [RFC7401]. When the HIP association is removed, the related ESP SAs MUST also be removed.3.3.2. Rekeying
After the initial HIP base exchange and SA establishment, both hosts are in the ESTABLISHED state. There are no longer Initiator and Responder roles, and the association is symmetric. In this subsection, the party that initiates the rekey procedure is denoted with I' and the peer with R'. An existing HIP-created ESP SA may need updating during the lifetime of the HIP association. This document specifies the rekeying of an existing HIP-created ESP SA, using the UPDATE message. The ESP_INFO parameter introduced above is used for this purpose. I' initiates the ESP SA updating process when needed (see Section 6.8). It creates an UPDATE packet with required information and sends it to the peer node. The old SAs are still in use, local policy permitting. R', after receiving and processing the UPDATE (see Section 6.9), generates new SAs: SA-I'R' and SA-R'I'. It does not take the new outgoing SA into use, but still uses the old one, so there temporarily exist two SA pairs towards the same peer host. The SPI for the new outgoing SA, SPI-R'I', is specified in the received ESP_INFO parameter in the UPDATE packet. For the new incoming SA, R' generates the new SPI value, SPI-I'R', and includes it in the response UPDATE packet.
When I' receives a response UPDATE from R', it generates new SAs, as described in Section 6.9: SA-I'R' and SA-R'I'. It starts using the new outgoing SA immediately. R' starts using the new outgoing SA when it receives traffic on the new incoming SA or when it receives the UPDATE ACK confirming completion of rekeying. After this, R' can remove the old SAs. Similarly, when the I' receives traffic from the new incoming SA, it can safely remove the old SAs.3.3.3. Security Association Management
An SA pair is indexed by the 2 SPIs and 2 HITs (both local and remote HITs since a system can have more than one HIT). An inactivity timer is RECOMMENDED for all SAs. If the state dictates the deletion of an SA, a timer is set to allow for any late arriving packets.3.3.4. Security Parameter Index (SPI)
The SPIs in ESP provide a simple compression of the HIP data from all packets after the HIP exchange. This does require a per HIT-pair Security Association (and SPI), and a decrease of policy granularity over other Key Management Protocols like Internet Key Exchange (IKE) [RFC7296]. When a host updates the ESP SA, it provides a new inbound SPI to and gets a new outbound SPI from its peer.3.3.5. Supported Ciphers
All HIP implementations MUST support AES-128-CBC and AES-256-CBC [RFC3602]. If the Initiator does not support any of the transforms offered by the Responder, it should abandon the negotiation and inform the peer with a NOTIFY message about a non-supported transform. In addition to AES-128-CBC, all implementations SHOULD implement the ESP NULL encryption algorithm. When the ESP NULL encryption is used, it MUST be used together with SHA-256 authentication as specified in Section 5.1.2. When an authentication-only suite is used (NULL, AES-CMAC-96, and AES-GMAC are examples), the suite MUST NOT be accepted if offered by the peer unless the local policy configuration regarding the peer host is explicitly set to allow an authentication-only mode. This is to prevent sessions from being downgraded to an authentication-only mode when one side's policy requests privacy for the session.
3.3.6. Sequence Number
The Sequence Number field is MANDATORY when ESP is used with HIP. Anti-replay protection MUST be used in an ESP SA established with HIP. When ESP is used with HIP, a 64-bit sequence number MUST be used. This means that each host MUST rekey before its sequence number reaches 2^64. When using a 64-bit sequence number, the higher 32 bits are NOT included in the ESP header, but are simply kept local to both peers. See [RFC4301].3.3.7. Lifetimes and Timers
HIP does not negotiate any lifetimes. All ESP lifetimes are local policy. The only lifetimes a HIP implementation MUST support are sequence number rollover (for replay protection), and SHOULD support timing out inactive ESP SAs. An SA times out if no packets are received using that SA. Implementations SHOULD support a configurable SA timeout value. Implementations MAY support lifetimes for the various ESP transforms. Each implementation SHOULD implement per-HIT configuration of the inactivity timeout, allowing statically configured HIP associations to stay alive for days, even when inactive.3.4. IPsec and HIP ESP Implementation Considerations
When HIP is run on a node where a standards compliant IPsec is used, some issues have to be considered. The HIP implementation must be able to co-exist with other IPsec keying protocols. When the HIP implementation selects the SPI value, it may lead to a collision if not implemented properly. To avoid the possibility for a collision, the HIP implementation MUST ensure that the SPI values used for HIP SAs are not used for IPsec or other SAs, and vice versa. Incoming packets using an SA that is not negotiated by HIP MUST NOT be processed as described in Section 3.2, paragraph 2. The SPI will identify the correct SA for packet decryption and MUST be used to identify that the packet has an upper-layer checksum that is calculated as specified in [RFC7401].
3.4.1. Data Packet Processing Considerations
For outbound traffic, the SPD (or coordinated SPDs, if there are two -- one for HIP and one for IPsec) MUST ensure that packets intended for HIP processing are given a HIP-enabled SA and that packets intended for IPsec processing are given an IPsec-enabled SA. The SP then MUST be bound to the matching SA, and non-HIP packets will not be processed by this SA. Data originating from a socket that is not using HIP MUST NOT have the checksum recalculated (as described in Section 3.2, paragraph 2), and data MUST NOT be passed to the SP or SA created by HIP. It is possible that in the case of overlapping policies, the outgoing packet would be handled by both IPsec and HIP. In this case, it is possible that the HIP association is end to end, while the IPsec SA is for encryption between the HIP host and a security gateway. In the case of a security gateway ESP association, the ESP always uses tunnel mode. In the case of IPsec tunnel mode, it is hard to see during the HIP SA processing if the IPsec ESP SA has the same final destination. Thus, traffic MUST be encrypted with both the HIP ESP SA and the IPsec SA when the IPsec ESP SA is used in tunnel mode. In the case of IPsec transport mode, the connection endpoints are the same. However, for HIP data packets it is not possible to avoid HIP SA processing, while mapping the HIP data packet's IP addresses to the corresponding HITs requires SPI values from the ESP header. In the case of a transport mode IPsec SA, the IPsec encryption MAY be skipped to avoid double encryption, if the local policy allows.3.4.2. HIP Signaling Packet Considerations
In general, HIP signaling packets should follow the same processing as HIP data packets. In the case of IPsec tunnel mode, the HIP signaling packets are always encrypted using an IPsec ESP SA. Note that this hides the HIP signaling packets from the eventual HIP middleboxes on the path between the originating host and the security gateway. In the case of IPsec transport mode, the HIP signaling packets MAY skip the IPsec ESP SA encryption if the local policy allows. This allows the eventual HIP middleboxes to handle the passing HIP signaling packets.
4. The Protocol
In this section, the protocol for setting up an ESP association to be used with a HIP association is described.4.1. ESP in HIP
4.1.1. IPsec ESP Transport Format Type
The HIP handshake signals the TRANSPORT_FORMAT_LIST parameter in the R1 and I2 messages. This parameter contains a list of the supported HIP transport formats of the sending host, in the order of preference. The transport format type for IPsec ESP is the type number of the ESP_TRANSFORM parameter, i.e., 4095.4.1.2. Setting Up an ESP Security Association
Setting up an ESP Security Association between hosts using HIP is performed by including parameters in the last three messages (R1, I2, and R2 messages) of the four-message HIP base exchange. Initiator Responder I1 ----------------------------------> R1: ESP_TRANSFORM <---------------------------------- I2: ESP_TRANSFORM, ESP_INFO ----------------------------------> R2: ESP_INFO <---------------------------------- The R1 message contains the ESP_TRANSFORM parameter, in which the sending host defines the possible ESP transforms it is willing to use for the ESP SA. Including the ESP_TRANSFORM parameter in the R1 message adds clarity to the TRANSPORT_FORMAT_LIST but may initiate negotiations for possibly unselected transforms. However, resource-constrained devices will most likely restrict support to a single transform for the sake of minimizing ROM overhead, and the additional parameter adds negligible overhead with unconstrained devices.
The I2 message contains the response to an ESP_TRANSFORM received in the R1 message. The sender must select one of the proposed ESP transforms from the ESP_TRANSFORM parameter in the R1 message and include the selected one in the ESP_TRANSFORM parameter in the I2 packet. In addition to the transform, the host includes the ESP_INFO parameter containing the SPI value to be used by the peer host. In the R2 message, the ESP SA setup is finalized. The packet contains the SPI information required by the Initiator for the ESP SA.4.1.3. Updating an Existing ESP SA
The update process is accomplished using three messages. The HIP UPDATE message is used to update the parameters of an existing ESP SA. The UPDATE mechanism and message are defined in [RFC7401], and the additional parameters for updating an existing ESP SA are described here. The following picture shows a typical exchange when an existing ESP SA is updated. Messages include SEQ and ACK parameters required by the UPDATE mechanism. H1 H2 UPDATE: SEQ, ESP_INFO [, DIFFIE_HELLMAN] -----------------------------------------------------> UPDATE: SEQ, ACK, ESP_INFO [, DIFFIE_HELLMAN] <----------------------------------------------------- UPDATE: ACK -----------------------------------------------------> The host willing to update the ESP SA creates and sends an UPDATE message. The message contains the ESP_INFO parameter containing the old SPI value that was used, the new SPI value to be used, and the index value for the keying material, giving the point from where the next keys will be drawn. If new keying material must be generated, the UPDATE message will also contain the DIFFIE_HELLMAN parameter defined in [RFC7401]. The host receiving the UPDATE message requesting update of an existing ESP SA MUST reply with an UPDATE message. In the reply message, the host sends the ESP_INFO parameter containing the corresponding values: old SPI, new SPI, and the keying material index. If the incoming UPDATE contained a DIFFIE_HELLMAN parameter, the reply packet MUST also contain a DIFFIE_HELLMAN parameter.
5. Parameter and Packet Formats
In this section, new and modified HIP parameters are presented, as well as modified HIP packets.5.1. New Parameters
Two HIP parameters are defined for setting up ESP transport format associations in HIP communication and for rekeying existing ones. Also, the NOTIFICATION parameter, described in [RFC7401], has two error values defined for this specification. Parameter Type Length Data ESP_INFO 65 12 Remote's old SPI, new SPI, and other info ESP_TRANSFORM 4095 variable ESP Encryption and Authentication Transform(s)5.1.1. ESP_INFO
During the establishment and update of an ESP SA, the SPI value of both hosts must be transmitted between the hosts. In addition, hosts need the index value to the KEYMAT when they are drawing keys from the generated keying material. The ESP_INFO parameter is used to transmit the SPI values and the KEYMAT index information between the hosts. During the initial ESP SA setup, the hosts send the SPI value that they want the peer to use when sending ESP data to them. The value is set in the NEW SPI field of the ESP_INFO parameter. In the initial setup, an old value for the SPI does not exist; thus, the OLD SPI field value is set to zero. The OLD SPI field value may also be zero when additional SAs are set up between HIP hosts, e.g., in the case of multihomed HIP hosts [RFC5206]. However, such use is beyond the scope of this specification. The KEYMAT index value points to the place in the KEYMAT from where the keying material for the ESP SAs is drawn. The KEYMAT index value is zero only when the ESP_INFO is sent during a rekeying process and new keying material is generated. During the life of an SA established by HIP, one of the hosts may need to reset the Sequence Number to one and rekey. The reason for rekeying might be an approaching sequence number wrap in ESP, or a local policy on the use of a key. Rekeying ends the current SAs and starts new ones on both peers.
During the rekeying process, the ESP_INFO parameter is used to
transmit the changed SPI values and the keying material index.
0 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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | KEYMAT Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OLD SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NEW SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 65
Length 12
KEYMAT Index index, in bytes, where to continue to draw ESP keys
from KEYMAT. If the packet includes a new
Diffie-Hellman key and the ESP_INFO is sent in an
UPDATE packet, the field MUST be zero. If the
ESP_INFO is included in base exchange messages, the
KEYMAT Index must have the index value of the point
from where the ESP SA keys are drawn. Note that
the length of this field limits the amount of
keying material that can be drawn from KEYMAT. If
that amount is exceeded, the packet MUST contain
a new Diffie-Hellman key.
OLD SPI old SPI for data sent to address(es) associated
with this SA. If this is an initial SA setup, the
OLD SPI value is zero.
NEW SPI new SPI for data sent to address(es) associated
with this SA.
5.1.2. ESP_TRANSFORM
The ESP_TRANSFORM parameter is used during ESP SA establishment. The first party sends a selection of transform families in the ESP_TRANSFORM parameter, and the peer must select one of the proposed values and include it in the response ESP_TRANSFORM parameter. 0 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 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Suite ID #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Suite ID #2 | Suite ID #3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Suite ID #n | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 4095 Length length in octets, excluding Type, Length, and padding. Reserved zero when sent, ignored when received. Suite ID defines the ESP Suite to be used. The following Suite IDs can be used: Suite ID Value RESERVED 0 [RFC7402] AES-128-CBC with HMAC-SHA1 1 [RFC3602], [RFC2404] DEPRECATED 2 [RFC7402] DEPRECATED 3 [RFC7402] DEPRECATED 4 [RFC7402] DEPRECATED 5 [RFC7402] DEPRECATED 6 [RFC7402] NULL with HMAC-SHA-256 7 [RFC2410], [RFC4868] AES-128-CBC with HMAC-SHA-256 8 [RFC3602], [RFC4868] AES-256-CBC with HMAC-SHA-256 9 [RFC3602], [RFC4868] AES-CCM-8 10 [RFC4309] AES-CCM-16 11 [RFC4309] AES-GCM with an 8-octet ICV 12 [RFC4106] AES-GCM with a 16-octet ICV 13 [RFC4106] AES-CMAC-96 14 [RFC4493], [RFC4494] AES-GMAC 15 [RFC4543]
The sender of an ESP transform parameter MUST make sure that there are no more than six (6) Suite IDs in one ESP transform parameter. Conversely, a recipient MUST be prepared to handle received transform parameters that contain more than six Suite IDs. The limited number of Suite IDs sets the maximum size of the ESP_TRANSFORM parameter. As the default configuration, the ESP_TRANSFORM parameter MUST contain at least one of the mandatory Suite IDs. There MAY be a configuration option that allows the administrator to override this default. Mandatory implementations: AES-128-CBC with HMAC-SHA-256. NULL with HMAC-SHA-256 SHOULD also be supported (see also Section 3.3.5). Under some conditions, it is possible to use Traffic Flow Confidentiality (TFC) [RFC4303] with ESP in BEET mode. However, the definition of such an operation is left for future work and must be done in a separate specification.5.1.3. NOTIFICATION Parameter
The HIP base specification defines a set of NOTIFICATION error types. The following error types are required for describing errors in ESP Transform crypto suites during negotiation. NOTIFICATION PARAMETER - ERROR TYPES Value ------------------------------------ ----- NO_ESP_PROPOSAL_CHOSEN 18 None of the proposed ESP Transform crypto suites was acceptable. INVALID_ESP_TRANSFORM_CHOSEN 19 The ESP Transform crypto suite does not correspond to one offered by the Responder.
5.2. HIP ESP Security Association Setup
The ESP Security Association is set up during the base exchange. The following subsections define the ESP SA setup procedure using both base exchange messages (R1, I2, R2) and UPDATE messages.5.2.1. Setup during Base Exchange
5.2.1.1. Modifications in R1
The ESP_TRANSFORM contains the ESP modes supported by the sender, in the order of preference. All implementations MUST support AES-128-CBC [RFC3602] with HMAC-SHA-256 [RFC4868]. The following figure shows the resulting R1 packet layout. The HIP parameters for the R1 packet: IP ( HIP ( [ R1_COUNTER, ] PUZZLE, DIFFIE_HELLMAN, HIP_CIPHER, ESP_TRANSFORM, HOST_ID, [ ECHO_REQUEST, ] HIP_SIGNATURE_2 ) [, ECHO_REQUEST ])5.2.1.2. Modifications in I2
The ESP_INFO contains the sender's SPI for this association as well as the KEYMAT index from where the ESP SA keys will be drawn. The old SPI value is set to zero. The ESP_TRANSFORM contains the ESP mode selected by the sender of R1. All implementations MUST support AES-128-CBC [RFC3602] with HMAC-SHA-256 [RFC4868].
The following figure shows the resulting I2 packet layout. The HIP parameters for the I2 packet: IP ( HIP ( ESP_INFO, [R1_COUNTER,] SOLUTION, DIFFIE_HELLMAN, HIP_CIPHER, ESP_TRANSFORM, ENCRYPTED { HOST_ID }, [ ECHO_RESPONSE ,] HMAC, HIP_SIGNATURE [, ECHO_RESPONSE] ) )5.2.1.3. Modifications in R2
The R2 contains an ESP_INFO parameter, which has the SPI value of the sender of the R2 for this association. The ESP_INFO also has the KEYMAT index value specifying where the ESP SA keys are drawn. The following figure shows the resulting R2 packet layout. The HIP parameters for the R2 packet: IP ( HIP ( ESP_INFO, HMAC_2, HIP_SIGNATURE ) )5.3. HIP ESP Rekeying
In this section, the procedure for rekeying an existing ESP SA is presented. Conceptually, the process can be represented by the following message sequence using the host names I' and R' defined in Section 3.3.2. For simplicity, HMAC and HIP_SIGNATURE are not depicted, and DIFFIE_HELLMAN keys are optional. The UPDATE with ACK_I need not be piggybacked with the UPDATE with SEQ_R; it may be ACKed separately (in which case the sequence would include four packets). I' R' UPDATE(ESP_INFO, SEQ_I, [DIFFIE_HELLMAN]) -----------------------------------> UPDATE(ESP_INFO, SEQ_R, ACK_I, [DIFFIE_HELLMAN]) <----------------------------------- UPDATE(ACK_R) ----------------------------------->
Below, the first two packets in this figure are explained.5.3.1. Initializing Rekeying
When HIP is used with ESP, the UPDATE packet is used to initiate rekeying. The UPDATE packet MUST carry an ESP_INFO and MAY carry a DIFFIE_HELLMAN parameter. Intermediate systems that use the SPI will have to inspect HIP packets for those that carry rekeying information. The packet is signed for the benefit of the intermediate systems. Since intermediate systems may need the new SPI values, the contents cannot be encrypted. The following figure shows the contents of a rekeying initialization UPDATE packet. The HIP parameters for the UPDATE packet initiating rekeying: IP ( HIP ( ESP_INFO, SEQ, [DIFFIE_HELLMAN, ] HMAC, HIP_SIGNATURE ) )5.3.2. Responding to the Rekeying Initialization
The UPDATE ACK is used to acknowledge the received UPDATE rekeying initialization. The acknowledgment UPDATE packet MUST carry an ESP_INFO and MAY carry a DIFFIE_HELLMAN parameter. Intermediate systems that use the SPI will have to inspect HIP packets for packets carrying rekeying information. The packet is signed for the benefit of the intermediate systems. Since intermediate systems may need the new SPI values, the contents cannot be encrypted. The following figure shows the contents of a rekeying acknowledgment UPDATE packet. The HIP parameters for the UPDATE packet: IP ( HIP ( ESP_INFO, SEQ, ACK, [ DIFFIE_HELLMAN, ] HMAC, HIP_SIGNATURE ) )
5.4. ICMP Messages
ICMP message handling is mainly described in the HIP base specification [RFC7401]. In this section, we describe the actions related to ESP security associations.5.4.1. Unknown SPI
If a HIP implementation receives an ESP packet that has an unrecognized SPI number, it MAY respond (subject to rate limiting the responses) with an ICMP packet with type "Parameter Problem", with the pointer pointing to the beginning of the SPI field in the ESP header.
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