RFC 7815
Minimal Internet Key Exchange Version 2 (IKEv2) Initiator Implementation
Pages: 41
Informational
Informational
Part 2 of 2 – Pages 17 to 41
Appendix A. Header and Payload Formats
This appendix describes actual packet payload formats. This is required to make the document self-contained. The descriptions are mostly copied from RFC 7296, and more information can be found from there. Various payloads contain RESERVED fields, and those MUST be sent as zero and MUST be ignored on receipt. All multi-octet fields representing integers are laid out in big endian order (also known as "most significant byte first" or "network byte order").A.1. The IKE Header
Each IKEv2 message begins with the IKE header, denoted HDR in this document. Following the header are one or more IKE payloads each identified by a Next Payload field in the preceding payload. Payloads are identified in the order in which they appear in an IKE message by looking in the Next Payload field in the IKE header and, subsequently, according to the Next Payload field in the IKE payload itself until a Next Payload field of zero indicates that no payloads follow. If a payload of type "Encrypted" is found, that payload is decrypted and its contents parsed as additional payloads. An Encrypted payload MUST be the last payload in a packet, and an Encrypted payload MUST NOT contain another Encrypted payload. The format of the IKE header is shown in Figure 1. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IKE SA Initiator's SPI | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IKE SA Responder's SPI | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload | MjVer | MnVer | Exchange Type | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: IKE Header Format
o Initiator's SPI (8 octets) - A value chosen by the initiator to
identify a unique IKE Security Association. This value MUST NOT
be zero.
o Responder's SPI (8 octets) - A value chosen by the responder to
identify a unique IKE Security Association. This value MUST be
zero in the first message of an IKE initial exchange.
o Next Payload (1 octet) - Indicates the type of payload that
immediately follows the header. The format and value of each
payload are defined below.
o Major Version (4 bits) - Indicates the major version of the IKE
protocol in use. Implementations based on this version of IKE
MUST set the major version to 2 and MUST drop the messages with a
higher major version number.
o Minor Version (4 bits) - Indicates the minor version of the IKE
protocol in use. Implementations based on this version of IKE
MUST set the minor version to zero. They MUST ignore the minor
version number of received messages.
o Exchange Type (1 octet) - Indicates the type of exchange being
used. This constrains the payloads sent in each message in an
exchange.
Exchange Type Value
----------------------------------
IKE_SA_INIT 34
IKE_AUTH 35
CREATE_CHILD_SA 36
INFORMATIONAL 37
o Flags (1 octet) - Indicates specific options that are set for the
message. Presence of options is indicated by the appropriate bit
in the flags field being set. The bits are as follows:
+-+-+-+-+-+-+-+-+
|X|X|R|V|I|X|X|X|
+-+-+-+-+-+-+-+-+
In the description below, a bit being 'set' means its value is
'1', while 'cleared' means its value is '0'. 'X' bits MUST be
cleared when sending and MUST be ignored on receipt.
* R (Response) - This bit indicates that this message is a
response to a message containing the same Message ID. This bit
MUST be cleared in all request messages and MUST be set in all
responses. An IKEv2 endpoint MUST NOT generate a response to a
message that is marked as being a response.
* V (Version) - This bit indicates that the transmitter is
capable of speaking a higher major version number of the
protocol than the one indicated in the Major Version field.
Implementations of IKEv2 MUST clear this bit when sending and
MUST ignore it in incoming messages.
* I (Initiator) - This bit MUST be set in messages sent by the
original initiator of the IKE SA and MUST be cleared in
messages sent by the original responder. It is used by the
recipient to determine which 8 octets of the SPI were generated
by the recipient. This bit changes to reflect who initiated
the last rekey of the IKE SA.
o Message ID (4 octets, unsigned integer) - Message identifier used
to control retransmission of lost packets and matching of requests
and responses. It is essential to the security of the protocol
because it is used to prevent message replay attacks.
o Length (4 octets, unsigned integer) - Length of the total message
(header + payloads) in octets.
A.2. Generic Payload Header
Each IKE payload begins with a generic payload header, as shown in
Figure 2. Figures for each payload below will include the generic
payload header, but for brevity, the description of each field will
be omitted.
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 2: Generic Payload Header
The Generic Payload Header 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. This field provides
a "chaining" capability whereby additional payloads can be added
to a message by appending each one to the end of the message and
setting the Next Payload field of the preceding payload to
indicate the new payload's type. An Encrypted payload, which must
always be the last payload of a message, is an exception. It
contains data structures in the format of additional payloads. In
the header of an Encrypted payload, the Next Payload field is set
to the payload type of the first contained payload (instead of
zero); conversely, the Next Payload field of the last contained
payload is set to zero). The payload type values needed for
minimal implementations are listed here.
Next Payload Type Notation Value
--------------------------------------------------
No Next Payload 0
Security Association SA 33
Key Exchange KE 34
Identification - Initiator IDi 35
Identification - Responder IDr 36
Certificate CERT 37
Certificate Request CERTREQ 38
Authentication AUTH 39
Nonce Ni, Nr 40
Notify N 41
Delete D 42
Traffic Selector - Initiator TSi 44
Traffic Selector - Responder TSr 45
Encrypted and Authenticated SK 46
o Critical (1 bit) - MUST be set to zero if the sender wants the
recipient to skip this payload if it does not understand the
payload type code in the Next Payload field of the previous
payload. MUST be set to 1 if the sender wants the recipient to
reject this entire message if it does not understand the payload
type. MUST be ignored by the recipient if the recipient
understands the payload type code. MUST be set to zero for
payload types defined in this document. Note that the critical
bit applies to the current payload rather than the "next" payload
whose type code appears in the first octet.
o Payload Length (2 octets, unsigned integer) - Length in octets of
the current payload, including the generic payload header.
A.3. Security Association Payload
The Security Association payload, denoted SA in this document, is used to negotiate attributes of a Security Association. An SA payload consists of one or more proposals. Each proposal includes one protocol. Each protocol contains one or more transforms -- each specifying a cryptographic algorithm. Each transform contains zero or more attributes (attributes are needed only if the Transform ID does not completely specify the cryptographic algorithm; currently, the only attribute is the Key Length attribute for variable-length ciphers, meaning there is exactly zero or one attribute). The responder MUST choose a single suite, which may be any subset of the SA proposal following the rules below. Each proposal contains one protocol. If a proposal is accepted, the SA response MUST contain the same protocol. Each IPsec protocol proposal contains one or more transforms. Each transform contains a Transform Type. The accepted cryptographic suite MUST contain exactly one transform of each type included in the proposal. For example: if an ESP proposal includes transforms ENCR_3DES, ENCR_AES w/keysize 128, ENCR_AES w/keysize 256, AUTH_HMAC_MD5, and AUTH_HMAC_SHA, the accepted suite MUST contain one of the ENCR_ transforms and one of the AUTH_ transforms. Thus, six combinations are acceptable. Minimal implementation can create very simple SA proposal, i.e., include one proposal, which contains exactly one transform for each Transform Type. It is important to only include one Diffie-Hellman group in the proposal, so there is no need to do INVALID_KE_PAYLOAD processing in responses. When parsing an SA, an implementation MUST check that the total Payload Length is consistent with the payload's internal lengths and counts. Proposals, Transforms, and Attributes each have their own variable-length encodings. They are nested such that the Payload Length of an SA includes the combined contents of the SA, Proposal, Transform, and Attribute information. The length of a Proposal includes the lengths of all Transforms and Attributes it contains. The length of a Transform includes the lengths of all Attributes it contains. Each Proposal/Protocol structure is followed by one or more transform structures. The number of different transforms is generally determined by the Protocol. AH generally has two transforms: Extended Sequence Numbers (ESNs) and an integrity check algorithm.
ESP generally has three: ESN, an encryption algorithm, and an integrity check algorithm. IKEv2 generally has four transforms: a Diffie-Hellman group, an integrity check algorithm, a PRF algorithm, and an encryption algorithm. For each Protocol, the set of permissible transforms is assigned Transform ID numbers, which appear in the header of each transform. If there are multiple transforms with the same Transform Type, the proposal is an OR of those transforms. If there are multiple transforms with different Transform Types, the proposal is an AND of the different groups. A given transform MAY have one or more Attributes. Attributes are necessary when the transform can be used in more than one way, as when an encryption algorithm has a variable key size. The transform would specify the algorithm, and the attribute would specify the key size. To propose alternate values for an attribute (for example, multiple key sizes for the AES encryption algorithm), an implementation MUST include multiple transforms with the same Transform Type each with a single Attribute. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ <Proposals> ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Security Association Payload o Proposals (variable) - One or more proposal substructures.
A.3.1. Proposal Substructure
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 (last) or 2 | RESERVED | Proposal Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Proposal Num | Protocol ID | SPI Size |Num Transforms| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ SPI (variable) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ <Transforms> ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Proposal Substructure o 0 (last) or 2 (more) (1 octet) - Specifies whether this is the last Proposal Substructure in the SA. o Proposal Length (2 octets, unsigned integer) - Length of this proposal, including all transforms and attributes that follow. o Proposal Num (1 octet) - When a proposal is made, the first proposal in an SA payload MUST be 1, and subsequent proposals MUST be one more than the previous proposal. When a proposal is accepted, the proposal number in the SA payload MUST match the number on the proposal sent that was accepted. o Protocol ID (1 octet) - Specifies the IPsec protocol identifier for the current negotiation. Protocol Protocol ID ----------------------------------- IKE 1 AH 2 ESP 3 o SPI Size (1 octet) - For an initial IKE SA negotiation, this field MUST be zero; the SPI is obtained from the outer header. During subsequent negotiations, it is equal to the size, in octets, of the SPI of the corresponding protocol (8 for IKE and 4 for ESP and AH). o Num Transforms (1 octet) - Specifies the number of transforms in this proposal.
o SPI (variable) - The sending entity's SPI. When the SPI Size
field is zero, this field is not present in the Security
Association payload.
o Transforms (variable) - One or more transform substructures.
A.3.2. Transform Substructure
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 (last) or 3 | RESERVED | Transform Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Transform Type | RESERVED | Transform ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Transform Attributes ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Transform Substructure
o 0 (last) or 3 (more) (1 octet) - Specifies whether this is the
last Transform Substructure in the Proposal.
o Transform Length - The length (in octets) of the Transform
Substructure including Header and Attributes.
o Transform Type (1 octet) - The type of transform being specified
in this transform. Different protocols support different
Transform Types. For some protocols, some of the transforms may
be optional. If a transform is optional and the initiator wishes
to propose that the transform be omitted, no transform of the
given type is included in the proposal. If the initiator wishes
to make use of the transform optional to the responder, it
includes a transform substructure with Transform ID = 0 as one of
the options.
o Transform ID (2 octets) - The specific instance of the Transform
Type being proposed.
The relevant Transform Type values are listed below. For more information see [RFC7296]. Description Trans. Used In Type ------------------------------------------------------------------ Encryption Algorithm (ENCR) 1 IKE and ESP Pseudorandom Function (PRF) 2 IKE Integrity Algorithm (INTEG) 3 IKE, AH, optional in ESP Diffie-Hellman group (D-H) 4 IKE, optional in AH & ESP Extended Sequence Numbers (ESN) 5 AH and ESP For Transform Type 1 (Encryption Algorithm), the relevant Transform IDs are listed below. Name Number --------------------------- ENCR_AES_CBC 12 ENCR_AES-CCM_8 14 For Transform Type 2 (Pseudorandom Function), the relevant Transform IDs are listed below. Name Number ---------------------------------- PRF_HMAC_SHA1 2 For Transform Type 3 (Integrity Algorithm), the relevant Transform IDs are listed below. Name Number --------------------------- AUTH_HMAC_SHA1_96 2 AUTH_AES_XCBC_96 5 For Transform Type 4 (Diffie-Hellman group), the relevant Transform IDs are listed below. Name Number ------------------------- 1536-bit MODP 5 2048-bit MODP 14
For Transform Type 5 (Extended Sequence Numbers), the relevant Transform IDs are listed below. Name Number -------------------------------------------- No Extended Sequence Numbers 0 Extended Sequence Numbers 1 Note that an initiator who supports ESNs will usually include two ESN transforms, with values "0" and "1", in its proposals. A proposal containing a single ESN transform with value "1" means that using normal (non-extended) sequence numbers is not acceptable.A.3.3. Valid Transform Types by Protocol
The number and type of transforms that accompany an SA payload are dependent on the protocol in the SA itself. An SA payload proposing the establishment of an SA has the following mandatory and optional Transform Types. A compliant implementation MUST understand all mandatory and optional types for each protocol it supports (though it need not accept proposals with unacceptable suites). A proposal MAY omit the optional types if the only value for them it will accept is NONE. Protocol Mandatory Types Optional Types --------------------------------------------------- IKE ENCR, PRF, INTEG, D-H ESP ENCR, ESN INTEG, D-H AH INTEG, ESN D-HA.3.4. Transform Attributes
Transform Type 1 (Encryption Algorithm) transforms might include one transform attribute: Key Length. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Attribute Type | Attribute Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Data Attributes o Attribute Type (15 bits) - Unique identifier for each type of attribute (see below). o Attribute Value - Value of the attribute associated with the attribute type.
Attribute Type Value
----------------------------
Key Length (in bits) 14
The Key Length attribute specifies the key length in bits (MUST use
network byte order) for certain transforms as follows:
o The Key Length attribute MUST NOT be used with transforms that use
a fixed-length key.
o Some transforms specify that the Key Length attribute MUST be
always included. For example, ENCR_AES_CBC.
A.4. Key Exchange 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 | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diffie-Hellman Group Num | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Key Exchange Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Key Exchange Payload Format
A Key Exchange payload is constructed by copying one's Diffie-Hellman
public value into the "Key Exchange Data" portion of the payload.
The length of the Diffie-Hellman public value for modular
exponentiation groups (MODPs) MUST be equal to the length of the
prime modulus over which the exponentiation was performed, prepending
zero bits to the value if necessary.
The Diffie-Hellman Group Num identifies the Diffie-Hellman group in
which the Key Exchange Data was computed. This Diffie-Hellman Group
Num MUST match a Diffie-Hellman group specified in a proposal in the
SA payload that is sent in the same message.
A.5. Identification Payloads
The Identification payloads, denoted IDi and IDr in this document,
allow peers to assert an identity to one another. When using the
ID_IPV4_ADDR/ID_IPV6_ADDR identity types in IDi/IDr payloads, IKEv2
does not require this address to match the address in the IP header
of IKEv2 packets or anything in the TSi/TSr payloads. The contents
of IDi/IDr are used purely to fetch the policy and authentication data related to the other party. In minimal implementation, it might be easiest to always use KEY_ID type. This allows the ID payload to be static. Using an IP address has problems in environments where IP addresses are dynamically allocated. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID Type | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Identification Data ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: Identification Payload Format o ID Type (1 octet) - Specifies the type of Identification being used. o Identification Data (variable length) - Value, as indicated by the Identification Type. The length of the Identification Data is computed from the size in the ID payload header. The following table lists the assigned semantics for the Identification Type field. ID Type Value ------------------------------------------------------------------- ID_IPV4_ADDR 1 A single four (4) octet IPv4 address. ID_FQDN 2 A fully qualified domain name string. An example of an ID_FQDN is "example.com". The string MUST NOT contain any terminators (e.g., NULL, CR, etc.). All characters in the ID_FQDN are ASCII; for an "internationalized domain name", the syntax is as defined in [IDNA], for example, "xn--tmonesimerkki-bfbb.example.net". ID_RFC822_ADDR 3 A fully qualified RFC 822 email address string based [RFC5322]. An example of an ID_RFC822_ADDR is "jsmith@example.com". The string MUST NOT contain any terminators. Because of [EAI], implementations would be wise to treat this field as UTF-8-encoded text, not as pure ASCII.
ID_IPV6_ADDR 5
A single sixteen (16) octet IPv6 address.
ID_KEY_ID 11
An opaque octet stream that may be used to pass vendor-
specific information necessary to do certain proprietary
types of identification. Minimal implementation might use
this type to send out a serial number or similar device-specific
unique static Identification Data for the device.
A.6. Certificate 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 | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cert Encoding | |
+-+-+-+-+-+-+-+-+ |
~ Certificate Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Certificate Payload Format
o Certificate Encoding (1 octet) - This field indicates the type of
certificate or certificate-related information contained in the
Certificate Data field.
Certificate Encoding Value
----------------------------------------------------
X.509 Certificate - Signature 4
Raw Public Key 15
o Certificate Data (variable length) - Actual encoding of
certificate data. The type of certificate is indicated by the
Certificate Encoding field.
The syntax of the types above are:
o "X.509 Certificate - Signature" contains a DER-encoded X.509
certificate whose public key is used to validate the sender's AUTH
payload. Note that with this encoding, if a chain of certificates
needs to be sent, multiple CERT payloads are used, only the first
of which holds the public key used to validate the sender's AUTH
payload.
o "Raw Public Key" contains a raw public key. In essence, the
Certificate Payload contains the SubjectPublicKeyInfo part of the
PKIX Certificate (see Section 4.1.2.7 of [RFC5280]). This is a
quite simple ASN.1 object that contains mostly static parts before
the actual public key values. See [RFC7670] for more information.
A.7. Certificate Request 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 | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cert Encoding | |
+-+-+-+-+-+-+-+-+ |
~ Certification Authority (CA) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Certificate Request Payload Format
o Certificate Encoding (1 octet) - Contains an encoding of the type
or format of certificate requested.
o Certification Authority (variable length) - Contains an encoding
of an acceptable certification authority for the type of
certificate requested.
The Certificate Encoding field has the same values as those defined
by the certificate payload. The Certification Authority field
contains an indicator of trusted authorities for this certificate
type. The Certification Authority value is a concatenated list of
SHA-1 hashes of the public keys of trusted Certification Authorities.
Each is encoded as the SHA-1 hash of the Subject Public Key Info
element (see Section 4.1.2.7 of [RFC5280]) from each Trust Anchor
certificate. The 20-octet hashes are concatenated and included with
no other formatting.
A.8. Authentication 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 | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Auth Method | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Authentication Data ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11: Authentication Payload Format o Auth Method (1 octet) - Specifies the method of authentication used. Mechanism Value ----------------------------------------------------------------- RSA Digital Signature 1 Using an RSA private key with an RSASSA-PKCS1-v1_5 signature scheme specified in [PKCS1]; see Section 2.15 of [RFC7296] for details. Shared Key Message Integrity Code 2 Computed as specified earlier using the shared key associated with the identity in the ID payload and the negotiated PRF. o Authentication Data (variable length) - see Section 2.1.A.9. Nonce 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 | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Nonce Data ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 12: Nonce Payload Format o Nonce Data (variable length) - Contains the random data generated by the transmitting entity.
The size of the Nonce Data MUST be between 16 and 256 octets, inclusive. Nonce values MUST NOT be reused.A.10. Notify Payload
The Notify payload, denoted N in this document, is used to transmit informational data, such as error conditions and state transitions, to an IKE peer. A Notify payload may appear in a response message (usually specifying why a request was rejected), in an INFORMATIONAL exchange (to report an error not in an IKE request), or in any other message to indicate sender capabilities or to modify the meaning of the request. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol ID | SPI Size | Notify Message Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Security Parameter Index (SPI) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Notification Data ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 13: Notify Payload Format o Protocol ID (1 octet) - If this notification concerns an existing SA whose SPI is given in the SPI field, this field indicates the type of that SA. If the SPI field is empty, this field MUST be sent as zero and MUST be ignored on receipt. o SPI Size (1 octet) - Length in octets of the SPI as defined by the IPsec protocol ID or zero if no SPI is applicable. For a notification concerning the IKE SA, the SPI Size MUST be zero and the SPI field must be empty. o Notify Message Type (2 octets) - Specifies the type of notification message. o SPI (variable length) - Security Parameter Index.
o Notification Data (variable length) - Status or error data
transmitted in addition to the Notify Message Type. Values for
this field are type specific.
A.10.1. Notify Message Types
Notification information can be error messages specifying why an SA
could not be established. It can also be status data that a process
managing an SA database wishes to communicate with a peer process.
Types in the range 0 - 16383 are intended for reporting errors. An
implementation receiving a Notify payload with one of these types
that it does not recognize in a response MUST assume that the
corresponding request has failed entirely. Unrecognized error types
in a request and status types in a request or response MUST be
ignored, and they should be logged.
Notify payloads with status types MAY be added to any message and
MUST be ignored if not recognized. They are intended to indicate
capabilities and, as part of SA negotiation, are used to negotiate
non-cryptographic parameters.
NOTIFY messages: error types Value
-------------------------------------------------------------------
UNSUPPORTED_CRITICAL_PAYLOAD 1
Indicates that the 1-octet payload type included in the
Notification Data field is unknown.
INVALID_SYNTAX 7
Indicates the IKE message that was received was invalid because
some type, length, or value was out of range or because the
request was rejected for policy reasons. To avoid a
Denial-of-Service (DoS) attack using forged messages, this
status may only be returned for and in an encrypted packet if
the Message ID and cryptographic checksum were valid. To avoid
leaking information to someone probing a node, this status MUST
be sent in response to any error not covered by one of the other
status types. To aid debugging, more detailed error information
should be written to a console or log.
NO_PROPOSAL_CHOSEN 14
None of the proposed crypto suites was acceptable. This can be
sent in any case where the offered proposals are not acceptable
for the responder.
NO_ADDITIONAL_SAS 35
Specifies that the node is unwilling to accept any more Child
SAs.
NOTIFY messages: status types Value
-------------------------------------------------------------------
INITIAL_CONTACT 16384
Asserts that this IKE SA is the only IKE SA currently active
between the authenticated identities.
A.11. Traffic Selector Payload
Traffic Selector (TS) payloads allow endpoints to communicate some of
the information from their Security Policy Database (SPD) to their
peers. TS payloads specify the selection criteria for packets that
will be forwarded over the newly set up SA.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of TSs | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Traffic Selectors> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Traffic Selectors Payload Format
o Number of TSs (1 octet) - Number of Traffic Selectors being
provided.
o Traffic Selectors (variable length) - One or more individual
Traffic Selectors.
The length of the Traffic Selector payload includes the TS header and
all the Traffic Selectors.
There is no requirement that TSi and TSr contain the same number of
individual Traffic Selectors. Thus, they are interpreted as follows:
a packet matches a given TSi/TSr if it matches at least one of the
individual selectors in TSi and at least one of the individual
selectors in TSr.
Two TS payloads appear in each of the messages in the exchange that
creates a Child SA pair. Each TS payload contains one or more
Traffic Selectors. Each Traffic Selector consists of an address
range (IPv4 or IPv6), a port range, and an IP protocol ID.
The first of the two TS payloads is known as TSi (Traffic Selector - initiator). The second is known as TSr (Traffic Selector - responder). TSi specifies the source address of traffic forwarded from (or the destination address of traffic forwarded to) the initiator of the Child SA pair. TSr specifies the destination address of the traffic forwarded to (or the source address of the traffic forwarded from) the responder of the Child SA pair. IKEv2 allows the responder to choose a subset of the traffic proposed by the initiator. When the responder chooses a subset of the traffic proposed by the initiator, it narrows the Traffic Selectors to some subset of the initiator's proposal (provided the set does not become the null set). If the type of Traffic Selector proposed is unknown, the responder ignores that Traffic Selector, so that the unknown type is not returned in the narrowed set. To enable the responder to choose the appropriate range, if the initiator has requested the SA due to a data packet, the initiator SHOULD include as the first Traffic Selector in each TSi and TSr a very specific Traffic Selector including the addresses in the packet triggering the request. If the initiator creates the Child SA pair not in response to an arriving packet, but rather, say, upon startup, then there may be no specific addresses the initiator prefers for the initial tunnel over any other. In that case, the first values in TSi and TSr can be ranges rather than specific values. As minimal implementations might only support one SA, the Traffic Selectors will usually be from the initiator's IP address to the responder's IP address (i.e., no port or protocol selectors and only one range).
A.11.1. Traffic Selector
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TS Type |IP Protocol ID | Selector Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Start Port | End Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Starting Address ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Ending Address ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 15: Traffic Selector o TS Type (1 octet) - Specifies the type of Traffic Selector. o IP protocol ID (1 octet) - Value specifying an associated IP protocol ID (such as UDP, TCP, and ICMP). A value of zero means that the protocol ID is not relevant to this Traffic Selector -- the SA can carry all protocols. o Selector Length - Specifies the length of this Traffic Selector substructure including the header. o Start Port (2 octets, unsigned integer) - Value specifying the smallest port number allowed by this Traffic Selector. For protocols for which port is undefined (including protocol 0), or if all ports are allowed, this field MUST be zero. o End Port (2 octets, unsigned integer) - Value specifying the largest port number allowed by this Traffic Selector. For protocols for which port is undefined (including protocol 0), or if all ports are allowed, this field MUST be 65535. o Starting Address - The smallest address included in this Traffic Selector (length determined by TS Type). o Ending Address - The largest address included in this Traffic Selector (length determined by TS Type).
The following table lists values for the Traffic Selector Type field
and the corresponding Address Selector Data.
TS Type Value
-------------------------------------------------------------------
TS_IPV4_ADDR_RANGE 7
A range of IPv4 addresses, represented by two 4-octet
values. The first value is the beginning IPv4 address
(inclusive), and the second value is the ending IPv4 address
(inclusive). All addresses falling between the two specified
addresses are considered to be within the list.
TS_IPV6_ADDR_RANGE 8
A range of IPv6 addresses, represented by two 16-octet
values. The first value is the beginning IPv6 address
(inclusive), and the second value is the ending IPv6 address
(inclusive). All addresses falling between the two specified
addresses are considered to be within the list.
A.12. Encrypted Payload
The Encrypted payload, denoted as SK{...} in this document, contains
other payloads in encrypted form.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initialization Vector |
| (length is block size for the encryption algorithm) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Encrypted IKE Payloads ~
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding (0-255 octets) |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| | Pad Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Integrity Checksum Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: Encrypted Payload Format
o Next Payload - The payload type of the first embedded payload.
Note that this is an exception in the standard header format,
since the Encrypted payload is the last payload in the message;
therefore, the Next Payload field would normally be zero. But
because the content of this payload is embedded payloads and there
was no natural place to put the type of the first one, that type
is placed here.
o Payload Length - Includes the lengths of the header,
initialization vector (IV), Encrypted IKE payloads, Padding, Pad
Length, and Integrity Checksum Data.
o Initialization Vector - For Cipher Block Chaining (CBC) mode
ciphers, the length of the initialization vector (IV) is equal to
the block length of the underlying encryption algorithm. Senders
MUST select a new unpredictable IV for every message; recipients
MUST accept any value. The reader is encouraged to consult
[MODES] for advice on IV generation. In particular, using the
final ciphertext block of the previous message is not considered
unpredictable. For modes other than CBC, the IV format and
processing is specified in the document specifying the encryption
algorithm and mode.
o IKE payloads are as specified earlier in this section. This field
is encrypted with the negotiated cipher.
o Padding MAY contain any value chosen by the sender and MUST have a
length that makes the combination of the payloads, the Padding,
and the Pad Length to be a multiple of the encryption block size.
This field is encrypted with the negotiated cipher.
o Pad Length is the length of the Padding field. The sender SHOULD
set the Pad Length to the minimum value that makes the combination
of the payloads, the Padding, and the Pad Length a multiple of the
block size, but the recipient MUST accept any length that results
in proper alignment. This field is encrypted with the negotiated
cipher.
o Integrity Checksum Data is the cryptographic checksum of the
entire message starting with the Fixed IKE header through the Pad
Length. The checksum MUST be computed over the encrypted message.
Its length is determined by the integrity algorithm negotiated.
Appendix B. Useful Optional Features
There are some optional features of IKEv2, which might be useful for minimal implementations in some scenarios. Such features include raw public keys authentication and sending an IKE SA delete notification.B.1. IKE SA Delete Notification
In some scenarios, a minimal implementation device creates an IKE SA, sends one or few packets, perhaps gets some packets back, and then the device goes back to sleep, forgetting the IKE SA. In such scenarios, it would be nice for the minimal implementation to send the IKE SA delete notification to tell the other end that the IKE SA is going away, so it can free the resources. Deleting the IKE SA can be done by sending one packet with a fixed Message ID and with only one payload inside the Encrypted payload. The other end will send back an empty response: Initiator Responder ------------------------------------------------------------------- HDR(SPIi=xxx, SPIr=yyy, INFORMATIONAL, Flags: Initiator, Message ID=2), SK {D} --> <-- HDR(SPIi=xxx, SPIr=yyy, INFORMATIONAL, Flags: Response, Message ID=2), SK {} The Delete payload format is: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol ID | SPI Size | Num of SPIs | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Security Parameter Index(es) (SPI) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 17: Delete Payload Format o Protocol ID (1 octet) - Must be 1 for an IKE SA.
o SPI Size (1 octet) - Length in octets of the SPI as defined by the
protocol ID. It MUST be zero for IKE (SPI is in the message
header).
o Num of SPIs (2 octets, unsigned integer) - The number of SPIs
contained in the Delete payload. This MUST be zero for IKE.
o Security Parameter Index(es) (variable length) - Identifies the
specific Security Association(s) to delete. The length of this
field is determined by the SPI Size and Num of SPIs fields. This
field is empty for the IKE SA delete.
B.2. Raw Public Keys
In some scenarios, the shared secret authentication is not safe
enough, as anybody who knows the secret can impersonate the server.
If the shared secret is printed on the side of the device, then
anybody who gets physical access to the device can read it. In such
environments, public key authentication allows stronger
authentication with minimal operational overhead. Certificate
support is quite complex, and minimal implementations do not usually
have need for them. Using Raw Public Keys is much simpler, and it
scales similar to certificates. The fingerprint of the raw public
key can still be distributed by, for example, printing it on the side
of the device allowing setup similar to using a shared secret.
Raw public keys can also be used in a "leap of faith" or baby duck
style initial setup, where the device imprints itself to the first
device it sees when it boots up the first time. After that initial
connection, it stores the fingerprint of the Raw Public Key of the
server in its own configuration and verifies that it never changes
(unless a "reset to factory settings" or similar command is issued).
This changes the initial IKE_AUTH payloads as follows:
Initiator Responder
-------------------------------------------------------------------
HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH,
Flags: Initiator, Message ID=1),
SK {IDi, CERT, AUTH, SAi2, TSi, TSr,
N(INITIAL_CONTACT)} -->
<-- HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH, Flags:
Response, Message ID=1),
SK {IDr, CERT, AUTH, SAr2, TSi, TSr}
The CERT payloads contain the raw public keys used to sign the hash of the InitiatorSignedOctects/ResponderSignedOctects when generating an AUTH payload. Minimal implementations should use SHA-1 as the hash function as that is the "SHOULD" support algorithm specified in RFC 7296, so it is the most likely one that is supported by all devices. Note that RFC 7296 already obsoleted the old Raw RSA Key method, and "Generic Raw Public-Key Support for IKEv2" [RFC7670] adds a new format to allow using any types of raw public keys with IKEv2. This document only specifies how to use the new format. In these setups, it might be possible that authenticating the server is not needed at all. If a minimal device is sending, for example, sensor information to the server, the server wants to verify that the sensor is who it claims to be using raw public keys, but the sensor does not really care who the server is. In such cases, the NULL authentication method [RFC7619] would be useful, as it allows devices to do one-way authentication.Acknowledgements
Most of the content of this document is copied from RFC 7296.Author's Address
Tero Kivinen INSIDE Secure Eerikinkatu 28 HELSINKI FI-00180 FINLAND Email: kivinen@iki.fi