3.8 Authentication Payload

The Authentication payload, denoted AUTH in this document, contains data used for authentication purposes. The syntax of the Authentication Data varies according to the Auth Method as specified below.

The Authentication payload is defined as follows:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Auth Method   |                RESERVED                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                      Authentication Data                      ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 14: Authentication Payload Format

Auth Method (1 octet) - Specifies the method of authentication used. The types of signatures are listed here. The values in the following table are only current as of the publication date of RFC 4306. Other values may have been added since then or will be added after the publication of this document. Readers should refer to [IKEV2IANA] for the latest values.

Mechanism	Value
RSA Digital Signature	1
Shared Key Message Integrity Code	2
DSS Digital Signature	3

RSA Digital Signature - Computed as specified in Section 2.15 using an RSA private key with RSASSA-PKCS1-v1_5 signature scheme specified in [PKCS1] (implementers should note that IKEv1 used a different method for RSA signatures). To promote interoperability, implementations that support this type SHOULD support signatures that use SHA-1 as the hash function and SHOULD use SHA-1 as the default hash function when generating signatures. Implementations can use the certificates received from a given peer as a hint for selecting a mutually understood hash function for the AUTH payload signature. Note, however, that the hash algorithm used in the AUTH payload signature doesn't have to be the same as any hash algorithm(s) used in the certificate(s).
Shared Key Message Integrity Code - Computed as specified in Section 2.15 using the shared key associated with the identity in the ID payload and the negotiated PRF.
DSS Digital Signature - Computed as specified in Section 2.15 using a DSS private key (see [DSS]) over a SHA-1 hash.
RESERVED - MUST be sent as zero; MUST be ignored on receipt.
Authentication Data (variable length) - see Section 2.15.

The payload type for the Authentication payload is thirty-nine (39).

3.8 Authentication Payload​

3.8 Authentication Payload