Note that I highlighted 2 Notify messages. Now, last IKE_AUTH message sent by Responder confirms which security parameters it picked ( Security Association message), repeats the same Traffic Selector messages (if correctly configured) and sends hash of message using pre-master key ( Authentication message) The first IKE_AUTH message negotiates the security parameters for production traffic (child SAs), authenticates each side and informs what is the source/destination IP/Port that is supposed to go through IPSec tunnel: The above payload is Encrypted using SK_e and Integrity-protected using SK_a (these keys are different for each direction). These are immediately applied to next 2 IKE_AUTH messages as seen below: Responder picked the 4 available security options also confirmed in Security Association -> Proposal -> Transform, Transform… payloads as seen above. In this case here the Initiator only sent one option for Encryption, Integrity, Pseudo-Random Function (PRF) and Diffie Hellman group so there are only 4 corresponding transforms but there could be more. payloads which contains the required security settings to protect IKE_AUTH phase as well as to generate the seed key ( SK_d) for production traffic (child SA): More specifically, the IPSec protocol used (ESP or AH - typically ESP as AH doesn't support encryption), the Encryption algorithm (AES128? AES256?) and Authentication algorithm (HMAC_SHA256? HMAC_SHA384?).įirst the Initiator sends a Security Association -> Proposal -> Transform, Transform. IKE_AUTH: negotiates security parameters to protect production traffic (CHILD_SA).SK_d (derivation): handed to IPSec to generate encryption and optionally authentication keys for production traffic.SK_a (authentication): computed for each direction (one for outbound and one for inbound) to hash (using HMAC) IKE_AUTH messages.
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