Initiator Responder --------------------------------------------------------------------- HDR(CREATE_CHILD_SA), SK {SA, Ni, KEi} --> <-- HDR(CREATE_CHILD_SA), SK {SA, Nr, KEr, N(ADDITIONAL_KEY_EXCHANGE)(link1)} HDR(IKE_FOLLOWUP_KE), SK {KEi(1), N(ADDITIONAL_KEY_EXCHANGE)(link1)} --> <-- HDR(IKE_FOLLOWUP_KE), SK {KEr(1), N(ADDITIONAL_KEY_EXCHANGE)(link2)} HDR(IKE_FOLLOWUP_KE), SK {KEi(2), N(ADDITIONAL_KEY_EXCHANGE)(link2)} --> <-- HDR(IKE_FOLLOWUP_KE), SK {KEr(2), N(ADDITIONAL_KEY_EXCHANGE)(link3)} HDR(IKE_FOLLOWUP_KE), SK {KEi(3), N(ADDITIONAL_KEY_EXCHANGE)(link3)} --> <-- HDR(IKE_FOLLOWUP_KE), SK {KEr(3)}