Subject: [IPsec] Few comments to draft-ietf-ipsecme-ikev2-intermediate

From: Tero Kivinen <[email-masked]>
Date: Wed, 28 Jul 2021 14:01:14 +0300

I was reading the draft-ietf-ipsecme-ikev2-intermediate through and I
think it might be good thing to add a note at the end of section 3.3.1
Protection of the IKE_INTERMEDIATE messages to clarify which SK_e[i/r]
and SK_a[i/r] are to be used for the IKE_AUTH after all
IKE_INTERMEDIATE exchanges (I assume it is the latest one). 

Also perhaps we should have appendix showing the full protocol
exchange example. I.e. something like this:

----------------------------------------------------------------------

Appendix A.  Example of IKE_INTERMEDIATE exchange.

   This appendix contains a short example of the messages using
   IKE_INTERMEDIATE. This appendix is purely informative; if it
   disagrees with the body of this document, the other text is
   considered correct.

   In this example there is one IKE_SA_INIT exchange, two
   IKE_INTERMEDIATE key exchanges followed by the IKE_AUTH exchange to
   authenticate the exchange. The xxx in the HDR(xxx,MID=yyy)
   indicates the exchange type, and yyy tells the message id used for
   that exchange. The keys used for each SK {} payload is indicated in
   the parenthesis after the SK. Otherwise payload notation is same as
   is used in the RFC7296.

   Initiator                      Responder
   -------------------------------------------------------------------
   HDR(IKE_SA_INIT,MID=0),
       SAi1, KEi, Ni,
       N(INTERMEDIATE_EXCHANGE_SUPPORTED)  -->

                                  <-- HDR(IKE_SA_INIT,MID=0),
				          SAr1, KEr, Nr, [CERTREQ],
                                          N(INTERMEDIATE_EXCHANGE_SUPPORTED)

   <Generate SK_[aip][ir] and store them as SK_[aip][ir]_1, start
   using them for SK {} payloads>

   HDR(IKE_INTERMEDIATE,MID=1),
       SK(SK_ei_1,SK_ai_1) { ... }  -->

   <Calculate IntAuth_1_I = prf(SK_pi_1, ...)>

                                  <-- HDR(IKE_INTERMEDIATE,MID=1),
				    	  SK(SK_er_1,SK_ai_1) { ...  }

   <Calculate IntAuth_1_R = prf(SK_pr_1, ...)>

   <If this IKE_INTERMEDIATE did a new key exchange then update
   SK_[aip][ir] and store them as SK_[aip][ir]_2, start using them for
   SK {} payloads>

   HDR(IKE_INTERMEDIATE,MID=2),
       SK(SK_ei_2,SK_ai_2) { ... }  -->

   <Calculate IntAuth_2_I = prf(SK_pi_2, ...)>

                                  <-- HDR(IKE_INTERMEDIATE,MID=2),
				      	  SK(SK_er_2,SK_ai_2) { ...  }

   <Calculate IntAuth_2_R = prf(SK_pr_2, ...)>

   <If this IKE_INTERMEDIATE did a new key exchange then update
   SK_[aip][ir] and store them as SK_[aip][ir]_3, start using them for
   SK {} payloads>

   HDR(IKE_AUTH,MID=3),
       SK(SK_ei_3,SK_ai_3) {IDi,
           [CERT,] [CERTREQ,]
       	   [IDr,] AUTH, SAi2,
       	   TSi, TSr}  -->

                                <-- HDR(IKE_AUTH,MID=3),
				        SK(SK_er_3,SK_ar_3) {IDr,
					    [CERT,] AUTH,
                                            SAr2, TSi, TSr}

----------------------------------------------------------------------

I think having such appendix would make things easier to understand.
-- 
[email-masked]

---

From: "Valery Smyslov" <[email-masked]>
Date: Fri, 30 Jul 2021 15:36:32 +0300

Hi Tero,

> IKE_INTERMEDIATE exchanges (I assume it is the latest one).

Your assumption is correct.

I can add the following text at the end of 3.3.1:

	Once all IKE_INTERMEDIATE exchanges are completed, the most recently calculated
            SK_e[i/r] and SK_a[i/r] keys are used for protection of the IKE_AUTH and all the
            subsequent exchanges.

Are you OK with this?

> exchange example. I.e. something like this:

OK, will add it.

Thank you,
Valery.

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