[RFC7296] IKEv2 정리 (Main)

읽기 전에..
- [CERTREQ]는 CERTREQ는 선택 사항이라는 것임. (Page 11)

   <--  HDR, SAr1, KEr, Nr, [CERTREQ]

중요한 룰
- Note that with these rules, there is no reason to negotiate and agree upon an SA lifetime.
If IKE presumes(추측하다) the partner is dead, based on repeated lack of acknowledgement to an IKE message,
then IKE SA and all Child SAs set up through that IKE SA are deleted.
(page 28)
- If an IKE endpoint choose to delete Child SAs, it MUST send Delete payloads to the other end notifying it of the deletion.

IKE SA가 셋업 하는 걸 막으면 안 되는, Notify message type들

   If creating the Child SA during the IKE_AUTH exchange fails for some reason, the IKE SA is still created as usual.  The list of Notify message types in the IKE_AUTH exchange that do not prevent an IKE SA from being set up include at least the following: NO_PROPOSAL_CHOSEN, TS_UNACCEPTABLE, SINGLE_PAIR_REQUIRED, INTERNAL_ADDRESS_FAILURE, and FAILED_CP_REQUIRED.


1. Introduction
- 모든 IKE 통신은 메시지 쌍 (request랑 response)로 구성됨.
- The pair is called an "exchange" or "request/response pair"
- The first two exchanges of messages establishing an IKE SA are called the IKE_SA_INIT exchange and the IKE_AUTH exchange;
- subsequent IKE exchanges are called either CREATE_CHILD_SA exchanges or INFORMATIONAL exchanges.
- In the common case, there is a single IKE_SA_INIT exchange and a single IKE_AUTH exchanges ( a total of four message) to establish the IKE_SA and the first Child SA.

- Subsequent exchanges MAY be used to establish additional Child SAs between the same authenticated pair of endpoints and to perform housekeeping fucntions.

Responsibility of the requester
- An IKE message flow always consist of a request follwed by a response. It is the responsibility of the requester to ensure reliablity. (신뢰성을 보장하는 것은 요청자 책임임)
- If the response is not received within a timeout interval, the requester need to retransmit the request (or abandon the connection)

- 첫 번째 교환, IKE_SA_INIT, this procedure negotitates security parameters for the IKE SA, sends nonces, and sends Diffie-Hellman values.
- 두 번째 교환, IKE_SA_AUTH, this procedure prove knowledge of the secrets corresponding to the tow identities.

1.3. The CREATE_CHILD_SA Exchnage
- The CREATE_CHILD_SA exchange is used to create new Child SAs nd to rekey both IKE SAs nd CHILD SAs.
- This exchange consists of a single request/response pair.

- endpoint 둘 다 CRETE_CHILD_SA exchange를 시작할 수 있음. 그래서 이 섹션에서, initiator는 이 exchnage를 시작한 endpoint라고 칭하겠음.


1.3.1. Creating New Child SAs with the CREATE_CHILD_SA Exchange

   Initiator                         Responder
   -------------------------------------------------------------------
   HDR, SK {SA, Ni, [KEi,]
              TSi, TSr}  -->

The Initiator sends;
1) SA offer(s) in the SA payload
2) a nonce in the Ni payload,
3) optionally a Diffie-Hellman value in the KEi payload,
4) the propsed Traffic Selectors for the proposed Child SA in the TSi, and TSr payload.

The CREATE_CHILD_SA response for creating a new Child SA is:

     <--  HDR, SK {SA, Nr, [KEr,]

The responder replies (using the same Message ID to respond) with
1) the acceptd offer in an SA payload
2) a nonce in the Nr payload,
3) and a Diffie-Hellman value in the KEr payload (if KEi was included in the request)
4) and the selected cryptographic suite includes that group.


Traffic selecter란?
2.9. Traffic Selector Negotiation
- When an RFC4301 IPsec subsystem receives an IP packet that matches a "protect" selector in SPD, the subsystem protects that packet with IPsec.

Security Policy Database(SPD)
- Maintenance of a system's SPD is outside the scope of IKE, although some implementations might update their SPD in connection With the running of IKE.

- Traffic Selector (TS) payloads allow endpoints to communicate some of the information from their SPD to ther peers.