5G非可信WiFi接入N3IWF与EAP-AKA'认证信令拆解

graph TB
    subgraph "非可信非3GPP接入域"
        UE["UE<br/>(WiFi连接)"]
        WiFi["WiFi AP<br/>(非可信)"]
    end

    subgraph "安全边界"
        N3IWF["N3IWF<br/>EAP Authenticator<br/>IKEv2 Responder"]
    end

    subgraph "5G核心网"
        AMF["AMF<br/>SEAF角色"]
        AUSF["AUSF"]
        UDM["UDM/ARPF<br/>SIDF"]
        UPF["UPF"]
    end

    UE -->|"Yu: IKEv2/IPsec<br/>EAP-AKA'"| N3IWF
    N3IWF -->|"N2: NGAP"| AMF
    AMF -->|"Nausf: Auth"| AUSF
    AUSF -->|"Nudm: Auth Get"| UDM
    N3IWF -->|"N3: GTP-U"| UPF
    UE -.->|"WiFi"| WiFi

    style N3IWF fill:#ff6b6b,color:#fff
    style UE fill:#4ecdc4,color:#fff
    style AUSF fill:#ffe66d,color:#333

sequenceDiagram
    participant UE
    participant N3IWF
    participant AMF
    participant AUSF
    participant UDM

    Note over UE,N3IWF: Phase 1: IKE_SA_INIT
    UE->>N3IWF: IKE_SA_INIT Request<br/>SAi1, KEi, Ni
    N3IWF->>UE: IKE_SA_INIT Response<br/>SAr1, KEr, Nr, [Cookie]

    Note over UE,N3IWF: Phase 2: IKE_AUTH + EAP-AKA'
    UE->>N3IWF: IKE_AUTH Request<br/>IDi([email protected]...), SAi2, TSi, TSr
    N3IWF->>UE: IKE_AUTH Response<br/>EAP-Request/AKA'-Start<br/>AT_KDF_INPUT, AT_KDF

    UE->>N3IWF: IKE_AUTH Request<br/>EAP-Response/AKA'-Identity<br/>(SUCI)
    N3IWF->>AMF: N2 NAS Transport<br/>NAS: Registration Request + EAP-5G(ID)

    Note over AMF,UDM: Phase 3: 5G AKA via EAP-AKA'
    AMF->>AUSF: Nausf_UEAuthentication_Auth<br/>SUCI, SNN
    AUSF->>UDM: Nudm_UEAuthentication_Get<br/>SUCI, SNN
    UDM->>AUSF: 5G AV(RAND, AUTN, KAUSF, XRES*)
    AUSF->>AMF: RAND, AUTN, HXRES*
    AMF->>N3IWF: N2 NAS Transport<br/>EAP-Request/AKA'-Challenge<br/>AT_RAND, AT_AUTN, AT_MAC

    N3IWF->>UE: IKE_AUTH Response<br/>EAP-Request/AKA'-Challenge

    Note over UE: UE验证AUTN<br/>计算RES*<br/>派生CK', IK', MK, MSK
    UE->>N3IWF: IKE_AUTH Request<br/>EAP-Response/AKA'-Challenge<br/>AT_RES, AT_MAC

    N3IWF->>AMF: N2 NAS Transport<br/>EAP-Response/AKA'-Challenge
    AMF->>AUSF: Nausf_UEAuthentication_Auth<br/>RES*
    AUSF->>AMF: Auth Success + KSEAF
    AMF->>N3IWF: N2 NAS Transport<br/>EAP-Success + KSEAF
    N3IWF->>UE: IKE_AUTH Response<br/>EAP-Success

    Note over UE,N3IWF: Phase 4: IPsec Child SA + NAS Registration
    N3IWF->>UE: IKE_AUTH Response<br/>IDr, AUTH, SAr2, TSi, TSr<br/>(IPsec Child SA建立)
    UE->>N3IWF: NAS: Registration Complete<br/>(通过IPsec隧道)
    N3IWF->>AMF: N2 NAS Transport<br/>NAS: Registration Complete
    AMF->>N3IWF: N2 NAS Transport<br/>NAS: Registration Accept
    N3IWF->>UE: NAS: Registration Accept<br/>(通过IPsec隧道)

CK || IK = KDF_K(RES || CK || IK)  -- 从USIM获取基础CK/IK
CK' || IK' = KDF(CK || IK, SNN)   -- 绑定网络名称
KAUSF = KDF(CK' || IK', SQN ⊕ AK) -- 绑定序列号

MK = PRF'(CK' || IK', <identity> || n)
MSK = MK[0..511]      -- 512-bit MSK，用于IPsec密钥
EMSK = MK[512..1023]  -- 512-bit EMSK，5G中不使用

KSEAF = KDF(KAUSF, SNN || SQN ⊕ AK)

UE → IPsec隧道 → N3IWF → N2(NGAP) → AMF

graph TD
    K["K<br/>永久密钥<br/>(USIM/UDM)"]
    K -->|"f1-f5算法<br/>+ RAND"| AV["5G AV<br/>CK, IK, AUTN<br/>RAND, XRES*"]
    AV --> CKIK["CK || IK"]
    CKIK -->|"KDF(CK‖IK, SNN)"| CKP_IKP["CK' || IK'<br/>绑定SNN"]
    CKP_IKP -->|"KDF(CK'‖IK',<br/>SQN⊕AK)"| KAUSF["KAUSF"]
    KAUSF -->|"KDF(KAUSF,<br/>SNN‖SQN⊕AK)"| KSEAF["KSEAF"]
    KAUSF -->|"MK = PRF'(CK'‖IK',...)"| MK["MK<br/>EAP-AKA'<br/>Master Key"]
    MK --> MSK["MSK (512-bit)<br/>→ IPsec密钥"]
    MK --> EMSK["EMSK (512-bit)<br/>5G未使用"]
    KSEAF -->|"KDF(KSEAF,<br/>SUPI‖ABBA)"| KAMF["KAMF<br/>NAS根密钥"]
    KAMF --> KNAS_INT["KNAS_int<br/>NAS完整性密钥"]
    KAMF --> KNAS_ENC["KNAS_enc<br/>NAS加密密钥"]
    MSK -->|"IKEv2 PRF+"| IPsec_KEYS["IPsec ESP SA密钥<br/>SK_e(入/出)<br/>SK_a(入/出)"]

    style K fill:#e74c3c,color:#fff
    style KAUSF fill:#f39c12,color:#fff
    style KSEAF fill:#2ecc71,color:#fff
    style KAMF fill:#3498db,color:#fff
    style MSK fill:#9b59b6,color:#fff

graph TD
    subgraph "IKE_AUTH载荷"
        EAP5G["EAP-5G<br/>Type=55<br/>Vendor-Id=3GPP"]
        subgraph "EAP-5G PDU"
            ANQP["AN-Parameters<br/>(接入网参数)"]
            NAS_PDU["NAS PDU<br/>(Registration Request等)"]
        end
        EAP5G --> ANQP
        EAP5G --> NAS_PDU
    end

    subgraph "最终封装"
        UDP["UDP 500/4500"]
        IKE["IKEv2 HDR"]
        ENC["SK{IKE_AUTH}"]
        UDP --> IKE --> ENC --> EAP5G
    end

# IKEv2协商阶段
udp.port == 500 || udp.port == 4500

# 过滤IKE_SA_INIT
ikev2 && ikev2.exchange_type == 34

# 过滤IKE_AUTH（含EAP-AKA'）
ikev2 && ikev2.exchange_type == 35

# 过滤EAP-AKA'消息
eap.type == 55 && eap.subtype == 1   # AKA'-Start
eap.type == 55 && eap.subtype == 2   # AKA'-Challenge

# N2接口（NGAP）
ngap && ngap.procedureCode == 44      # UplinkNASTransport

┌─────────────────────────────────────┐
│         IPsec ESP Tunnel            │ ← MSK派生密钥保护
│  ┌───────────────────────────────┐  │
│  │     NAS Registration          │  │ ← KAMF派生密钥保护
│  ┌───────────────────────────────┐  │
│  │     PDU Session User Data     │  │ ← UPF N3隧道保护
│  └───────────────────────────────┘  │
└─────────────────────────────────────┘

stateDiagram-v2
    [*] --> WiFi_Connected: WiFi关联成功
    WiFi_Connected --> IKE_SA_Init: 发起IKE_SA_INIT
    IKE_SA_Init --> IKE_SA_Established: IKE SA建立成功
    IKE_SA_Established --> EAP_AKA_Start: 发送IKE_AUTH(IDi)
    EAP_AKA_Start --> EAP_AKA_Identity: 收到AKA'-Start
    EAP_AKA_Identity --> EAP_AKA_Challenge: 发送Identity
    EAP_AKA_Challenge --> EAP_AKA_Verifying: 收到Challenge
    EAP_AKA_Verifying --> EAP_Success: USIM验证AUTN成功
    EAP_AKA_Verifying --> EAP_Failure: AUTN验证失败
    EAP_Success --> IPsec_Child_SA: 收到EAP-Success+AUTH
    IPsec_Child_SA --> NAS_Registration: Child SA建立
    NAS_Registration --> Registered: Registration Accept
    Registered --> [*]: 注册完成

    EAP_Failure --> [*]: 认证失败
    IKE_SA_Init --> [*]: IKE超时