VoNR IMS注册双轮鉴权与IPSec协商拆解

5G Registration → IMS PDU Session (5QI=5) → P-CSCF Discovery → SIP REGISTER (Round 1) → 401 Challenge → SIP REGISTER (Round 2) → 200 OK + IPSec SA

sequenceDiagram
    participant UE
    participant gNB
    participant AMF
    participant SMF
    participant UPF
    participant PCF

    UE->>gNB: UL NAS Transport<br/>(PDU Session Establishment Request)
    gNB->>AMF: N2 UL NAS Transport
    AMF->>SMF: Nsmf_PDUSession_CreateSMContext
    SMF->>PCF: Npcf_SMPolicyControl_Create
    PCF-->>SMF: Policy + P-CSCF Address
    SMF->>UPF: N4 Session Establishment
    SMF-->>AMF: N1N2Transfer<br/>(PDU Session Accept + P-CSCF via PCO)
    AMF->>gNB: N2 PDUSessionReq + NAS PDU
    gNB-->>UE: PDU Session Establishment Accept<br/>PCO: P-CSCF IPv6 Address

    Note over UE: UE now has P-CSCF address<br/>and IMS signaling bearer (5QI=5)

sequenceDiagram
    participant UE
    participant P-CSCF as P-CSCF
    participant I-CSCF as I-CSCF
    participant HSS as UDM/HSS
    participant S-CSCF as S-CSCF

    rect rgb(230, 245, 255)
    Note over UE,S-CSCF: Round 1 — 初始REGISTER（无凭据）
    UE->>P-CSCF: SIP REGISTER<br/>To: sip:[email protected]<br/>From: sip:[email protected]<br/>Contact: sip:user@[UE_IP]:port<br/>Security-Client: ipsec-3gpp;alg=AES-CBC<br/>Require: sec-agree
    P-CSCF->>I-CSCF: REGISTER + Path + Via<br/>Path: sip:pcscf@addr;lr
    I-CSCF->>HSS: Cx: UAR (User-Authorization-Request)<br/>Public Identity + Private Identity
    HSS-->>I-CSCF: Cx: UAA<br/>S-CSCF Name / Capability Set
    I-CSCF->>S-CSCF: REGISTER (forwarded)
    end

    rect rgb(255, 230, 230)
    Note over UE,S-CSCF: 401 Unauthorized Challenge
    S-CSCF->>HSS: Cx: MAR (Multimedia-Auth-Request)<br/>获取鉴权向量 AV(RAND,AUTN,XRES,CK,IK)
    HSS-->>S-CSCF: Cx: MAA<br/>AV + SIP-Auth-Data-Item
    S-CSCF-->>I-CSCF: 401 Unauthorized<br/>WWW-Authenticate: Digest<br/>nonce=Base64(RAND||AUTN)<br/>algorithm=AKAv2-MD5<br/>qop="auth,auth-int"<br/>opaque=SIP-Auth-Data-Item
    I-CSCF-->>P-CSCF: 401 Unauthorized
    P-CSCF->>P-CSCF: 分配Server SPI/Port<br/>添加Security-Server头
    P-CSCF-->>UE: 401 Unauthorized<br/>Security-Server: ipsec-3gpp;alg=AES-CBC<br/>port-s=port-c' (对称端口对)
    end

    rect rgb(230, 255, 230)
    Note over UE,S-CSCF: Round 2 — 带凭据REGISTER
    UE->>UE: ISIM计算 RES = f2(RAND,K)<br/>检测AUTN有效性<br/>计算CK,IK → IPSec密钥
    UE->>P-CSCF: SIP REGISTER (via IPSec SA)<br/>Authorization: Digest<br/>response=MD5(H(A1):nonce:H(A2))<br/>A1 = H(IMPI:realm:RES)<br/>Security-Verify: ipsec-3gpp
    P-CSCF->>P-CSCF: 验证IPSec SA完整性
    P-CSCF->>I-CSCF: REGISTER (via IPSec tunnel)
    I-CSCF->>HSS: Cx: UAR
    HSS-->>I-CSCF: Cx: UAA → S-CSCF
    I-CSCF->>S-CSCF: REGISTER
    end

    rect rgb(255, 255, 230)
    Note over UE,S-CSCF: 鉴权成功 + 注册确认
    S-CSCF->>S-CSCF: 比对 response vs XRES<br/>验证通过
    S-CSCF->>HSS: Cx: SAR (Server-Assignment-Request)<br/>注册IMPU → S-CSCF绑定
    HSS-->>S-CSCF: Cx: SAA (用户配置/IFCs)
    S-CSCF-->>I-CSCF: 200 OK<br/>Service-Route, P-Associated-URI
    I-CSCF-->>P-CSCF: 200 OK
    P-CSCF-->>UE: 200 OK<br/>Service-Route, Path, Security-Server<br/>绑定IPSec SA有效期
    end

graph TB
    subgraph "WWW-Authenticate Digest 头"
        A["algorithm=AKAv2-MD5<br/>IMS AKA版本号"]
        B["nonce=Base64(RAND ∥ AUTN)<br/>Base64编码的挑战参数"]
        C["realm=ims.mnc.mcc.3gppnetwork.org<br/>认证域"]
        D["qop=auth,auth-int<br/>保护质量"]
        E["opaque=Base64(SIP-Auth-Data-Item)<br/>S-CSCF认证上下文"]
        F["ik=[" + CK="]<br/>可选: 密钥推衍参数"]
    end

    subgraph "Security-Server 头"
        G["ipsec-3gpp<br/>选定安全协议"]
        H["alg=AES-CBC<br/>加密算法"]
        I["ealg=AES-CBC<br/>加密封装算法"]
        J["port-s=5061<br/>P-CSCF服务器端口"]
        K["port-c=5060<br/>期望UE使用的客户端端口"]
    end

    B --> |"UE解析"| L["RAND: 128bit随机数<br/>AUTN: 认证令牌"]
    L --> |"ISIM计算"| M["RES = f2(RAND, K)<br/>CK = f3(RAND, K)<br/>IK = f4(RAND, K)"]
    M --> |"密钥推衍"| N["IPSec SA密钥材料:<br/>CK' = CK XOR IK<br/>用于ESP加密"]

输入: RAND（从nonce解码）, K（ISIM存储的共享密钥）
计算:
  RES = f2(RAND, K)        // 期望响应，64bit→128bit
  CK  = f3(RAND, K)        // 加密密钥，128bit
  IK  = f4(RAND, K)        // 完整性密钥，128bit
  AUTS（如果SQN不同步）   // 同步失败时计算

H(A1) = MD5(IMPI : realm : RES)
H(A2) = MD5("REGISTER" : Request-URI)
response = MD5(H(A1) : nonce : nc : cnonce : qop : H(A2))

CK' = CK || IK（256位，用于AES-CBC加密）
IK' = 从IK推衍（用于HMAC-SHA-1完整性保护）
SPI: 从Security-Server头获取
Port: 使用对称端口对（port-c/port-s）

graph LR
    subgraph "Cx接口消息流"
        A["UAR<br/>User-Authorization-Request<br/>I-CSCF → HSS<br/>查询: IMPU是否已注册?"]
        B["UAA<br/>User-Authorization-Answer<br/>HSS → I-CSCF<br/>返回: S-CSCF名称/能力集"]
        C["MAR<br/>Multimedia-Auth-Request<br/>S-CSCF → HSS<br/>请求: 鉴权向量AV"]
        D["MAA<br/>Multimedia-Auth-Answer<br/>HSS → S-CSCF<br/>返回: AV(RAND,AUTN,XRES,CK,IK)"]
        E["SAR<br/>Server-Assignment-Request<br/>S-CSCF → HSS<br/>通知: IMPU注册到本S-CSCF"]
        F["SAA<br/>Server-Assignment-Answer<br/>HSS → S-CSCF<br/>返回: 用户Profile/IFCs"]
    end

    A --> B
    C --> D
    E --> F

    style A fill:#E6F3FF
    style C fill:#FFE6E6
    style E fill:#E6FFE6

输入: CK（128bit）, IK（128bit）来自ISIM AKA计算

密钥材料 = CK || IK = 256bit

IPSec ESP加密密钥: 从密钥材料前128/256bit派生（取决于算法）
IPSec ESP完整性密钥: 从密钥材料后bit派生
SPI: 由发起方分配（UE分配SPI-c，P-CSCF分配SPI-s）

stateDiagram-v2
    [*] --> NotRegistered: UE开机/PDU Session建立
    NotRegistered --> RegPending: 发送REGISTER(R1)<br/>无凭据
    RegPending --> Challenged: 收到401<br/>解析nonce→RAND/AUTN<br/>建立IPSec SA
    RegPending --> RegFailed: 超时/网络错误
    Challenged --> AuthProcessing: 发送REGISTER(R2)<br/>经IPSec SA<br/>携带Digest响应
    AuthProcessing --> Registered: 收到200 OK<br/>保存Service-Route/Path
    AuthProcessing --> RegFailed: 鉴权失败<br/>SIP 403/401(重试)
    Registered --> ReRegistration: Expires到期前重注册
    Registered --> DeRegistered: UE发送REGISTER(Expires=0)
    Registered --> RegFailed: 网络侧注销(423 Interval Too Brief)
    ReRegistration --> Registered: 200 OK
    ReRegistration --> Challenged: 收到401(网络要求重鉴权)
    RegFailed --> NotRegistered: 等待重试
    DeRegistered --> NotRegistered: 注销确认