IMS注册鉴权四步信令与AKA博弈

sequenceDiagram
    participant UE
    participant P_CSCF as P-CSCF
    participant I_CSCF as I-CSCF
    participant HSS
    participant S_CSCF as S-CSCF

    Note over UE,S_CSCF: 第一轮REGISTER——鉴权挑战下发

    UE->>P_CSCF: SIP REGISTER (无Authorization头)<br/>CSeq: 1 REGISTER<br/>Contact: expires=600000
    P_CSCF->>P_CSCF: 记录UE IP:Port<br/>建立Path头部
    P_CSCF->>I_CSCF: SIP REGISTER (添加Path, P-Visited-Network-ID)

    I_CSCF->>HSS: Diameter UAR<br/>User-Name=IMPI<br/>Public-Identity=IMPU<br/>Visited-Network-Identifier
    HSS->>I_CSCF: Diameter UAA<br/>Server-Name=S-CSCF地址<br/>或 Capability-Set

    Note over I_CSCF: 若UAA未返回S-CSCF地址<br/>则按能力集选择S-CSCF

    I_CSCF->>S_CSCF: SIP REGISTER (转发)

    S_CSCF->>HSS: Diameter MAR<br/>SIP-Number-Auth-Items=1<br/>SIP-Authentication-Scheme=Digest-AKAv1-MD5
    HSS->>S_CSCF: Diameter MAA<br/>SIP-Auth-Data-Item:<br/>  RAND || AUTN || XRES || CK || IK

    S_CSCF->>S_CSCF: 构造nonce<br/>nonce = Base64(RAND‖AUTN‖<br/>server-specific-data)<br/>存储XRES等待验证

    S_CSCF->>I_CSCF: SIP 401 Unauthorized<br/>WWW-Authenticate: Digest<br/>  realm, nonce, algorithm=AKAv1-MD5<br/>  ik=..., ck=..., qop=auth-int
    I_CSCF->>P_CSCF: SIP 401 Unauthorized
    P_CSCF->>P_CSCF: 提取IK/CK<br/>准备IPSec SA参数
    P_CSCF->>UE: SIP 401 Unauthorized

    Note over UE,S_CSCF: UE侧AKA计算

    UE->>UE: ISIM/USIM输入RAND→<br/>计算RES, 验证AUTN<br/>推导IK/CK

    Note over UE,S_CSCF: 第二轮REGISTER——携带鉴权响应

    UE->>P_CSCF: SIP REGISTER (含Authorization)<br/>CSeq: 2 REGISTER<br/>Authorization: Digest<br/>  response=H(RES,nonce,...)<br/>algorithm=AKAv1-MD5
    P_CSCF->>P_CSCF: 验证IPSec SA<br/>建立安全关联
    P_CSCF->>I_CSCF: SIP REGISTER (IPSec保护)

    I_CSCF->>HSS: Diameter UAR (第二轮)
    HSS->>I_CSCF: Diameter UAA (Server-Name)

    I_CSCF->>S_CSCF: SIP REGISTER

    S_CSCF->>S_CSCF: 比较response vs H(XRES,...)<br/>验证通过→注册成功

    S_CSCF->>HSS: Diameter SAR<br/>Server-Assignment-Type=REGISTRATION
    HSS->>S_CSCF: Diameter SAA<br/>User-Profile (iFC, 服务配置)

    S_CSCF->>I_CSCF: SIP 200 OK<br/>P-Associated-URI<br/>Service-Route
    I_CSCF->>P_CSCF: SIP 200 OK
    P_CSCF->>UE: SIP 200 OK

REGISTER sip:ims.mnc460.mcc3gppnetwork.org SIP/2.0
Via: SIP/2.0/UDP [2001:db8::1]:5060;branch=z9hG4bK1234
From: <sip:[email protected]>;tag=abc123
To: <sip:[email protected]>
Call-ID: cb03a0s09a2sdfglkj490333
CSeq: 1 REGISTER
Contact: <sip:460001234567890@[2001:db8::1]:5060>;+sip.instance="<urn:gsma:imei:35693803-123456-0>";expires=600000
Expires: 600000
Require: sec-agree
Proxy-Require: sec-agree
Security-Client: digest, ipsec-3gpp; alg=hmac-sha-256-128; ealg=aes-cbc; spi-c=234567; spi-s=345678; port-c=5062; port-s=5064
Content-Length: 0

SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP [2001:db8::1]:5060;branch=z9hG4bK1234;rport
...
WWW-Authenticate: Digest realm="ims.mnc460.mcc3gppnetwork.org",
    nonce="RCM2R0FEQ0JNQUNBQT09fnRlc3Q=",
    algorithm=AKAv1-MD5,
    qop="auth-int",
    ik="736f6d65696b76616c7565",
    ck="736f6d65636b76616c7565",
    opaque="5f06c423c50e"
Security-Server: ipsec-3gpp; alg=hmac-sha-256-128; ealg=aes-cbc; spi-c=987654; spi-s=876543; port-c=5063; port-s=5065
Content-Length: 0

graph LR
    A[RAND<br/>128 bit] --> B["Base64编码<br/>H(RAND)"]
    C[AUTN<br/>128 bit] --> B
    D[SQN⊕AK<br/>隐藏序列号] --> C
    E[AMF<br/>认证管理域] --> C
    F[MAC-A<br/>消息认证码] --> C
    B --> G["nonce = Base64<br/>(H(RAND) ‖ AUTN ‖ <br/>server-specific-data)"]

flowchart TD
    A["UE收到401<br/>提取nonce → RAND, AUTN"] --> B["USIM/ISIM卡<br/>输入K(长期共享密钥) + RAND"]
    B --> C["f1算法 → XMAC"]
    B --> D["f2算法 → RES"]
    B --> E["f3算法 → CK"]
    B --> F["f4算法 → IK"]
    B --> G["f5算法 → AK<br/>用于解隐藏SQN"]
    C --> H{"XMAC == MAC<br/>(AUTN中的MAC)?"}
    H -->|否| I["❌ 网络认证失败<br/>UE拒绝注册"]
    H -->|是| J["验证SQN范围<br/>防止重放攻击"]
    J -->|SQN有效| K["✅ 双向认证通过<br/>构造Authorization头"]
    J -->|SQN异常| L["发起AUTS同步<br/>Synchronization failure"]
    K --> M["response = H(RES, nonce, ...)<br/>AKAv1-MD5 Digest计算"]

response = H(A1, A2) 其中:
  A1 = H(username : realm : password)    ← password = RES
  A2 = H(Method : digest-uri)

实际计算：
  A1 = H(IMPI : realm : RES)
  A2 = H(REGISTER : sip:ims.mnc460.mcc3gppnetwork.org)
  response = H(A1 : nonce : nc : cnonce : qop : A2)

REGISTER sip:ims.mnc460.mcc3gppnetwork.org SIP/2.0
Via: SIP/2.0/UDP [2001:db8::1]:5064;branch=z9hG4bK5678;rport
From: <sip:[email protected]>;tag=abc123
To: <sip:[email protected]>
Call-ID: cb03a0s09a2sdfglkj490333
CSeq: 2 REGISTER
Contact: <sip:460001234567890@[2001:db8::1]:5064>;+sip.instance="<urn:gsma:imei:35693803-123456-0>";expires=600000
Authorization: Digest username="[email protected]",
    realm="ims.mnc460.mcc3gppnetwork.org",
    nonce="RCM2R0FEQ0JNQUNBQT09fnRlc3Q=",
    uri="sip:ims.mnc460.mcc3gppnetwork.org",
    response="6629fae49393a05397450978507c4ef1",
    algorithm=AKAv1-MD5,
    qop=auth-int,
    nc=00000001,
    cnonce="0a4f113b",
    opaque="5f06c423c50e"
Security-Verify: ipsec-3gpp; alg=hmac-sha-256-128; ealg=aes-cbc; spi-c=987654; spi-s=876543; port-c=5063; port-s=5065
Content-Length: 0

SIP/2.0 200 OK
Via: SIP/2.0/UDP [2001:db8::1]:5064;branch=z9hG4bK5678;rport=5065
...
Contact: <sip:460001234567890@[2001:db8::1]:5064>;expires=600000
Date: Sat, 23 May 2026 08:30:00 GMT
P-Associated-URI: <sip:[email protected]>,
    <tel:+8613800138000>
Service-Route: <sip:[email protected];lr>
Path: <sip:pcscf.ims.mnc460.mcc3gppnetwork.org;lr>
Content-Length: 0

graph TB
    subgraph "Cx接口三阶段"
        D1["阶段1: UAR/UAA<br/>I-CSCF → HSS<br/>目的: 查询S-CSCF分配"]
        D2["阶段2: MAR/MAA<br/>S-CSCF → HSS<br/>目的: 获取认证向量AV"]
        D3["阶段3: SAR/SAA<br/>S-CSCF → HSS<br/>目的: 通知注册完成+下载用户档案"]
    end
    D1 -->|"S-CSCF地址<br/>或能力集"| D2
    D2 -->|"AV五元组<br/>RAND/AUTN/XRES/CK/IK"| D3
    D3 -->|"用户Profile<br/>iFC/Service-Profile"| Done["注册完成"]

    style D1 fill:#e1f5fe
    style D2 fill:#fff3e0
    style D3 fill:#e8f5e9

flowchart TD
    subgraph "密钥材料获取"
        A["401中的ik/ck"] --> B["P-CSCF提取<br/>IK(完整性)<br/>CK(加密)"]
    end
    subgraph "IPSec SA参数协商"
        B --> C["Security-Client<br/>(UE提议)"]
        B --> D["Security-Server<br/>(网络提议)"]
        C --> E["匹配算法<br/>alg=hmac-sha-256-128<br/>ealg=aes-cbc"]
        D --> E
    end
    subgraph "SA建立"
        E --> F["SPI-c/SPI-s<br/>端口映射<br/>port-c/port-s"]
        F --> G["IPSec ESP隧道<br/>UE ↔ P-CSCF"]
    end

# 过滤所有REGISTER相关消息
sip.Request-Line contains "REGISTER" || sip.Status-Code == 401 || (sip.Status-Code == 200 && sip.CSeq.method == "REGISTER")

# 过滤Diameter Cx接口
diameter.Application-Id == 16777216 && (diameter.Command-Code == 300 || diameter.Command-Code == 303 || diameter.Command-Code == 301)

stateDiagram-v2
    [*] --> 未注册: UE开机/IMS启用
    未注册 --> 鉴权进行中: 发送REGISTER(CSeq=1)
    鉴权进行中 --> 网络鉴权中: 收到401<br/>USIM执行AKA
    网络鉴权中 --> 鉴权响应发送: AUTN验证通过<br/>计算RES/response
    网络鉴权中 --> SQN同步: SQN验证失败<br/>构造auts
    SQN同步 --> 鉴权进行中: 重发REGISTER(含auts)
    网络鉴权中 --> 认证失败: AUTN中MAC不匹配<br/>UE拒绝
    认证失败 --> 未注册: 等待重试
    鉴权响应发送 --> 已注册: 收到200 OK
    鉴权响应发送 --> 认证失败: 收到403<br/>response验证失败
    已注册 --> 已注册: 周期性重注册<br/>(刷新注册)
    已注册 --> 未注册: 发送REGISTER(expires=0)<br/>或注册超时
    已注册 --> 鉴权进行中: 重注册需重新鉴权<br/>(根据网络策略)