5G SEPP N32跨域PRINS保护与消息安全信令全链路拆解

graph LR
    subgraph VPLMN["Visited PLMN (vPLMN)"]
        AMF_v[AMF]
        SMF_v[SMF]
        NRF_v[NRF]
        SEPP_v[SEPP<br/>c-SEPP]
    end

    subgraph IPX["IPX Provider Network"]
        IPX_Proxy[IPX Proxy<br/>可选中间节点]
    end

    subgraph HPLMN["Home PLMN (hPLMN)"]
        SEPP_h[SEPP<br/>p-SEPP]
        AUSF_h[AUSF]
        UDM_h[UDM]
        NRF_h[NRF]
    end

    AMF_v -->|SBI| SEPP_v
    SMF_v -->|SBI| SEPP_v
    SEPP_v -->|N32-c + N32-f| IPX_Proxy
    IPX_Proxy -->|N32-c + N32-f| SEPP_h
    SEPP_h -->|SBI| AUSF_h
    SEPP_h -->|SBI| UDM_h

    style SEPP_v fill:#e74c3c,color:#fff
    style SEPP_h fill:#3498db,color:#fff
    style IPX_Proxy fill:#f39c12,color:#fff

sequenceDiagram
    participant cSEPP as c-SEPP (vPLMN)
    participant pSEPP as p-SEPP (hPLMN)

    Note over cSEPP,pSEPP: 阶段一：TLS隧道建立
    cSEPP->>pSEPP: TLS ClientHello<br/>[SNI: sepp.hplmn.example]
    pSEPP->>cSEPP: TLS ServerHello + Certificate
    cSEPP->>pSEPP: Certificate + CertificateVerify
    pSEPP->>cSEPP: TLS Finished
    Note over cSEPP,pSEPP: TLS 1.3 mutual auth完成<br/>双向证书验证

    Note over cSEPP,pSEPP: 阶段二：安全能力协商
    cSEPP->>pSEPP: POST /n32c-handshake/v1/exchange-capability<br/>{seppId, plmnId, supportedSecCapability,<br/>n32fContextId, senderIdentity}
    pSEPP->>cSEPP: 200 OK<br/>{selectedSecCapability, n32fContextId,<br/>senderIdentity, protectionPolicy}

    alt 协商失败
        pSEPP->>cSEPP: 403 Forbidden<br/>{cause: "Unsupported security capability"}
    end

    Note over cSEPP,pSEPP: N32-c安全上下文建立完成<br/>后续N32-f消息使用协商参数

graph TD
    A[Protection Policy<br/>保护策略] --> B[INTEGRITY_PROTECTION<br/>仅完整性保护]
    A --> C[INTEGRITY_AND_CIPHERING<br/>完整性+机密性保护]
    A --> D[CLEAR_TEXT<br/>明文传输]
    A --> E[MODIFICATION_REPLACEMENT<br/>替换修改]
    A --> F[MODIFICATION_DELETION<br/>删除修改]

    B --> B1[JWS签名<br/>IPX可读不可改]
    C --> C1[JWE加密+JWS签名<br/>IPX完全不可读]
    D --> D1[不保护<br/>路由等公共信息]
    E --> E1[cSEPP替换敏感值<br/>pSEPP恢复原值]
    F --> F1[cSEPP删除字段<br/>pSEPP不恢复]

    style B fill:#27ae60,color:#fff
    style C fill:#e74c3c,color:#fff
    style D fill:#95a5a6,color:#fff
    style E fill:#f39c12,color:#fff
    style F fill:#8e44ad,color:#fff

sequenceDiagram
    participant AMF as vPLMN AMF
    participant cSEPP as c-SEPP
    participant IPX as IPX Provider
    participant pSEPP as p-SEPP
    participant AUSF as hPLMN AUSF

    Note over AMF: UE发起注册<br/>需要hPLMN认证

    AMF->>cSEPP: POST /nausf-auth/v1/ue-authentications<br/>Body: {supi: SUCI, servingNetworkName: "5G:mnc460.mcc001"...}

    Note over cSEPP: 步骤1：策略匹配<br/>匹配Protection Policy<br/>- supi → INTEGRITY_PROTECTION<br/>- servingNetworkName → INTEGRITY_PROTECTION

    Note over cSEPP: 步骤2：JWS签名<br/>对integrity保护字段生成<br/>JWS Compact Serialization签名

    Note over cSEPP: 步骤3：拓扑隐藏<br/>内部NF地址替换<br/>amf.internal.vplmn → placeholder-001

    cSEPP->>IPX: POST /nausf-auth/v1/ue-authentications<br/>Header: Content-Type: application/json<br/>Body: {<br/>"protectedHeader": {...},<br/>"signature": "BASE64URL(SIG)",<br/>"payload": {<br/>  "supi": "SUCI_value",<br/>  "servingNetworkName": "5G:mnc460.mcc001"<br/>}<br/>}

    Note over IPX: IPX仅读取路由头<br/>无法修改被保护字段<br/>（JWS签名会校验失败）

    IPX->>pSEPP: 转发请求<br/>（消息内容不变）

    Note over pSEPP: 步骤4：JWS验证<br/>验证签名完整性<br/>确认消息未被篡改

    Note over pSEPP: 步骤5：拓扑恢复<br/>placeholder-001 →<br/>amf.internal.vplmn<br/>（使用replacementMap）

    pSEPP->>AUSF: POST /nausf-auth/v1/ue-authentications<br/>Body: {supi: SUCI,<br/>servingNetworkName: "5G:mnc460.mcc001"...}

    AUSF->>pSEPP: 201 Created<br/>Body: {authType: "5G-AKA",<br/>5gAuthData: {rand, autn, hxstarstar*},<br/>links: {...}}

    Note over pSEPP: 步骤6：出站策略匹配<br/>- 5gAuthData → INTEGRITY_AND_CIPHERING<br/>- rand → INTEGRITY_PROTECTION<br/>- hxstarstar* → INTEGRITY_AND_CIPHERING

    Note over pSEPP: 步骤7：JWE加密敏感字段<br/>对认证向量等施加JWE加密<br/>使用协商的加密密钥

    pSEPP->>IPX: 201 Created<br/>Body: {<br/>"encrypted": "BASE64URL(JWE)",<br/>"signature": "BASE64URL(SIG)",<br/>"clearFields": {authType: "5G-AKA"}<br/>}

    IPX->>cSEPP: 转发响应

    Note over cSEPP: 步骤8：JWE解密<br/>使用本地密钥解密<br/>恢复认证向量

    Note over cSEPP: 步骤9：JWS验证<br/>验证响应完整性

    cSEPP->>AMF: 201 Created<br/>Body: {authType: "5G-AKA",<br/>5gAuthData: {rand, autn, hxstarstar*}}

BASE64URL(ProtectedHeader) . BASE64URL(Payload) . BASE64URL(Signature)

{
  "alg": "ES256",
  "kid": "csepp-key-2026-001",
  "typ": "PRINS-JWS",
  "n32fCtxId": "ctx-v2plmn-hplmn-001",
  "iat": 1716422400,
  "jti": "msg-uuid-a1b2c3d4"
}

{
  "protected": "BASE64URL({alg:A256KW, enc:A256GCM})",
  "encrypted_key": "BASE64URL(CEK_wrapped)",
  "iv": "BASE64URL(initialization_vector)",
  "ciphertext": "BASE64URL(encrypted_payload)",
  "tag": "BASE64URL(authentication_tag)",
  "unprotected": {
    "kid": "csepp-enc-key-2026-001",
    "n32fCtxId": "ctx-v2plmn-hplmn-001"
  }
}

graph TD
    TLS[TLS 1.3 Master Secret] -->|TLS-Exporter| MK[N32 Master Key<br/>TS 33.501 13.2.1.3]
    MK -->|KDF| IK[Integrity Key<br/>用于JWS签名/验证]
    MK -->|KDF| EK[Encryption Key<br/>用于JWE加密/解密]
    MK -->|KDF| SALT[Key Salt<br/>密钥更新种子]

    SALT -->|密钥轮换| MK2[Updated Master Key]

    style TLS fill:#2c3e50,color:#fff
    style MK fill:#e74c3c,color:#fff
    style IK fill:#27ae60,color:#fff
    style EK fill:#3498db,color:#fff

{
  "sender": "sepp.vplmn.example",
  "receiver": "sepp.hplmn.example",
  "n32fContextId": "ctx-v2plmn-hplmn-001",
  "messageBody": {
    "originalHttpMethod": "POST",
    "originalTargetApi": "/nausf-auth/v1/ue-authentications",
    "httpHeaders": {
      "content-type": "application/json"
    },
    "jsonData": {
      "supi": {
        "integritySignature": "eyJhbGciOiJFUzI1NiIs..."
      },
      "servingNetworkName": {
        "integritySignature": "eyJhbGciOiJFUzI1NiIs..."
      }
    },
    "replacementsMap": {
      "placeholder-001": "amf.internal.vplmn.mnc460.mcc001.3gppnetwork.org"
    }
  }
}

stateDiagram-v2
    [*] --> INIT: N32-c握手发起
    INIT --> NEGOTIATING: ExchangeCapabilityRequest发送
    NEGOTIATING --> ACTIVE: 协商成功<br/>密钥建立
    NEGOTIATING --> FAILED: 能力不匹配<br/>返回403
    FAILED --> [*]

    ACTIVE --> ACTIVE: 密钥轮换<br/>计数器或时间触发
    ACTIVE --> EXPIRED: 安全上下文超时
    ACTIVE --> TERMINATED: SEPP重启/策略变更
    EXPIRED --> INIT: 自动重协商
    TERMINATED --> INIT: 手动触发重新握手

    note right of ACTIVE
        正常N32-f消息传输
        每条消息携带n32fCtxId
        JWS签名计数器递增
    end note