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資安案例 (Cybersecurity Case) 與評估

#iso-21434 #concept-note #project-dependent #case #assessment

兩個關鍵 WP

WP 由誰製作 用途
Cybersecurity Case 執行者（CS Manager + Team） 論證資安目標達成
Cybersecurity Assessment Report 獨立評估員 評估 Case 是否成立
Important

兩者配對存在：Case 是「主張+證據」，Assessment 是「第三方確認」。

Cybersecurity Case 結構

定義 (Clause 3)

structured argument, supported by evidence, providing a compelling, comprehensible and valid case that cybersecurity goals are satisfied.

┌───────────────────────────────────────┐
│        Top Claim                      │
│ "TCU 達成所有資安目標"                  │
└────────────────┬──────────────────────┘
                 │ Argument
       ┌─────────┴─────────┐
       │                   │
   Sub-claim 1         Sub-claim 2
   "CG-001 達成"       "CG-002 達成"
       │                   │
   ┌───┴───┐           ┌───┴───┐
 Evidence Evidence   Evidence Evidence
 (Pen test)(TARA)   (Verif)  (Review)

常見論證框架

框架 全名 特色
CAE Claim - Argument - Evidence 直觀，易讀
GSN Goal Structuring Notation 圖形化，標準化（多用於 Safety Case）
混合 CAE + GSN 結合兩者優點

ISO 21434 不強制特定框架。

CS Case 內容應包含

cs_case:
  metadata:
    item: "TCU-2026"
    version: 1.0
    release_date: 2027-07-01

  scope:
    item_definition_ref: "..."
    applicable_phases: [Concept, Development, Validation]

  top_claim:
    statement: "TCU achieves all cybersecurity goals throughout its operational lifecycle"

  cybersecurity_goals:
    - id: CG-001
      claim: "Firmware integrity is protected against unauthorized modification"
      arguments:
        - "Secure boot enforced (CSR-001, CSR-002)"
        - "Signed update only (CSR-005)"
      evidence:
        - "Verification Report Section 4.2"
        - "Pen Test Report PT-2027-018"
        - "Review Record RR-Arch-005"

  residual_risks:
    - id: RR-001
      description: "Side-channel attack on RSA signing"
      level: "Low"
      treatment: "Retain + monitor"
      acceptor: "VP Engineering (signed 2027-06-15)"

  ots_components:
    - "OpenSSL 3.0.12 (see SBOM v2.1)"
    - "AUTOSAR BSW (Vector, see OoC ref)"

  reused_components:
    - "Gateway SW v1.5 (reused from project G2, Delta TARA done)"

  assumptions:
    - "Vehicle OEM provides physically secured OBD port (CS Claim CL-002)"

  references:
    - "CS Plan v2.3"
    - "TARA Report v3.1"
    - "Verification Report v1.0"
    - "Validation Report v1.0"

證據 (Evidence) 來源

證據類型 範例
分析 TARA Report、Threat Model、Attack Tree
設計 架構文件、Design Review Record
驗證 Verification Report、SAST 報告、單元測試
驗證 (車輛級) Validation Report、Pen Test Report
流程 CS Plan、Audit Records
變更管理 Change Request、Impact Analysis
持續活動 Monitoring Records、Incident Reports

Cybersecurity Assessment

定義 (Clause 6.4.10)

independent judgement of the cybersecurity engineering performed for the item or component.

評估目的

1. CS Case 是否成立？
2. Argument 是否合理？
3. Evidence 是否充分？
4. Residual Risk 是否合理被接受？
5. Tailoring 是否合理？
6. 是否符合 Clause 5-15 要求？

評估員資格

要求 說明
獨立性 不可為專案執行者
能力 21434 條文、TARA、滲透測試基本
權威 有「拒絕 Release」的權力
位階 通常向 Top Management 報告

Assessment Report 結構

cs_assessment_report:
  metadata:
    project: "TCU-2026"
    assessor: "Bob Smith (Independent CS Officer)"
    assessment_date_range: 2027-06-01 to 2027-06-25
    cs_case_version_reviewed: 1.0

  methodology:
    - Document review
    - Sample-based evidence verification
    - Interview with CS team, architects, testers
    - Independent verification of selected TARA scenarios

  findings:
    - id: F-001
      severity: Major
      description: "CSR-005 (DPA countermeasure) test data missing"
      recommendation: "Re-execute DPA test or remove CSR-005 (and update TARA)"

    - id: F-002
      severity: Observation
      description: "CS Case mixes evidence and conclusion structure"
      recommendation: "Restructure for next release"

  overall_assessment:
    cs_case_completeness: "Partial — F-001 blocking"
    residual_risk_acceptance: "Acceptable for non-blocking risks"
    tailoring_assessment: "Reasonable"

  recommendation: "REJECT release until F-001 resolved"

  next_assessment: "Upon F-001 resolution"

評估結果可能

結果 後續行動
Approve 可進入 Release for Post-Development
Conditional Approve 完成指定改善後 Release
Reject 不可 Release，需修正後重評
Withdraw 評估範圍嚴重不足，重做

CS Case 是 Living Document

Initial CS Case (Release 1.0)
        │
新威脅出現 / 新弱點 / OTA 更新
        │
        ↓
Updated CS Case (Release 1.1)
        │
        ↓
…直至 EoS
Tip

CS Case 在後開發階段持續更新，每次 OTA 都可能需要更新。

證照考點

高頻考點

  1. CS Case ≠ CS Plan：Plan = 計畫；Case = 證據+論證
  2. CS Case 結構：Claim - Argument - Evidence
  3. CS Case 是 Living Document
  4. Assessment 由獨立人員執行
  5. Assessment 有「拒絕 Release」權力
  6. Assessment Report 是必要 WP
  7. ISO 21434 不強制特定論證框架（GSN/CAE 皆可）
  8. 殘餘風險需被適當層級接受並在 CS Case 中記錄

Practice