| 摘要: | 在軟體定義車輛（Software-Defined Vehicle，SDV）中，韌體與應用程式的程式碼量動輒超過 2 億行，透過 OTA 更新（Over-the-Air）來確保行車安全已成為業界常態。現代車輛由數十個 電子控制單元（Electronic Control Unit，ECU）組成，各自負責煞車、資訊娛樂、車聯網等功能。主流標準 Uptane 提供簽章與版本管理機制，但假設每顆 ECU 內的作業系統與儲存皆可信。若資訊娛樂或車聯網 ECU 遭到攻陷，攻擊者仍可竄改映像或重播過期中繼資料，危及煞車、動力傳動與駕駛輔助等關鍵控制。
我們提出 CASTR-OTA：將晶片內建的 (f)TPM 2.0 與 Arm TrustZone 結合，建立硬體信任根，同時加入 情境感知更新閘門與 A/B/Q 三槽隔離機制。CASTR-OTA 在「下載、解密、槽位切換、早期執行」四個檢查點評估車輛狀態，阻斷不安全的安裝。所有新映像首先被沙盒到隔離的 Quarantine 槽；唯有通過測試後才晉升為使用中槽位，確保未驗證程式碼無法奪取任何 ECU 的控制權。
實驗結果顯示，即使攻擊者完全掌控 Rich OS 及車內網路，系統仍能滿足嚴苛的安全目標。此外，即便部分供應鏈金鑰外洩，硬體量測與單調遞增計數器仍可維護完整性，並在必要時安全回滾至最近的已知良好版本。;In software-defined vehicles (SDVs), firmware and applications routinely exceed 200 million lines of code, and ensuring road safety by means of over-the-air (OTA) updates has become industry practice. Modern vehicles consist of dozens of ECUs (Electronic Control Units), each responsible for specific functions such as braking, infotainment, or telematics. The prevailing standard, Uptane, provides signature and version-management mechanisms, yet assumes that the operating system and storage inside each ECU are trustworthy. If an infotainment or telematics ECU is compromised, an attacker can still tamper with images or replay stale metadata, endangering critical controls such as braking, power-train, and driver assistance.
We present CASTR-OTA, which fuses an on-chip (f)TPM 2.0 with Arm TrustZone to form a hardware root of trust, and adds a context-aware update gate together with an A/B/Q tri-slot isolation scheme. CASTR-OTA evaluates vehicle state at four checkpoints—download, decryption, slot switch, and early runtime—to block unsafe installations. Every new image is first sandboxed in an isolated Quarantine slot; only after it passes this test is it promoted to the active slot, ensuring that unverified code can never seize control of any ECU.
Experiments show that the system meets stringent security goals even against an adversary who controls the rich OS and the in-vehicle network. Moreover, should a subset of supply-chain keys be leaked, hardware measurements and a monotonic counter still preserve integrity and trigger a safe rollback to the last known-good version. |
