Commercial-off-the-shelf (COTS) components are often preferred over custom Integrated Circuits (ICs) to achieve reduced system development time and cost, easy adoption of new technologies, and replaceability. Unfortunately, the integration of COTS components introduces serious security concerns. None of the entities in the COTS IC supply chain are trusted from a consumer's perspective, leading to a ''zero trust'' threat model. Any of these entities could introduce hidden malicious circuits or hardware Trojans within the component, allowing an attacker in the field to extract secret information (e.g., cryptographic keys) or cause a functional failure. Existing solutions to counter hardware Trojans are inapplicable in such a zero-trust scenario as they assume either the design house or the foundry to be trusted and consider the design to be available for either analysis or modification. In this work, we have proposed a software-oriented countermeasure to ensure the confidentiality of secret assets against hardware Trojans that can be seamlessly integrated in existing COTS microprocessors. The proposed solution does not require any supply chain entity to be trusted and does not require analysis or modification of the IC design. To protect secret assets in an untrusted microprocessor, the proposed method leverages the concept of residue number coding (RNC) to transform the software functions operating on the asset to be fully homomorphic. We have implemented the proposed solution to protect the secret key within the Advanced Encryption Standard (AES) program and presented a detailed security analysis. We also have developed a plugin for the LLVM compiler toolchain that automatically integrates the solution in AES. Finally, we compare the execution time overhead of the operations in the RNC-based technique with comparable homomorphic solutions and demonstrate significant improvement.

翻译：商用现货（COTS）组件通常比定制集成电路（IC）更受青睐，因其能缩短系统开发时间和降低成本，便于采用新技术且易于更换。然而，COTS组件的集成引入了严重的安全隐患。从消费者视角看，COTS IC供应链中的任何实体都不可信，由此形成"零信任"威胁模型。供应链中任一实体都可能在组件中植入隐藏恶意电路或硬件木马，使得攻击者能在实际部署中窃取秘密信息（如加密密钥）或导致功能故障。现有硬件木马防御方案在零信任场景中不适用，因为这些方案要么假设设计方或代工厂可信，要么要求设计文件可用于分析或修改。本文提出一种面向软件的防护措施，可无缝集成至现有COTS微处理器中，确保秘密资产的机密性不受硬件木马威胁。该方案无需信任任何供应链实体，也无需分析或修改IC设计。为保护不可信微处理器中的秘密资产，所提方法利用余数编码（RNC）概念，使处理该资产的软件函数具有全同态性。我们通过保护高级加密标准（AES）程序中的密钥实现了所提方案，并进行了详细的安全分析。此外，我们开发了LLVM编译器工具链插件，可自动将解决方案集成至AES程序。最后，将基于RNC技术的运算执行时间开销与同态可比方案进行对比，结果表明我们的方案具有显著优势。