Design for Testability and Hardware Security

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The new generation of integrated circuits include high performance analog and digital blocks, processing units, memories, and sensors. While such new microchips provide opportunities to enhance the performance of portable devices significantly, they also pose new challenges. Developing manufacturing tests for advanced integrated circuits while ensuring their hardware security is a formidable task. A great deal of progress has been made in developing various test methodologies for microchips. Efficient Design-for-Testability (DFT) techniques such as scan and Built-in Self-Test (BIST) are widely used to carry out tests on digital circuits. However, the DFT methodologies have been developed without adequate attention to security implications. For instance scan-chain insertion, one of the most effective DFT techniques, can be utilized to access the critical information inside a chip. The requirements for testability and hardware security are in sharp contrast with one another. To test a chip, access to the internal circuits are needed to apply test vectors to desired sub-circuits and observe their responses. While such full access is considered ideal for manufacturing tests, it is clear that such unrestricted access to the internal circuits of a device can undermine its security. For decades, hardware was assumed to be the source of trust-and-security but this assumption is not true anymore due to outsourcing. The costs of a fabrication line are so high that only a few companies can afford to have an in-house fabrication line. The outsourcing of in-house fabrication to overseas foundries provides opportunities for malicious activities and paves the way for potential security threats known as hardware Trojans. The current solutions for testability have to be modified to detect undesired hardware modifications and prevent security breaches using the test infrastructure.