A Graph Theory Approach towards IJTAG Security via Controlled Scan Chain Isolation

The IEEE Std. 1687 (IJTAG) was designed to provide on-chip access to the various embedded instruments (e.g. built-in self test, sensors, etc.) in complex system-on-chip designs. IJTAG facilitates access to on-chip instruments from third party intellectual property providers with hidden test-data registers. Although access to on-chip instruments provides valuable data specifically for debug and diagnosis, it can potentially expose the design to untrusted sources and instruments that can sniff and possibly manipulate the data that is being shifted through the IJTAG network. This paper provides a comprehensive protection scheme against data sniffing and data integrity attacks by selectively isolating the data flowing through the IJTAG network. The proposed scheme is modeled as a graph coloring problem to optimize the number of isolation signals required to protect the design. It is shown that combining the proposed approach with other existing schemes can also bolster the security against unauthorized user access as well. The proposed countermeasure is shown to add minimal overhead in terms of area and power consumption.