Security Preserving Integration and Resynthesis of Reconfigurable Scan Networks

Reliable operation, test, debug and diagnosis of complex integrated systems are ensured by embedded instruments, such as sensors, aging monitors or Built-In Self-Test (BIST) registers. Reconfigurable Scan Networks (RSNs) offer a flexible and efficient way to access such test instruments throughout the whole life-cycle. However, improper RSN integration might introduce additional connectivity properties to the device under test (DUT), which can be exploited to perform unauthorized access or cause information leakage. The existence of such additional connectivity through the RSN can compromise the security of the DUT and is considered as a security threat.In this paper, a method is presented to resolve all such security compliance violations. The problem is formulated in terms of Integer Linear Programming (ILP) as a minimum cut problem in multicommodity flow. An efficient heuristic is presented, which, to our knowledge, for the first time allows to consider the whole set of violations simultaneously and thereby to find a minimized number of changes to the RSN structure in order to make it compliant with the initial security requirements of the DUT and prevent the information leakage through the scan chain.