A smart test controller for scan chains in secure circuits

Structural testing is one important step in the production of integrated circuits. The most common DIT technique is the insertion of scan-chains, which increases the observability and the controllability of the circuit's internal nodes. Nevertheless, malicious users can use the scan chains to observe confidential data stored in devices implementing cryptographic primitives. Therefore, scan chains inserted in secure ICs can be considered as a source of information leakage. Several countermeasures exist to cope with this type of problem. However, they either introduce high area overheads or they require modifications to the original design or the test protocol. In this paper we present a smart test controller that is able to prevent all known scan attacks. The controller does not require any additional signals, it is transparent to the designer and it does not require any modifications of the test protocol and procedure. Moreover, it introduces a very small area overhead.