Scan Design and Secure Chip

Testing a secure system is often considered as a severebottleneck. While testability requires to an increase inboth observability and controllability, secure chips aredesigned with the reverse in mind, limiting access to chipcontent and on-chip controllability functions. As a result,using usual design for testability techniques whendesigning secure ICs may seriously decrease the level ofsecurity provided by the chip. This dilemma is even moresevere as secure applications need well-tested hardwareto ensure that the programmed operations are correctlyexecuted. In this paper, a security analysis of the scantechnique is performed. This analysis aims at pointing outthe security vulnerability induced by using such a DfTtechnique. A solution securing the scan is finally proposed.