Abstract:
This report unveils a severe security threat for cryptographic integrated circuits (ICs) that
use scan-based design-for-testability (DFT) techniques. Scan chains significantly improve
manufacturing test efficiency while also inadvertently creating a seemingly secure-bydesign
covert channel for key extraction. Prior differential scan attacks typically focus
on some special hamming weight patterns, and thus their effectiveness can be reduced by
design tweaks. In this report, we introduce the Co-relation Scan Attack (COSA), a generic
attack framework that overcomes these limitations and works equally well irrespective of
hamming weight distribution. This increases the attack surface by a significant amount,
requiring them to implement a much more secure security measure in design. Results: We
have implemented COSA and shown via experiments the practicality of recovering AES
secret keys with an average time of 22 us on a standard desktop machine. Its very fast
key extraction underlines the need of increased awareness within users and better-planned
countermeasures by IC designers
