  The threat of hardware Trojans has been widely recognized by academia,
industry, and government agencies. A Trojan can compromise security of a system
in spite of cryptographic protection. The damage caused by a Trojan may not be
limited to a business or reputation, but could have a severe impact on public
safety, national economy, or national security. An extremely stealthy way of
implementing hardware Trojans has been presented by Becker et al. at CHES'2012.
Their work have shown that it is possible to inject a Trojan in a random number
generator compliant with FIPS 140-2 and NIST SP800-90 standards by exploiting
non-zero aliasing probability of Logic Built-In-Self-Test (LBIST). In this
paper, we present two methods for modifying LBIST to prevent such an attack.
The first method makes test patterns dependent on a configurable key which is
programed into a chip after the manufacturing stage. The second method uses a
remote test management system which can execute LBIST using a different set of
test patterns at each test cycle.
