  Logic locking proposed to protect integrated circuits from serious hardware
threats has been studied extensively over a decade. In these years, many
efficient logic locking techniques have been proven to be broken. The
state-of-the-art logic locking techniques, including the prominent corrupt and
correct (CAC) technique, are resilient to satisfiability (SAT)-based and
removal attacks, but vulnerable to structural analysis attacks. To overcome
this drawback, this paper introduces an improved version of CAC, called CAC
2.0, which increases the search space of structural analysis attacks using
obfuscation. To do so, CAC 2.0 locks the original circuit twice, one after
another, on different nodes with different number of protected primary inputs
using CAC, while hiding original protected primary inputs among decoy primary
inputs. This paper also introduces an open source logic locking tool, called
HIID, equipped with well-known techniques including CAC 2.0. Our experiments
show that CAC 2.0 is resilient to existing SAT-based, removal, and structural
analysis attacks. To achieve this, it increases the number of key inputs at
most 4x and the gate-level area between 30.2% and 0.8% on circuits with low and
high complexity with respect to CAC.
