Time Domain Sequential Locking for Increased Security

In this paper, the state space of an integrated circuit (IC) is used to increase the security of an IC against a variety of threats including intellectual property theft, IC counterfeiting, and IC overproduction. Hidden state transitions, state dependent keys, and temporal based transitions are implemented as a means to combat probing style attacks, such as the SAT attack. SPICE simulations are performed on modified state machines to characterize the overhead of implementing the three techniques in a circuit. Implementing temporal based transitions increases the area of the circuit by 68.42%, the power by 43.17%, and did not impact circuit delay. However, increasing the circuit size significantly reduces the overhead of state space encryption. For example, encrypting two registers in the s15850 ISCAS89 benchmark circuit resulted in an area overhead of 0.026%, presenting a low overhead means of securing sequential logic.