Timing Camouflage Enabled State Machine Obfuscation

State machine obfuscation is an important step to harden circuits against reverse engineering. The work presents a state machine obfuscation enabled by Timing Camouflage. Flip-flops of state machines often have a combinational feedback path. This makes it challenging to directly apply Timing Camouflage. Therefore, we developed two methods to redesign a state machine, such that at least one of its flip-flops is free of combinational feedback paths while the original functionality stays the same. The Timing Camouflage enabled state machine obfuscation additionally allows a beneficial combination with logic locking. The results demonstrate that state-of-the-art techniques fail to extract a correct state machine or show decreased success in extracting a correct secret locking key from an obfuscated design.