Due to the outsourcing of chip manufacturing, countermeasures against Integrated Circuit (IC) piracy, reverse engineering, IC overbuilding and hardware Trojans (HTs) become a hot research topic. To protect an IC from these attacks, logic encryption techniques have been considered as a low-cost defense mechanism. In this paper, our proposal is to insert the multiplexer (MUX) with two cases: (i) we randomly insert MUXs equal to half of the output bit number (half MUX insertions); and (ii) we

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... t MUXs equal to the number of output bits (full MUX insertions). Hamming distance is adopted as a security evaluation. We also measure the delay, power and area overheads with the proposed technique. Electronics 2017, 6, 16 2 of 20 manufacturing foundry, a logic-gate level encryption technique is applied to protect the IP design with low cost. After retrieving the fabricated chips, in order to exhibit its correct functionality (produce correct outputs), the valid key has to be supplied to the encrypted design, for a certified IP owner to unlock the chips. However, upon employing the wrong key, the encrypted design will show the wrong functionality (produce wrong outputs).