Hardware piracy is a threat that is becoming more and more serious these last years. The different types of threats include mask theft, illegal overproduction, as well as the insertion of malicious alterations to a circuit, referred to as Hardware Trojans. To protect circuits from overproduction, circuits can be encrypted so that only authorized users can use the circuits. In this paper, we propose an encryption technique that also helps thwarting Hardware Trojan insertion. Assuming that an attacker will attach a Hardware Trojan to signals with low controllability in order to make it stealthy, the principle of the encryption is to minimize the number of signals with low controllability.