Expanding In-Cone Obfuscated Tree for Anti SAT Attack

Logic locking is a hardware security technology to protect circuit designs from overuse, piracy, and reverse engineering. It protects a circuit by inserting key gates to hide the circuit functionality, so that the circuit is functional only when a correct key is applied. In recent years, encrypting the point function, e.g., AND-tree, in a circuit has been shown to be promising to resist SAT attack. However, the encryption technique may suffer from two problems: First, the tree size may not be large enough to achieve desired security. Second, SAT attack could break the encryption in one iteration when it finds a specific input pattern, called remove-all DIP. Thus, in this paper, we present a new method for constructing the obfuscated tree. We first apply the sum-of-product transformation to find the largest AND-tree in a circuit, and then insert extra variables with the proposed split-compensate operation to further enlarge the AND-tree and mitigate the remove-all DIP issue. The experimental results show that the proposed obfuscated tree can effectively resist SAT attack.