邏輯鎖定是一種硬體安全技術，用以保護電路設計免受過度製造、設計盜竊及逆向工程的侵害。邏輯鎖定藉由插入額外的邏輯閘如多工器、互斥閘及查找表(LUT)，將電路設計上鎖。只有當正確的密鑰被套用時，才能夠正確的啟用電路的功能。布林滿足性攻擊(SAT attack)是對於邏輯鎖定最強力的攻擊方式，他利用SAT 求解器快速的排除錯誤的密鑰組合。布林滿足性攻擊可以在短時間內輕易地破解早期的邏輯鎖定技術。近來，已經有非常多的研究提出了對抗布林滿足性攻擊的邏輯鎖定方法，其中一種是以加密電路中的point function來保護電路，例如與樹(AND-tree)。

然而，電路中的與樹存在著兩個問題。首先，在某些電路中，與樹的大小並不能滿足加密的基本需求。第二，對於布林滿足性攻擊來說，與樹的加密方法存在著某些條件使得攻擊能夠經歷一個迭代就完成。本研究提出了一建構加密混淆樹方法。首先利用combine-concatenate操作將電路中的與樹合併為更大的與樹，接著會藉由split-compensate操作進一步放大合併後的與樹，並降低remove-all DIP的影響。實驗結果顯示，此方法在大部分的電路中可以有效地抵禦布林滿足性攻擊，並且在不同的加密條件下，部分的電路的加密效果能夠優於先前的防禦技術。

Logic locking is a hardware security technology to protect circuit designs from IP overuse, IP Piracy, and reverse engineering. Logic locking protects circuits by inserting key gates such as MUX gates, XOR/XNOR gates, and LUTs. The circuit will be correct only when the correct key is applied. SAT attack is the most powerful attack in recent times. It uses an SAT solver to prune the wrong key quickly. For the early defense, SAT attacks can easily succeed in a short time. Previous studies have presented many techniques for defending against SAT attacks. One of them is to protect circuits by encrypting in-cone point-function, i.e., AND-tree.

However, in-cone AND-tree has some problems. First of all, in the circuit, its size cannot meet the encryption requirements, and secondly, for the SAT attack, there is a specific condition that allows the attack to succeed in one iteration. In this paper, we present a new method for constructing obfuscated trees. We first use combine-concatenate operations to combine AND-trees in a circuit to obtain a larger AND-tree and then use split-compensate operations to insert extra variables further amplify the AND-tree and reduce the impact of remove-all DIP. The experimental results show that our obfuscated tree can effectively resist SAT attacks. We can achieve better results under different encryption conditions than previous methods.

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