## 2 Related Work  
Safeguarding source code against unauthorized use and theft has perennially been a paramount concern for practitioners in relevant fields, with ongoing research dedicated to addressing this issue. In response to the insecurity factors of code, many technical means to enhance code security have been produced. Code obfuscation technology is one of the very important technologies. In the 1990s, [PERSON] et al. [5] first elaborated on the concept and classification of code obfuscation in their article. They put various evaluation criteria to assess the effectiveness and performance of obfuscation algorithms. [PERSON] et al. [5] categorized obfuscation transformations into four distinct types: layout obfuscation, data obfuscation, control obfuscation, and preventive obfuscation. Following this groundwork, [PERSON] et al. [6] extended these obfuscation methods to RTL code. However, the outcomes did not meet expectations. Despite certain methods proving unsuitable for RTL code, these early efforts laid the groundwork for subsequent research in RTL code obfuscation. [PERSON] et al. [7] proposed an opaque predicate obfuscation technique that is difficult to find through static analysis. By using existing suitable signals or adding small circuits, when they are not enabled or in a waiting state in the circuit, as opaque predicates participate in code obfuscation. This technology has been improved in concealment and has good performance in ensuring low overhead. [PERSON] and [PERSON] [8] introduce a novel hybrid approach in which multilevel structural obfuscation is employed to safeguard RTL descriptions, coupled with encrypted chromosomal DNA impressions for securing IP in digital signal processing (DSP) applications. The method involves embedding stealth DNA impressions into structure-obfuscated DSP designs through robust encoding and encryption using multi-iterative Feistel ciphers. This approach demonstrates greater robustness in terms of providing digital evidence and resistance against tampering. [PERSON] et al. [9] proposed an RTL finite state machine obfuscation technology called ReTrustFSM. This technology includes three types of secrecy methods: explicit secrecy using external keys, implicit secrecy based on specific clocks, and internal secrecy through hidden FSM transformation functions. The adoption of this hybrid obfuscation scheme significantly enhances the circuit's resilience against attacks on logic locking, especially attacks against FSM obfuscation. As electronic packaging continues to evolve and innovate with technologies such as finite substrates with layered dielectric forms [10], an increasing number of hardware obfuscation techniques are coming to the forefront. [PERSON] and [PERSON] [11] first proposed the concept of hardware metering, specifically by selecting a part of the circuit for programming, and finally, the circuit gets a unique signature. [PERSON] et al. [12] devised a key-based obfuscation scheme aimed at safeguarding intellectual property from infringement. The method is to embed a key in the power-up state of an integrated circuit. Without the corresponding key for unlocking, the circuit's efficiency is significantly reduced. Additionally, the implicit key can be used as a concealed watermark. [PERSON] and [PERSON] [13] proposed three techniques for securing RTL Intellectual Property. The first technique is proposed in the early design phase of High-Level Synthesis (HLS). Given a control data flow graph, obfuscation logic is inserted during and after HLS using synthesized information. The second technique proposes a design lockout mechanism that embeds a comparator on obfuscation logic output to check if the key is correct. When the number of errors exceeds the allowed number, a finite state machine checker is used to enforce design lockout. The third technique designs four obfuscated module variants to disguise the RTL design.