在現在的電子系統中物理不可複製功能(PUF)用於設備的身分驗證及密鑰生成。其中靜態隨機存取記憶體(SRAM)的PUF為受歡迎的一種，因為SRAM為大多數電子設備中的標準元件。以前的方法僅選擇SRAM中高度穩定的位元當作PUF位元，以達到高可靠性，因此需要相對較大面積的SRAM。此外由於只使用高度穩定位元，SRAM PUF可能會遭受到PUF複製攻擊。而該攻擊利用光子發射分析(PEA)觀察穩定位元的行為，並進行聚焦離子束電路編輯(FIBCE)複製出相同的物理響應。在本文中，我們提出了兩種方法，除了使用穩定位元之外，還使用不穩定位元作為PUF位元來增加SRAM位元的使用比率。我們還表明這兩種方法可以有效抵抗PUF複製攻擊。實驗結果顯示，即使我們提出的方法使用不穩定位元作為PUF位元，它們仍然可以實現高可靠性及高隨機性。方法一的內漢明距離平均2%，間漢明距離為49.33%; 方法二的內漢明距離平均0.21%，間漢明距離為49.5%。而且這兩種方法都適合現今IoT系統的機密防護。

Physical Unclonable Function (PUF) is recently used in modern electronic systems for device authentication and secret key generation. SRAM PUF is a popular memory-based PUF because SRAM is a standard component for most electronic devices. Previously only strongly stable SRAM bits are selected as PUF bits in order to achieve high reliability, hence requiring relatively large SRAM. Furthermore, SRAM PUF might suffer from PUF clone attack for using stable bits. Attackers may use Photon Emission Analysis (PEA) to observe the behavior of the stable bits and conducted Focused Ion Beam circuit edit (FIBCE) to produce an identical physical response. In this work, we propose two methods that employ unstable bits as PUF bits in addition to the stable bits to increase the SRAM bit usage rate. We also show that these two methods can efficiently resist the PUF clone attack. Experimental results show that even though our proposed methods use unstable bits as PUF bits, they can still achieve high reliability and high randomness. The first proposed method can reach an average 2% intra-HD under various conditions and an average inter-HD of 49.33%. The second proposed method can reach an average 0.21% intra-HD and 49.5% inter-HD. These two proposed methods can be suited for the recent IoT system for security use.

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