Ring Oscillator Physical Unclonable Functions (RO-PUFs) exploit the inherent manufacturing process variations, such as systematic and stochastic variations, to generate secret PUF responses that are unique to the device. Stochastic variations are random, while systematic variation exhibits a strong spatial correlation. Therefore, systematic process variation reduces the randomness of the PUF response. This lowers the ability of a PUF response to uniquely identify and authenticate individual devices. Further, the impact of systematic variation is paramount when the two ROs in comparison are placed far apart. Comparing the ROs that are close to each other does improve the randomness, but the responses generated are unreliable and limiting the possible Challenge-Response Pairs (CRPs). In this article, we are proposing a method to reduce the impact of systematic process variation on the RO oscillation frequencies by using Principal Component Analysis (PCA). Principal Components (PCs) model the directions of systematic and stochastic variation present on a device. By projecting the oscillation frequencies in the direction of stochastic variation, the impact of systematic variation can be reduced. Our proposed method neither restricts the placement of ROs to close groups nor limits the possible CRPs. The method is evaluated on a large population of 218 Xilinx Artix-7 FPGAs. To evaluate the efficiency of the proposed method, we purposely paired the ROs that are placed far apart on the FPGA fabric. Results obtained prove the ability of the proposed method in removing the impact of systematic variation on the oscillation frequencies and thereby producing truly random responses.

中文翻译：

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通过主成分分析 (PCA) 提高 FPGA RO-PUF 的质量

环形振荡器物理不可克隆功能 (RO-PUF) 利用固有的制造工艺变化（例如系统性和随机性变化）来生成设备独有的秘密 PUF 响应。随机变化是随机的，而系统变化表现出很强的空间相关性。因此，系统过程变化会降低 PUF 响应的随机性。这降低了 PUF 响应唯一识别和验证单个设备的能力。此外，当两个 RO 相距较远时，系统变化的影响至关重要。比较彼此接近的 RO 确实提高了随机性，但生成的响应不可靠并限制了可能的挑战响应对 (CRP)。在本文中，我们提出了一种通过使用主成分分析 (PCA) 来减少系统过程变化对 RO 振荡频率的影响的方法。主成分 (PC) 对设备上存在的系统和随机变化的方向进行建模。通过将振荡频率投射到随机变化的方向，可以减少系统变化的影响。我们提出的方法既不限制 RO 的位置​​接近组也不限制可能的 CRP。该方法在大量 218 个 Xilinx Artix-7 FPGA 上进行了评估。为了评估所提出方法的效率，我们特意将在 FPGA 架构上相距很远的 RO 配对。