Research on Optimization Methods for Static Random-Access Memory–Physical Unclonable Function Key Extraction

JIANG Dongmei; TANG Xusheng; LI Bing; ZHANG Qingyu; HE Weiguo

doi:10.11999/JEIT250551

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JIANG Dongmei, TANG Xusheng, LI Bing, ZHANG Qingyu, HE Weiguo. Research on Optimization Methods for Static Random-Access Memory–Physical Unclonable Function Key Extraction[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250551

Citation:

JIANG Dongmei, TANG Xusheng, LI Bing, ZHANG Qingyu, HE Weiguo. Research on Optimization Methods for Static Random-Access Memory–Physical Unclonable Function Key Extraction[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250551

Citation:

JIANG Dongmei, TANG Xusheng, LI Bing, ZHANG Qingyu, HE Weiguo. Research on Optimization Methods for Static Random-Access Memory–Physical Unclonable Function Key Extraction[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250551

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Research on Optimization Methods for Static Random-Access Memory–Physical Unclonable Function Key Extraction

doi: 10.11999/JEIT250551 cstr: 32379.14.JEIT250551

1.
School of Cyberspace Security, Southeast University, Nanjing 210000, China
2.
University of Electronic Science and Technology, Chengdu 610000, China
3.
Sanlingjia Microelectronics Co.Ltd, Chengdu 610000, China

Received Date: 2025-06-16
Rev Recd Date: 2025-09-16

Available Online: 2025-09-19

Abstract

Abstract

Objective Non-Volatile Memory (NVM) storage keys are exposed to physical attacks, and most lightweight Internet-of-Things (IoT) devices cannot deploy costly protection. A Physical Unclonable Function (PUF) offers a practical defense. However, Static Random-Access Memory PUFs (SRAM-PUFs) used as key generators exhibit environmental sensitivity that degrades stability. Therefore, optimization methods for SRAM-PUF–based key extraction fall into three main categories: (1) circuit-level enhancements that modify the SRAM cell to strengthen its inherent 0/1 bias; (2) cell selection methods that identify and retain only stable cells through dedicated algorithms; and (3) fuzzy-extractor schemes tailored to SRAM-PUFs that correct residual noise to yield reproducible cryptographic keys. Methods The selection of SRAM cells can markedly enhance bit stability. However, although reducing the complexity of Error-Correcting Code (ECC) encoding and decoding, this approach requires consuming a large number of stable cells to satisfy key entropy requirements, which in turn increases ECC code length. To address this contradiction, this paper proposes a new key extraction scheme (Figure 2). In the proposed method, SRAM bits are divided into stable and noisy categories. The high entropy of noisy bits is leveraged for key generation: noisy bits are hashed to produce entropy-rich values, whereas stable bits with a low bit error rate are used to generate PUF responses. In the registration stage, the synthesized key is rearranged to form m vectors (R₁,R₂,…,Rm)according to m different rules. These m vectors are then combined into a new vector R . A repetition code of length 2t+1 (able to correct t errors) is applied to R to generate a codeword C . The codeword C is XORed with the PUF response to obtain helper data w, which is stored in NVM. In the reconstruction stage, w is XORed with a new PUF response to obtain C ′. Due to the repetition coding applied during registration, decoding is performed using a majority decision rule with a threshold of t+1. The decoding result R ' is reshaped into a matrix D with m rows and x columns, followed by reverse interleaving based on the rules used in registration. A majority decision is then executed independently for each column, with a decision threshold of m/2+1. The recovered key is output as the final result. Results and Discussions SRAM. Tests at −40 °C, 25 °C, and 85 °C show that the proposed bit-selection algorithm reduces the bit-change rate of SRAM-PUFs, with the number of screenings inversely proportional to the average change rate. The bit-change rate is highest at elevated temperatures. After 20 screenings, the average change rate at 85 °C decreases from 0.14 to 0.07, and after 80 screenings, it further decreases to 0.06. A quantitative analysis of error-correction capability is also performed. Based on the measured bit-change rates at high temperatures, the probability of key reconstruction failure is derived as low as 1.487 6E-9. In addition, 1 024 bytes of SRAM cells are shown to yield entropy keys of 128 bits. Conclusions This paper proposes a novel SRAM-PUF key extraction scheme that resolves the trade-off between stability requirements and high entropy demands by employing a bit-selection algorithm. The scheme simplifies error-correction encoding and decoding while enhancing the entropy of the generated keys. Compared with existing approaches, the computational complexity is reduced by 40% relative toScheme 2, by 98.9% relative to Scheme 3, and by 99.12% relative to Scheme 4. Furthermore, the method provides an integrated solution for screening stable SRAM cells, highlighting its practical application potential. Based on the bit error rate of 28 nm SRAM-PUFs, the key reconstruction success rate is calculated as (1-1.4876E-9). In tests conducted at –40 °C, 25 °C, and 85 °C, with 200 key reconstruction attempts per condition, all 11 chips achieved successful reconstruction. Considering variations across different fabrication processes, the number of screening cycles as well as parameters m and t can be adjusted to accommodate other process nodes.
- Physical Unclonable Function (PUF),
- Stable node selection,
- Key extraction,
- High entropy value

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References(19)

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