Zhang Xu, Jiang Chunsheng, Dai Gang, Zhong Le, Fang Wen, Gu Ke, Xiao Guoping, Ren Shangqing, Liu Xin, Zou Sanyong
Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang 621999, China.
Microsystem and Terahertz Research Center, China Academy of Engineering Physics, Chengdu 610200, China.
Sensors (Basel). 2020 Oct 28;20(21):6132. doi: 10.3390/s20216132.
Encryption is an important step for secure data transmission, and a true random number generator (TRNG) is a key building block in many encryption algorithms. Static random-access memory (SRAM) chips can be easily available sources of true random numbers, benefiting from noisy SRAM cells whose start-up values flip between different power-on cycles. Embarking from this phenomenon, a novel performance (i.e., randomness and throughput) improvement method of SRAM-based TRNG is proposed, and its implementation can be divided into two phases: irradiation exposure and hardware postprocessing. As the randomness of original SRAM power-on values is fairly low, ionization irradiation is utilized to enhance its randomness, and the min-entropy can increase from about 0.03 to above 0.7 in the total ionizing irradiation (TID) experiments. Additionally, while the data remanence effect hampers obtaining random bitstreams with high speed, the ionization irradiation can also weaken this impact and improve the throughput of TRNG. In the hardware postprocessing stage, Secure Hash Algorithm 256 (SHA-256) is implemented on a Field Programmable Gate Array (FPGA) with clock frequency of 200 MHz. It can generate National Institute of Standards and Technology (NIST) SP 800-22 compatible true random bitstreams with throughput of 178 Mbps utilizing SRAM chip with 1 Mbit memory capacity. Furthermore, according to different application scenarios, the throughput can be widely scalable by adjusting clock frequency and SRAM memory capacity, which makes the novel TRNG design applicable for various Internet of Things (IOT) devices.
加密是安全数据传输的重要步骤，而真随机数发生器（TRNG）是许多加密算法中的关键组成部分。静态随机存取存储器（SRAM）芯片可以很容易地成为真随机数的来源，这得益于其噪声SRAM单元，其启动值在不同的上电周期之间翻转。基于这一现象，提出了一种基于SRAM的TRNG的新颖性能（即随机性和吞吐量）改进方法，其实现可分为两个阶段：辐照曝光和硬件后处理。由于原始SRAM上电值的随机性相当低，因此利用电离辐照来增强其随机性，并且在总电离剂量（TID）实验中，最小熵可以从约0.03增加到0.7以上。此外，虽然数据残留效应阻碍了高速获取随机比特流，但电离辐照也可以减弱这种影响并提高TRNG的吞吐量。在硬件后处理阶段，安全哈希算法256（SHA-256）在时钟频率为200 MHz的现场可编程门阵列（FPGA）上实现。利用具有1 Mbit存储容量的SRAM芯片，它可以生成符合美国国家标准与技术研究院（NIST）SP 800-22标准的真随机比特流，吞吐量为178 Mbps。此外，根据不同的应用场景，通过调整时钟频率和SRAM存储容量，吞吐量可以广泛扩展，这使得新颖的TRNG设计适用于各种物联网（IOT）设备。
