The growth of the Internet of Things (IoT) market has motivated widespread proliferationof microcontroller- (MCU) based embedded systems. Suitable due to their abundance,low cost, low power consumption and small footprint. The memory architecture typicallyconsists of volatile memory such as block(s) of SRAM, and non-volatile memory (NVM)for code storage. Authentication and encryption safeguard these endpoints within an IoTframework, which requires storage of a secure key. Keys stored within integrated circuits(ICs) are susceptible to attack via reverse engineering of the NVM. Newer approaches usePhysical Unclonable Functions (PUFs), which produce unique identi ers that takes advantageof device-level randomness induced by manufacturing process variation in silicon.The unclonable property of PUFs is demonstrated with an analytical model. The unpredictableyet repeatable start-up values (SUVs) of SRAM bit-cells form the basis of anSRAM PUF. Performance measures, such as reliability, randomness, symmetry, and stability,dictate the quality of a PUF. Two commercial o -the-shelf (COTS) ARM-Cortex basedMCU products, the STM32F429ZIT6U and ATSAMR21G18A, underwent automated andmanual power cycling experiments that examined their embedded SRAM SUVs. Thecharacterization framework provided acquires data via debug software and a developed Cprogram, power cycling using a USB controlled relay and post-processing using Python.Applications of PUFs include cryptographic key generation, device identi cation and truerandom number hardware generation.Statistical results and a comparative analysis are presented. Amongst the total bitcellcount of the embedded SRAM in STM and ATSAM MCUs, 36:86% and 28:86% areclassi ed as non- or partially-skewed, respectively across N = 10; 000 samples. The AtmelMCU outperforms the STM MCU in reliability by 1.42 %, randomness by 0.65 % andstability by 8.00 %, with a 4.74 % SUV bias towards a logic '1'. Max errors per 128-bitdata item is 22 and 38 bits for MCU #1 and MCU #2, respectively. The STM MCUexhibits column-wise correlation illustrated in a heatmap, where the Atmel MCU shows arandom signature. The embedded SRAM in the Atmel MCU outperforms the STM MCU'sand is thereby considered the more suitable PUF.
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