Memristors have recently been explored for hardware security applications such as true random number generators (TRNGs) and physical unclonable functions (PUFs). Several typical designs for memristor‐based PUFs and TRNGs are summarized. PUFs are a novel hardware security primitive utilizing the intrinsic randomness of a physical system, and PUFs have broad potential applications in key protection and authentication. Unlike most conventional PUFs based on manufacturing variations, memristors have both manufacturing variations and intrinsic randomness in their resistance‐switching mechanisms that can be utilized as entropy sources; for instance, device to device (D2D) variation and probabilistic switching behaviors. TRNGs are a cornerstone of hardware security and are widely used in secure chips and encryption protocols. Memristors have random telegraph noise (RTN) and cycle to cycle (C2C) variation characteristics that can be used for high‐quality TRNGs. Here, research progress in memristor‐based PUFs and TRNGs is reviewed, and how these sources of randomness are leveraged to generate security primitives is discussed.

A physically unclonable function (PUF) is a creditable and lightweight solution to the mistrust in billions of Internet of Things devices. Because of this remarkable importance, PUF need to be immune to multifarious attack means. Making the PUF concealable is considered an effective countermeasure but it is not feasible for existing PUF designs. The bottleneck is finding a reproducible randomness source that supports repeatable concealment and accurate recovery of the PUF data. In this work, we experimentally demonstrate a concealable PUF at the chip level with an integrated memristor array and peripherals. The correlated filamentary switching characteristic of the hafnium oxide (HfO x )-based memristor is used to achieve PUF concealment/recovery with SET/RESET operations efficiently. PUF recovery with a zero-bit error rate and remarkable attack resistance are achieved simultaneously with negligible circuit overhead. This concealable PUF provides a promising opportunity to build memristive hardware systems with effective security in the near future.

The safe disposal of waste tyres has been seen as having a negative impact on the environment. To mitigate this impact, the components of waste tyres can be used in the production of green concrete. This study explores the effects of the curing and drying regime on the mechanical properties and permeation characteristics of concrete containing both crumbed rubber and steel fibres that are removed from waste tyres. Five concrete mixes were designed and concrete cubes, cylinders, and prisms were cast using waste tyres extracts. Crumb rubber was treated by submersion in sodium hydroxide and then used to partially replace 10% and 30% of fine aggregates in the concrete mix. Extracted steel fibres were added at the rate of 1% and 2% per volume of each mix. Compressive, indirect splitting tensile as well as flexural strengths were conducted after normal curing while observing several drying conditions. Additionally, air permeability was assessed using a portable apparatus which was developed to assess permeability easily. For the concrete test specimens containing 10% partial replacement of fine aggregate by crumb rubber and 1% steel fibres, it was discovered that the splitting tensile strength and flexural strength were higher than that of the control mix by 21% and 22.6%, respectively. For specimens, that included the 10% crumb rubber and 1% steel fibres, when exposed to oven drying at 105°C for 12 hours, the compressive strength results increased by 17% compared to the control specimens exposed to the same conditions. Unlike the compressive strength results, the splitting tensile and flexural strength results decreased after exposing the specimens to elevated temperature. The addition of crumb rubber and steel fibres as a partial fine aggregate replacement resulted in increasing the air permeability of the concrete to different degrees depending on the percentages used. The oven drying curing regime improved the permeability by reducing it in specimens containing the 10% crumb rubber and 1% steel fibres as indicated by increasing their permeability time index by 15% when compared to air-dried specimens. Using waste tyre extracts as a partial replacement of concrete fine aggregate can be recommended for both indoor and outdoor applications. This study showed that this was a viable, economic and environmentally friendly method for reducing carbon footprint.

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