Oscillator Selection Strategies to Optimize a Physically Unclonable Function for IoT Systems Security

Physically unclonable functions avoid storing secret information in non-volatile memories and only generate a key when it is necessary for an application, rising as a promising solution for the authentication of resource-constrained IoT devices. However, the need to minimize the predictability of physically unclonable functions is evident. The main purpose of this work is to determine the optimal way to construct a physically unclonable function. To do this, a ring oscillator physically unclonable function based on comparing oscillators in pairs has been implemented in an FPGA. This analysis shows that the frequencies of the oscillators greatly vary depending on their position in the FPGA, especially between oscillators implemented in different types of slices. Furthermore, the influence of the chosen locations of the ring oscillators on the quality of the physically unclonable function has been analyzed and we propose five strategies to select the locations of the oscillators. Among the strategies proposed, two of them stand out for their high uniqueness, reproducibility, and identifiability, so they can be used for authentication purposes. Finally, we have analyzed the reproducibility for the best strategy facing voltage and temperature variations, showing that it remains stable in the studied range.

Application of a MEMS-Based TRNG in a Chaotic Stream Cipher

In this work, we used a sensor-based True Random Number Generator in order to generate keys for a stream cipher based on a recently published hybrid algorithm mixing Skew Tent Map and a Linear Feedback Shift Register. The stream cipher was implemented and tested in a Field Programmable Gate Array (FPGA) and was able to generate 8-bit width data streams at a clock frequency of 134 MHz, which is fast enough for Gigabit Ethernet applications. An exhaustive cryptanalysis was completed, allowing us to conclude that the system is secure. The stream cipher was compared with other chaotic stream ciphers implemented on similar platforms in terms of area, power consumption, and throughput.