Abstract-FPGAs are widely used to integrate cryptographic primitives, algorithms, and protocols in cryptographic systemson-chip (CrySoC). As a building block of CrySoCs, True Random Number Generators (TRNGs) exploit analog noise sources in electronic devices to generate confidential keys, initialization vectors, challenges, nonces, and random masks in cryptographic protocols. TRNGs aimed at cryptographic applications must fulfill the security requirements defined in the German Federal Bureau for Information Security's (BSI) recommendations AIS-20/31, which has become a de facto standard in Europe. Many TRNG cores have already been published, only a few of which are suitable for FPGAs and even fewer comply with AIS-20/31. Here we present the results of the implementation of AIS-20/31 compliant TRNG cores in three FPGA families: Xilinx Spartan 6, Altera Cyclone V and Microsemi SmartFusion 2. In addition to common design parameters like area, bit rate and power/energy consumption, we compare and discuss the feasibility of generator cores in different FPGAs and the statistical quality of their output. These results will help designers select the best generator and the device family to match the requirements of the data security application. To ensure reproducibility of the results, the open source VHDL code of all generators adapted to individual families can be downloaded from the dedicated web page.

Today, life is becoming increasingly connected. From TVs to smartphones, including vehicles, buildings, and household appliances, everything is interconnected in what we call the "Internet of Things" (IoT). IoT is now part of our life and we have to deal with it. More than 10 billion devices are already connected and five times more are expected to be deployed in the next five years. While deployment and integration of IoT is expanding, one of the main challenge is to provide practical solutions to security, privacy and trust issues in IoT. Protection and security mechanisms need to include features such as interoperability and scalability but also traceability, authentication and access control while remaining lightweight. Among the most promising approaches to such security mechanisms, physical unclonable functions (PUF) provide a unique identifier for similar but different integrated circuits using some of their physical characteristics. These types of functions can thus be used to authenticate integrated circuits, provide traceability and access control. This paper presents a comprehensive case study of the transient effect ring oscillator (TERO) PUF from its implementation on FPGAs to its complete characterization. The implementation of the PUF is detailed for two different families of FPGAs: Xilinx Spartan 6 and Altera Cyclone V. All the metrics used for the characterization are explained in detail and the results of the characterization include robustness to environmental parameters including variations in temperature and voltage. Finally, we compare our results with those obtained for another PUF: the ring oscillator (RO) PUF. All the design files are available online to ensure repeatability and enable comparison of our contribution with other studies.

Oscillating rings are widely used in CMOS logic devices because they are easy to integrate, require low area and low power. Their main disadvantage is that they tend to lock to each other and/or to an external periodic signal. This locking phenomenon can render a system based on a freely running oscillator non-functional. A detailed study of the causes of the phenomenon and how to avoid it, is therefore of paramount importance. In this paper, we conduct a detailed examination of the locking phenomenon using the most commonly used rings: ring oscillators, transient effect ring oscillators and selftimed rings. We then analyze the consequences of locking on different use cases based on oscillating rings and provide design recommendations to minimize its impact. Our results could help designers better anticipate locking phenomenon in their future designs. To ensure reproducibility of the results, the VHDL code of all the experiments is available and can be downloaded from a dedicated web page. Index Terms-Free running oscillators, ring oscillator, transient effect ring oscillator, self-timed ring oscillator, locking phenomenon I. INTRODUCTION Electronic oscillators are key elements in many data processing applications. They are used in communication systems for radio and television signal modulation and demodulation or channel selection. They are also used in most digital circuits as a time reference for synchronizing operations or for serial data communication [1]. PLL based frequency synthesis and clock signal generation are also based on oscillators [2], [3]. In data security applications, oscillators serve as source of entropy for true random number generators (TRNGs) [4], [5] or physical unclonable functions (PUFs) [6], [7]. Ideally, electronic oscillator produces a perfect time reference (i.e. a periodic signal, often with a sine waveform or a square waveform). In practice, all types of oscillators are affected by perturbations and noises, and their output is not perfectly periodic. Numerous types of oscillator circuitries are available, but the principle of operation, the frequency stability and the robustness against variations in environmental conditions like supply voltage, temperature and electromagnetic interference are specific to each. The most commonly used are harmonic oscillators (i.