A Highly-Portable True Random Number Generator Based on Coherent Sampling

True Random Number Generators (TRNGs) are indispensable in modern cryptosystems. Unfortunately, in order to guarantee high entropy of the generated numbers, many TRNG designs require a complex implementation procedure, often involving manual placement and routing. In this work, we introduce a dynamic calibration mechanism for the Coherent Sampling Ring Oscillator based TRNG (COSO-TRNG) enabling easy integration of the entropy source into complex systems. The TRNG setup procedure automatically selects a configuration that guarantees the security requirements. In the experiments, we show that the proposed mechanism is capable of assuring correct TRNG operation even when an automatic placement is carried out and when the design is ported to another FPGA family. We generated random bits on both a Xilinx Spartan 6 and a Microsemi SmartFusion2 implementation that, without post processing, passed AIS-31 statistical tests at a throughput of 3.30 Mbit/s and 1.47 Mbit/s respectively.