Dual-Metastability Time-Competitive True Random Number Generator

The paper introduces a new concept of a true random number generator (TRNG). Most metastability-based solutions operate on the uncertainty of a logical output state of a device (flip-flop, D-latch) aimed to be resolved from an exact metastable point. However, it has been shown that the metastable point of a bistable circuit (which is practically impossible to reach) does not guarantee absolute randomness or sufficient entropy. We propose the concept of a device in which the direct proximity of the metastable point is not mandatory. In our concept the transition times of two devices are compared. Such construction is less sensitive to the proximity of the metastable point, temperature fluctuations, and power supply instabilities. The paper briefly describes the metastability phenomena in general and other known metastability-based TRNG concepts. A new concept of a dual-metastability time-competitive generator is presented, analyzed both numerically and theoretically, and verified based on the sample circuit's implementation. Empirical and statistical test results are presented.