Enhancing the Randomness of a Combined True Random Number Generator Based on the Ring Oscillator Sampling Method

An efficient method for generating number sequences that pass all statistical tests is combining numbers produced by many independent generators. Excellent statistical properties are very important in many applications but they are not sufficient in cryptography. We need the unpredictability of numbers that ensures the irreproducibility of sequences by an attacker. This paper proposes a new method for enhancing the randomness of a combined true random number generator (TRNG) using jitter observed in ring oscillators (ROs). To enhance the quality of output streams, we use an auxiliary source of randomness (ASR) that perturbs signals produced by ROs. The increase of entropy is obtained by combining XOR bits produced by many biased RO-based TRNGs. It increases the degree of unpredictability but requires a measure of the quality of this process, which is different from statistical testing of time sequences. To assess the unpredictability of output bits, we used the restarts mechanism proposed in earlier papers.