Consideration for Affects of an XOR in a Random Number Generator Using Ring Oscillators

Abstract

A cloud service to offer entropy has been paid much attention to. As one of the entropy sources, a physical random number generator is used as a true random number generator, relying on its irreproducibility. This paper focuses on a physical random number generator using a field-programmable gate array as an entropy source by employing ring oscillator circuits as a representative true random number generator. This paper investigates the effects of an XOR gate in the oscillation circuit by observing the output signal period. It aims to reveal the relationship between inputs and the output through the XOR gate in the target generator. The authors conduct two experiments to consider the relevance. It is confirmed that combining two ring oscillators with an XOR gate increases the complexity of the output cycle. In addition, verification using state transitions showed that the probability of the state transitions was evenly distributed by increasing the number of ring oscillator circuits.

Transition Probability Test for an RO-Based Generator and the Relevance between the Randomness and the Number of ROs

“…In this context, the authors introduce the transition probability by considering the Markov process for an RO-based generator from previous research [ 14 ]. It is noted that the readers can refer to [ 4 ], as a work related to this paper.…”

“…In a previous work [ 14 ], the authors discussed the importance of an XOR gate in a generator based on ROs by approximating the periodicity and investigating the transition probabilities of 2-bit patterns. It was revealed that an XOR gate in an RO-based generator contributes to extending the period length, and the number of ROs is of relevance to the distribution property.…”