MRCO: A Multi-ring Convergence Oscillator-based High-Efficiency True Random Number Generator

The entropy source structure with embedded XOR gates in a ring oscillator (RO) as a true random number generator (TRNG) can improve the speed of accumulating jitter in the oscillator. However, the XOR gate has a certain response time to the input change, and when the potential at the input flips too fast, the XOR gate will output short pulses. In this paper, we propose a TRNG design based on a multi-ring convergence oscillator (MRCO) making use of the characteristics of short pulses propagating in the circuit. We study the effect of jitter on the output of the XOR gate when the XOR gate has high-speed changing inputs. Excessively small short pulses will be eliminated in the circuit and suppresses the accumulation of jitter in the oscillator. Our proposed TRNG cleverly avoids the concatenation of the short pulses with the inverter so that the short pulses are only input to the XOR gate, affecting the oscillation of the circuit by interfering with the change of the XOR gate output by another input change. The proposed TRNG design is implemented in Xilinx Virtex-6 FPGA, making it comparable to the state-of-the-art TRNG also implemented on FPGAs. The results show that this TRNG has the highest ratio of throughput rate to hardware resources. The generated random sequence pass both NIST SP800-22 test and NIST SP800-90B test.