Design of True Random Number Generator Based on Multi-Ring Convergence Oscillator Using Short Pulse Enhanced Randomness

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 input changes 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. We study the output of the XOR gate when facing different inputs. By modeling the time of a fibonacci ring oscillator (FIRO) as an example, we find that the loss of short pulses in an inverter chain is the reason for making the FIRO enter into periodic oscillation. This phenomenon suppresses the accumulation of jitter and occurs periodically in existing structures. Our proposed structure uses independent sub-rings to accumulate jitter, allowing the main-ring to quickly generate short pulses to provide analog randomness. The proposed TRNG design is implemented in Xilinx Virtex-6 FPGA. The experimental results show that it 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.