A novel technique for the generation of a true random bit sequence is demonstrated. This technique could find application in measuring the performance of very high bit rate (> 10 Gbit/s) optical communication systems where conventional methods may prove impractical.
True random number generators, which output truly random numbers by extracting entropy from physical phenomena such as thermal and electronic noises, are widely used in the field of the cryptographic communication systems. We have been developing a superconductive true random number generator that can generate truly random number sequences, impossible to be predicted, by utilizing the high-speed operation and high-sensitivity of superconductive integrated circuits. In this study, we have calculated the dependences of correlation of output random bits on the generation rate. Statistical tests have been performed on the basis of the NIST statistical test suite in order to evaluate the quality of the randomness of sequences generated by the superconductive true random number generator at high generation rate. We have generated a random number sequence consisting of 3.2 M-bit at the generation rate of 30 Gbit/s using the superconductive true random number generator, fabricated by the ISTEC-SRL 2.5 kA/cm2Nb standard process. The generated random number sequences passed 13 kinds of the statistical tests in the NIST statistical test suit, although the 3 tests were not performed because of the shortage of the generated random numbers. The result sufficiently proves that a superconductive true random number generator can generate a high quality of random numbers that can be used for practical cryptographic applications, at a generation rate of up to 30 Gbit/s.
Chaotic light generated by optical feedback semiconductor laser is employed as entropy source. We experimentally obtain random bit sequences of different rates by using a series of processing on chaotic signals, such as photoelectric conversion, analog-digital conversion, and exclusive OR operation. Based on the principle, we develop a 2.5 Gbit/s physical random bit generator prototype which can steadily run for a long time. It can generate random bit sequence at 155 Mbit/s, 622 Mbit/s, 1.25 Gbit/s, 2.5 Gbit/s and so on, whose rates are consistent with the current communication rates. All random bit sequences with different bit rates pass all of the NIST statistical tests. The generated random bits will be used as high-speed real-time physical keys for the one-time padding secure communication.