2.5Gbit/s Physical Random Bit Generator

Secure communications are important in many areas such as national security, financial stability, personal privacy, and many other aspects. The random numbers are often used as keys in the secure communications. It is clear that random numbers play an important role in secure communications.According to the mechanism of the generation of random numbers, it can be divided into two major categories of pseudo random numbers and physical random numbers. Pseudo random numbers are generated by some iteration algorithms and initial seeds. Because pseudo random numbers are generated by the algorithm. They have some advantages of building easily and high rate. However, attackers once know the initial random number seeds, they can recover the same random numbers through the same iteration algorithm and even predict the random numbers. According to Shannon’s theory, absolute security of communications needs the following conditions:(1) the key length should not shorter than the length of plaintext;(2) The key must be completely random;(3) The key can’t be reused. It requires that the rate of random numbers are not lower than the rate of communications, and must ensure that the random numbers are completely random. However, pseudo random numbers have a certain periodicity and are not completely random due to its mechanism.The physical random phenomenon in the nature has been used as the entropy source of physical random numbers. The physical random numbers have the advantages of complete randomness and unpredictability. Traditional physical entropy sources include electronic thermal noise, oscillator frequency jitter and chaotic circuit and so on. Nevertheless, the random bit rate is so low that it is difficult to adapt to the needs of fast communications nowadays due to the limitation of electronic devices physical.In recent years, the chaotic laser is a hot topic research. We proposed an idea that the chaotic laser can be used as the physical entropy source to generate physical random numbers based the characteristics of chaotic laser. High speed random numbers can be produced using the chaotic laser as entropy source. High speed random numbers can cater to the need of the current communications encryption. We have done many researchs based the chaotic laser in this article. Specific researches are as follows:1. Chaotic laser generated by optical feedback semiconductor laser is employed as entropy source. We experimentally obtain random bits of different rates by using photoelectric conversion, analog-digital conversion, exclusive OR and a rate-tunable clock. Based on the principle, we develop a physical random bit generator prototype whose maximum bit rate is2.5Gbit/s. This prototype can steadily run for a long time and output the random bits in real-time whose rates are consistent with the communication rates. For example155Mbit/s,622Mbit/s,1.25Gbit/s,2.5Gbit/s and so on. All random bits with different bit rates passes the all of the NIST statistical tests. It provide high-speed real-time physical keys for the one-time-pad secure communication.2. The chaotic laser with single feedback has a certain periodicity. If we use one bit ADC to quantify the chaotic signals, the generated random numbers have a periodicity too. And the random numbers can not pass the NIST statistical tests. I proposed a new method in which we segment some threshold by amplitude of the chaotic signal and then quantize the chaotic signal. The rate of random numbers can reach to40Gbit/s by using this method.3.I have done the detailed comparative analysis between the segmentation threshold method and one bit ADC method from some aspects such as the balance of0and1, the amplitude distribution and the NIST tests of generated random numbers.