In the communication through the network, it is essential to encrypt information to secure safety of the communication. An encryption method used for communication is a public key cryptosystem and a hybrid cryptosystem that put a public key cryptosystem and a private-key cryptosystem together mainly now. The safe grounds of these methods are to need vast calculation time to decode private key from a public key, but, by a cloud computing using the network accomplishing rapid progress and the development of the study of a quantum computer, the safe securing of information security by the cryptographic technology is becoming difficult for these past several years. One method to solve this problem includes quantum cryptography communication technology using a quantum key distribution. Because the quantum communication can detect the wiretapping on the channel, we can realize complete secret communication by letting both transmission and reception believers share private key. The randomness of the private key (i.e., the random number for secret codes) becomes important to assure the safety of this technique. Therefore the development of the technique that can generate chaotic random numbers (i.e., physical random number) fast becomes the urgent need. This thesis focuses on a very high-speed frequency noise of the laser diode to generate a physical random number fast, and assumed this frequency noise as a source for physical random number generation. We detected a high-speed frequency noise of the laser diode as a fluctuation of the transmitted light intensity using a frequency discriminator. This principle is the same as a principle of slope detection which is a kind of the demodulation technology in the FM communication. We used a Fabry-Perot type laser diode of wavelength 780nm for a noise source, and the D_2 absorption line of the rubidium atom for a frequency discriminator. We converted a transmitted light intensity signal into binary data by an A/D converter, and produced the binary physical random number sequences by extracting binary sequence from binary data. Generated physical random number sequences are statistically confirmed its quality by means of a de facto standard “NIST SP800-22” of the random number test for the secret code. Physical random number sequences are generated from binary data by two methods. The first method produced random number sequences per digits using least significant bits of binary data obtained from the A/D converter of vertical resolution 8 bits in parallel. The second method produced the binary random number sequence by connecting the data of each digit of binary data to one. We can make the generation speed of the physical random number sequence faster than the sampling speed of the A/D converter by using these methods. And, the operation such as performing EX-OR (XOR) between different random numbers is necessary for using it as a random number for the code because the physical random number usually has bad equal probability characteristics. The method called the Reverse XOR method that developed this XOR operation is recently suggested to improve the generation speed of the physical random number in other precedent studies. In this study, both this Reverse XOR and the normal XOR (XOR method) methods are used for generating a physical random number. And, a physical random number sequence generating speed of 120 Gb/s was confirmed by a method of generating random number sequences from several digits of 8-bits-binary-data in parallel. In addition, Improved XOR and Improved Reverse XOR methods proposed in this thesis generated the physical random number sequence faster than the normal XOR and the Reverse XOR methods. As a result, this thesis reported that a physical random number sequence was generated at 160 Gb/s. The relations between the frequency discriminator and the oscillation frequency of the laser diode bring big influence in the quality of the physics random number in our physical random number generation method. This is because frequency properties of the detected noise signal will change by the relation between the slant of the frequency discriminator and the frequency of the laser diode. Therefore the relation between the frequencies of the oscillation spectrum of this laser diode and the frequency discriminator was investigated, and the most suitable condition for generating a physical random number was discussed. In addition, the oscillation frequency of the laser diode greatly changes by a fluctuation of the environment temperature and the driving current. Therefore it is necessary to stabilize and control the oscillation frequency of the laser diode to the limited area within the absorption line of the rubidium atom in order to generate a physical random number stably for a long time. Therefore the oscillation frequency of the laser diode was controlled by using a technique of Phase-locked-Loop to the frequency of the slope of the rubidium atom absorption curve.
In the communication through the network, it is essential to encrypt information to secure safety of the communication. An encryption method used for communication is a public key cryptosystem and a hybrid cryptosystem that put a public key cryptosystem and a private-key cryptosystem together mainly now. The safe grounds of these methods are to need vast calculation time to decode private key from a public key, but, by a cloud computing using the network accomplishing rapid progress and the development of the study of a quantum computer, the safe securing of information security by the cryptographic technology is becoming difficult for these past several years. One method to solve this problem includes quantum cryptography communication technology using a quantum key distribution. Because the quantum communication can detect the wiretapping on the channel, we can realize complete secret communication by letting both transmission and reception believers share private key. The randomness of the private key (i.e., the random number for secret codes) becomes important to assure the safety of this technique. Therefore the development of the technique that can generate chaotic random numbers (i.e., physical random number) fast becomes the urgent need. This thesis focuses on a very high-speed frequency noise of the laser diode to generate a physical random number fast, and assumed this frequency noise as a source for physical random number generation. We detected a high-speed frequency noise of the laser diode as a fluctuation of the transmitted light intensity using a frequency discriminator. This principle is the same as a principle of slope detection which is a kind of the demodulation technology in the FM communication. We used a Fabry-Perot type laser diode of wavelength 780nm for a noise source, and the D_2 absorption line of the rubidium atom for a frequency discriminator. We converted a transmitted light intensity signal into binary data by an A/D converter, and produced the binary physical random number sequences by extracting binary sequence from binary data. Generated physical random number sequences are statistically confirmed its quality by means of a de facto standard “NIST SP800-22” of the random number test for the secret code. Physical random number sequences are generated from binary data by two methods. The first method produced random number sequences per digits using least significant bits of binary data obtained from the A/D converter of vertical resolution 8 bits in parallel. The second method produced the binary random number sequence by connecting the data of each digit of binary data to one. We can make the generation speed of the physical random number sequence faster than the sampling speed of the A/D converter by using these methods. And, the operation such as performing EX-OR (XOR) between different random numbers is necessary for using it as a random number for the code because the physical random number usually has bad equal probability characteristics. The method called the Reverse XOR method that developed this XOR operation is recently suggested to improve the generation speed of the physical random number in other precedent studies. In this study, both this Reverse XOR and the normal XOR (XOR method) methods are used for generating a physical random number. And, a physical random number sequence generating speed of 120 Gb/s was confirmed by a method of generating random number sequences from several digits of 8-bits-binary-data in parallel. In addition, Improved XOR and Improved Reverse XOR methods proposed in this thesis generated the physical random number sequence faster than the normal XOR and the Reverse XOR methods. As a result, this thesis reported that a physical random number sequence was generated at 160 Gb/s. The relations between the frequency discriminator and the oscillation frequency of the laser diode bring big influence in the quality of the physics random number in our physical random number generation method. This is because frequency properties of the detected noise signal will change by the relation between the slant of the frequency discriminator and the frequency of the laser diode. Therefore the relation between the frequencies of the oscillation spectrum of this laser diode and the frequency discriminator was investigated, and the most suitable condition for generating a physical random number was discussed. In addition, the oscillation frequency of the laser diode greatly changes by a fluctuation of the environment temperature and the driving current. Therefore it is necessary to stabilize and control the oscillation frequency of the laser diode to the limited area within the absorption line of the rubidium atom in order to generate a physical random number stably for a long time. Therefore the oscillation frequency of the laser diode was controlled by using a technique of Phase-locked-Loop to the frequency of the slope of the rubidium atom absorption curve.
Random numbers have great application value in the fields of secure communications, which are commonly used as secret keys to encrypt the information. To guarantee that the information is absolutely secure in the current high-speed communication, the applied random keys should possess a generation speed not less than the encrypted data rate, according to one-time pad theory found by Shannon (Shannon C E 1949 Bell.Syst.Tech.J. 28 656) Pseudo-random numbers generated by algorithm may easily reach a fast speed, but a certain periodicity makes them difficult to meet the aforementioned demand of information security. Utilizing physical stochastic phenomena can provide reliable random numbers, called physical random number generators (RNGs). However, limited by the bandwidth of the conventional physical sources such as electronic noise, frequency jitter of oscillator and quantum randomness, the traditional physical RNG has a generation speed at a level of Mb/s typically. Therefore, real-time and ultrafast physical random number generation is urgently required from the view of absolute security for high-speed communication today. With the advent of wideband photonic entropy sources, in recent years lots of schemes for high-speed random number generation are proposed. Among them, chaotic laser has received great attention due to its ultra-wide bandwidth and large random fluctuation of intensity. The real-time speed of physical RNG based on chaotic laser is now limited under 5 Gb/s, although the reported RNG claims that an ultrafast speed of Tb/s is possible in theory. The main issues that restrict the real-time speed of RNG based on chaotic laser are from two aspects. The first aspect is electrical jitter bottleneck confronted by the electrical analog-to-digital converter (ADC). Specifically, most of the methods of extracting random numbers are first to convert the chaotic laser into an electrical signal by a photo-detector, then use an electrical ADC driven by radio frequency (RF) clock to sample and quantify the chaotic signal in electronic domain. Unfortunately, the response rate of ADC is below Gb/s restricted by the aperture jitter (several picoseconds) of RF clock in the sample and hold circuit. The second aspect comes from the complex post-processes, which are fundamental in current RNG techniques to realize a good randomness. The strict synchronization among post-processing components (e.g., XOR gates, memory buffers, high-order difference) is controlled by an RF clock. Similarly, it is also an insurmountable obstacle to achieve an accurate synchronization due to the electronic jitter of the RF clock. In this paper, we propose a method of ultrafast multi-bit physical RNG based on chaotic laser without any post-process. In this method, a train of optical pulses generated by a GHz mode-locked laser with low temporal jitter at a level of fs is used as an optical sampling clock. The chaotic laser is sampled in the optical domain through a low switching energy and high-linearity terahertz optical asymmetric demultiplexer (TOAD) sampler, which is a fiber loop with an asymmetrical nonlinear semiconductor optical amplifier. Then, the peak amplitude of each sampled chaotic pulse is digitized by a multi-bit comparator (i.e., a multi-bit ADC without sample and hold circuit) and converted into random numbers directly. Specifically, a proof-of-principle experiment is executed to demonstrate the aforementioned proposed method. In this experiment, an optical feedback chaotic laser is used, which has a bandwidth of 6 GHz. Through setting a sampling rate to be 5 GSa/s and selecting 4 LSBs outputs of the 8-bit comparator, 20 Gb/s (=5 GSa/s4 LSBs) physical random number sequences are obtained. Considering the ultrafast response rate of TOAD sampler, the speed of random numbers generated by this method has the potential to reach several hundreds of Gb/s as long as the used chaotic laser has a sufficient bandwidth.
Not so long ago, pseudo random numbers generated by numerical formulae were considered to be adequate for encrypting important data-files, because of the time needed to decode them. With today’s ultra high-speed processors, however, this is no longer true. So, in order to thwart ever-more advanced attempts to breach our system’s protections, cryptologists have devised a method that is considered to be virtually impossible to decode, and uses what is a limitless number of physical random numbers. This research describes a method, whereby laser diode’s frequency noise generate a large quantities of physical random numbers. Using two types of photo detectors (APD and PIN-PD), we tested the abilities of two types of lasers (FP-LD and VCSEL) to generate random numbers. In all instances, an etalon served as frequency discriminator, the examination pass rates were determined using NIST FIPS140-2 test at each bit, and the Random Number Generation (RNG) speed was noted.
Random numbers can be classified as either pseudo- or physical-random in character. Pseudo-random numbers' periodicity renders them inappropriate for use in cryptographic applications, but naturally-generated physical-random numbers have no calculable periodicity, thereby making them ideally-suited to the task. The laser diode naturally produces a wideband "noise" signal that is believed to have tremendous capacity and great promise, for the rapid generation of physical-random numbers for use in cryptographic applications. We measured a laser diode's output, at a fast photo detector and generated physical-random numbers from frequency noises. We then identified and evaluated the binary-number-line's statistical properties. The result shows that physical-random number generation, at speeds as high as 40Gbps, is obtainable, using the laser diode's frequency noise characteristic.
Precisely frequency-stabilized semiconductor lasers produce physical-random numbers, allowing for optimal noise-suppression with one notable exception: white frequency-modulation (FM) noise. However, this component can also be converted into physical-random numbers. The interference created between two beams of rubidium (Rb) gas-cell-stabilized lasers allows for laser frequency noise to be extracted. Using this technique, we produce physical-random numbers from the relative frequency noise. Finally, we confirm that the numbers produced are, in fact, random, by means of the standard National Institute of Standards and Technology Federal Information Processing Standard (NIST FIPS) 140-2 test.
We describe a method of generating physical random numbers by means of a diode laser that has an extremely wide-band frequency-noise profile. Fluctuations in the laser frequency affect the intensity of the light transmitted through the optical frequency discriminator, detected thereafter as random fluctuations. This allows us to simultaneously generate 8 random bit streams, due to the parallel processing of 8-digit binary numbers sampled by an 8-bit analog-to-digital converter. Finally, we generated physical random numbers at a rate of 3 Gbit/s, by combining one data stream with another stream that is delayed by 2 ms, by exclusive-OR.
The security of transmission and retrieval depends on the encryption of information sent over public networks. At present, approaches to data protection based on cryptography methods using one-way mathematical functions are widely used. Symmetric and asymmetric methods of key transmission over open communication channels have been developed. The stability of information protection methods using one-way mathematical functions is based on the algorithmic complexity of their hacking for modern computers. The emergence of quantum computers of sufficient power will radically change the situation. Therefore, at present, the question of developing methods for distributing cryptographic keys based on new principles is acute. Such methods include quantum cryptography and cryptography based on stochastic physical processes. In this work, a brief review of the key generation methods based on the principles of quantum physics is carried out, and then the possibility of using fluctuations of the received radiation power caused by atmospheric turbulence to generate keys is investigated. Numerical and experimental modeling of the process of wave propagation in a system of two coupled transceivers operating in a turbulent medium (atmosphere) has been performed. For this purpose, appropriate algorithms for numerical simulation of the characteristics of optical fields distorted by the atmospheric propagation channel have been developed. An experimental setup has been developed and a model experimental study of the formation of correlated random signals in transmit-receive laser systems has been carried out. The need to use low-frequency filtering of the received signals was found. The efficiency of this filtration has been studied. The results of the work allow us to conclude that the use of atmospheric turbulence as a random signal generator makes it possible to form an almost identical cryptographic key in two communication channels directed towards each other.