| Chaos has been widely used in the field of security encryption in recent years based on its characteristics such as wide spectrum,high sensitivity to initial values and noise-like,and has been developed rapidly.Chaotic systems derived from traditional chaotic systems such as high-dimensional hyperchaos and fractional-order chaos have also achieved various applications.At the same time,the image security algorithm of DNA coding operation based on the concept of base pairing in biology has also become an important topic in this field.In the current security encryption field,the encryption algorithm combining chaos and DNA coding has become one of the mainstream because of its strong unpredictability and the ability to realize parallel operation of massive data.However,in the in-depth process of research,in addition to the image encryption algorithm,the transmission process of data in the system and optical fiber will inevitably be involved,and the security and complexity of the transmission system will also become one of the research points that cannot be ignored.As one of the key technologies in the 5G communication era,OFDM has attracted wide attention due to its characteristics of resistance to multipath expansion,inter-symbol interference and high frequency band utilization.OFDM-PON system has become one of the key systems in the transmission field,but it does not guarantee the high security and anti-interception ability of data in the transmission process.On this basis,combining with chaos and DNA coding is a necessary research direction,The image data can be covered with high security from encryption to transmission to recovery at the receiving end.Based on this,on the basis of many research thesiss on chaotic communication,DNA coding encryption and OFDM-PON,starting with the security of image encryption and data transmission,this thesis proposes different security encryption schemes for color image and transmission systems based on chaos.The main work and achievements are as follows:(1)The thesis simulates an improved optical chaos scrambling transmission system based on orthogonal frequency division multiplexing passive optical network.This scheme ensures the stability and security of the transmission process by using optical chaos to realize double scrambling in OFDM-PON system.In the system structure,a laser chaos generation scheme based on injection feedback was deployed at the sender and receiver,where the chaotic optical signal generated by the laser is replaced and scrambled by the I/Q data obtained from 16 QAM modulation after photoelectric conversion,and performs iterative scrambling on random interpolation and 3D Arnold operations after spread spectrum,convolutional coding and serial-parallel transformation,and sets the basic iteration unit and the number of iterations to achieve overall two-reset scrambling.Then,in the phase of inverse fast Fourier transform,the corresponding relationship between its subcarriers and parallel data is disturbed by chaotic sequence,and the cyclic prefix is introduced to achieve the ISI effect in transmission.The realization effect of encryption is discussed by using chaotic dynamics analysis,constellation diagram,error rate curve and comparison diagram of data sequence before and after transmission of synchronous laser.The results show that:From the simulation results of the output power,Lyapunov exponent,photon number and cross-correlation coefficient of the synchronous chaotic laser,it can be seen that with the increase of the feedback intensity,the laser undergoes steady state,double period,and finally reaches the chaotic state,and the laser at the receiving and transmitting ends is in the complete synchronization state.The system simulation results also show that the receiver and transmitter constellations are consistent when the offset factor caused by the influence of Gaussian noise in the channel is removed;At the same time,in the scrambling transmission system with spread spectrum introduced in this thesis,compared with the previous OFDM-PON transmission system,the bit error rate is lower,the key space is large,and the anti-interference interception ability is strong,which ensures the security of the system at all stages in the transmission process.(2)Then,based on the current research status of color plaintext image encryption,this thesis proposes and simulates a color image DNA encryption algorithm based on fractional hyperchaos synchronization.In this algorithm,a fractional-order system is introduced,which uses the fractional-order super Lorenz chaotic system to drive the fractional-order financial system into the synchronization state to obtain the chaotic time series for encryption.In the chaos generation system of the algorithm,first of all,the fractional order system and its mathematical concepts are dissected,the system equations about the drive and response are established,the mapping operation is performed,and the synchronization conditions are studied based on the control term equation,the error dynamic equation is obtained,and the initial parameters are set so that both the drive fractional super Lorenz system and the response fractional L ü system have chaotic characteristics,Then the synchronization state is analyzed and the chaotic time series of the system is obtained by numerically solving the fractional integral function equation under the condition of fractional coefficient q=0.98.For different chaotic sequences generated by fractional hyperchaos synchronization system,they are used in different processing stages of the algorithm,mainly including RGB component diffusion of plaintext image pixels,DNA coding and operation stage of diffusion component and chaotic sequence itself,and then the key sensitivity before and after encryption,histogram,information entropy,differential attack,correlation between adjacent pixels,anti-noise and cutting ability The PNSR and MSE parameters of the image are analyzed to prove the feasibility and security of the algorithm.The results show that:From the error curve results of the fractional-order hyperchaos synchronization system,it can be seen that after a certain time point,the error approaches to zero,that is,the drive and response achieve complete synchronization.At the same time,the chaotic time series diagram also shows the chaotic behavior with the maximum Lyapunov index of 2.83 and Kaplan-York dimension of 1,and the maximum ACF and XCF coefficients approaching to 1 further confirm the synchronization quality of the system.In the encryption of the plaintext image,compared with the plaintext image,the grayscale information of the ciphertext image is highly chaotic,and the ciphertext image changes greatly when only one key is changed;The simulation shows that the pixel points of each value in the histogram are evenly distributed,the information entropy is 7.9993,which is close to 8,and the correlation coefficient between the three pixel points is approximately 0,indicating that the ciphertext image processed by the algorithm has high disorder and all statistical features are hidden,while the plaintext image restoration results under different noise and cutting conditions and PNSR,MSE statistical results show that the security is strong against external interference.In conclusion,based on the research of color image encryption algorithm and transmission system security related to chaos,this thesis proposes optical chaos scrambling transmission system based on orthogonal frequency division multiplexing passive optical network and image encryption algorithm based on fractional-order hyperchaos synchronization,and from theoretical derivation,model building,numerical analysis and solution,security performance,complexity analysis,synchronization performance Information transmission and encryption result analysis are studied.The main conclusions are as follows: the diffusion and DNA encryption operation based on chaotic time series of the plaintext image by fractional chaotic synchronization can well hide the gray level information and statistical features in the plaintext image,and has excellent anti-interference ability,and can achieve high security color image encryption;At the same time,applying chaotic signal to the security processing of different stages of data transmission in OFDM-PON system can ensure the correct recovery of data at the transmitter and receiver,and make the bit error rate lower,the key space larger,the system complexity and anti-interference and interception ability stronger.This thesis is the author’s further innovation and development of the research on image encryption and secure transmission based on chaos,which can enrich and expand the theory and application of image encryption and secure transmission,and has very important practical and long-term significance for promoting the further development of this field. |
