Research On Improved DNA Coding And Three-dimensional Scrambling Diffusion Algorith

In the information age,people can exchange information anytime through the Internet and smartphones.However,this convenient communication method also faces the risk of information leakage.As one of the most important carriers in information exchange,digital images mainly include grayscale and color images.Compared with grayscale images,color images contain richer information and occupy most digital images.Therefore,it is crucial to design a good-performing color image encryption algorithm.The existing image encryption algorithms mainly include chaotic image encryption,DNA encoding,scrambling and diffusion,etc.Due to the limitations of these algorithms,this thesis focuses on researching and improving them,and the research contents are as follows:(1)One-dimensional chaotic systems have inherent problems,such as their system equations are not complex enough,resulting in insufficient dynamic characteristics.Also,the key space of the algorithm is relatively small when applied to image encryption due to the fewer system parameters,which makes its security performance relatively low.In contrast,high-dimensional chaotic systems have a larger key space,but the dimensionality is too high,making the system too complex to implement.To solve these problems,this thesis introduced a pulse function to control a four-dimensional hyperchaotic system,increasing the complexity and adjustability of the chaotic system and making the system’s behaviour more unpredictable.In addition,introducing nonlinear functions adds three new parameters to the system,thereby expanding the algorithm’s key space and improving its security performance.To test the performance of the improved chaotic system,NIST tests are conducted on the generated chaotic sequence,and the results show that the sequence has strong randomness and can be used for image encryption.(2)The traditional DNA encoding algorithm has weak anti-exhaustive attack ability due to the fixed rules of DNA base complementary pairing and base operation rules,which makes it easy to produce security risks.Therefore,this thesis proposed an improved method that introduces the concept of base substitution.This method uses a chaotic sequence as the seed for a pseudo-random sequence generator to generate a random sequence,which is then encoded into a lookup table.At the same time,the plaintext pixel value is encoded and used as the row and column coordinates of the lookup table.The corresponding base pair stored in the lookup table is obtained by indexing,and the plaintext pixel value is replaced.This base substitution method is based on a chaotic system that generates pseudo-random sequences twice and forms a lookup table through various encoding methods,increasing the algorithm’s complexity and randomness and enhancing its security performance.(3)Aiming at the low efficiency of the traditional scrambling diffusion encryption algorithm in processing images with a large amount of data,the 3D Rubik’s Cube scrambling and 3D six-way diffusion algorithms have been proposed.By extending the scrambling and diffusion operations on the two-dimensional plane to the threedimensional space,and then processing each layer in a parallel operation mode,the operating efficiency of the algorithm is improved.Finally,this thesis has carried out experimental simulation and result analysis on the algorithm,and found that it not only has a good scrambling effect,but also has a significant reduction in time complexity.(4)Based on the four-dimensional multi-scroll chaotic system,this thesis uses "improved DNA coding-three-dimensional Rubik’s cube scrambling-three-dimensional and six-directional diffusion" as the encryption framework,and carried out simulation experiments and performance analysis on the MATLAB platform.The analysis results show that the algorithm has good encryption and decryption effect,large key space,high key sensitivity,strong security,can resist differential attack and statistical attack well,and has good robustness.