Digital Image Encryption In Double Domain Based On Hyper Chaos

Nowadays,people are more closely connected thanks to the fast growing of internet.Communication industry is so prosperous that large size information transmission with high speed become possible.Given these conditions,with people longing for information-visualization,digital images are transmitted and applied fully around in every aspect of our life,which makes it the main stream of transmission media.Under such circumstances,it is vital to protect digital images from being intercepted and eavesdropped.Thus,transmission technologies of digital images should be developed,and image encryption algorithms with higher efficiency and stronger robustness are in desperate need.Classical encryption algorithms,such as DES(Data Encryption Standard)and RSA are originally designed for one-dimensional(1-D)data;while the digital images are far more complex and miscellaneous than any of the 1-D data.If digital images were to be encrypted with those classical data encryption algorithms,with the images being spread into onedimensional sequences,it would cost unnecessary complex computation yet output less satisfying results.Thus,digital images need ‘made-to-measure' encryption methods to be encrypted with.On the other hand,it becomes easier to decrypt the data or obtain the secure keys using the method of brute-force attacks,since the computation speed of computers are developed exponentially.Thus,a new encryption algorithm is deadly in need to enlarge the key space,in case the encryptions being nominal against super computers.This thesis aims to study the double-domain digital image encryptions based on hyper chaos,where a huge key space would be achieved.In the mean time,plain-text related techniques will also be incorporated into the research for resisting chosen-plaintext attacks and known-plaintext attacks.The main topics of the thesis could be divided as following:1.How digital chaos(low-dimensional/hyper-dimensional)effect the digital image encryptions.Different digital chaos(Hénon,Chens chaos and a new 4-D chaos)are utilized to encrypt digital images,and the encryption results are to be compared.Encryption algorithm in this part uses chaos to generate the chaotic sequences,which would further be calculated with the plain image using XOR operations to perform the encryption.The simulation tells that the 4-D hyper-chaos performs better in statistical effect and robustness.2.A double-domain image encryption method based on hyper chaos.The 4-D hyper chaos is utilized to generate chaotic sequences for encryption with the plain image in both frequency-and spatial-domains.The digital image is first encrypted in frequency-domain,and then performed with inverse discrete FFT(Fast Fourier Transform)to obtain the corresponding spatial-domain image;the spatial-domain image is then further scrambled and confused.Comparisons are also presented in terms of different encryption schemes;for example,the encryption methods with spatial-domain encryption first or frequency-domain encryption first are compared to evaluate the effect brought by the changing of processing order.The simulation shows that the introduction of frequency-domain encryption discombobulates the images,which makes the double-domain encryption performs much better than singledomain encryptions statistically,such as the correlation coefficients,entropy and histograms,and it is better to perform frequency-domain encryption first.3.A multifold double-domain encryption method based on hyper chaos and plaintext correlation.Classical encryption algorithms perform poorly against chosen-or known-plaintext attacks.In this thesis,plaintext related techniques are utilized based on the frequency-domain processing;both the chaotic sequences and plain image participate in the encryption,calculating with the spatial-domain encrypted image.In other words,each one cipher pixel is correlated with the chaotic sequences,the current plain pixel,and all its former cipher pixels.Simulations implies that,the proposed encryption enhances the encryption effect,and also helps resist chosen-or known-plaintext attacks.These novel digital image encryptions are proposed,utilizing the digital chaos,frequency/spatial-domains encryption,and plaintext related technology,which improve the secure capability against various classical attacks.Hyper chaos is applied as key generator to provide chaotic sequences for the multifold encryptions,which enlarges the key space for the proposed encryption against any brute-force attacks;it also makes the encryption more robust due to the high sensitivity to the chaotic initial values.With the frequency-domain encryption introduced,the ciphers and plain images are less correlative,and the statistical properties are more polished away,which provides the capability against any differential attacks and attacks based on statistical analysis.With the introduction of plaintext inside the scrambling process,every single cipher pixel would be related with all of the former plain pixels,which makes dynamical keys if considering the results of chaotic sequences operating with also the random plain pixels as the final keys.Thus the encryption is able to resist any chosen-and known-plaintext attacks.The encryption schemes proposed in this thesis are based on the combination of several algorithms,which successfully promote the ability for efficiently and robustly resisting all kinds of classical attacks.Detailed secure analyses are further presented.