CN104050625A - Compound chaos image encryption method with initial secret keys built through plaintext - Google Patents

Abstract

The invention discloses a compound chaos image encryption method with initial secret keys built through a plaintext. The compound chaos image encryption method is characterized by including the steps of (1) preprocessing an image according to pixel values of the plaintext image and initial given values, and determining iteration initial values; (2) respectively carrying out scrambling and diffusion on the plaintext image through a compound chaos system to achieve the aim of encrypting the plaintext image. The compound chaos image encryption method has the advantages that existing encryption modes basically pay close attention to scrambling and diffusion of images, the compound chaos image encryption method pays attention to processing on the initial secret keys, and due to the improvement, factors needing to be noticed when a safe and reliable encryption algorithm is designed are further improved.

Description

A kind of plaintext builds the composite chaotic image encryption method of initial key

Technical field

The composite chaotic image encryption method that the present invention relates to a kind of initial key producing based on plaintext image, belongs to communications electronics technology and technical field of image signal processing.

Background technology

Along with developing rapidly of Internet of Things infotech, it is convenient and quick that Internet Transmission becomes, and increasing information and communication are transmitted in network.Image, due to content and the implication of embodiment transmission of information that can be very visual and clear, transmits intention and object preferably, is therefore widely used in communication.For transmitting image, due to its inherent singularity (comprising secret and privacy), so must be encrypted in transmission, to prevent information, steal, data tampering.Image encryption is the important branch that image is processed, and in recent years, increasing focus of attention is also studied the application of chaology in image encryption.Due to its inherent pseudo-randomness of chaos system, unpredictability, aperiodicity, features such as extreme responsive type to starting condition, be therefore applicable to very much secret communication.

In recent years, domestic and international many academic research personnel had proposed a series of new chaos algorithm.Deng's Yue for example, Wang Guangyi, Yuan Fang utilizes chaos sequence and the out of order mapping of Rossler system, has realized that secondary pixel is encrypted and a key mapping is encrypted, thus the Chaotic Image Encryption Algorithm of proposition; Zhang Ping, Zhang Dinghui, Zhang Yaqi is encrypted image respectively according to Composite Chaotic System, and what to improve key space, propose shines upon and Rossler chaotic maps cryptographic algorithm based on Henon.Thereby these two kinds of cipher modes are all iterated and reached encryption to image is carried out to xor operation by chaos system, also expanded key space simultaneously, effectively resist heavy attack, so cipher round results is better.Aspect patent, the color image encrypting method of the patent of Du Cuixia, Zhang Dinghui, Zhang Zongnan---hyperchaos Rossler system (patent publication No.: CN103440613A) provide a kind of algorithm that utilizes hyperchaotic system to be encrypted; People's patents such as bavin is beautiful, Wu Xiangjun---color image encryption based on chaos sequence and hyperchaotic system (patent publication No.: CN103489151A) relate to and a kind of original color image is carried out to position level associating scramble, recycling hyperchaotic system is combined diffusion to it, reaches encryption; The patent of Zhang Qiang, Xue Xianglian, Wei little Peng---the image fusion encryption method (patent publication No.: CN101706947A) propose the 2 D chaotic sequence scrambling and coding original image of a kind of Cubic of utilization mapping and wavelet function generation and two DNA sequence dna matrixes that template image obtains based on DNA sequence dna and many chaotic maps; Then two DNA sequence dna matrixes after scramble are done to additive operation; Finally utilize the chaos sequence that Logistic mapping produces and the DNA sequence dna matrix being obtained by additive operation to be used for mutually obtaining encrypted image.

Existing most of Chaotic Encryption System is substantially all based on hyperchaotic system or the cascade of several three-dimensional chaotic system phase, although can expand its key space, effectively resists heavy attack, still has certain defect aspect confidentiality.For example, for hyperchaotic system, the encryption time cycle is oversize, calculates more complicated; Composite chaotic is encrypted, although expanded key space, its cryptographic algorithm is extremely responsive to plaintext, key; Meanwhile, in there is no in building cryptographic algorithm process between some Composite Chaotic System correlativity, they compound is only application quantitatively, is merely able to play the effect of expansion key space, so cannot resist differential attack.

Summary of the invention

The object of the invention is to make the confidentiality of image encryption to be improved and algorithm to expressly extremely responsive, thereby can effectively resist differential attack.

In order to achieve the above object, technical scheme of the present invention has been to provide the composite chaotic image encryption method that a kind of plaintext builds initial key, it is characterized in that, step is:

Step 1, foundation plaintext image pixel value and initial set-point are realized image pre-service, determine iteration initial value, comprising:

Step 1.1, get arbitrary level of image pixel expressly, any most vertically and on diagonally opposing corner form three ordered series of numbers;

Numeral in step 1.2, three ordered series of numbers that step 1.1 is obtained is added respectively, then with 1000 ask mould to obtain three numerical value, be designated as respectively R, C, H;

Step 1.3, get three initial values arbitrarily, be designated as respectively X ₁₀, X ₂₀, X ₃₀, the span of each initial value, between [1,1], and is accurate to after radix point four; Step 1.4, by X ₁₀, X ₂₀, X ₃₀with R, C, H is added respectively summation, then expands 1000 times, asks mould to 255, then divided by 255, obtains initial key, is designated as respectively X ₁₁, X ₂₁, X ₃₁;

Step 2, utilize Composite Chaotic System respectively plaintext image to be carried out to scramble and diffusion, reach the object to plaintext image encryption, comprising:

Step 2.1, by initial key X ₁₁, X ₂₁, X ₃₁substitution Lorenz system, grey iterative generation sequence x, y, z;

Step 2.2, the plaintext image that is M * N by size are converted to gray level image, obtain gray level image picture element matrix, gray level image picture element matrix is converted to [M * N, 1] the plaintext image digitization matrix of form, respectively from sequence x, y, chooses numeral in z again, the scramble character matrix that forms [M * N, 1] form;

Step 2.3, thereby each numerical value in scramble character matrix is arranged and to be formed new scramble character matrix by pre-defined rule order, the rule of the change in location of each numerical value while adopting scramble character matrix in step 2.2 to be converted into the new scramble character matrix in step 2.3, plaintext image digitization matrix in step 2.2 is changed, restore into [M * N] pattern, obtain scramble image;

Step 2.4, by sequence x, y, z sues for peace respectively, then to 255, asks value that mould and being divided by obtains as the initial value of Rossler system iterative respectively;

Step 2.5, the sequence x ' obtaining via Rossler system iterative, y ', z ', at sequence x ', y ', gets respectively some numerals in z ', forms the matrix of [M * N] pattern;

Step 2.6, matrix and scramble image phase XOR that step 2.5 is obtained, complete the encryption to plaintext image.

The present invention obtains any three sequences (being respectively level, vertical, oblique) from plaintext image pixel, making itself and three arbitrarily given initial values do summation processes, gap is too not large at this, to it is noted that two several of summation, prevents a certain factor impact little; For required and ask again mould and ask business to process, obtain the number of scope between [1,1], using this as iteration initial value (being key); After adopt composite chaotic equation to carry out scramble and diffusion to image, first the iterative initial value using initial value as Lorenz system carries out iteration and obtains sequence x, y, z; Again sequence x, y, z summation, to 255, ask mould respectively and the value that obtains of being divided by as the initial value of Rossler system iterative, finally utilize respectively Lorenz sequence of iterations and Rossler sequence of iterations to be encrypted plaintext image.

The invention has the advantages that: existing cipher mode is substantially all to pay close attention to the scramble of image and diffusion, and realization of the present invention is, be exactly to the processing on initial key, this improvement is further perfect designs the factor that a kind of cryptographic algorithm safely and reliably will be noted, that is: whether key space is enough large; Whether uncorrelatedly mutually between ciphertext pixel, distribute; Whether cryptographic algorithm is enough responsive to plaintext and key.And existing most of cipher mode, for example hyperchaos is encrypted, composite chaotic cipher mode, and they mostly only consider the first two factor, for algorithm, to key and dependence expressly, do not do too much consideration, just by key, control cryptographic algorithm merely.The present invention is from expressly starting with at first, and cryptographic algorithm, key are tightly depended on expressly.Such processing, has not only expanded key space, also makes algorithm below have substantial connection with plaintext simultaneously, increases and decodes difficulty, effectively resists differential attack; Simultaneously, in recycling Composite Chaotic System ciphering process, taking previous system iterative value is the iterative initial value of a rear system, making has like this had certain contact between two chaos equations, strengthen algorithm susceptibility, increase cipher round results, to make whole ciphering process form an integral body, slight error Anywhere all can make to encrypt and make a mistake, and improves the sensitivity of encrypting.

Accompanying drawing explanation

Fig. 1 is pretreatment module block diagram of the present invention;

Fig. 2 is system chart of the present invention;

Fig. 3 is chaos system iteration initial value of the present invention source.

Embodiment

For the present invention is become apparent, hereby with preferred embodiment, and coordinate accompanying drawing to be described in detail below.

The invention provides the composite chaotic image encryption method that a kind of plaintext builds initial key, the steps include:

Step 1, foundation plaintext image pixel value and initial set-point are realized image pre-service, determine iteration initial value, comprising:

Step 1.1, get arbitrary level of image pixel expressly, any most vertically and on diagonally opposing corner form three ordered series of numbers;

Numeral in step 1.2, three ordered series of numbers that step 1.1 is obtained is added respectively and obtains three numerical value, then to 1000, asks mould respectively, obtains R, C, H;

Step 1.3, get three initial values arbitrarily, be designated as respectively X ₁₀, X ₂₀, X ₃₀, the span of each initial value, between [1,1], and is accurate to after radix point four;

Step 1.4, by X ₁₀, X ₂₀, X ₃₀with R, C, H is added respectively summation, then with expand 1000 times, then to 255, ask mould, then divided by 255, obtain initial key, be designated as respectively X ₁₁, X ₂₁, X ₃₁;

In conjunction with Fig. 1, in the present invention the key of encrypting has been done to some processing, object is exactly in order to strengthen the antidecoding capability of key, because the iteration initial value (key) after processing is to expressly having very strong dependence, choosing of parameter, to note: original three given initial value spans will be [1,1], between, after reservation radix point, four above significant figure are designated as X ₁₀, X ₂₀, X ₃₀; Recycling is expressly as described in above-mentioned steps, get arbitrary level of image pixel expressly, any most vertically, on diagonally opposing corner form three ordered series of numbers, numeral in three ordered series of numbers is added respectively and obtains three bit digital that expressly form, in order to guarantee plaintext, the susceptibility of initial set-point to key, to three figure places that expressly form, also to do corresponding processing, guarantee that digit is identical, this three figure place is asked to mould to 1000, obtain R, C, H; And then according to step 1.4 X ₁₀, X ₂₀, X ₃₀with R, C, H is added respectively summation, then expands 1000 times, then to 255, asks mould, then divided by 255, is designated as initial value key, just can access the key value X of span between [1,1] ₁₁, X ₂₁, X ₃₁.

Step 2, utilize Composite Chaotic System respectively plaintext image to be carried out to scramble and diffusion, reach the object to plaintext image encryption.

The present invention also adopts Composite Chaotic System to carry out scramble to image simultaneously and encrypts with diffusion, and Composite Chaotic System used be Lorenz system and Rossler system, concrete chaos equation is as follows:

The kinetics equation of Lorenz system is $\left\{\begin{array}{c}\stackrel{\·}{x}=-\mathrm{\σx}+\mathrm{\σy}\\ \stackrel{\·}{y}=\mathrm{\ρx}-y-\mathrm{xz}\\ \stackrel{\·}{z}=-\mathrm{\βz}+\mathrm{xy}\end{array}\right.,$ When parameter value is σ=16, ρ=45.92, β=4 o'clock, system is chaos, in formula representative system quantity of state x, y, the differentiate of z to time t.Give the certain initial value of system, sequence of iterations is chaos.

The kinetics equation of Rossler system is $\left\{\begin{array}{c}{\stackrel{\·}{x}}_1=-x_2-x_3\\ {\stackrel{\·}{x}}_2=x_1+a{x}_2\\ {\stackrel{\·}{x}}_3=b+x_3(x_1-c)\end{array}\right..$ In formula, represent system state amount x _i(i=1,2,3) differentiate to time t; A, b, c is systematic parameter, works as a=0.2, b=0.2, during c=5.7, system is chaos.

Next in conjunction with Fig. 2 and Fig. 3, utilize Composite Chaotic System to be encrypted operation to image, specifically to the scramble of image pixel and diffusion.What after the initial value to given processes, obtain that we want has the key X of dependence to plaintext image ₁₁, X ₂₁, X ₃₁after, using its iterative initial value as Lorenz system, produce iteration chaos sequence x, y, z, the plaintext image that is M * N size is converted to gray level image, obtain gray level image picture element matrix, gray level image picture element matrix is converted to [M * N, 1] the plaintext image digitization matrix of form, again respectively from sequence x, y, in z, choose numeral, form [M * N, 1] the scramble character matrix of form, each numerical value in scramble character matrix is pressed to pre-defined rule order, and (pre-defined rule order can be for descending, or ascending) thus arrangement forms new scramble character matrix, the rule of the change in location of each numerical value while adopting scramble character matrix to be converted into new scramble character matrix, plaintext image digitization matrix is changed, restore into [M * N] pattern, obtain scramble image.

And then with Rossler system, image is carried out to DIFFUSION TREATMENT: the sequence of iterations x that first utilizes said system to produce, y, z, it is dealt with, sequence x, y, z sues for peace respectively, to 255, ask mould respectively again and be divided by and obtain span [1 255, 1] three numerals between, iteration initial value using these three numerals as Rossler chaos system again, the sequence x ' obtaining by Rossler system iterative, y ', z ', at sequence of iterations x ', y ', in z ', get respectively some numerals, form and image pixel matrix same form matrix [M * N, 1] form, this matrix and Scrambling Matrix phase XOR, complete image encryption.The object of processing is like this exactly for whole encryption system process is linked to be to an integral body, makes to occur that in any one step small deviation all can infinitely be amplified by system, thereby makes encryption occur mistake, improves the sensitivity of anti-decoding.

By the pre-service before encrypting and the application of Composite Chaotic System, make the algorithm encrypted not only key space expanded, and the sensitivity of system improved, this method is more suitable for encryption.

Claims (1)

1. plaintext builds a composite chaotic image encryption method for initial key, it is characterized in that, step is:

Step 1, foundation plaintext image pixel value and initial set-point are realized image pre-service, determine iteration initial value, comprising:

Step 1.1, get arbitrary level of image pixel expressly, any most vertically and on diagonally opposing corner form three ordered series of numbers;

Numeral in step 1.2, three ordered series of numbers that step 1.1 is obtained is added respectively, then with 1000 ask mould to obtain three numerical value, be designated as respectively R, C, H;

Step 1.3, get three initial values arbitrarily, be designated as respectively X ₁₀, X ₂₀, X ₃₀, the span of each initial value, between [1,1], and is accurate to after radix point four;

Step 1.4, by X ₁₀, X ₂₀, X ₃₀with R, C, H is added respectively summation, then expands 1000 times, asks mould to 255, then divided by 255, obtains initial key, is designated as respectively X ₁₁, X ₂₁, X ₃₁;

Step 2, utilize Composite Chaotic System respectively plaintext image to be carried out to scramble and diffusion, reach the object to plaintext image encryption, comprising:

Step 2.1, by initial key X ₁₁, X ₂₁, X ₃₁substitution Lorenz system, grey iterative generation sequence x, y, z;

Step 2.2, the plaintext image that is M * N by size are converted to gray level image, obtain gray level image picture element matrix, gray level image picture element matrix is converted to [M * N, 1] the plaintext image digitization matrix of form, respectively from sequence x, y, chooses numeral in z again, the scramble character matrix that forms [M * N, 1] form;

Step 2.3, thereby each numerical value in scramble character matrix is arranged and to be formed new scramble character matrix by pre-defined rule order, the rule of the change in location of each numerical value while adopting scramble character matrix in step 2.2 to be converted into the new scramble character matrix in step 2.3, plaintext image digitization matrix in step 2.2 is changed, restore into [M * N] pattern, obtain scramble image;

Step 2.4, by sequence x, y, z sues for peace respectively, then to 255, asks value that mould and being divided by obtains as the initial value of Rossler system iterative respectively;

Step 2.5, the sequence x ' obtaining via Rossler system iterative, y ', z ', at sequence x ', y ', gets respectively some numerals in z ', forms the matrix of [M * N] pattern;

Step 2.6, matrix and scramble image phase XOR that step 2.5 is obtained, complete the encryption to plaintext image.