CN111756949B

CN111756949B - Chaos-based optical single-channel multi-color image encryption method

Info

Publication number: CN111756949B
Application number: CN202010117218.0A
Authority: CN
Inventors: 唐晨; 申玉馨
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2020-02-25
Filing date: 2020-02-25
Publication date: 2021-08-13
Anticipated expiration: 2040-02-25
Also published as: CN111756949A

Abstract

The invention belongs to the field of optical encryption and information security, and aims at the encryption problem of a multi-color image with CMYK four-color channels. (1) Encryption: step 1: decomposing the QR code image into four color channels of cyan, magenta, yellow and black; then fusing the four channels through Inverse Discrete Wavelet Transform (IDWT) to obtain a gray image to be encrypted; step 2: generating a chaotic random phase plate CRPM through Standard chaotic mapping, and then modulating an image to be encrypted by the CRPM; and step 3: the modulated image is subjected to linear regular transformation (LCT) firstly, and then phase taking operation and amplitude taking operation are carried out to obtain a private key and a primary encryption result; and 4, step 4: the preliminary encryption result and the private key are further Arnold scrambled; the decryption process is a reverse operation. The invention is mainly applied to the image encryption occasion.

Description

Chaos-based optical single-channel multi-color image encryption method

Technical Field

The invention belongs to the field of optical encryption technology and information security, and relates to a single-channel multi-color image optical encryption method in CMYK space based on IDWT and Standard chaotic mapping.

Background

With the continuous development of image acquisition technology and the continuous improvement of acquisition precision, it is not uncommon for lawbreakers to acquire printed matter images by a high-precision scanner and print again to make counterfeit products and disturb the market order. A CMYK (cyan-magenta-yellow-black) color space is generally used in the printing process, and digital images obtained by a scanner are mostly displayed in an RGB (red-green-blue) color space. The adoption of two different color spaces in the printing and scanning processes inevitably leads to the conversion of the color space of the image in the printing and scanning processes, and leads to the transfer and even loss of partial information, which increases the difficulty of protecting the printed image. Compared with digital images, the colors of the printed images are relatively dull, so that the colors of the printed images are not as vivid as those of digital images, and some of the printed images even have larger color distortion. The digital image is displayed in an RGB color space, the color gamut of the digital image is wider than that of a CMYK color space, colors which can be displayed are richer, the printed image is represented by the CMYK color space, and partial pixel points are lost or changed by conversion of the color space to a certain extent, so that color distortion is caused. Therefore, it is an urgent research issue to solve the problems of color image encryption with CMYK four channels in four-color printing and how to protect the printed information from illegal acquisition or copying.

The optical information security technology is a novel security technology which is developed on the basis of optical information processing and is intersected by multiple subjects, and is important supplement and promotion to the traditional information security technology. Optical information security technology uses light as the carrier of information and processes the information using optical techniques such as optical transformation, optical holography, phase recovery, and optical coherence. The physical properties of light such as wavelength, phase, amplitude, polarization state and the like can be used for realizing the encoding processing of information. In addition, compared with the traditional information security technology, the optical information security technology has the advantages of high speed, large capacity, natural parallelism, capability of quickly realizing convolution and related operation and the like. Therefore, the development, research and design of optical information security systems will be an important research direction in the field of information security in the future. In recent years, the research on encryption of optical color images is attracting more and more researchers' attention, because color images can carry more abundant information. Currently, existing optical color image encryption methods can be divided into two categories as a whole: (1) the method is used for encrypting the color image by three color channels of the color image respectively and then combining the three encrypted color channels together to form a final encrypted image. But has the problem of occupying a large space and reducing transmission efficiency. (2) The single-channel color image encryption method is used for directly and simultaneously encrypting three color channels of a color image. In the prior art, in order to implement single-channel encryption of a color image, related researchers have proposed that a color image is first fused into a two-dimensional grayscale image by combining different technologies, and then encrypted. In this scheme, it is proposed to apply IDWT (inverse discrete wavelet transform) to a color image having CMYK color spaces, and convert it into a two-dimensional gray scale image. CRPM (hyper-chaotic random phase plate) is generated through the Standard chaotic mapping, and then the two-dimensional gray image is modulated. The PTLCT (phase-cut linear regular transformation) designed by the scheme is encrypted to obtain an initial encryption result and an initial private key. In order to improve the security, an Arnold scrambling algorithm is introduced to further scramble the preliminary encryption result. In the encryption process, the control parameters and initial values of the Standard chaotic system, the parameters in linear regular transformation and the parameters in Arnold scrambling are all used as auxiliary keys to improve the security of the encryption system. In addition, for multi-color image encryption, the problem exists at present that crosstalk noise caused by mutual crosstalk in the process of simultaneously encrypting and decrypting a plurality of color images causes the condition that the quality of decrypted images is seriously reduced in the process of decrypting the multi-color images. Therefore, the invention introduces QR code (quick response coding), effectively reducing the crosstalk problem in the multi-image encryption process.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a single-channel multi-color-image optical encryption method in CMYK space based on inverse discrete wavelet transform and Standard chaotic mapping, and provides a multi-color image encryption algorithm based on inverse discrete wavelet transform and Standard chaotic random phase coding aiming at the encryption problem of multi-color images with CMYK four-color channels in the full-color printing process. Therefore, the technical scheme adopted by the invention is that the chaos-based optical single-channel multi-color image encryption method comprises the following steps:

(1) encryption of single-color cyan-magenta-yellow-black CMYK images:

step 1: decomposing a to-be-encrypted CMYK color space color quick response code QR code image f obtained by QR coding software coding into cyan f_cMagenta f_mYellow f_yBlack, f_kFour color channels; then, four channels are fused by Inverse Discrete Wavelet Transform (IDWT) to obtain a gray image f to be encrypted_cmyk；

f_cmyk＝IDWT(f_c,f_m,f_y,f_k) (1)

Step 2: generating a chaotic random phase plate CRPM through Standard chaotic mapping, and then generating an image f to be encrypted_cmykModulated by CRPM to obtain modulated image f_cmyk'；

f_cmyk'＝f_cmyk·CRPM (3)

Wherein the function

Representing the chaotic random phase generated by the Standard mapping;

and step 3: modulated image f_cmykFirstly, LCT is transformed through linear regularization, and then phase taking operation and amplitude taking operation are carried out to obtain a private key P₁' and preliminary encryption result E_cmyk'；

E_cmyk'＝PT[LCT_a,b,d(f_cmyk')] (4)

P₁'＝AT[LCT_a,b,d(f_cmyk′)] (5)

Wherein the LCT_a,b,d(. cndot.) represents a linear canonical transformation, a, b, and d are three parameters of LCT, PT [. cndot. ]]And AT [. C]Respectively representing a phase taking operation and an amplitude taking operation;

and 4, step 4: to further increase the security of the encryption system, the preliminary encryption result E_cmyk' and private Key P₁' further Arnold scrambling

E_cmyk＝Arnold(E_cmyk,a_a,b_a,n) (6)

P₁＝Arnold(P₁,a_a,b_a,n) (7)

Wherein Arnold (. cndot.) stands for Arnold scrambling, a_aAnd b_aFor scrambling parameters, n represents the scrambling times, and the final scrambling result E is obtained_cmykAnd P₁Are treated as an encrypted image and a private key, respectively;

(2) and (3) decryption process:

step 1: encryption result E_cmykAnd a private key P generated by the encryption process₁Respectively decoding through inverse-Arnold scrambling operation to obtain primary decryption result d_cmykAnd dP₁

d_cmyk＝inArnold(E_cmyk′,a_a,b_a,n) (8)

dP₁＝inArnold(P₁′,a_a,b_a,n) (9)

Wherein inArnold (·) represents the inverse Arnold scrambling process,

step 2: initial decryption result d_cmykAnd private key dP₁Multiplication followed by an inverse linear canonical transform

d_cmyk′＝LCT_-a,-b,-d(d_cmyk·dP₁) (10)

And step 3: result d obtained by inverse linear canonical transformation_cmykConjugation of' and CRPM

Multiplying to obtain an encrypted result D_cmyk′；

D_cmyk′＝d_cmyk′·CRPM^-1 (11)

And 4, step 4: finally, the obtained decryption result D is subjected to_cmyk' performing wavelet transformation, and decomposing to obtain four parts which are respectively cyan parts D_cMagenta moiety D_mYellow moiety D_yBlack moiety D_k；

[D_c,D_m,D_y,D_k]＝DWT(D_cmyk′) (12)

Will D_c，D_m，D_y，D_kColor QR code D for synthesizing CMYK color space_qFinally, obtaining a decrypted color image F_cmyk。

By P obtained in the encryption process₁As private key, with K, x₁，y₁，a，b，d，a_a，b_aN is an auxiliary key, wherein K is a control parameter in the Standard chaotic system, and x₁And y₁Set as K-64, x as initial value₁＝0.2，y₁＝0.3。

The invention has the characteristics and beneficial effects that:

in the encryption system, the invention provides a chaotic double random phase coding encryption scheme based on phase-cut linear regular transformation, different color channels have different encryption processes to generate different encryption keys, and when a plurality of color images are input, each color image corresponds to a different key, so that the encryption key space is greatly expanded. The influence caused by noise crosstalk is reduced to a certain extent by introducing a QR code (quick response coding). The encrypted image and the private key generated in the encryption process are scrambled through Arnold transformation, so that the security of an encryption system is improved. In addition, the parameters of the chaotic random phase plate, the parameters of the linear regular transformation and the parameters in the Arnold transformation can be used as auxiliary keys of an encryption system, so that the safety of the encryption system is further improved.

Compared with the proposed color image encryption algorithm, the invention mainly aims at the security of the color printing image of CMYK color space with four channels, designs the single-channel multi-color encryption algorithm based on IDWT and Standard chaotic system by providing an encryption module consisting of an asymmetric optical encryption system, and has the advantages that: (1) the CMYK color graphics are converted by introducing IDWT operation, the proposed cryptosystem can be realized on a single-channel optical path, and the problems of key distribution and management can be solved; (2) the proposed scheme directly encrypts CMYK space images with four channels, thereby avoiding color information loss caused by space conversion; (3) by introducing the QR coding technology, the influence of crosstalk noise on the quality of a decrypted image is effectively reduced on the original basis; (4) the scheme is also suitable for simultaneously encrypting the multicolor images and shows high encryption efficiency; (5) the cryptographic system has higher robustness to statistical attack, shearing attack, various noise attacks, plaintext attack selection attack and brute force attack.

Description of the drawings:

fig. 1 is a flow chart of encryption and decryption of the encryption algorithm, in which:

(a) the schematic diagram of the encryption principle provided by the invention;

(b) the decryption principle provided by the invention is shown schematically;

fig. 2 is an encryption system inputting N-4 CMYK color images;

fig. 3 is an original CMYK color image to be encrypted and a corresponding QR-encoded CMYK color image:

(a) is "Eckhart";

(b) QR code for "Eckhart";

FIG. 4 is an encrypted image and a private key generated during the encryption process;

(a) is the result of the encryption;

(b) a private key generated for the encryption process;

fig. 5 shows the decrypted QR-code image with all keys correct and the corresponding QR-decoded CMYK color image:

(a) the decrypted QR code corresponding to the step 3 (b);

(b) QR decoding "Eckhart";

fig. 6 is an image decrypted from fig. 4(a) with different keys, wherein:

(a) is a secret key P₁A decryption result in case of error;

(b) the decryption result is the decryption result when the key K is wrong;

(c) is a secret key x₁A decryption result in case of error;

(d) is a secret key y₁A decryption result in case of error;

(e) is the decryption result when the key a is wrong;

(f) the decryption result is the decryption result when the key b is wrong;

(g) the decryption result is the decryption result when the secret key d is wrong;

(h) is a secret key a_aA decryption result in case of error;

(i) is a secret key b_aA decryption result in case of error;

(j) is the decryption result when the key n is wrong;

fig. 7 is a decrypted image in the case of gaussian noise attack:

(a) the QR code of "Eckhart" decrypted from fig. 4(a) when attacked by 50% gaussian noise;

(b) QR decoding "Eckhart" for 7 (a);

fig. 8 is a decrypted image in the case of a cut attack:

(a) is an encrypted image subject to 25% shear attack;

(b) a QR code of "Eckhart" decrypted from 8 (a);

(c) QR decode "Eckhart" for 8 (b);

in the drawings, the components represented by the respective reference numerals are listed below:

in FIG. 1 (a): f. of_o: original CMYK color images; f. of_q: carrying out QR coding on the Original image to obtain a CMYK color space color QR code image; f. of_c：f_qC (cyan) channel of (a); f. of_m：f_qM (magenta) channel of (a); f. of_y：f_qY (yellow) channel of (a); f. of_k：f_qK (black) channel of (a); IDWT: inverse discrete wavelet transform; f. of_cmyk: fusing the four channels through IDWT to obtain a gray image to be encrypted; CRPM: a hyperchaotic random phase plate; f. of_cmyk': image f to be encrypted_cmykAn image modulated by CRPM; LCT_a,b,d(. cndot.) represents a linear canonical transform, and a, b, and d are three parameters of LCT, where a is 2, b is 1, and d is 7; PT [. to]And AT [. C]Respectively representing a phase taking operation and an amplitude taking operation; e_cmyk': a preliminary encryption result; p₁': a private key obtained in the encryption process; arnold (. cndot.) stands for Arnold scrambling, a_aAnd b_aFor the scrambling parameter, n represents the number of scrambles, where a is set_a＝3，b_a＝5，n＝10；E_cmykAnd P₁: the final encryption result and the private key.

In FIG. 1 (b): inArnold (·) represents the inverse Arnold scrambling process; d_cmykAnd dP₁Representing the preliminary decryption result; d_cmyk' represents a result obtained by inverse linear canonical transformation; CRPM^-1: conjugation of CRPM

D_cmyk' represents the preliminary decryption result; DWT: discrete wavelet transform; d_c: obtained by decryptionA C color channel; d_m: decrypting the obtained M color channel; d_y: decrypting the obtained Y color channel; d_k: decrypting the obtained K color channel; d_q: a color QR code of the synthesized CMYK color space; f_cmyk: and QR decoding the obtained CMYK color image.

In fig. 2: f. of₁，f₂，f₃，f₄: four color images to be encrypted; EP: the encryption process of the scheme; DP: the decryption process of the scheme; p₁₁，P₁₂，P₁₃，P₁₄: four private keys generated in the first layer encryption process; e_cmyk1，E_cmyk2，E_cmyk3，E_cmyk4: the encryption result generated by the first layer encryption process; p₁: private keys generated by the second layer encryption process; e_cmyk: final encryption result of the second layer encryption process.

Detailed Description

In order to overcome the defects of the prior art, the invention aims to provide a multi-color image encryption algorithm based on inverse discrete wavelet transform and Standard chaotic random phase coding aiming at the encryption problem of multi-color images with CMYK four-color channels in the full-color printing process, and has the advantages that: (1) the CMYK color graphics are converted by introducing IDWT operation, the proposed cryptosystem can be realized on a single-channel optical path, and the problems of key distribution and management can be solved; (2) the proposed scheme directly encrypts CMYK space images with four channels, thereby avoiding color information loss caused by space conversion; (3) by introducing the QR coding technology, the influence of crosstalk noise on the quality of a decrypted image is effectively reduced on the original basis; (4) the scheme is also suitable for simultaneously encrypting the multicolor images and shows high encryption efficiency; (5) the cryptographic system has higher robustness to statistical attack, shearing attack, various noise attacks, plaintext attack selection attack and brute force attack.

The invention discloses an optical single-channel multi-color image encryption method based on chaos, which comprises the following steps of:

(1) encryption of single-layer CMYK images:

step 1: decomposing a CMYK color space color QR code image f to be encrypted, which is obtained by encoding QR encoding software, into f_c、f_m、f_y、f_kFour color channels; then fusing the four channels through IDWT to obtain a gray image f to be encrypted_cmyk。

f_cmyk＝IDWT(f_c,f_m,f_y,f_k) (1)

Step 2: generating a chaotic random phase plate CRPM through Standard chaotic mapping, and then generating an image f to be encrypted_cmykModulated by CRPM to obtain modulated image f_cmyk'。

f_cmyk'＝f_cmyk·CRPM (3)

Wherein the function

Representing the chaotic random phase generated by the Standard mapping.

And step 3: modulated image f_cmykFirstly, Linear Canonical Transformation (LCT) is carried out, and then phase extraction operation and amplitude extraction operation are carried out to obtain a private key P₁' and preliminary encryption result E_cmyk'。

E_cmyk'＝PT[LCT_a,b,d(f_cmyk')] (4)

P₁'＝AT[LCT_a,b,d(f_cmyk')] (5)

Wherein the LCT_a,b,d(. cndot.) represents a linear canonical transformation, and a, b, and d are three parameters of LCT, where a-2, b-1, and d-7 are taken. PT [. to]And AT [. C]Respectively representing a phase-taking operation and an amplitude-taking operation.

And 4, step 4: to further increase the security of the encryption system, the preliminary encryption result E_cmyk' and private Key P₁' further Arnold scrambled.

E_cmyk＝Arnold(E_cmyk,a_a,b_a,n) (6)

P₁＝Arnold(P₁,a_a,b_a,n) (7)

Wherein Arnold (. cndot.) stands for Arnold scrambling, a_aAnd b_aFor the scrambling parameter, n represents the number of scrambles. Where is set to a_a＝3，b_a5, n is 10. The scrambling result E finally obtained_cmykAnd P₁Respectively treated as an encrypted image and a private key.

(3) And (3) decryption process:

step 1: encryption result E_cmykAnd a private key P generated by the encryption process₁Respectively decoding through inverse-Arnold scrambling operation to obtain primary decryption result d_cmykAnd dP₁。

d_cmyk＝inArnold(E_cmyk',a_a,b_a,n) (8)

dP₁＝inArnold(P₁',a_a,b_a,n) (9)

Wherein inArnold (·) represents the inverse Arnold scrambling process.

Step 2: initial decryption result d_cmykAnd private key dP₁Multiplied and then inverse linear canonical transform.

d_cmyk'＝LCT_-a,-b,-d(d_cmyk·dP₁) (10)

Multiplying to obtain an encrypted result D_cmyk'。

D_cmyk'＝d_cmyk'·CRPM^-1 (11)

And 4, step 4: finally, the obtained decryption result D is subjected to_cmyk' wavelet transform is carried out, and four parts obtained by decomposition are respectively D_c，D_m，D_y，D_k。

[D_c,D_m,D_y,D_k]＝DWT(D_cmyk') (12)

Will D_c，D_m，D_y，D_kColor QR code D for synthesizing CMYK color space_qThen, the decrypted color image F can be obtained by scanning the mobile phone_cmyk. Summarizing the above single CMYK color image encryption process is the EP encryption algorithm and the decryption process is DP. By P obtained in the encryption process₁As private key, with K, x₁，y₁，a，b，d，a_a，b_aAnd n is an auxiliary key. Wherein K is a control parameter in the Standard chaotic system, x₁And y₁For the initial value, we set them to K-64, x, respectively₁＝0.2，y₁＝0.3。

To test the encryption capacity and efficiency of the present solution, we extended the solution to color image encryption for multiple CMYK spaces. When the number N of input color images is 4, the final encrypted image can be obtained through a two-layer encryption process. In the first layer, four color images are respectively encrypted into four grayscale images E_cmyk1，E_cmyk2，E_cmyk3，E_cmyk4And four private keys P₁₁，P₁₂，P₁₃，P₁₄. In the second layer, four gray scale password images are respectively taken as approximate details, horizontal details, vertical details and diagonal details, then are fused through IDWT operation, and then are further encrypted to obtain a final real value gray scale password image E_cmykAnd a private key P₁. In addition, the respective encryption and decryption paths for each color image are different. Therefore, the cryptosystem has high security among multiple users.

For clearly illustrating the objects, technical solutions and advantages of the present invention, the following describes the embodiments of the encryption algorithm and the decryption process in the present invention in further detail.

(1) Encryption of single-layer CMYK images:

step 1: decomposing a CMYK color space color QR code image f to be encrypted, which is obtained by encoding QR encoding software, into f_c、f_m、f_y、f_kFour color channels; the four channels are then fused by IDWTObtaining a gray image f to be encrypted_cmyk。

f_cmyk＝IDWT(f_c,f_m,f_y,f_k) (1)

f_cmyk'＝f_cmyk·CRPM (3)

Wherein the function

Representing the chaotic random phase generated by the Standard mapping.

E_cmyk'＝PT[LCT_a,b,d(f_cmyk')] (4)

P₁'＝AT[LCT_a,b,d(f_cmyk')] (5)

E_cmyk＝Arnold(E_cmyk,a_a,b_a,n) (6)

P₁＝Arnold(P₁,a_a,b_a,n) (7)

(2) And (3) decryption process:

d_cmyk＝inArnold(E_cmyk',a_a,b_a,n) (8)

dP₁＝inArnold(P₁',a_a,b_a,n) (9)

Wherein inArnold (·) represents the inverse Arnold scrambling process.

d_cmyk'＝LCT_-a,-b,-d(d_cmyk·dP₁) (10)

Multiplying to obtain an encrypted result D_cmyk'。

D_cmyk'＝d_cmyk'·CRPM^-1 (11)

[D_c,D_m,D_y,D_k]＝DWT(D_cmyk') (12)

Will D_c，D_m，D_y，D_kColor QR code D for synthesizing CMYK color space_qThen, the decrypted color image F can be obtained by scanning the mobile phone_cmyk. Is summarized withThe encryption process of the single CMYK color image of the surface is an EP encryption algorithm, and the decryption process is DP. By P obtained in the encryption process₁As private key, with K, x₁，y₁，a，b，d，a_a，b_aAnd n is an auxiliary key. Wherein K is a control parameter in the Standard chaotic system, x1 and y₁For the initial value, we set them to K-64, x, respectively₁＝0.2，y₁＝0.3。

In order to verify the effectiveness of the method, an experimental result is given to the encryption and decryption process of inputting a color image.

FIG. 1(a) is the encryption process of the proposed encryption algorithm, input as the original CMYK color image f_oAnd carrying out a coding process on the color QR code by QR coding software to obtain the color QR code f which is the CMYK color space_qDecompose it into f_c、f_m、f_y、f_kFour color channels, then f is passed through IDWT_qConversion into a grayscale image f_cmyk. Meanwhile, a chaotic random phase plate CRPM is generated by using a Standard chaotic system, and an image f to be encrypted_cmykObtaining an image f after CRPM modulation_cmyk'. Then obtaining a primary encrypted image E through phase-cut linear canonical transformation_cmyk' and private Key P₁'. In order to improve the security of the encryption system, an Arnold scrambling algorithm is introduced to further process the primary encryption result to obtain a final encryption result E_cmykAnd a private key P₁。

FIG. 1(b) shows the decryption process of the proposed encryption algorithm, the encryption result E_cmykAnd a private key P₁Firstly, obtaining a primary decryption result d by an inverse Arnold scrambling algorithm_cmykAnd dP₁. Then d is_cmykAnd dP₁The multiplied result is subjected to inverse linear regular transformation to obtain d_cmyk'。CRPM^-1Is the conjugate of CRPM. d_cmyk' and CRPM^-1Obtaining a preliminary decryption result D through modulation_cmyk'. By DWT to D_cmyk' decomposition can result in four encrypted color channels D_c、D_m、D_y、D_k. Then synthesizing them to obtain the color QR code D of CMYK color space_qFinally, a final decrypted image F is obtained through QR decoding_cmyk。

Fig. 2 is an encryption flow of the proposed encryption algorithm applied to four color images, mainly two-layer encryption. In the first layer of encryption, f₁，f₂，f₃，f₄For four color images to be encrypted, obtaining corresponding encrypted images E through respective encryption processes EP_cmyk1，E_cmyk2，E_cmyk3，E_cmyk4And four private keys P₁₁，P₁₂，P₁₃，P₁₄. In the second layer of encryption process, the encryption result obtained in the first layer is regarded as four detail parts of wavelet transform to carry out IDWT fusion operation, and then EP encryption is carried out to obtain the final encryption result E_cmykAnd a private key P₁。

Fig. 3(a) shows an original CMYK color image to be encrypted "Eckhart" (size 250 × 250 × 4), and the CMYK color QR code image obtained by QR-encoding is as shown in fig. 3 (b). The gray scale encryption map encrypted by the proposed encryption algorithm and the private key generated by the encryption process are shown in fig. 4(a) and 4 (b).

As can be seen from fig. 4, the information of the color QR code image is encrypted, and when all keys are correct and are not attacked, all the information of the color QR code image can be completely restored (as shown in fig. 5 (a)), and the original image can be successfully obtained by the QR decoding software (as shown in fig. 5 (b)). The success of the encryption and decryption of the CMYK color image by the system is shown.

When one of the keys is wrong and the other key is correct, the decryption result of the color QR code is as shown in fig. 6(a) -6 (j). Therefore, the security of the encryption system can be ensured.

Fig. 7 shows a color QR code decrypted image (fig. 7(a)) and a corresponding QR decoded image (fig. 7(b)) when the encrypted image is subjected to a gaussian noise attack of 50%.

Fig. 8 is a color QR code decrypted image (fig. 8(b)) of a 25% cut-attack image (fig. 8(a)) on an encrypted image, and a corresponding QR decoded image (fig. 8 (c)). Therefore, even if the encrypted image is polluted by noise to a great extent or partial information is lost, the method can decrypt the identifiable original color image, verifies the feasibility of the system and meets various requirements in practical application.

While the present invention has been described with reference to the drawings, the foregoing embodiments are illustrative rather than limiting, and that those skilled in the art, having the benefit of the teachings herein, may make numerous modifications thereto without departing from the spirit or scope of the invention as set forth in the appended claims.

Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-described embodiments of the present invention are merely provided for description and do not represent the merits of the embodiments.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. An optical single-channel multi-color image encryption method based on chaos is characterized by comprising the following steps:

(1) encryption of single-color cyan-magenta-yellow-black CMYK images:

f_cmyk＝IDWT(f_c，f_m，f_y，f_k) (1)

Step 2: generating a chaotic random phase plate CRPM through Standard chaotic mapping, and then generating an image f to be encrypted_cmykModulated by CRPM to obtain modulated image f_cmyk′；

f_cmyk′＝f_cmyk·CRPM (3)

Wherein the function

Representing the chaotic random phase generated by the Standard mapping;

and step 3: modulated image f_cmykFirstly, LCT is transformed through linear regularization, and then phase taking operation and amplitude taking operation are carried out to obtain a private key P₁' and preliminary encryption result E_cmyk′；

E_cmyk′＝PT[LCT_a,b,d(f_cmyk′)] (4)

P₁′＝AT[LCT_a,b,d(f_cmyk′)] (5)

and 4, step 4: to further increase the security of the encryption system, the preliminary encryption result E_cmyk' and private Key P₁' further Arnold scrambled;

E_cmyk＝Arnold(E_cmyk’ , a_a，b_a，n) (6)

P₁＝Arnold(P₁’ , a_a，b_a，n) (7)

(2) and (3) decryption process:

step 1: encryption result E_cmykAnd a private key P generated by the encryption process₁Respectively decoding through inverse-Arnold scrambling operation to obtain primary decryption result d_cmykAnd dP_1;

d_cmyk＝inArnold(E_cmyk,a_a,b_a,n) (8)

dP₁＝inArnold(P₁,a_a，b_a，n) (9)

Wherein inArnold (·) represents the inverse Arnold scrambling process,

step 2: initial decryption result d_cmykAnd private key dP₁Multiplying, and then carrying out inverse linear canonical transformation;

d_cmyk′＝LCT_-a，-b，-d(d_cmyk·dP₁) (10)

Multiplying to obtain a decryption result D_cmyk′；

D_cmyk′＝d_cmyk′·CRPM^-1 (11)

And 4, step 4: finally, the obtained decryption result D is subjected to_cmykPerforming wavelet transformation DWT to obtain four parts, namely, cyan part D_cMagenta moiety D_mYellow moiety D_yBlack moiety D_k；

[D_c,D_m，D_y，D_k]＝DWT(D_cmyk′) (12)

2. The method of claim 1, wherein the P obtained in the encryption process is used as the encryption key₁As private key, with K, x₁，y₁，a，b，d，a_a，b_aN is an auxiliary key, wherein K is a control parameter in the Standard chaotic system, and x₁And y₁Are set as initial values respectivelyK＝64，x₁＝0.2，y₁＝0.3。