CN101394553A - Image encryption and decryption method and device - Google Patents

Abstract

The embodiment of the present invention discloses an image encryption method, comprising: acquiring low-frequency coefficients of an image; dividing the low-frequency coefficients into at least two groups of coefficients; selecting at least one group of coefficients from the at least two groups of coefficients, and selecting the selected At least one set of coefficients is encrypted. At the same time, a method for decrypting an image is also provided, including: receiving an encrypted image; obtaining low-frequency coefficients of the image; dividing the low-frequency coefficients into at least two groups of coefficients; selecting at least one of the at least two groups of coefficients A set of coefficients, decrypting the selected at least one set of coefficients. The above solution overcomes the problem of poor confidentiality caused by fixed and public encrypted coefficients in the prior art by dividing the low-frequency coefficients of the image into at least two groups and selecting at least one group of coefficients for encryption. The embodiment of the invention also correspondingly discloses an image encryption device and an image decryption device.

Description

Image encryption and decryption method and device

technical field

The present invention relates to the technical field of image multimedia, in particular to image decryption, a method and a device for decrypting.

Background technique

With the rapid transmission and wide use of images in the network. Users have put forward higher requirements for copyright authentication and secure transmission of image information. For the authentication of image copyright, digital watermarking technology can be used to hide copyright information in the image to achieve the purpose of identifying the ownership of the work and tracking the source of illegal infringement; for the safe transmission of image information, image encryption technology can be used to hide the identity of the image itself. Authentic information to ensure the safe transmission of information in the channel.

In order to meet the requirements of copyright authentication and secure transmission of image information, a method of jointly protecting images by watermarking and encryption is proposed. The method includes: dividing the image into image blocks of 8*8 pixels, performing DCT (Discrete Cosine Transform, discrete cosine transform) transformation on each image block, and obtaining a coefficient matrix of DCT transformation of 8*8, wherein each coefficient matrix The DC system is used for encryption, and the AC system is used for embedding watermarks. After network transmission, the user gets the encrypted and watermarked image, and decrypts it with a legal key to get the watermarked image.

In the process of realizing the present invention, the inventors found that there are at least the following problems in the prior art: the coefficients embedded in the watermark and encrypted in the above method are respectively fixed as the AC coefficient and the DC coefficient in the coefficient matrix, that is, the encrypted area is fixed, and the encryption is easy. Being cracked by an attacker, the security is not high.

Contents of the invention

The embodiment of the present invention provides an image encryption and decryption method and device, the encryption area is not fixed, and the security is improved.

An image decryption method, comprising:

Obtain the low frequency coefficient of the image;

dividing the low frequency coefficients into at least two groups of coefficients;

Select at least one set of coefficients from the at least two sets of coefficients, and encrypt the selected at least one set of coefficients.

An image decryption method, comprising:

Receive encrypted images;

Obtaining low-frequency coefficients of the image;

dividing the low frequency coefficients into at least two groups of coefficients;

Select at least one set of coefficients from the at least two sets of coefficients, and decrypt the selected at least one set of coefficients.

An image encryption device, comprising:

A coefficient acquisition module, configured to acquire low-frequency coefficients of an image;

a coefficient grouping module, configured to divide the low-frequency coefficients into at least two groups of coefficients;

An encryption module, configured to select at least one set of coefficients from the at least two sets of coefficients, and encrypt the selected at least one set of coefficients.

An image decryption device, comprising:

An image receiving module, configured to receive encrypted images;

A coefficient acquisition module, configured to acquire low-frequency coefficients of the image;

a coefficient grouping module, configured to divide the low-frequency coefficients into at least two groups of coefficients;

A decryption module, configured to select at least one set of coefficients from the at least two sets of coefficients, and decrypt the selected at least one set of coefficients.

The image processing method and device provided by the embodiments of the present invention divide the low-frequency coefficients of the image into at least two groups, select at least one group of coefficients for encryption, and overcome the problem of poor confidentiality caused by the fixed and public encrypted coefficients in the prior art.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is a schematic flow chart of an image encryption method according to an embodiment of the present invention;

FIG. 2 is a schematic flow chart of step 102 in FIG. 1;

FIG. 3 is a schematic flow chart of step 104 in FIG. 1;

FIG. 4 is a schematic flow diagram of an image decryption method according to an embodiment of the present invention;

FIG. 5 is a schematic flow chart of step 403 in FIG. 4;

FIG. 6 is a flowchart of step 405 in FIG. 4;

7 is a schematic structural diagram of an image encryption device according to an embodiment of the present invention;

Fig. 8 is a schematic structural diagram of an image decryption device according to an embodiment of the present invention;

Fig. 9 is a schematic diagram of grouping low-frequency coefficients of wavelet transform according to an embodiment of the present invention;

FIG. 10 is a schematic diagram of the coefficient quantization principle when embedding a watermark according to an embodiment of the present invention;

FIG. 11 is a schematic diagram of repeated watermark embedding according to an embodiment of the present invention;

Figure 12(a) is the original Lena image;

Figure 12(b) is the encrypted and watermarked Lena image;

Figure 12(c) is the decrypted and watermarked Lena image;

Figure 13(a) is the original cameraman image;

Figure 13(b) is the encrypted and watermarked cameraman image;

Figure 13(c) is the decrypted and watermarked cameraman image.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

An image processing method in the embodiment of the present invention is described in detail below, referring to Fig. 1, the method includes:

101. Obtain the low frequency coefficient of the image

In this example, perform 3-level wavelet transform on the image waiting to be sent, and obtain the low-frequency coefficients {a ₁ , a ₂ , a ₃ , a ₄ , a ₅ , a ₆ .......a _n } of the image wavelet transform .

102. Divide the low-frequency coefficients into at least two groups of coefficients:

The low-frequency coefficients are divided into at least two groups of coefficients according to certain rules, as shown in Figure 2, this step includes:

201. Randomly generate binary numbers through keys

In this example, the key randomly generates binary numbers with the same number of low-frequency coefficients as

202. Compare the low frequency coefficient with the binary number

In this example, the low-frequency coefficients are compared with the binary numbers in the corresponding positions:

a ₁ a ₂ a ₃ a ₄ a ₅ a ₆ ...... a _n

0 1 0 1 1 0... 1

203. According to the low-frequency coefficients corresponding to the positions of the binary numbers "0" and "1", divide the low-frequency coefficients into a coefficient "0" group and a coefficient "1" group

In this example, a ₁ , a ₃ , a ₆ ... the binary number at the corresponding position is "0", then a ₁ , a ₃ , a ₆ ... are divided into the coefficient "0"group;

a ₂ , a ₄ , a ₅ ... a _n correspond to a binary number of "1", then a ₂ , a ₄ , a ₅ ... a _n are divided into the coefficient "1" group.

204. The coefficient "0" group is the first group of coefficients, and the coefficient "1" group is the second group of coefficients

In this example, let the coefficient "0" group be the first group of coefficients, and the coefficient "1" group be the second group of coefficients, then the first group of coefficients is {a ₁ , a ₃ , a ₆ ...}; the second group of coefficients It is {a ₂ , a ₄ , a ₅ ... a _n }.

103. Select at least one set of coefficients for encryption;

There are two ways to process images as follows:

(1) Embed watermark and encrypt image

selecting at least one set of coefficients, encrypting and embedding a watermark on the at least one selected set of coefficients; or

Selecting at least one group of coefficients, encrypting the at least one group of selected coefficients, and simultaneously selecting at least another group of coefficients, and embedding a watermark in the selected at least one group of coefficients.

(2) Only encrypt the image

Randomly select at least one group of coefficients, and encrypt the selected at least one group of coefficients.

In this example, the image processing method is the first method. Embed watermarks on the first set of coefficients {a ₁ , a ₃ , a ₆ ...}, and perform DES (Data Encryption Standard) encryption on the second set of coefficients {a ₂ , a ₄ , a ₅ ...}.

After embedding the watermark on the coefficients {a ₁ , a ₃ , a ₆ ...}, the coefficients become

After encrypting the coefficients {a ₂ , a ₄ , a ₅ ... a _n }, the coefficients become

104. Obtain the encrypted image, see Figure 3 for the specific process:

301. After the encryption process is completed, merge the first group of coefficients and the second group of coefficients according to the positions of "0" and "1" of the binary number to obtain the combined low-frequency coefficients;

In this example, restore the first group of coefficients to their original positions according to the position of "0" in the binary number; restore the second group of coefficients to their original positions according to the position of "1" in the binary number. The combined low-frequency coefficients are obtained.

的“0”的位置，将第一组系数为

还原到原来的位置，按照所述二进制数

的“1”的位置，将第二组系数为

还原到原来的位置，得到合并后的低频系数为 $\{a_1^{\′},a_2^{\′},a_3^{\′},a_4^{\′},a_5^{\′},a_6^{\′}\·\·\·\·\·\·a_n^{\′}\}.$ according to the binary number

In the "0" position, the first set of coefficients will be

Restore to original position, follow the binary number

In the "1" position, the second set of coefficients will be

Restored to the original position, the combined low-frequency coefficients are obtained as $\{a_1^{\′},a_2^{\′},a_3^{\′},a_4^{\′},a_5^{\′},a_6^{\′}\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\·\·a_{\mathrm{no}}^{\′}\}.$

302. Perform wavelet inverse transform on the combined low-frequency coefficients to obtain an encrypted image.

In this example, for the low frequency coefficients $\{a_1^{\′},a_2^{\′},a_3^{\′},a_4^{\′},a_5^{\′},a_6^{\′}\·\·\·\·\·\&Center\; Dot;a_{\mathrm{no}}^{\′}\}$ Carry out wavelet inverse transform to get the encrypted image. If in the above embodiment, not only encryption, but also a set of coefficients are selected to embed the watermark, then steps 301 and 302 are correspondingly after the encryption and watermark embedding process is completed, according to the "0" and "1" of the binary number position, combining the first group of coefficients and the second group of coefficients to obtain the combined low-frequency coefficients; performing wavelet inverse transform on the combined low-frequency coefficients to obtain an encrypted and watermarked image.

The method provided by the embodiment of the present invention is based on wavelet transform, and low-frequency coefficients are randomly partitioned, part of which is used for encryption and part of which is used for embedding watermarks. Band can achieve better scrambling effect.

The image decryption method in the embodiment of the present invention is described in detail below, as shown in Figure 4, including:

401. Receive an encrypted image;

402. Perform level 3 wavelet transform on the encrypted image;

In this example, the receiving end performs three-level wavelet transform on the embedded watermark and encrypted image to obtain low-frequency coefficients $\{a_1^{\′},a_2^{\′},a_3^{\′},a_4^{\′},a_5^{\′},a_6^{\′}\·\·\·\·\·\&Center\; Dot;a_{\mathrm{no}}^{\′}\}.$

403. Divide the low-frequency coefficients into at least two groups of coefficients, see FIG. 5 for the specific process:

The low-frequency coefficients are divided into at least two groups of coefficients using the same rules as .

As shown in Figure 5, step 403 includes:

501. Randomly generate binary numbers through keys

In this example, the receiving end uses the same key as the sending end to randomly generate binary numbers with the same number of low-frequency coefficients

502. Compare the low frequency coefficient with the binary number

In this example, the low-frequency coefficients are compared with the binary numbers in the corresponding positions:

$\begin{array}{cccccccc}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& <span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span>& {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\end{array}$

0 1 0 1 1 0... 1

503. According to the low-frequency coefficients corresponding to the positions of the binary numbers "0" and "1", divide the low-frequency coefficients into a coefficient "0" group and a coefficient "1" group

……对应位置的二进制数为“0”，则

……被分到系数“0”组；In this example,

...the binary number at the corresponding position is "0", then

...are assigned to the coefficient "0"group;

被分到系数“1”组。 The binary number at the corresponding position is "1", then

are assigned to the coefficient "1" group.

504. The coefficient "0" group is the third group of coefficients, and the coefficient "1" group is the fourth group of coefficients

第四组系数为 In this example, let the coefficient "0" group be the third group of coefficients, and the coefficient "1" group be the fourth group of coefficients, then the third group of coefficients is

The fourth set of coefficients is

404. Select at least one group of coefficients respectively to decrypt.

According to the different image processing methods at the sending end, the image processing methods at the receiving end can be divided into two categories, namely:

Type 1: Receive an image embedded with a watermark and encrypted

1) Decrypt the image

Selecting at least one set of coefficients used for encryption for decryption;

2) Extract the watermark from the image

extracting the watermark from at least one set of coefficients selected for embedding the watermark;

3) Decrypt and extract the watermark

At least one set of coefficients selected for encryption is selected for decryption and the watermark is extracted from at least one set of coefficients selected for embedding the watermark.

Second class: Receive only encrypted images

1) Decryption;

Selecting at least one set of coefficients used for encryption for decryption;

2) After decrypting the selected encryption coefficients, select at least one group of coefficients, and embed a watermark in the selected at least one group of coefficients. The selected at least one group of coefficients can be the same as the decrypted coefficients, or can be the same as the decrypted coefficients different.

Watermarks and encrypted areas do not affect each other. Image encryption, watermark embedding, image decryption, watermark extraction, these four processes are configurable. Provide users with a variety of options to meet the different needs of users. That is, the sender can choose: 1) encrypt the image and embed the watermark to obtain an encrypted and embedded watermark image, or 2) only encrypt the image to obtain an encrypted image. The receiver can choose: 1) Decrypt and extract the watermarked image to obtain the decrypted image with watermark and watermark; 2) only decrypt the image encrypted and embedded with watermark to obtain the decrypted image with watermark , 3) Only extract the watermark from the encrypted and watermarked image to obtain the watermark, 4) Decrypt and add the watermark to the encrypted image at the sending end to obtain the decrypted image with the watermark. 5) Embedding a watermark into the image that has only been encrypted at the sending end to obtain an encrypted image with a watermark embedded in it.

中提取水印，对第二组系数 $\{a_2^{\&prime;},a_4^{\&prime;},a_5^{\&prime;}\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\}$ 进行DES解密。In this example, an image embedded with a watermark and encrypted is received, and the processing method for the image is the third method of the first category. From the first set of coefficients

Extract the watermark from the second set of coefficients $\{a_2^{\&prime;},a_4^{\&prime;},a_5^{\&prime;}\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\}$ Perform DES decryption.

From the coefficient $\{a_1^{\&prime;},a_3^{\&prime;},a_6^{\&prime;}\&CenterDot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\}$ After extracting the watermark, the coefficients become $\{a_1,a_3,a_6\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\};$

pair coefficient $\{a_2^{\&prime;},a_4^{\&prime;},a_5^{\&prime;}\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;a_{\mathrm{no}}^{\&prime;}\}$ After decryption, the coefficients become $\{a_2,a_4,a_5\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;a_{\mathrm{no}}\}.$

405. Obtain the decrypted image, see Figure 6 for the specific process:

601. After decrypting and extracting the watermark, combine the third group of coefficients and the fourth group of coefficients according to the positions of "0" and "1" of the binary number to obtain combined low-frequency coefficients;

In this example, the third group of coefficients are restored to their original positions according to the position of "0" in the binary number; and the fourth group of coefficients are restored to their original positions according to the position of "1" in the binary number. The combined low-frequency coefficients are obtained.

的“0”的位置，将第三组系数为{a₁，a₃，a₆……}，还原到原来的位置，按照所述二进制数

的“1”的位置，将第四组系数为{a₂，a₄，a₅……a_n}还原到原来的位置，得到合并后的低频系数为{a₁，a₂，a₃，a₄，a₅，a₆.......a_n}。According to the binary number as

The "0" position of the third group of coefficients is {a ₁ , a ₃ , a ₆ ...}, restored to the original position, according to the binary number

The "1" position of the fourth group of coefficients is restored to the original position as {a ₂ , a ₄ , a ₅ ... a _n }, and the combined low-frequency coefficients are {a ₁ , a ₂ , a ₃ , a ₄ , a ₅ , a ₆ ...... a _n }.

602. Perform wavelet inverse transform on the combined low-frequency coefficients to obtain an image after decryption and watermark extraction.

In this example, wavelet inverse transform is performed on the low-frequency coefficients {a ₁ , a ₂ , a ₃ . . . a _n } to obtain a decrypted image with a watermark.

The method provided by the embodiment of the present invention randomly distributes the low-frequency coefficients of the image through a key, and then a decrypted image with a watermark can be obtained, and the display effect of the image has no obvious difference from the original image, and at the same time, the purpose of copyright protection is achieved.

Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be implemented through computer programs to instruct related hardware, and the programs can be stored in a computer-readable storage medium. During execution, it may include the processes of the embodiments of the above-mentioned methods. Wherein, the storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only Memory, ROM) or a random access memory (Random Access Memory, RAM), etc.

An image processing device provided by an embodiment of the present invention is described in detail below, the device is suitable for encrypting an image or encrypting and embedding a watermark, see Figure 10:

An image encryption device, comprising:

A coefficient acquisition module 701, configured to acquire low-frequency coefficients of an image;

A coefficient grouping module 702, configured to divide the low-frequency coefficients into at least two groups of coefficients;

An encryption module 703, configured to select at least one set of coefficients from the at least two sets of coefficients, and encrypt the selected at least one set of coefficients.

The image processing device also includes:

The embedding watermark module 705 is configured to select at least one set of coefficients from the at least two sets of coefficients, and embed a watermark in the selected at least one set of coefficients.

The coefficient grouping module 702 may further include:

Binary number obtaining unit 706, for randomly generating binary numbers through the key;

A comparing unit 707, configured to compare the low-frequency coefficients with the binary number;

The grouping unit 708 is configured to divide the low-frequency coefficients into a coefficient "0" group and a coefficient "1" group according to the low-frequency coefficients corresponding to the positions of the binary numbers "0" and "1".

The coefficient acquisition module is used to perform wavelet transformation on the image to obtain low-frequency coefficients after wavelet transformation, and the device also includes:

The coefficient merging module 709 is used to merge the coefficient "0" group and the coefficient "1" group according to the positions of "0" and "1" of the binary number to obtain the combined low-frequency coefficients;

The inverse transform module 710 is configured to perform wavelet inverse transform on the combined low-frequency coefficients to obtain an encrypted image.

The image device provided by the embodiment of the present invention is described in detail below, and the device is suitable for decrypting an image or decrypting and extracting a watermark, see FIG. 11 :

An image receiving module 801, configured to receive encrypted images;

A coefficient acquisition module 802, configured to acquire low-frequency coefficients of the image;

A coefficient grouping module 803, configured to divide the low-frequency coefficients into at least two groups of coefficients;

A decryption module 804, configured to select at least one set of coefficients from the at least two sets of coefficients, and decrypt the selected at least one set of coefficients.

The image processing device also includes:

Extracting a watermark module 806, configured to select at least one set of coefficients from the at least two sets of coefficients, and extract a watermark from the selected at least one set of coefficients.

The coefficient grouping module 803 may further include:

Binary number acquisition unit 807, for randomly generating binary numbers through the key;

A comparing unit 808, configured to compare the low-frequency coefficients with the binary number;

The grouping unit 809 is configured to divide the low-frequency coefficients into a coefficient "0" group and a coefficient "1" group according to the low-frequency coefficients corresponding to the positions of the binary numbers "0" and "1".

The coefficient acquisition module 802 is used to perform wavelet transformation on the image to obtain low-frequency coefficients after wavelet transformation, and the device also includes:

The coefficient merging module 810 is configured to merge the coefficient "0" group and the coefficient "1" group according to the positions of "0" and "1" of the binary number to obtain the combined low-frequency coefficients;

The inverse transform module 811 is configured to perform wavelet inverse transform on the low-frequency coefficients to obtain a decrypted image.

The image encryption device provided by the embodiment of the present invention divides the low-frequency coefficients of the image into at least two groups, and selects at least one group for encryption, so that the encryption area is not fixed, which improves the security of image transmission; That is to encrypt, and select at least one set of embedded watermarks, that is, to combine encryption and watermarks so that the image can be protected by both transmission and copyright. Decryption and/or watermark extraction can be performed by image decryption.

The process of embedding watermark and extracting watermark is introduced below with application examples.

The specific steps of encrypting and embedding the watermarked image at the sending end are as follows: 1) Perform 3-level 2-D DWT (Discrete Wavelet Transform) on the original image f(x, y) to extract DWT low-frequency sub-band coefficients; 2) pass the key Key0 randomly divides the low-frequency coefficients into two irrelevant parts S1 and S2; 3) The S1 area is used to embed the watermark W to generate S1', and the S2 area is used for DES encryption to generate S2'; 4) The S1' and S2 'Synthesis, the image f'(x, y) that is encrypted and embedded with a watermark is obtained through wavelet inverse transformation;

The steps to obtain the decrypted image with watermark and watermark at the receiving end are as follows: 1) Perform 3-level 2-D DWT (Discrete Wavelet Transform) on the image f'(x, y) to be processed, and extract the DWT low-frequency subband coefficients; 2) pass The key Key0 randomly divides the low-frequency coefficients into two irrelevant parts S1' and S2'; 3) The S1' area is used to extract the watermark W, and the S2' area is used for DES decryption to generate S2; 4) The S1' and S2 synthesis, the decrypted image f"(x, y) with watermark is obtained through wavelet inverse transformation. The following is a detailed introduction to wavelet coefficient grouping, watermark embedding and watermark extraction:

A. Grouping of low-frequency coefficients of wavelet transform

Firstly, three-layer orthogonal wavelet decomposition is performed on the original grayscale image with a size of 256*256. Let LL ₃ be the low frequency sub-band, HL _i , LH _i , HH _i (i=1, 2, 3) be the horizontal, vertical and diagonal middle and high frequency sub-bands respectively. A random binary array A is generated from the key Key0, the size of which is the same as _LL3 . By comparing with the low-frequency coefficient LL ₃ , at the position where the element value of the A array is '1', the value of the corresponding position in LL ₃ is taken out as the S1 area; at the position where the element value of the A array is ' ₀ ', the The value of the corresponding position is taken out as the S2 area. As shown in Figure 9:

B. Watermark embedding process

The coefficient to be embedded in the S1 area is E, which is E1 after embedding; the embedded watermark is W; the quantization step is Q, and Q=20.

Figure 10 is a schematic diagram of the quantization principle:

1) According to the quantization step size Q, the coordinate axis is divided into the M interval set and the N interval set shown in the above figure.

2) The actual value of the coordinate axis represents the value of the coefficient E to be embedded. At the same time, the M interval sets on the coordinate axis all represent the binary watermark '1', and the N interval sets on the coordinate axis all represent the binary watermark '0'.

rem＝E-fix*Q3) Take the integer quotient and remainder operation of the quantized coefficient E:

rem=E-fix*Q

4) According to the interval set where the coefficient E to be quantized is located and the watermark W, quantize E: when W=1, make the quantization result E1 the intermediate coordinate value in the M interval set closest to E; when W=0 , let E1 be the intermediate coordinate value in the N interval set closest to E.

The quantization process can be expressed as follows:

(1) When fix=0 and W=1 E1=Q/2

(2) When fix=0 and W=0, E1=3Q/2

(3) When fix≠0 and W=1

$\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\left\{\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; if</span>}& \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ,</span>\\ \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; if</span>}& \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; and</span>}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; rem</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}\\ \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; if</span>}& \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; and</span>}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; rem</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}\end{array}\right.$

(4) When fix≠0 and W=0

$\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\left\{\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; if</span>}& \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\\ \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; if</span>}& \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; and</span>}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; rem</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}\\ \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; if</span>}& \mathrm{<span\; class="notranslate">\; fix</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; and</span>}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; rem</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}\end{array}\right.$

(5) Repeated watermark embedding: one bit embedded in watermark W corresponds to three consecutive bits in E, as shown in Figure 11, if the current watermark bit to be embedded is "1", the actual embedded watermark is "111"; if If the bit of the watermark to be embedded is currently "0", the actual embedded watermark is "000".

In this embodiment, a grayscale image with a size of 256*256 is taken as an example. The random binary array generated by the key Key0 is selected. The size of the area E is about 500 bits, so a 166-bit watermark can be embedded.

C. Watermark extraction process

A three-level orthogonal wavelet decomposition is performed on the encrypted and watermarked grayscale image, and LL3 is the low frequency subband. A random binary array A is still generated from the key Key0, the size of which is the same as LL ₃ '. By comparing with the low-frequency coefficient LL ₃ ', at the position where the element value of the A array is '1', take out the value of the corresponding position in LL ₃ ' as the S1'area; at the position where the element value of the A array is '0', set The value of the corresponding position in LL ₃ ' is taken out as the S2' area.

Take out the S1' area, the watermark information is determined by judging its amplitude value E1', if it belongs to the M area, then extract the binary watermark '1', if it belongs to the N area, then extract the binary watermark '0', the expression is as follows:

$\mathrm{<span\; class="notranslate">\; wxya</span>}<span\; class="notranslate">\; =</span>\left\{\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; if</span>}& <span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="m"\; filenames="A200810168853E00262.png,A200810168853E00263.png"\; state="\{\{state\}\}">m</figure-callout></span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; if</span>}& <span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; N</span>}\end{array}\right.$

Because this method also uses repeated embedding, the complete watermark can be determined through the election process, which greatly improves the probability of correctly extracting the watermark.

The test results of the experiment with two representative images of lena and cameraman are given here.

Fig. 12 shows the result of embedding watermark and encrypting the image Lena with the method of the embodiment of the present invention. Figure 15(a) is the original Lena image, and Figure 15(b) is the encrypted and watermarked Lena image. It can be seen from the figure that the encrypted image and the original image have a good visual scrambling effect, and Figure 15(c) is Decrypted and watermarked Lena image, it can be seen from the figure that there is no obvious difference between the decrypted image and the original image that still contains the watermark.

Fig. 13 shows the result of using the method of the present invention to embed watermark and encrypt the image cameraman. Figure 16(a) is the original cameraman image, and Figure 16(b) is the encrypted and watermarked cameraman image. It can be seen from the figure that the encrypted image and the original image have a good visual scrambling effect, and Figure 16(c) is Decrypted and watermarked cameraman images, it can be seen from the figure that there is no significant difference between the decrypted image and the original image that still contains the watermark.

In the embodiment of the present invention, wavelet transform is used as an example for introduction, but in fact, the present invention can also be applied to other transforms, such as DCT transform. Taking DCT transformation as an example, after the image is transformed by DCT, DC coefficients and AC coefficients are obtained respectively. Two groups, the same two groups are determined as the watermark embedding area and the encryption area, which are used for watermark embedding and encryption respectively. After embedding the watermark or encrypting the object, the processed image is obtained by inverse DCT transformation. At the receiving end, the processing method is similar to that described in the previous embodiments and will not be repeated here. At the same time, the idea of the present invention can also be used in audio and video fields.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (16)

1, a kind of image encryption method is characterized in that, comprising:

Obtain the low frequency coefficient of image;

Described low frequency coefficient is divided at least two group coefficients;

From described at least two group coefficients, choose at least one group of coefficient, the described at least one group of coefficient of choosing encrypted.

2, the method for claim 1 is characterized in that, also comprises:

From described at least two group coefficients, choose at least one group of coefficient, watermarked in the described at least one group of coefficient of choosing.

3, method as claimed in claim 1 or 2 is characterized in that, described low frequency coefficient is divided at least two group coefficients, comprising:

Produce binary number at random by key;

Described low frequency coefficient and described binary number are compared;

According to the pairing low frequency coefficient in position of described binary number " 0 " and " 1 ", described low frequency coefficient is divided into coefficient " 0 " group, coefficient " 1 " group.

4, the method for claim 1 is characterized in that, the described low frequency coefficient that obtains image comprises:

Described image is carried out wavelet transformation, the low frequency coefficient behind the acquisition wavelet transformation;

Described method also comprises:

After encryption is finished,, merge described coefficient " 0 " group, coefficient " 1 " group, the low frequency coefficient after obtaining merging according to " 0 " of described binary number and the position of " 1 ";

Low frequency coefficient after the described merging is carried out wavelet inverse transformation, the image after obtaining encrypting.

5, a kind of image decryption method is characterized in that, comprising:

Receive the image of encrypting;

Obtain the low frequency coefficient of described image;

Described low frequency coefficient is divided at least two group coefficients;

From described at least two group coefficients, choose at least one group of coefficient, the described at least one group of coefficient of choosing is decrypted.

6, method as claimed in claim 5 is characterized in that, also comprises:

From described at least two group coefficients, choose at least one group of coefficient, in the described at least one group of coefficient of choosing, extract watermark.

7, as the method for claim 5 or 6, it is characterized in that, described low frequency coefficient be divided at least two group coefficients comprise:

Produce binary number at random by key;

Described low frequency coefficient and described binary number are compared;

According to the pairing low frequency coefficient in position of described binary number " 0 " and " 1 ", described low frequency coefficient is divided into coefficient " 0 " group, coefficient " 1 " group.

8, method as claimed in claim 7 is characterized in that, the described low frequency coefficient that obtains described image comprises:

Described image is carried out wavelet transformation, the low frequency coefficient behind the acquisition wavelet transformation;

Described method also comprises:

After decryption processing is finished,, merge described coefficient " 0 " group, coefficient " 1 " group, the low frequency coefficient after obtaining merging according to " 0 " of described binary number and the position of " 1 ";

Low frequency coefficient after the described merging is carried out wavelet inverse transformation, the image after obtaining deciphering.

9, a kind of image encrypting apparatus is characterized in that, comprising:

The coefficient acquisition module is used to obtain the low frequency coefficient of image;

The coefficient grouping module is used for described low frequency coefficient is divided at least two group coefficients;

Encrypting module is used for choosing at least one group of coefficient from described at least two group coefficients, and the described at least one group of coefficient of choosing encrypted.

10, device as claimed in claim 9 is characterized in that, also comprises:

Watermarked module is used for choosing at least one group of coefficient from described at least two group coefficients, and is watermarked in the described at least one group of coefficient of choosing.

11, device as claimed in claim 9 is characterized in that, described coefficient grouping module comprises:

The binary number acquiring unit is used for producing binary number at random by key;

Comparing unit is used for described low frequency coefficient and described binary number are compared;

Grouped element is used for the pairing low frequency coefficient in position according to described binary number " 0 " and " 1 ", and described low frequency coefficient is divided into coefficient " 0 " group, coefficient " 1 " group.

12, device as claimed in claim 9 is characterized in that, described coefficient acquisition module is used for described image is carried out wavelet transformation, the low frequency coefficient behind the acquisition wavelet transformation, and described device also comprises:

Coefficient merges module, is used for according to " 0 " of described binary number and the position of " 1 " merge coefficient " 0 " group, coefficient " 1 " group, the low frequency coefficient after obtaining merging;

Inverse transform module is used for the low frequency coefficient after the described merging is carried out wavelet inverse transformation, the image after obtaining encrypting.

13, a kind of image decrypting device is characterized in that, comprising:

The image receiver module is used to receive the image of encryption;

The coefficient acquisition module is used to obtain the low frequency coefficient of described image;

The coefficient grouping module is used for described low frequency coefficient is divided at least two group coefficients;

Deciphering module is used for choosing at least one group of coefficient from described at least two group coefficients, and the described at least one group of coefficient of choosing is decrypted.

14, device as claimed in claim 13 is characterized in that, also comprises:

Extract the watermark module, be used for choosing at least one group of coefficient, in the described at least one group of coefficient of choosing, extract watermark from described at least two group coefficients.

15, device as claimed in claim 13 is characterized in that, described coefficient grouping module comprises:

The binary number acquiring unit is used for producing binary number at random by key;

Comparing unit is used for described low frequency coefficient and described binary number are compared;

Grouped element is used for the pairing low frequency coefficient in position according to described binary number " 0 " and " 1 ", and described low frequency coefficient is divided into coefficient " 0 " group, coefficient " 1 " group.

16, device as claimed in claim 13 is characterized in that, described coefficient acquisition module is used for described image is carried out wavelet transformation, the low frequency coefficient behind the acquisition wavelet transformation, and described device also comprises:

Coefficient merges module, is used for according to " 0 " of described binary number and the position of " 1 ", merges described coefficient " 0 " group, coefficient " 1 " group, the low frequency coefficient after obtaining merging;

Inverse transform module is used for described low frequency coefficient is carried out wavelet inverse transformation, the image after obtaining deciphering.

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