CN104077739A - Color image quick encryption method - Google Patents

Abstract

The invention discloses a color image fast encryption method, which is realized based on Arnold transformation. The specific steps include: performing block processing on the image according to the image size before encryption; The degree of scrambling is carried out to complete the encryption of the color image; and then the transformation in the above encryption step is inversely transformed to complete the decryption of the encrypted image. The invention improves the encryption effect, increases the encryption efficiency and expands the scope of application by improving the prior art.

Description

A Fast Encryption Method for Color Image

technical field

The invention relates to a digital signal encryption method, in particular to a color image fast encryption method.

Background technique

As a main component of multimedia data, color images must be encrypted reliably in order to ensure their security during transmission. Many current encryption algorithms are limited to binary or grayscale images. Compared with general text data, color image data has a large amount of data information and a high degree of correlation between data. The encryption process must consider not only the change of subjective visual effects but also the change of objective correlation between data. The amount of calculation is large and time-consuming; the encryption of transmitted color images requires real-time performance, so the research on encryption efficiency is particularly important.

In recent years, many articles have proposed image encryption algorithms based on chaotic systems or hyperchaotic systems, but they have improved and analyzed encryption security such as: key space, pixel correlation, etc., and usually ignore encryption. system efficiency. In fact, since the generation of the chaotic sequence itself takes a long time, even if only one scrambling is required during encryption, the total time is relatively long.

Arnold transform is a commonly used image scrambling encryption technology because of its simple encryption and no need to generate an encrypted sequence, but it has the following disadvantages:

(1) The low-dimensional Arnold scrambling transformation cannot change the gray distribution characteristics of pixels, has low security, and the encryption effect is not ideal, and the time of encryption and decryption depends on the encryption cycle, and the speed is limited by the cycle;

(2) The high-dimensional Arnold transformation can change the gray distribution characteristics of pixels, which has good security, but the iteration cycle of the high-dimensional Arnold scrambling transformation is longer, and the decryption efficiency is low;

(3) The Arnold transform has requirements on the shape of the image, and the Arnold transform operation is only applicable to the square matrix, which greatly restricts the scope of use of the encryption system.

Contents of the invention

The object of the present invention is to provide a color image fast encryption method, which improves the encryption effect, improves the encryption efficiency and expands the scope of application by improving the prior art.

In order to achieve the above-mentioned purpose of the invention, the technical solution adopted in the present invention is: a kind of color image fast encryption method, realizes based on Arnold transformation, it is characterized in that, comprises the following steps:

1) Divide the image into blocks according to the image size;

2) Use the Arnold transform to simultaneously scramble the positions and gray levels of the three primary color components of the image pixel to complete the encryption of the color image;

3) Inverse transform the transformation in step 2) to complete the decryption of the encrypted image.

In the above technical solution, in step 1), if the length and width of the image are wm and wn respectively, then , divide the image into N blocks, and the size of each block is ,in, , Indicates to take When encrypting, the smallest integer is encrypted block by block in sequence. If the length of the last block is less than wn, the adjacent image that has already been encrypted is used to make up the length wn.

In the above technical solution, in the step 2), the sampling data of the color image is set as a three-dimensional matrix W , W ( x , y,1 ), W ( x , y,2 ) and W ( x , y,3 ) represents the gray value of the three primary color components of the pixel at the coordinates ( x,y ), W' ( x , y,1 ), W' ( x , y,2 ) and W' ( x , y,3 ) represents the changed gray value, and the values of the three primary color components of the pixel at the coordinates ( x,y ) are changed and then moved to the coordinates ( x',y' ), as shown in formula (1):

(1)

In formula (1), the relationship between position ( x, y ) and ( x' , y' ) is converted according to formula (2); the relationship between gray value W and W' is converted according to formula (3):

(2)

(3).

In the above technical solution, in the step 3), when decrypting, the values of the three primary color components of the pixel at the coordinates ( x', y' ) are changed and then moved to the coordinates ( x, y ), as shown in the formula ( 4) shows that the decryption process is an inverse process of encryption and does not depend on the transformation period.

(4)

In formula (4), the positional relationship between ( x' , y' ) and ( x, y ) is inversely converted according to formula (5); the relationship between gray value W' and W is according to formula (6) Inverse conversion:

(5)

(6).

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

1. The invention adopts the block encryption method, so that the shape of the image is no longer limited to a square, thereby expanding the scope of application.

2. The present invention changes the position and gray value of image pixels at the same time, which improves the security of encryption and improves the encryption effect.

3. The invention adopts the improved inverse transformation to make the decryption process independent of the transformation period, thereby improving the decryption efficiency.

Description of drawings

Fig. 1 is the flowchart of the present invention in the first embodiment.

Fig. 2 is an effect diagram of encrypting and decrypting a square image in the second embodiment.

Fig. 3 is a comparison diagram of encryption effects in the second embodiment.

Fig. 4 is a schematic diagram of the gray distribution characteristics of the image before and after encryption in the second embodiment.

Fig. 5 is a schematic diagram of the encryption and decryption of the rectangular image in the second embodiment.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Embodiment one: referring to shown in Fig. 1, a kind of color image fast encryption method, realizes based on Arnold transformation, comprises the steps:

1) Process the image into blocks according to the image size;

2) Use the Arnold transform to simultaneously scramble the positions and gray levels of the three primary color components of the image pixel to complete the encryption of the color image;

3) Inverse transform the transformation in step (2) to complete the decryption of the encrypted image.

In this embodiment, in the step 1), if the length and width of the image are respectively wm and wn, then , divide the image into N blocks, and the size of each block is ,in, , Indicates to take When encrypting, the smallest integer is encrypted block by block in sequence. If the length of the last block is less than wn, the adjacent image that has already been encrypted is used to make up the length wn.

In the step (2), it is assumed that the sampling data of the color image is a three-dimensional matrix W , and W ( x , y,1 ), W ( x , y,2 ) and W ( x , y,3 ) represent the coordinates as The gray value of the three primary color components of the pixel at ( x, y ). W' ( x , y,1 ), W' ( x , y,2 ) and W' ( x , y,3 ) represent the changed gray value. Change the values of the three primary color components of the pixel at the coordinate ( x,y ) and move to the coordinate ( x',y' ). As shown in formula (1):

(1)

In formula (1), the relationship between position ( x, y ) and ( x' , y' ) is converted according to formula (2); the relationship between gray value W and W' is converted according to formula (3):

(2)

(3).

In the step (3), when decrypting, the values of the three primary color components of the pixel at the coordinates ( x', y' ) are changed and then moved to the coordinates ( x, y ), as shown in formula (4) , the decryption process is an inverse process of encryption and does not depend on the transformation cycle,

(4)

In formula (4), the positional relationship between ( x' , y' ) and ( x, y ) is inversely converted according to formula (5); the relationship between gray value W' and W is according to formula (6) Inverse conversion:

(5)

(6).

Embodiment 2: See Figure 2, encrypt and decrypt a 256×256 color image, where (a) and (b) are the encrypted and decrypted images respectively, and the total time required for encryption and decryption is 0.703000s , Compared with the existing technology, the efficiency can be increased by up to 80 times.

As shown in Figure 3, different methods are used to encrypt the same color image, where (a) is the original image; (b) is the encrypted image based on the two-dimensional Arnold transformation, which can only change the position of the pixel, The gray value of the pixel cannot be changed; (c) is an encrypted image based on the three-dimensional Arnold transformation, which only changes the gray value of the pixel, leaving the outline of the original image in some areas; (d) encrypted for the technical solution of the present invention The image has uniform color distribution and good intuitive effect.

Referring to FIG. 4 , it shows the gray distribution characteristics of the red component of the color image. The horizontal axis in the figure is the gray level, the transformation range is 0 to 255, and the vertical axis is the number of pixels corresponding to each gray level. Among them, (a) is the grayscale distribution of the original image; (b) is the grayscale distribution of the image encrypted by the two-dimensional Arnold transform; (c) is the grayscale distribution of the image encrypted by the three-dimensional Arnold transform; (d) is the grayscale distribution of the image in the present invention The technical solution encrypts the gray distribution of the image. It can be seen that the grayscale distribution of (b) is the same as the original image, so the grayscale distribution characteristics of the image do not change after the two-dimensional Arnold transform encryption.

As shown in Figure 5, a 414×187 rectangular color image is encrypted and decrypted, where (a) is the original image; (b) is the encrypted image; (c) is the decrypted image, the encrypted It takes 0.766000s to decrypt and decrypt. It can be seen that the image encrypted by the technical scheme of the present invention is not limited by the shape.

Claims (4)

1. a kind of color image fast encryption method, realizes based on Arnold transformation, is characterized in that, comprises the steps: 1) Divide the image into blocks according to the image size; 2) Use the Arnold transform to simultaneously scramble the positions and gray levels of the three primary color components of the image pixel to complete the encryption of the color image; 3) Inverse transform the transformation in step 2) to complete the decryption of the encrypted image. 2. A color image fast encryption method according to claim 1, characterized in that: in the step 1), if the length and width of the image are respectively wm and wn, then , divide the image into N blocks, and the size of each block is ,in, , Indicates to take The smallest integer of . 3. A color image fast encryption method according to claim 1, characterized in that: in the step 2), the sampling data of the color image is set as a three-dimensional matrix W , W ( x , y, 1 ), W ( x , y,2 ) and W ( x , y,3 ) represent the grayscale values of the three primary color components of the pixel at coordinates ( x,y ), W' ( x , y,1 ), W' ( x , y,2 ) and W' ( x , y,3 ) represent the changed gray value, after changing the values of the three primary color components of the pixel at the coordinate ( x, y ) to the coordinate ( x ',y' ), as shown in formula (1): (1) In formula (1), the relationship between position ( x, y ) and ( x' , y' ) is converted according to formula (2); the relationship between gray value W and W' is converted according to formula (3): (2) (3). 4. A color image fast encryption method according to claim 1, characterized in that: in step 3), when decrypting, the coordinates are the values of the three primary color components of the pixel at ( x', y' ) After changing, move to the coordinates ( x, y ), as shown in formula (4), (4) In formula (4), the positional relationship between ( x' , y' ) and ( x, y ) is inversely converted according to formula (5); the relationship between gray value W' and W is according to formula (6) Inverse conversion: (5) (6).