CN106157231A - A kind of based on image information encryption and the decryption method of improving Arnold conversion and LSB - Google Patents

Abstract

The invention discloses a kind of based on image information encryption and the decryption method of improving Arnold conversion and LSB, first this method uses the Arnold conversion of improvement that image carries out pretreatment, then it is embedded in background image with LSB algorithm and constructs the new images containing encrypted image.Ciphering process is broadly divided into four big steps: calculates quantity of information, input key that background image can accommodate, and uses the Arnold conversion of improvement hiding frame to carry out pretreatment, the size of the hiding frame of storage, uses LSB algorithm to be embedded in background image by hiding frame.Decrypting process is broadly divided into three big steps: extracts hiding frame size, LSB algorithm extracts and hide frame, input key and the hiding frame after extracting is carried out Arnold inverse transformation deciphering.The present invention has been greatly reinforced the confidentiality of information.

Description

An Image Information Encryption and Decryption Method Based on Improved Arnold Transform and LSB

technical field

The invention relates to the technical field of information hiding, in particular to an image information encryption and decryption method based on improved Arnold transformation and LSB.

Background technique

Steganography technique is a technology for image encryption and hiding in the field of information security research. At the same time, it is also a typical solution to the covert channel problem in the field of computer applications. It has a wide range of applications in the military field, information camouflage and other information encrypted transmission fields.

Aiming at the problem of information hiding technology, at this stage, there are mainly two solutions: space-time domain algorithm and transform domain algorithm. However, due to their own inherent shortcomings, the two methods cannot be directly used in the practical application of image information hiding. The main disadvantage of the space-time domain is that the hidden information is easy to be detected. Although the encryption technology of the transform domain is relatively good, the capacity of information hiding is small, and it is limited by the pixel distribution of the image.

Although image information hiding technology has been widely studied, there is no perfect solution so far, and the hiding schemes adopted for different application scenarios are also different. In 2007, Shao Liping and others discussed several algorithms of the improved Arnold transform for non-equal-length image encryption transformation in the article "Two-dimensional non-equal-length image scrambling transformation"; in 2012, Xia Yu et al. "A Review of Image Information Hiding Analysis Technology" discusses the development of image hiding analysis technology at the present stage, and introduces the detection methods of images embedded with hidden information. At present, the purpose of image information hiding is mainly to prevent detection and cracking; however, how to prevent detection and cracking is still an urgent problem to be solved.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art, and provide a kind of image information encryption and decryption method based on the improved Arnold transform and LSB, utilize the improved Arnold transform to transform the hidden information image that needs steganography, and then Using the LSB algorithm to embed the hidden information image into the background image to generate an encrypted image, the encrypted image and the background image cannot be distinguished from the naked eye; only the encrypted image is needed to separate the hidden information image during decryption.

The present invention adopts the following technical solutions for solving the problems of the technologies described above:

A kind of image information encryption and decryption method based on improved Arnold transform and LSB proposed according to the present invention comprises the following steps:

Step 1, load the background image, and calculate the maximum number of pixels that the background image can accommodate; if the number of pixels of the hidden information image exceeds the maximum number of pixels, the user crops the hidden information image;

Step 2, using the improved Arnold transform to preprocess the hidden information image; specifically as follows:

Step 2.1), the user inputs the values key1 and key2 of the two keys, and both key1 and key2 are positive integers;

Step 2.2), the user chooses any one of the following encryption methods to encrypt the hidden information image:

The first encryption method: the new coordinates of each hidden information image pixel are (x', y'), wherein: x'=(x+key2*y), y'=y;

The second encryption method: the new coordinates of each hidden information image pixel are (x', y'), wherein, x'=x, y'=(key2*x+y); wherein, (x, y) is the original pixel coordinate of the hidden information image to be encrypted;

Then x', y' carry out remainder operation to width A.width and height A.height of hidden information image respectively: x "=x'mod A.width; y "=y'mod A.height;

Step 2.3), move the pixel point whose original coordinates are (x, y) to the new pixel point (x″, y″);

Step 2.4), repeat step 2.2)-step 2.3) key1 times;

Step 3, storing the size of the hidden information image at the beginning of the background image;

Step 4, embedding the hidden information image preprocessed in step 2 into the background image using the LSB algorithm, thereby generating an encrypted image;

Step 5, extract hidden information image size;

Step 6, extracting the hidden information image by the LSB algorithm;

Step 7. The user enters the key and performs Arnold inverse transformation and decryption on the extracted hidden information image, thereby recovering the original data of the hidden information image.

As a further optimization scheme of the image information encryption and decryption method based on the improved Arnold transform and LSB described in the present invention, the step 3 is specifically as follows:

Step 3.1), traverse the first 4 pixels of the background image, each pixel contains 3 bytes; first split the height A.height of the hidden information image into groups of 2 bits, and directly replace the first 6 characters in the background image in order The last 2 bits of each byte in the section;

Step 3.2), split the width A.width of the hidden image A into groups of 2 bits, and directly replace the last 2 bits of each byte in the last 6 bytes in the background image in order.

As a further optimization scheme of the image information encryption and decryption method based on the improved Arnold transform and LSB described in the present invention, the step 4 is specifically as follows:

Step 4.1), skip the size storage area of the hidden information image of the first 4 pixels of the background image, and perform LSB encryption on the hidden information image; set the initial number of iterations i=1;

Step 4.2), take out the i-th byte in the hidden information image in turn, store the highest 2 bits of the byte in the last 2 bits of the first byte of the (4+i) pixel of the background image, and replace it directly Drop the last 2 bits of the first byte of the (4+i)th pixel of the background image;

Step 4.3), then take out the 6th and 5th data of the byte and put it in the last 2bit of the 2nd byte of the (4+i)th pixel of the background image;

Step 4.4), when i is less than all the bytes of the hidden information image, then i=i+1, repeat steps 4.2)-step 4.4); until all the bytes of the hidden information image are all put into the background image, like this An encrypted image is generated.

As a further optimization scheme of the image information encryption and decryption method based on the improved Arnold transform and LSB described in the present invention, the step 5 is specifically as follows:

Step 5.1), load the encrypted image to the memory;

Step 5.2), extract the first 4 pixel data of the encrypted image, wherein, according to the encryption principle, the first 2 pixels are the height data of the image, and the last 2 pixels are the width data of the image; in the first 2 pixels, each Pixels directly extract the last 2 bits of each byte in order, and then splice them together to form a 12-bit value, which is the height value A.height of the hidden information image;

Step 5.3), extract the last 2 pixel data of the first 4 pixels of the encrypted image, and in the last 2 pixels, each pixel directly extracts the last 2 bits of each byte in order, and directly stitches them in order into a 12-bit value, which is the width value A.width of the hidden information image.

As a further optimization scheme of the image information encryption and decryption method based on the improved Arnold transform and LSB described in the present invention, the step 6 is specifically as follows:

Step 6.1), skipping the first 4 pixels of the encrypted image;

Step 6.2) Starting from the fifth pixel of the encrypted image, the last 2 bits of each byte of each pixel are extracted and spliced in order to finally generate a hidden information image with an improved Arnold transform.

As a further optimization scheme of the image information encryption and decryption method based on the improved Arnold transform and LSB described in the present invention, the step 7 is specifically as follows:

Step 7.1), if it is the first encryption method, then according to the formula x1=(x″-key2*y″), y1=y″ carries out image Arnold inverse transformation decryption; if it is the second encryption method, then according to the formula x1 =x ", y1=(-key2*x "+y") carries out image Arnold inverse transform decryption;

Step 7.2), then x1, y1 respectively carry out remainder operation on width A.width and height A.height of hidden information image: x=x1 mod A.width, y=y1 mod A.height; if x<0 then x= x+A.width, if y<0 then y=y+A.height;

Step 7.3), repeat step 7.1) to step 7.2) key1 times, thus recovering the original data of the hidden information image.

Compared with the prior art, the present invention adopts the above technical scheme and has the following technical effects:

(1) Arnold transform is used in image information hiding technology;

(2) Using the LSB algorithm combined with the Arnold transform to embed the image, so that the hidden information capacity is larger, and because the image is irregularly arranged after transformation, it is difficult to detect the hidden information;

(3) The user encrypts in the form of 3 keys, which greatly enhances the confidentiality of information;

(4) The encrypted image has a certain anti-destruction ability, and the image that loses certain pixel information and hides information can still be restored;

(5) Using the improved Arnold transformation algorithm, images of non-equal length can be encrypted, while traditional Arnold can only encrypt and scramble rectangular images.

Description of drawings

Fig. 1 is a schematic diagram of encryption and decryption of the present invention.

Figure 2 is a flowchart of the encryption process of the present invention.

Fig. 3 is a flowchart of the decryption process of the present invention.

FIG. 4 is a logical diagram of LSB storage data used in the method.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

For the convenience of description, the main variables in the simple definition algorithm are: hidden information image A, background image B, and encrypted image C generated after embedding, where height represents the height of the image, width represents the width of the image, and A.width represents A The width of the image, A.height indicates the height of the A image. The same is true for B and C images. Among them, the user needs to enter two keys, key1 and key2, and the encryption position is No. 1 or No. 2;

Fig. 1 is a schematic diagram of encryption and decryption of the present invention. This method first uses the improved Arnold transform to preprocess the image, and then embeds it in the background image with the LSB algorithm to construct a new image containing the encrypted image. The encryption process is mainly divided into four steps: calculate the amount of information that the background image can hold, input the key, and use the improved Arnold transform to preprocess the hidden information image, store the size of the hidden information image, and use the LSB algorithm to convert the hidden information The image is embedded in the background image. The decryption process is mainly divided into three steps: extracting the size of the hidden information image, extracting the hidden information image by the LSB algorithm, inputting the key, and decrypting the extracted hidden information image by Arnold inverse transformation.

Fig. 2 is the flowchart of encryption process of the present invention, and encryption step is:

Step 1) Load the background image B, and estimate how much hidden information the background image B can hold:

Step 1.1) by the formula Calculate the maximum number of pixels that can accommodate hidden information images;

Step 1.2) If the number of pixels of the hidden information image A does not exceed the maximum number of pixels calculated in the previous step, perform the next step; otherwise, the user needs to crop the hidden information image A.

Step 2) Preprocess the hidden information image A using the improved Arnold transform:

Step 2.1) The user inputs the values of two keys, key1 and key2, both of which are positive integers;

Step 2.2) The user selects the encrypted position as No. 1 or No. 2; key1, key2 and the encrypted position cannot be lost by the user, and all three values need to be correct to restore the image; wherein key1 is used as the number of transformations of the Arnold transformation;

Step 2.3) The improved Arnold transformation is adopted for the hidden information image A. If the user selects the encrypted position as position No. 1, the new x-coordinate and new y-coordinate calculation formula of each image pixel is: x′=(x +key2*y), y'=y, if the user selects the encrypted position as the No. 2 position, then the new x-coordinate and new y-coordinate calculation formula of each image pixel is: x'=x, y'=(key2 *x+y), then x' and y' respectively perform remainder operations on the width A.width and height A.height of the hidden information image: x"=x'mod A.width; y"=y'mod A. height;

Step 2.4) After calculating the new coordinates (x″, y″), move the pixel point of the original (x, y) coordinate to the new pixel point (x″, y″);

Step 2.5) Repeat step 2.3) to step 2.4) key1 times according to the value of key1;

Step 3) Store the dimensions of hidden information image A at the beginning of background image B:

Step 3.1) Traversing the first 4 pixels of the background image B, because each pixel contains 3 bytes after the image is loaded into the memory, corresponding to the B channel, G channel, and R channel (blue channel, green channel, red channel). So the first 4 pixels total 12 bytes. Since modifying the last 2 bits of each byte does not affect the quality of the image, the user cannot distinguish it with the naked eye. Therefore, the last 2 bits of each byte can be used to store data. First store the width A.height of the hidden information image A into the first 2 pixels (that is, the first 6 bytes), where each byte can store 2bit data, so the total is 12bit, and the maximum can store 2 ¹² -1=4095 pixel height , the storage method is to split the height A.height of the hidden information image A into groups of 2 bits, and directly replace the last 2 bits of each byte of the first 6 bytes of the background image in order;

Step 3.2) Store the width A.width of the hidden image A into the last 2 pixels (that is, the last 6 bytes), which is the same as the first 6 bytes, and each byte has 2 bits of data, so the total is 12 bits, and the maximum storage is 2 ¹² - 1 = hidden information image of 4095 pixel height. The storage method is the same as the height A.height storage method of the hidden information image A in step 3.1);

Step 4) Embed the hidden information image A after the Arnold transformation into the background image B:

Step 4.1) Skip the hidden image A size storage area of the first 4 pixels of the background image B, and start to perform LSB encryption on the image. First, take out 1 byte (8bit) of hidden image A (denoted as t), store the highest 2bit of this tbyte in the last 2bit of the first byte of the 5th pixel of background image B, and directly replace the background The last 2 bits of the first byte of the fifth pixel of image B.

Step 4.2) Then take out the second highest 2 bits of t, that is, its 6 and 5 bits of data are placed in the last 2 bits of the 2nd byte of the 5th pixel of the background image, and so on until all the words of the hidden information image A section all into the background image. In this way, the encrypted image C is generated.

Step 5) Save the encrypted image C.

Fig. 3 is a flowchart of the decryption process of the present invention, and the decryption steps are:

Step 1) Extract hidden information image size:

Step 1.1) Load the encrypted image C to memory.

Step 1.2) Extract the first 4 pixel data of the encrypted image C, wherein, according to the encryption principle, the first 2 pixels are the height data of the image, and the last 2 pixels are the width data of the image. In the first two pixels, each pixel directly extracts the last 2 bits of each byte in order, and then stitches them together to form a 12-bit value, which is the height value A.height of the hidden information image;

Step 1.3) Extract the data of the last 2 pixels in the first 4 pixels of the encrypted image C and extract the last 2 bits of each byte in order according to the method of step 1.2) and directly splice them into a 12-bit value, which is the hidden information Image width value Awidth;

Step 2) Extract hidden information image:

Step 2.1) Skip the first 4 pixels of the encrypted image;

Step 2.2) Starting from the 5th pixel, the last 2 bits of each byte of each pixel (3 bytes) are extracted and spliced; first, the first byte of the 5th pixel extracts the last 2 bits of data to hide Bits 7 and 8 of the first byte of the first pixel of the information image A;

Step 2.3) Extract the last 2bit data of the 2nd byte of the 5th pixel to the 5th and 6th bits of the 1st byte of the 1st pixel of the hidden information image A,

Step 2.4) By analogy, after extracting the first byte of the first pixel of the hidden information image A (8bit corresponds to 1 byte), extract the second byte, or extract in order, until all hidden information images After the pixel points are extracted, the size of the hidden information image is the size extracted in step 1.2) and step 1.3); finally generate the hidden information image A with the improved Arnold transform;

Step 3) Carry out Arnold inverse transform decryption to the hidden information image A after extraction:

Step 3.1) The user inputs two keys key1, key2 and an encryption location;

Step 3.2) If it is the No. 1 position, then according to the formula x1=(x″-key2*y″), y1=y″, carry out image Arnold inverse transformation decryption, if it is the No. 2 position, then according to the formula x1=x″, y1= (-key2*x″+y″) performs image Arnold inverse transformation decryption;

Step 3.3) Then x1 and y1 respectively carry out remainder operation on the width A.width and height A.height of the hidden information image: x=x1 mod A.width; y=y1 mod A.height; if x<0 then x= x+A.width, if y<0 then y=y+A.height;

Step 3.4) Repeat step 3.2) to step 3.3) key1 times according to the numerical value of the key key1, so that the original data of the hidden information image is recovered;

Step 4) Save the hidden information image, and the restoration work is completed.

The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and can also be made without departing from the gist of the present invention within the scope of knowledge possessed by those of ordinary skill in the art. Variations.

Fig. 4 is the core idea of the LSB algorithm in the decryption process of the present invention:

It can be seen that the decryption idea of the LSB algorithm of the present invention is to take out the last 2-bit data of each byte of each pixel and replace them with the data to be embedded in binary form.

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. All should be covered within the protection scope of the present invention.

Claims (6)

1. encrypt and decryption method based on the image information improving Arnold conversion and LSB for one kind, it is characterised in that include following Step:

Step 1, loading background image, and calculate this background image open ended maximum pixel number；If hiding frame Pixel count exceedes maximum pixel number, then user carries out cutting to hiding frame；

The Arnold conversion that step 2, employing improve carries out pretreatment to hiding frame；Specific as follows:

Step 2.1), user input numerical value key1, key2 of 2 keys, key1 and key2 is positive integer；

Step 2.2), user select any one in following cipher mode that hiding frame is encrypted:

The first cipher mode: the new coordinate of each hiding frame pixel is (x ', y '), wherein: x '=(x+key2* Y), y '=y；

The second cipher mode: the new coordinate of each hiding frame pixel is (x ', y '), wherein, x '=x, y '= (key2*x+y)；Wherein, (x y) is the original pixels coordinate of hiding frame needing encryption；

Then x ', y ' carry out complementation respectively to the width A.width of hiding frame and height A.height: x "=x ' mod A.width；Y "=y ' mod A.height；

Step 2.3), by original coordinate be (x, pixel y) move new pixel (x ", y ") place；

Step 2.4), repeated execution of steps 2.2)-step 2.3) key1 time；

Step 3, the size of hiding frame is stored in the beginning of background image；

Step 4, LSB algorithm will be used to be embedded in background image through the pretreated hiding frame of step 2, thus raw Become the image after encryption；

Frame size is hidden in step 5, extraction；

Step 6, by LSB algorithm extract hide frame；

Step 7, user input key and the hiding frame after extracting are carried out Arnold inverse transformation deciphering, thus recovering Hide the initial data of frame.

A kind of image information encryption based on improvement Arnold conversion and LSB the most according to claim 1 and decryption method, It is characterized in that, described step 3 is specific as follows:

Step 3.1), traversal background image front 4 pixels, each pixel comprises 3 bytes；First by hiding frame Highly A.height every 2bit mono-assembling and dismantling divide, and the most directly replace in background image in front 6 bytes each byte End 2bit；

Step 3.2), width A.width every 2bit mono-assembling and dismantling of hidden image A are divided, the most directly replace background image In most end 2bit of each byte in rear 6 bytes.

A kind of image information encryption based on improvement Arnold conversion and LSB the most according to claim 2 and decryption method, It is characterized in that, described step 4 is specific as follows:

Step 4.1), skip the size memory block of the hiding frame of front 4 pixels of background image, to hiding frame Carry out LSB encryption；If primary iteration number of times i=1；

Step 4.2), take out the i-th byte hidden in frame successively, leave the highest 2bit of this byte in Background In the last 2bit of the 1st byte of (4+i) individual pixel of picture, directly replace (4+i) individual pixel the 1st of background image The last 2bit of byte；

Step 4.3), then take out the 6th of this byte, the data of the 5th be placed on background image (4+i) individual pixel In the last 2bit of 2 bytes；

Step 4.4), when i less than hide frame all byte quantity, then i=i+1, repeat step 4.2)-step 4.4)；Until all bytes of hiding frame being all placed in background image, thus generate image after encryption.

A kind of image information encryption based on improvement Arnold conversion and LSB the most according to claim 3 and decryption method, It is characterized in that, described step 5 is specific as follows:

Step 5.1), load encryption after image to internal memory；

Step 5.2), extract front 4 pixel datas of image after encryption, wherein, according to encryption principle, front 2 pixels are figure The altitude information of picture, rear 2 pixels are the width data of image；In front 2 pixels, each pixel extracting directly in order its In most end 2bit of each byte, be then stitched together and form the numerical value of 12bit, this numerical value is exactly the height hiding frame Number of degrees value A.height；

Step 5.3), extract rear 2 pixel datas in front 4 pixels of image after encryption, in rear 2 pixels, each picture Most end 2bit of the element the most each byte of extracting directly in order, and direct splicing becomes the numerical value of 12bit in order, this numerical value It is exactly the width numerical value A.width hiding frame.

A kind of image information encryption based on improvement Arnold conversion and LSB the most according to claim 4 and decryption method, It is characterized in that, described step 6 is specific as follows:

Step 6.1), skip front 4 pixels of image after encryption；

Step 6.2) from the beginning of the 5th pixel of the image after encryption, most end 2bit of each byte of each pixel is extracted Splice the most in order, the hiding frame after ultimately generating with improvement Arnold conversion.

A kind of image information encryption based on improvement Arnold conversion and LSB the most according to claim 4 and decryption method, It is characterized in that, described step 7 is specific as follows:

Step 7.1) if the first cipher mode, then according to formula x1=(x "-key2*y "), y1=y " carries out image Arnold inverse transformation is deciphered；If the second cipher mode, then according to formula x1=x ", y1=(-key2*x "+y ") is carried out Image Arnold inverse transformation is deciphered；

Step 7.2), then x1, y1 carry out remainder fortune to the width A.width of hiding frame and height A.height respectively Calculate: x=x1mod A.width, y=y1mod A.height；If x < 0, x=x+A.width, if y < 0, y=y+ A.height；

Step 7.3), repeated execution of steps 7.1) to step 7.2) key1 time, thus recovered the original of hiding frame Data.