TW201424364A - Methods for encoding and decoding to digital image - Google Patents

Abstract

The present invention relates to a method for encoding and decoding to a digital image. In the present invention, one image would be divided into K encoded shared images. When one obtains n encoded shared images, the image can be decoded by a random grid algorithm. In addition, a simplified function is adapted to increase the efficiency of decoding. In the embodiment, it depicts the present invention can decode a substantial lossless image as the original image. Also the efficiency is better than the conventional method.

Description

Digital image encryption and decryption method

The present invention relates to a digital image processing technique, and more particularly to a method for applying a random parameter polynomial to encrypt and decrypt a digital image.

As digital technology advances people's lives, digital products are widely used to record information. These recorded information, such as images, sounds or words, are often exchanged openly via the Internet. We can easily obtain the desired digital information through the use of the Internet. However, when copyrighted and confidential information is transmitted via the Internet, people who are interested will use certain tools to obtain illegal content. These protected information faces A considerable degree of threat. In order to effectively protect important data from interference and protect different types of security measures, video sharing technology has been developed.

Image sharing is a method of sharing a secret image into k shared images. Each shared image is placed in a different place and handed to different participants for security to ensure the security of the secret image. FIG. 1 is a schematic diagram of image sharing in the prior art. To restore a secret image, you must obtain a shared image above the threshold to identify the secret message, or obtain n shared images to completely restore the secret image information.

In 1995, Naor and Shamir [1] proposed a method based on Visual Cryptography (VC) to protect secret images. It is a technology that uses human vision to decrypt. Visual cryptography is different from traditional cryptography in the process of encoding and decoding, and does not consume too much system resources. The concept of visual cryptography proposed by Naor and Shamir is mainly to use a black and white original image R of image size h×w, which is recoded according to the corresponding code pixel using the codebook shown in Fig. 2. After the image is encoded, it is divided into k shared images (shares), and then the shared images are delivered to each participant (participants) to ensure the security of the original images. When the original image secret information is to be obtained, the shared images owned by the n participants are collected, and the superimposed images can be visually recognized to identify the secret information.

FIG. 3 illustrates a shared image and an overlapped decoded image formed by using the above-described prior art codebook. As can be seen from Fig. 3, the two coded images are magnified by 4 times, causing a problem of Pixel Expansion, and the synthesized image is recognizable, but the contrast is much reduced.

It is an object of the present invention to provide a digital image encryption and decryption method for solving Pixel Expansion and increasing the contrast of a decoded image.

The digital image encryption and decryption method of the present invention discusses a fast confidential sharing method based on the (k,n) threshold data sharing theory using a random grid, and increases the efficiency in decoding by the simplified equation. The experimental results show that the study Not only can it be close to the original image without distortion, the execution efficiency is better than the previous algorithm, and it can save system resources and play the mobile device. Maximum work efficiency.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

Certain terms are used throughout the description and following claims to refer to particular elements. Those of ordinary skill in the art should understand that a hardware manufacturer may refer to the same component by a different noun. The scope of this specification and the subsequent patent application do not use the difference of the names as the means for distinguishing the elements, but the difference in function of the elements as the criterion for distinguishing. The term "including" as used throughout the specification and subsequent claims is an open term and should be interpreted as "including but not limited to". In addition, the term "coupled" is used herein to include any direct and indirect electrical connection. Therefore, if a first device is coupled to a second device, it means that the first device can be directly electrically connected to the second device or indirectly electrically connected to the second device through other devices or connection means.

4 is a flow chart of a digital image encryption method according to an embodiment of the present invention. Referring to FIG. 4, the digital image encryption method comprises the following steps: Step S401: providing an encryption operation mathematical expression as follows: s ( x )=( M + S ₁ X + S ₂ X +..+ S _{n -1} X ^{n -1} )

Among them, S ₁ , S ₂ ... S _n-1 are randomly generated numbers, and n is a threshold value, which means that several original images can be decoded to decode the original image. In order to make it easy for a person skilled in the art to understand the technology, it is assumed that the threshold n is equal to 2 (that is, the original image can be decoded by the specific decoding method of the embodiment as long as two encrypted confidential images are obtained). , then the above expression changes as follows: S ( X ) = ( M + S ₁ X )

Step S402: Generate K groups of different random numbers Q1~QK, where K is the number of encrypted images that are desired to be generated. The assumption here is 4 (Q1~Q4).

Step S403: Substituting each pixel value of the digital image into M of the above-mentioned encryption operation mathematical expression, and substituting the different random numbers Q1 to Q4 into the X of the encryption operation mathematical expression, and obtaining the obtained result S(Q1), S (Q2), S(Q3), and S(Q4) are respectively used as pixels of the first, second, third, and fourth encrypted images, thereby generating four encrypted images.

D1=(P[i,j]+S ₁ ×Q1)

D2=(P[i,j]+S ₁ ×Q2)

D3=(P[i,j]+S ₁ ×Q3)

D4=(P[i,j]+S ₁ ×Q4)

Where P[i,j] represents the pixel of the (i,j)th coordinate, and D1~D4 represents the first First, second, third, and fourth encrypted images.

Step S404: generating a random number image K0, wherein the random number image is the same size as the digital image, and the pixel value of the random number image is randomly generated.

Step S405: Perform one logical operation of the above four encrypted images one by one with the random number image K0 to perform a logical reduction inverse operation to generate K confidential images.

R1=D1♁K0

R2=D2♁K0

R3=D3♁K0

R4=D4♁K0

The above R1 to R4 represent the first, second, third, and fourth confidential images, and ♁ denotes a mutually exclusive or arithmetic operation.

In this case, the logical operation is, for example, mutual exclusion or XOR. Mutual exclusion or XOR is characterized by reusing the mutual exclusion or retrieving the data. By the same token, anti-mutation or XNOR can also be used, and the invention is not limited thereto.

As for the above example, why should the encrypted image be re-excluded with the random image again? The reason is that the algorithm of the encrypted image may cause the recognition rate to be too high. Therefore, for the sake of insurance, the above encryption is required. The afterimage was disrupted again.

FIG. 5 is a flowchart of a digital image decryption method according to an embodiment of the present invention. Referring to FIG. 5, the digital image decryption method includes the following steps:

Step S501: Acquire n confidential images from K confidential images. Continuing with the above embodiment, K is equal to 4 and the threshold n is equal to 2.

Step S502: Perform a logical reduction inverse operation on each pixel of the random image generated by the encryption end in a one-to-one correspondence with each pixel of the n confidential images to obtain n encrypted images, where The size of the random number image is the same as the size of the above n confidential images.

D1=R1♁K0

D2=R2♁K0

D3=R3♁K0

D4=R4♁K0

Step S503: Four Q1~Q4 are taken out from the above four confidential images.

Step S504: Substituting each of the two encrypted images into S(X), and substituting the specific numbers Q1 to Q4 corresponding to the two encrypted images into X, and obtaining two simultaneous equations corresponding to each pixel. For example, if the receiving end obtains the first and third confidential images, the following equation can be solved: PD1[i,j]=M+S1×Q1

PD3[i,j]=M+S1×Q3

The M pixel P[i,j] of the original image can be obtained by solving M. Wherein, PD1[i,j] represents a pixel value of the [i,j]th coordinate of the first encrypted image D1, PD3[i,j] represents the pixel value of the [i,j]th coordinate of the third encrypted image D3.

Further, assuming that the threshold value is increased and the number of encrypted images is too large, the embodiment of the present invention can solve the decoding speed by solving the root of M by using the Largrange internal difference method. In addition, in order to make the data processing more simplified, the above mathematical formula can be modified as follows: S ( X )=( M + S ₁ X + S ₂ X ² +..+ S _{n -1} X ^{n -1} ) mod p

Among them, mod is the remainder operation. The above p must be a prime number. The present invention sets the p value to 257, and saves 255 when it is 256. In the decoding, the two solutions are separately calculated by the principle of pixel neighbor correlation, and the similar selection with the neighbor pixel is restored. Value, this is a pioneering work in image sharing.

Hereinafter, the applicant conducted the following experiment on the present invention, and the applicant used the gray scale image as an experiment.

[Experimental results]

We use a BMP format grayscale image Lena of size 512×512 as a secret image, as shown in Figure 7(a). In the image sharing phase, we use the threshold mechanism of (2, 4) to sequentially input p values of 23, 137, 191, 251 to generate shared images.

When the p value is 23, the resulting four shared images are as shown in Fig. 6. We use the secret image 601 constructed by any two shared images. It can be found from the secret image 6(f) that it is constructed when the input p value is 23. The restored image is almost completely black, and it is very difficult to recognize the graphic information in the secret image. In other words, the p-value is too small, and the probability of the solution of the simultaneous equation is too much, causing a decoding error.

When the p value is 137, the resulting four shared images are shown in Fig. 7(b)~(e), and the secret image constructed by any two shared images is shown in Fig. 7(f). It can be seen from Fig. 7(f) that although the restored image constructed by inputting the p value of 137 can visually recognize the secret image information, it can be found that the quality of the reconstructed image constructed is deteriorated.

When the p value is 191, the resulting four shared images are shown in Fig. 8(b)~(e). The secret image constructed by any two shared images is shown in Fig. 8(f). It can be seen from Fig. 8(f) that the reconstructed image constructed when the input p value is 191 is almost the same as the secret image, and only some details in the figure are slightly distorted. It can be seen that the increase in the p value has reduced the possibility of the solution of the simultaneous equation, and the decoding error is also reduced.

When the p value is 251, the resulting four shared images are shown in Fig. 9(b)~(e). The secret image constructed by any two shared images is shown in Fig. 9(f). It can be seen from Fig. 9(f) that the reconstructed image constructed when the input p value is 251 can clearly visually identify the secret information in the image, and captures the image by means of digital detection. Figure 9(a) and Fig. 9(f) For pixel comparison, we designed the codec method to construct a secret image without distortion when the p value is 251. From this experimental result, in the case of a p value of 251, the simultaneous equation can obtain a unique solution, but in some images, 257 can be solved.

Table 1 compares the performance of the embodiment of the present invention with the performance of the prior art, and performs codec by the method proposed in the prior art under the same input conditions. The total time required is 3639ms. The total codec method mentioned in this paper is 2319.09ms, and the total time is about 36.27%. The experimental results show that the amount of calculation is significantly improved.

In summary, the safety technology of Zitong is a hot topic of research. How to effectively protect confidential information has become the goal of research in various fields. In recent years, along with the growth of network technology, notebook computers, smart phones, or tablets have been widely used by the Internet as a medium to allow users to share information conveniently. However, these electronic products that are convenient for people should pay attention to the problem of information security. How to effectively protect confidential information from being intercepted or modified when intercepted, many scholars are committed to researching further protection measures in this field. This paper designs a fast sharing image mechanism using the formula s ( x )=( M + S ₁ X + S ₂ X +..+ S _{n -1} X ^{n -1} )

Export fast solutions to make decoding fast and efficient. This method also scattered the original image and scattered the confidential information, which not only preserves the security of the confidential data, but also effectively avoids interference when the data is intercepted, and saves system resources with better encoding and decoding speed. Enable mobile devices to achieve greater work efficiency.

The specific embodiments of the present invention are intended to be illustrative only and not to limit the invention to the above embodiments, without departing from the spirit of the invention and the following claims. The scope of the invention and the various changes made are within the scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

S401~S405‧‧‧ Flow steps of the digital image encryption method in the embodiment of the present invention

S401~S405‧‧‧ Flow steps of the digital image decryption method in the embodiment of the present invention

FIG. 1 is a schematic diagram of image sharing in the prior art.

2 is a schematic diagram of a prior art codebook.

FIG. 3 illustrates a shared image and an overlapped decoded image formed by using the codebook of the prior art of FIG. 2.

4 is a flow chart of a digital image encryption method according to an embodiment of the present invention.

FIG. 5 is a flowchart of a method for decrypting a digital image according to an embodiment of the present invention.

FIG. 6 is a diagram showing experimental results when the p value is 23 according to an embodiment of the present invention.

FIG. 7 is a diagram showing experimental results when the p value is 137 according to an embodiment of the present invention.

FIG. 8 is a diagram showing experimental results when the p value is 191 according to an embodiment of the present invention.

FIG. 9 is a diagram showing experimental results when the p value is 251 according to an embodiment of the present invention.

S401~S405‧‧‧ steps of the digital image encryption method of the embodiment of the present invention

Claims (9)

A digital image encryption method for dividing a digital image into K confidential images, wherein after obtaining at least n encrypted images, the digital image can be restored by a digital image decryption method, and the digital image encryption method includes Providing an encryption operation mathematical expression, wherein the encryption operation mathematical expression is as follows, S ( X )=( M + S ₁ X + S ₂ X ² +..+ S _{n -1} X ^{n -1} ) wherein, S ₁ , S ₂ ... S _n-1 are randomly generated numbers, wherein when n is equal to 2, the encryption operation mathematical expression is, S ( X )=( M + S ₁ X ), when n is equal to 3, the encryption The mathematical expression is: S ( X )=( M + S ₁ X + S ₂ X ² ); generating K sets of specific numbers Q1~QK, and substituting each pixel value of the digital image into the M of the encryption operation mathematical expression, And substituting the specific numbers Q1~QK into the X of the encryption operation mathematical expression to generate K encrypted images; generating a random number image, wherein the random number image is the same size as the digital image, and the random number image is a pixel value is randomly generated; and one of the K encrypted images and the random number image are subjected to a logical reduction inverse operation Logical operations to generate K confidential images. The digital image encryption method as claimed in claim 1, wherein the logical operation comprises: a mutually exclusive OR operation. The digital image encryption method as described in claim 2, wherein the logical reduction inverse operation comprises: a mutual exclusion or operation. For example, the digital image encryption method described in the first aspect of the patent application includes: storing the specific numbers Q1~QK into the blank fields of the K confidential images. The digital image encryption method as claimed in claim 1, wherein the encryption operation mathematical expression further comprises: S ( X )=( M + S ₁ X + S ₂ X ² +..+ S _{n -1} X ^{n -1} ) mod p, where p is a specific prime number and mod is a remainder operation, and the digital image encryption method further comprises: storing the specific number Q1~QK and the specific prime number p into the blank fields of the K confidential images respectively . A digital image decryption method for obtaining a restored digital image, the digital image decryption method comprising: obtaining n confidential images from K confidential images; and each pixel in a random image generated by the encrypted end, Each of the n confidential images is subjected to a logical reduction inverse operation in a one-to-one correspondence to obtain n encrypted images, wherein the size of the random number image is the same as the size of the n confidential images; and the n confidential images are Extracting N Q1~QNs; providing an encryption operation mathematical expression, wherein the encryption operation mathematical expression is as follows, S ( X )=( M + S ₁ X + S ₂ X ² +..+ S _{n -1} X ^{n - 1} ) Substituting each of the n encrypted images into S(X), substituting the specific numbers Q1~QN corresponding to the n encrypted images into X, obtaining N simultaneous equations corresponding to each pixel; The variable M of the equation obtains each pixel of the reduced digital image. The digital image decryption method as described in claim 6 , wherein the logical reduction inverse operation comprises: A mutually exclusive or arithmetic operation. The digital image decryption method described in claim 6 of the patent application further includes: storing Q1 to QK into blank fields of K confidential images. The digital image decryption method according to claim 6, wherein the encryption operation mathematical expression further comprises: S ( X )=( M + S ₁ X + S ₂ X ² +..+ S _{n -1} X ^{n -1} ) mod p, where p is a specific prime number and mod is a remainder operation, and the digital image decryption method further comprises: extracting N Q1~QN and the specific prime number p from the n confidential images.