WO2018076409A1

WO2018076409A1 - Method for realizing two dimensional code copy prevention and realization system thereof

Info

Publication number: WO2018076409A1
Application number: PCT/CN2016/105867
Authority: WO
Inventors: 陈昌盛; 谢宁; 黄继武
Original assignee: 深圳大学
Priority date: 2016-10-28
Filing date: 2016-11-15
Publication date: 2018-05-03
Also published as: CN106529637A; CN106529637B

Abstract

Provided are a method for realizing two dimensional code copy prevention and a realization system thereof. The method comprises: acquiring input information of a user, and converting the input information into an image gray value, and then adding a finder pattern to obtain a two dimensional code (S100); when the two-dimensional code is obtained through photographing, sequentially recovering, demodulating and decoding the image to obtain encoded information (S200); and performing spectrum analysis according to the two dimensional code after image recovering, and determining whether extreme points obtained through the spectrum analysis meet an expected distribution, and when the expected distribution is not met, prompting the two dimensional code has been copied (S300). By combining a communication channel model of the two dimensional code with physical device characteristics, the method analyzes resample spectral characteristics of the image signal, and on the basis of ensuring a robustness of a low-resolution mobile camera device reading the two dimensional code, by utilizing an aliasing feature and a strong correlation noise feature of the image signal, the method obtains a valid evidence of a scanning-printing attack of the two dimensional code.

Description

Anti-copy implementation method and implementation system of two-dimensional code

Technical field

The present invention relates to the field of information security technologies, and in particular, to a method and an implementation system for preventing copying of a two-dimensional code.

Background technique

Currently, there are special printing materials or processes that control the generation and reproduction of two-dimensional codes. The special printed material in the printing process, such as holographic materials and polymeric liquid crystal materials having unique optical characteristics, can be used to print the two-dimensional code to prevent it from being copied. Special printing inks can also be applied to the printing of two-dimensional codes. For example, ultraviolet fluorescent inks make the printed two-dimensional code invisible under visible light to prevent it from being copied. Special production processes can also be used to enhance the security of QR codes. For example, special halftone printing technology can generate two-dimensional codes hidden under visible light.

In the prior art, there are also encryption algorithms and security protocols for controlling the generation and reading of two-dimensional codes. An asymmetric key encryption algorithm (for example, RSA algorithm) and a PKI public key encryption system can be used to control the generation of the two-dimensional code and verify the authenticity of the information. Such a system with encryption protection is also applied to the construction of the anti-counterfeiting platform. The Chaotic Equation can be used to generate the QR code identity number to ensure its uniqueness and the random string cannot be copied in batches, thus effectively controlling the generation of the QR code. Similarly, the ECDSA digital signature algorithm is applied within the AuthPaper system to prevent document counterfeiters from tampering with the content. In addition to the encryption algorithm, the researchers also proposed some security protocols based on the communication architecture to enhance the security of the displayed two-dimensional code. For example, the researcher proposed a communication protocol called "all or nothing" based on the duplex communication system of the mobile device front camera device and the display screen. Only when the receiver can acquire the transmitted and received signals at the same time can the information of the two-dimensional code in the channel be decoded, thereby enhancing the confidentiality of the information.

There is also a digital watermarking technique used in the prior art to control the generation of a two-dimensional code. The digital watermarking technique can embed information related to the two-dimensional code in the two-dimensional code image. For example, directly using DCT and DFT to decompose the image frequency information of the two-dimensional code, it is possible to embed watermark information that is not easily perceptible to the naked eye. After the two-dimensional code image is taken, it can be decoded and the authenticity of the digital watermark information can be evaluated at the same time. Similarly, digital watermarking It can also be stored in the DWT domain. However, one way to ensure that the watermark information is more robust is to use the information redundancy of the two-dimensional code to modify the overall brightness of some of the modules to store the digital signature of the two-dimensional code content. Considering the robustness and capacity of the watermark information, the distortion tolerance of each module in the two-dimensional code decoding process can be utilized to modify the module's style to store the watermark information.

There are also pattern patterns or physical unclonable features with copy detection features in the prior art to control the generation and copying of two-dimensional codes. For the sake of decoding stability, the conventional two-dimensional code is composed of a large black and white block unit. However, this design is easy to copy. Some pattern patterns with more detail features can be used in the design of two-dimensional codes to resist the most direct scan-print form reproduction. A graphic composed of high-density black-and-white cells is used for copy detection, and a log-normal distribution is used as a key model of the print-scan channel during the detection process. In addition to black and white binary images, grayscale images can also be used in copy detection patterns. The decision of the copy detection may be based on a variation feature of the grayscale image in the print-scan channel, and mainly includes high frequency features of the image, such as sharpness. Compared to grayscale images, the color pattern contains information on four channels of CMYK. After copying, the characteristics of the colors (color mean, variance, entropy, etc. within the module) will make a significant difference. In addition to the above detailed pattern features, the physical unclonable function in the printed document is also used to identify illegal copying of the printed document. The Physical Unclonable Function (PUF) is a random change produced by printing equipment and paper. Its features are easy to extract and analyze but are not easily copied and forged. For example, printing random variations in toner and paper, microscopic roughness of the paper.

The above types of methods can enhance the security of the QR code to varying degrees, but it also brings some problems:

1) Reduce the advantages of QR codes in versatility. Making a two-dimensional code with a special printing material or process can strengthen the control of the generation process to resist the illegal copying of the two-dimensional code, but inevitably reduces the versatility of the two-dimensional code (adding the two-dimensional code Production costs and dependence on special equipment). Compared with similar technologies (such as RFID and smart sensors), the main advantages of QR codes are their extremely low cost and flexibility that does not depend on special hardware. Therefore, such methods based on special printed materials or processes will greatly reduce the competitiveness of two-dimensional codes for large-scale applications in the Internet of Things.

2) Increase the complexity of use. Compared with the traditional two-dimensional code, the introduction of algorithms based on encryption and digital watermarking or security protocols can control the unauthorized generation of the two-dimensional code and the illegal tampering of the data, but it increases the complexity of the system. Taking the encryption and watermarking algorithms as an example, the complexity is mainly reflected in the following two aspects: First, the generation and control of the two-dimensional code is performed by using the asymmetric encryption algorithm and the digital signature technology. In the process, a Public Key Infrastructure (PKI) needs to be deployed. The security of each user's private key must be guaranteed and the corresponding public key distributed through a secure communication channel. Secondly, in the process of using the information, the steps of decrypting or extracting the two-dimensional code are additionally added.

3) It is impossible to effectively resolve the contradiction between resisting illegal copying and universal applicability. Most importantly, even if the two-dimensional code applies a copy detection pattern and a physical unclonable function, or the above-mentioned security (encryption and digital watermark) algorithm, it is difficult to prevent the counterfeiter from copying the two-dimensional code under the system framework of the Internet of Things. Image features extracted based on physical unclonable functions relate to details in the printed output image. In order to accurately capture such features, there is a certain limit to the verification environment of the two-dimensional code, which does not meet the general applicability of the Internet of Things. For example, placing the verified document in a relatively fixed distance and lighting environment. On the other hand, since the above security algorithm only guarantees the reliability of the information in the two-dimensional code in terms of information encryption, and cannot change the visibility of the information in the two-dimensional code, it is also difficult to effectively resist illegal copying. In addition, since the copy detection pattern usually determines the authenticity of the image based on the attenuation of the high frequency information, the copying device (high-precision scanner, copying machine, etc.) used by the attacker tends to have higher resolution and high-frequency information. The reservation is more complete. Therefore, it is difficult to prevent the counterfeiter from copying it while ensuring the general type of the verification device.

It can be seen that in recent years, people have realized the problems of QR code generation and copy control, and proposed some solutions, and brought effective control to the generation control. However, the comprehensive performance of these methods in ensuring the uniqueness of the two-dimensional code, that is, resisting illegal copying, needs to be further improved.

Therefore, the prior art has yet to be improved and developed.

Summary of the invention

In view of the above-mentioned deficiencies of the prior art, an object of the present invention is to provide a method and an implementation system for preventing copying of a two-dimensional code, which aims to solve the problem of improving the security of the two-dimensional code in the prior art, and the versatility is low. Increase the complexity of use, and can not effectively solve the contradiction of resisting the contradiction between illegal copying and universal applicability.

The technical solution of the present invention is as follows:

A method for implementing copy prevention of a two-dimensional code, wherein the method comprises the following steps:

A, obtaining user input information, converting the input information into image gray value and adding the finder image to obtain a two-dimensional code;

B. When the two-dimensional code is acquired by shooting, image restoration, demodulation, and decoding are sequentially performed to obtain encoded information;

C. Perform spectrum analysis according to the two-dimensional code after image restoration, and determine whether the extreme point obtained by the spectrum analysis conforms to the expected distribution. When the expected distribution is not met, the two-dimensional code is prompted to perform the copy operation.

The anti-copy implementation method of the two-dimensional code, wherein the step A specifically includes:

A1. Acquire user input information, and convert user information into a bit stream by using source and channel coding;

A2, the bit stream is modulated, converted into image gray value, and then the image gray value is converted into a corresponding halftone dot matrix;

A3. Add a finder pattern to the two-dimensional code module composed of the halftone dot matrix to generate a two-dimensional code.

The anti-copy implementation method of the two-dimensional code, wherein the spectrum structure of the halftone dot matrix is:

Where p is the two-dimensional coordinate of the spectrum, G(p) is the spectrum of the halftone dot matrix, G _w (p) is the spectrum of the halftone dot matrix of the white point black matrix, and G _b (p) is the black dot white background The spectrum of the halftone dot matrix, C _w represents the area of the entire module occupied by the white halftone dot matrix, C _b represents the area of the entire module occupied by the black halftone dot matrix, and a ₁ and a ₂ are the image sensor pixels of the photographing device. The constructed grid vectors, b ₁ and b ₂ , are grid vectors of halftone lattices in the two-dimensional code generation process. α ₁ , α ₂ and β ₁ , β ₂ can be normalized vectors obtained by normalizing a ₁ , a ₂ and b ₁ , b ₂ .

The anti-copying implementation method of the two-dimensional code, wherein the step B specifically includes:

B1, when the two-dimensional code is read by the mobile imaging device, the two-dimensional code image is acquired, and the image is restored by the two-dimensional code image, and the shape distortion of the two-dimensional code image in the communication channel is restored, and the restored shape is obtained. QR code;

B2: extracting a two-dimensional code module according to the restored two-dimensional code, and performing demodulation corresponding to the modulation on each two-dimensional code module to obtain a bit stream;

B3. Perform bit source and channel decoding on the bit stream to obtain coded information.

The anti-copying implementation method of the two-dimensional code, wherein the step C specifically includes:

C1, extracting a two-dimensional code module according to the two-dimensional code after performing image restoration;

C2, performing spectrum analysis on the two-dimensional code module to obtain a periodic feature of the signal;

C3. Determine whether the distance between the extreme point in the spectrum analysis and the calculated extreme point meets the expected distribution. When the expected distribution is not met, the two-dimensional code is prompted to perform the copy operation.

A copy prevention implementation system for a two-dimensional code, comprising:

a two-dimensional code generating module, configured to obtain input information of the user, convert the input information into an image gray value, and increase the finder image to obtain a two-dimensional code;

a two-dimensional code decoding module, configured to perform image recovery, demodulation, and decoding in sequence when acquiring the two-dimensional code by photographing, to obtain encoded information;

The two-dimensional code verification module is configured to perform spectrum analysis according to the two-dimensional code after image restoration, and determine whether the extreme point obtained by the spectrum analysis conforms to the expected distribution, and prompts the two-dimensional code to be copied when the expected distribution is not met. operating.

The anti-copy implementation system of the two-dimensional code, wherein the two-dimensional code generation module specifically includes:

a source and channel coding unit, configured to acquire user input information, and convert user information into a bit stream by using source and channel coding;

a modulating unit configured to modulate the bit stream, convert it into an image gradation value, and convert the image gradation value into a corresponding halftone dot matrix;

An image adding unit is configured to add a finder pattern to the two-dimensional code module composed of the halftone dot matrix to generate a two-dimensional code.

The anti-copy implementation system of the two-dimensional code, wherein the spectral structure of the halftone dot matrix is:

The anti-copy implementation system of the two-dimensional code, wherein the two-dimensional code decoding module specifically includes:

An image restoration unit, configured to acquire a two-dimensional code image when the two-dimensional code is read by the mobile imaging device, and perform image restoration on the two-dimensional code image to restore shape distortion of the two-dimensional code image in the communication channel , obtaining the restored two-dimensional code;

a demodulation unit, configured to extract a two-dimensional code module according to the restored two-dimensional code, perform demodulation corresponding to the modulation on each two-dimensional code module, to obtain a bit stream;

The source and channel decoding unit is configured to perform bit source and channel decoding on the bit stream to obtain coded information.

The anti-copy implementation system of the two-dimensional code, wherein the two-dimensional code verification module specifically includes:

a module extracting unit, configured to extract a two-dimensional code module according to the two-dimensional code after performing image restoration;

a spectrum analysis unit, configured to perform spectrum analysis on the two-dimensional code module to obtain a periodic feature of the signal;

The determining unit is configured to determine whether the distance between the extreme point in the spectrum analysis and the calculated extreme point meets the expected distribution, and when the expected distribution is not met, the two-dimensional code is prompted to perform the copy operation.

The method and implementation system for preventing copying of a two-dimensional code provided by the present invention comprises: obtaining input information of a user, converting the input information into an image gray value, and adding a finder image to obtain a two-dimensional code; In the two-dimensional code, image restoration, demodulation and decoding are sequentially performed to obtain encoded information; spectrum analysis is performed according to the two-dimensional code after image restoration, and whether the extreme point obtained by the spectrum analysis conforms to the expected distribution is determined. If the expected distribution is not met, the QR code is prompted to be copied. The invention combines the communication channel model and the physical device features of the two-dimensional code in the scanning-printing process, and analyzes the spectral characteristics of the image signal in the scanning-printing operation to ensure the reading of the two-dimensional code by the low-resolution mobile imaging device. On the basis of robustness, the method of using the aliasing features of image signals and the features of strong correlation noise is proposed to obtain effective evidence for the scanning and printing attacks of two-dimensional codes.

DRAWINGS

1 is a flow chart of a preferred embodiment of a method for implementing copy prevention of a two-dimensional code according to the present invention.

2 is a two-dimensional code including a halftone dot matrix in a method for implementing copy prevention of a two-dimensional code according to the present invention; schematic diagram.

Figure 3a is a schematic diagram of a two-dimensional code after one print-shot.

Figure 3b is a schematic diagram of a two-dimensional code after one print-scan-print-shoot.

Figure 4a is a spectrogram of a two-dimensional code that has been printed-shot.

Figure 4b is a spectrogram of a two-dimensional code after one print-scan-print-shoot.

Fig. 5 is a schematic diagram showing the spectrum structure of a halftone dot matrix.

FIG. 6 is a functional block diagram of a preferred embodiment of a copy prevention implementation system for a two-dimensional code according to the present invention.

detailed description

The present invention provides a method and an implementation system for preventing copying of a two-dimensional code. In order to make the objects, technical solutions and effects of the present invention more clear and clear, the present invention will be further described in detail below. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

FIG. 1 is a flowchart of a preferred embodiment of a method for implementing copy prevention of a two-dimensional code according to the present invention, the method comprising the following steps:

Step S100: Obtain input information of the user, convert the input information into an image gray value, and increase the finder image to obtain a two-dimensional code;

Step S200: When the two-dimensional code is acquired by shooting, image restoration, demodulation, and decoding are sequentially performed to obtain encoded information.

Step S300: Perform spectrum analysis according to the two-dimensional code after the image restoration, and determine whether the extreme point obtained by the spectrum analysis conforms to the expected distribution. When the expected distribution is not met, the two-dimensional code is prompted to perform the copy operation.

In the embodiment of the present invention, the input information of the user includes a character string, a web address, etc., after the user input information is acquired, the input information is converted into an image gray value, and the image gray value is converted into a corresponding halftone point. Array, and increase the finder image to get the QR code.

Specifically, the existing two-dimensional code is composed of a black and white block (low frequency square wave) structure, and the frequency thereof is far from the sampling frequency of the scanning-printing device, and the signal aliasing phenomenon after resampling is not obvious. In order to make this feature more obvious, a halftone dot matrix similar to the sampling frequency of the scanning-printing device which is prone to significant signal aliasing can be used to form a two-dimensional code module, as shown in FIG. In FIG. 2, in the two-dimensional code, the average brightness of the halftone dot matrix in the region can be used to represent information, for example, the two-dimensional code module in FIG. 2 has 16 different gray values, each of which can carry 4 bits of information. In the example, each gray value occupies a space of 4 x 4 modules. In actual use, the gray value of each module in the two-dimensional code can be modulated according to the encoded information.

Preferably, the step S100 specifically includes:

Step S101: Acquire user input information, and convert user information into a bit stream by using source and channel coding;

In the present invention, the characters of the text message can be converted into another format defined by the character encoding library. Different languages have their own coding schemes/standards. For example, for English characters, the commonly used standard is ASCII (American Standard Code for Information Interchange). For Chinese characters, the commonly used standard is UTF-8 (Wanguo code). Other languages also have their own standards. The characters of a text message can be converted to any other format defined by the character encoding library. With a character encoding library, a single character within a text message can be encoded into a binary data codeword having a particular number of bits (eg, 8 bits). After the text message is encoded, the header can be placed at the front end of the encoded message. Here, the header may indicate the length of the character in the message and the encoding scheme employed in the decoding process (described later) of the image two-dimensional code.

In addition, it is foreseeable that errors may be introduced during the transmission of the two-dimensional code (for example due to environmental or channel reasons), which will corrupt the data and may eventually result in failure of the decoding of the message 30. Therefore, in the present embodiment, the channel coding algorithm in the source and channel coding modules may use an error correction code to protect the data. Any error correction code that can detect and correct the error can be used.

As an example, the error correction code of the present embodiment may employ a Reed-Solomon code. Error correcting codes can detect and correct multiple character anomalies, including erasures and errors. Among them, erasure refers to an error symbol at a known location. An error is an error symbol at an unknown location.

Step S102, modulating the bit stream, converting it into an image gray value, and converting the image gray value into a corresponding halftone dot matrix;

As an example, the modulation algorithm in this embodiment may be a group of 3 bits. The bit groups can be mapped to different gray values depending on the value of the bit group. For example, the bit groups 000, 001, 010, 011, 100, 101, 110, 111 can be mapped to image gray values 30, 60, 90, 120, 150, 180, 210, 240, respectively.

In addition, the halftone dot matrix conversion method in the present embodiment may be based on the difference in the gray value of each image region. According to the principle of keeping the average gray value in the image region unchanged, it is converted into a circular lattice with different sizes and densities. This halftone dot matrix conversion algorithm is identical to the corresponding algorithm built into the printer.

Step S103: adding a finder pattern to the two-dimensional code module composed of the halftone dot matrix to generate a two-dimensional code.

The imaginary pattern may be any pattern that helps locate the two-dimensional code position and measure its size during the two-dimensional code detection process as long as it has a mark on the boundary of the two-dimensional code. In the present embodiment, the imaginary pattern is a rectangular frame (for example, a square) composed of a solid line portion and a broken line (dotted line) portion. In the reading of the image two-dimensional code described later, the positioning mark can be used to distinguish the two-dimensional code from the background. In the positioning identifier, the dotted line portion can be used to locate the coordinates of the block in the two-dimensional code and determine the physical size of the two-dimensional code.

Specifically, the spectrum structure of the halftone dot matrix is:

Taking α ₁ and α ₂ as examples, the normalized vector is defined as follows:

Where ||| is the norm of the vector. In addition, k ₁ , k ₂ and l ₁ , l ₂ represent the length of the vector, δ(·) is the impact function, SPOT(·) is the two-dimensional sampling function of the imaging device, and APER(·) is the spectrum of the fuzzy function of the imaging device. , HDOT (·) is the spectrum of the halftone point function.

The anti-copying implementation method of the two-dimensional code, wherein the step S200 specifically includes:

Step S201: When the two-dimensional code is read by the mobile imaging device, the two-dimensional code image is acquired, and the image is restored by the two-dimensional code image, and the shape distortion of the two-dimensional code image in the communication channel is restored, and the image is restored. After the two-dimensional code;

As an example, in the present embodiment, the two-dimensional code is first binarized, and the two-dimensional code is separated from the bright background by a dark area detection algorithm based on the difference in brightness between the background and the two-dimensional code. Specifically, it is only necessary to detect the four corner points in the finder pattern of the two-dimensional code to separate it from the background.

Due to the distortion of the two-dimensional code image during shooting, the shape of the acquired two-dimensional code image region may be an arbitrary quadrilateral. Since the original two-dimensional code image is square, it can be reduced to a square to eliminate shape distortion.

Step S202, extracting a two-dimensional code module according to the restored two-dimensional code, performing demodulation corresponding to the modulation on each two-dimensional code module, to obtain a bit stream;

As an example, the module of the two-dimensional code can be extracted according to the dashed point in the imaginary pattern. Specifically, the black and white pixel conversion point in the dotted line portion of the imaginary pattern edge may be used as a reference point. In addition, since the solid line portion of the imaginary pattern is as long as 7 modules. Therefore, the solid line portion of the finder pattern can be divided into seven equal parts to obtain corresponding reference points. The upper and lower reference points are connected in a straight line, and the left and right reference points are also connected. In this way, the middle area of the two-dimensional code is divided into a single module by a straight line.

As an example, the demodulation algorithm in this embodiment maps it to a corresponding set of bits according to different image gray values. For example, image gray values 30, 60, 90, 120, 150, 180, 210, 240 may be mapped to bit groups 000, 001, 010, 011, 100, 101, 110, 111, respectively. In the actual situation, the gray value of the image needs to be classified according to its distance from the preset gray value, that is, 30, 60, 90, 120, 150, 180, 210, 240, and the gray scale after classification. The value will be set to 30, 60, 90, 120, 150, 180, 210, 240.

Step S203: Perform bit source and channel decoding on the bit stream to obtain coded information.

Preferably, the step S300 specifically includes:

Step S301: Extract a two-dimensional code module according to the two-dimensional code after performing image restoration;

Step S302, performing spectrum analysis on the two-dimensional code module to obtain a periodic feature of the signal;

As an example, the method of spectrum analysis may be a two-dimensional Fourier transform, a two-dimensional discrete cosine transform (DCT), a two-dimensional discrete wavelet transform (DWT), and the like. The input of the spectrum analysis is a QR code image. Module, the output is the two-dimensional spectrum of the image signal.

Step S303, determining whether the distance between the extreme point in the spectrum analysis and the calculated extreme point meets the expected distribution, and when the expected distribution is not met, prompting the two-dimensional code to perform the copy operation.

As an example, the measure of distance can be a European distance. By comparing the distance between the extreme point in the spectrum analysis and the calculated extreme point, and comparing with the preset threshold, it can be known whether the two-dimensional code image has undergone the copying operation. Among them, the threshold can be obtained by analyzing the original of a large number of two-dimensional codes and copying samples.

The signal aliasing feature vector model is one of the key theoretical foundations of this two-dimensional code copy prevention. This model is built to help analyze signal aliasing and identify two-dimensional code images containing multiple sets of aliased signals that are subject to scan-print attacks. Using the Fourier transform (or other frequency domain transform) to analyze the obtained spectrum, the two-dimensional code subjected to the scan-print attack can be effectively identified. As shown in Figures 3a, 3b, 4a, 4b and 5, the coordinates of the four extreme points {P ₁ , P ₂ , P ₃ , P ₄ } near the origin of the spectrum can be determined by the parameters of the physical device (print resolution, The halftone dot matrix density, the pixel size of the image sensor) is calculated. By observing whether the number and position of extreme points in the image region surrounded by the four extreme points conform to the expected distribution, it can be distinguished whether the two-dimensional code has undergone a copy operation.

It can be seen that in the present invention, the two-dimensional code is directly designed in the form of a halftone dot matrix, instead of the brightness conversion to the halftone dot matrix by the printer during the two-dimensional code printing process, so that a more stable detection effect can be achieved.

Further, based on the halftone dot matrix and its signal resampling (periodic) characteristics displayed during the print-scan-print-shooting process, the two-dimensional code subjected to the above operation is identified.

Based on the foregoing method embodiments, the present invention also provides a copy prevention implementation system for a two-dimensional code. As shown in FIG. 6, the anti-copy implementation system of the two-dimensional code includes:

The two-dimensional code generating module 100 is configured to acquire input information of the user, convert the input information into an image gray value, and increase the finder image to obtain a two-dimensional code;

The two-dimensional code decoding module 200 is configured to perform image recovery, demodulation, and decoding in sequence when the two-dimensional code is acquired by photographing, to obtain encoded information;

The two-dimensional code verification module 300 is configured to perform spectrum analysis according to the two-dimensional code after performing image restoration, and determine whether the extreme point obtained by the spectrum analysis conforms to the expected distribution, and prompts the two-dimensional code to be performed when the expected distribution is not met. Copy operation.

Preferably, in the anti-copy implementation system of the two-dimensional code, the two-dimensional code generation module 100 specifically includes:

Preferably, in the anti-copy implementation system of the two-dimensional code, the spectrum structure of the halftone dot matrix is:

Preferably, in the anti-copy implementation system of the two-dimensional code, the two-dimensional code decoding module 200 specifically includes:

Preferably, in the anti-copy implementation system of the two-dimensional code, the two-dimensional code verification module 300 is specific include:

In summary, the method and implementation system for preventing copying of a two-dimensional code provided by the present invention includes: obtaining input information of a user, converting the input information into an image gray value, and adding a finder image to obtain a two-dimensional code When the two-dimensional code is acquired by shooting, image restoration, demodulation, and decoding are sequentially performed to obtain encoded information; spectrum analysis is performed according to the two-dimensional code after image restoration, and whether the extreme point obtained by the spectrum analysis is determined is It conforms to the expected distribution, and when it does not meet the expected distribution, it prompts the QR code to be copied. The invention combines the communication channel model and the physical device features of the two-dimensional code in the scanning-printing process, and analyzes the spectral characteristics of the image signal in the scanning-printing operation to ensure the reading of the two-dimensional code by the low-resolution mobile imaging device. On the basis of robustness, the method of using the aliasing features of image signals and the features of strong correlation noise is proposed to obtain effective evidence for the scanning and printing attacks of two-dimensional codes.

It is to be understood that the application of the present invention is not limited to the above-described examples, and those skilled in the art can make modifications and changes in accordance with the above description, all of which are within the scope of the appended claims.

Claims

A method for implementing copy prevention of a two-dimensional code, characterized in that the method comprises the following steps:

A, obtaining user input information, converting the input information into image gray value and adding the finder image to obtain a two-dimensional code;

B. When the two-dimensional code is acquired by shooting, image restoration, demodulation, and decoding are sequentially performed to obtain encoded information;

C. Perform spectrum analysis according to the two-dimensional code after image restoration, and determine whether the extreme point obtained by the spectrum analysis conforms to the expected distribution. When the expected distribution is not met, the two-dimensional code is prompted to perform the copy operation.
The anti-copying implementation method of the two-dimensional code according to claim 1, wherein the step A specifically includes:

A1. Acquire user input information, and convert user information into a bit stream by using source and channel coding;

A2, the bit stream is modulated, converted into image gray value, and then the image gray value is converted into a corresponding halftone dot matrix;

A3. Add a finder pattern to the two-dimensional code module composed of the halftone dot matrix to generate a two-dimensional code.
The anti-copy implementation method of the two-dimensional code according to claim 2, wherein the spectral structure of the halftone dot matrix is:

Where p is the two-dimensional coordinate of the spectrum, G(p) is the spectrum of the halftone dot matrix, G w (p) is the spectrum of the halftone dot matrix of the white point black matrix, and G b (p) is the black dot white background The spectrum of the halftone dot matrix, C w represents the area of the entire module occupied by the white halftone dot matrix, C b represents the area of the entire module occupied by the black halftone dot matrix, and a 1 and a 2 are the image sensor pixels of the photographing device. The constructed grid vector, b 1 and b 2 are the grid vectors formed by the halftone lattice in the process of generating the two-dimensional code, and α 1 , α 2 and β 1 , β 2 can be a 1 and a 2 The normalized vector obtained after b 1 and b 2 are normalized.
The anti-copying implementation method of the two-dimensional code according to claim 3, wherein the step B specifically includes:

B1, when the two-dimensional code is read by the mobile imaging device, the two-dimensional code image is acquired, and the image is restored by the two-dimensional code image, and the shape distortion of the two-dimensional code image in the communication channel is restored, and the restored shape is obtained. QR code;

B2: extracting a two-dimensional code module according to the restored two-dimensional code, and performing demodulation corresponding to the modulation on each two-dimensional code module to obtain a bit stream;

B3. Perform bit source and channel decoding on the bit stream to obtain coded information.
The anti-copying implementation method of the two-dimensional code according to claim 4, wherein the step C specifically includes:

C1, extracting a two-dimensional code module according to the two-dimensional code after performing image restoration;

C2, performing spectrum analysis on the two-dimensional code module to obtain a periodic feature of the signal;

C3. Determine whether the distance between the extreme point in the spectrum analysis and the calculated extreme point meets the expected distribution. When the expected distribution is not met, the two-dimensional code is prompted to perform the copy operation.
A anti-copy implementation system for a two-dimensional code, comprising:

a two-dimensional code generating module, configured to obtain input information of the user, convert the input information into an image gray value, and increase the finder image to obtain a two-dimensional code;

a two-dimensional code decoding module, configured to perform image recovery, demodulation, and decoding in sequence when acquiring the two-dimensional code by photographing, to obtain encoded information;

The two-dimensional code verification module is configured to perform spectrum analysis according to the two-dimensional code after image restoration, and determine whether the extreme point obtained by the spectrum analysis conforms to the expected distribution, and prompts the two-dimensional code to be copied when the expected distribution is not met. operating.
The anti-copy implementation system of the two-dimensional code according to claim 6, wherein the two-dimensional code generating module specifically includes:

a source and channel coding unit, configured to acquire user input information, and convert user information into a bit stream by using source and channel coding;

a modulating unit configured to modulate the bit stream, convert it into an image gradation value, and convert the image gradation value into a corresponding halftone dot matrix;

An image adding unit for adding a finder pattern to a two-dimensional code module composed of a halftone dot matrix to generate QR code.
The anti-copy implementation system for a two-dimensional code according to claim 7, wherein the spectral structure of the halftone dot matrix is:

Where p is the two-dimensional coordinate of the spectrum, G(p) is the spectrum of the halftone dot matrix, G w (p) is the spectrum of the halftone dot matrix of the white point black matrix, and G b (p) is the black dot white background The spectrum of the halftone dot matrix, C w represents the area of the entire module occupied by the white halftone dot matrix, C b represents the area of the entire module occupied by the black halftone dot matrix, and a 1 and a 2 are the image sensor pixels of the photographing device. The constructed grid vector, b 1 and b 2 are the grid vectors formed by the halftone lattice in the process of generating the two-dimensional code, and α 1 , α 2 and β 1 , β 2 can be a 1 and a 2 The normalized vector obtained after b 1 and b 2 are normalized.
The anti-copy implementation system of the two-dimensional code according to claim 8, wherein the two-dimensional code decoding module specifically includes:

An image restoration unit, configured to acquire a two-dimensional code image when the two-dimensional code is read by the mobile imaging device, and perform image restoration on the two-dimensional code image to restore shape distortion of the two-dimensional code image in the communication channel , color / brightness distortion, get the restored two-dimensional code;

a demodulation unit, configured to perform demodulation corresponding to the modulation of the restored two-dimensional code to obtain a bit stream;

The source and channel decoding unit is configured to perform bit source and channel decoding on the bit stream to obtain coded information.
The anti-copy implementation system of the two-dimensional code according to claim 9, wherein the two-dimensional code verification module specifically includes:

a module extracting unit, configured to extract a two-dimensional code module according to the two-dimensional code after performing image restoration;

a spectrum analysis unit, configured to perform spectrum analysis on the two-dimensional code module to obtain a periodic feature of the signal;

The determining unit is configured to determine whether the distance between the extreme point in the spectrum analysis and the calculated extreme point meets the expected distribution, and when the expected distribution is not met, the two-dimensional code is prompted to perform the copy operation.