KR100697952B1 - Security processed image extraction method of mobile communication terminal and mobile communication terminal for same - Google Patents

Abstract

The present invention relates to a method for extracting a secured image of a mobile communication terminal and a mobile communication terminal for the same, and in particular, to receive encrypted image data and to store key image data stored in advance according to independent component analysis (ICA). The present invention relates to a method of separating and extracting the transferred image data from encrypted image data and a mobile communication terminal therefor.

To this end, the present invention is an image data receiving step of determining whether the image data is decodable by independent component analysis (ICA), if any encrypted image data is received; A key image data loading step of reading preset key image data when the determination result is data decodable by the independent factor analysis; A transfer image data separation step of separating and extracting the transfer image data to be delivered from the received image data and the concealed image data to conceal the corresponding transfer image data according to the independent factor analysis using the key image data. Provided is a method for extracting a secure processed image of a mobile communication terminal.

Mobile terminal, security, independent factor analysis

Description

Secured image extraction method of mobile communication terminal and mobile communication terminal for same {method for extracting secure image by mobile phone and mobile phone etc}

1 is a conceptual diagram of an image data service system according to an embodiment of the present invention.

2 is a block diagram of an image data service server according to an embodiment of the present invention.

3 is a block diagram of a first mobile communication terminal according to an embodiment of the present invention.

4 is a flowchart illustrating a method for processing delivery data security of an image data service server according to an exemplary embodiment of the present invention.

5 is a flowchart illustrating a method for extracting a security processed image of a mobile communication terminal according to an embodiment of the present invention.

6 is a flowchart illustrating a method of separating and extracting transmission image data according to fast fixed point independent factor analysis according to an embodiment of the present invention.

7A to 7D are exemplary views of an image processed by an image data service server according to an embodiment of the present invention.

8A and 8B are exemplary diagrams of images mixed in an image data service server according to an embodiment of the present invention.

9A to 9D are exemplary views of an image separated and extracted by a mobile communication terminal according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: image data service server 120: communication unit

140: storage unit 160: central processing unit

162: control unit 164: image data mixing unit

166: image data compression unit 200: Internet network

300: IWF (inter-working function) 400: mobile communication network

500: first mobile communication terminal 510: input unit

520: display unit 530: wireless communication unit

540: storage unit 550: control unit

552: mobile communication processing unit 554: image data determination unit

556: Image data load unit 558: Image data separator

600: second mobile communication terminal

The present invention relates to a method for extracting a secured image of a mobile communication terminal and a mobile communication terminal therefor, in particular, receiving image data encrypted by mixing delivery image data and concealed image data by a linear mixing method, and analyzing independent factors. and a method for extracting a secure processed image of a mobile communication terminal for extracting and extracting the transmitted image data from encrypted image data using prestored key image data according to independent component analysis (ICA).

Due to the development of mobile communication terminal and related mobile communication network and internet network technology, video data service using mobile communication terminal is increasing rapidly in quality and quantity. In particular, mobile video data services that transmit celebrity photobook files to mobile communication terminals for a fee have recently increased, but there are not many security technologies to prevent the video data from being exposed to unauthorized third parties. to be.

In particular, the security technologies applied to existing mobile communication terminals can be hacked, and when a video data is transmitted by wireless communication, a third party can easily wirelessly communicate with a third party because of the characteristics of a wireless communication that transmits a video data signal through the air. There is a problem in that image data can be taken by sniffing a signal.

An object of the present invention is to solve the above problems, it is possible to send and receive the secured video data through the mobile communication terminal so that mathematically impossible to release without key image data without worrying about hacking in the mobile communication terminal To transmit image data.

Another object of the present invention is to use a differential pulse code modulation method and independent factor analysis together to separate and extract the delivered video data from the receiving mobile communication terminal even if the transmitted video is quantized and compressed after being transmitted to the 8-bit level. It can also be repaired correctly.

Still another object of the present invention is to prevent exposure of image data to unauthorized third parties in transmitting and receiving image data to or from a mobile communication terminal, thereby preventing information leakage and providing mobile image data service. It is also about enabling the industry to be activated.

According to an aspect of the present invention for achieving the above object, when any encrypted image data is received, the image data to determine whether the image data is decodable by independent component analysis (ICA) Receiving step; A key image data loading step of reading preset key image data when the determination result is data decodable by the independent factor analysis; And a transfer image data separation step of separating and extracting the transfer image data to be delivered from the received image data and the concealed image data to conceal the corresponding transfer image data according to the independent factor analysis using the key image data. It is characterized in that the secured image extraction method of the mobile communication terminal.

Preferably, the independent factor analysis is independent factor analysis by a fast fixed-point algorithm.

More preferably, after the image data receiving step, the image data decoding step of decoding the received image data according to the image compression method; further includes.

More preferably, the image compression method is differential pulse code modulation (DPCM).

More preferably, the key image data is the concealed image data.

More preferably, the key image data is image data mixed by linear matrix operation different from the received image data.

According to another aspect of the present invention for achieving the above object, a storage unit for embedding the key image data for decrypting any encrypted image data; When any encrypted image data is received, the key image data is read, and the image data to be delivered from the received image data and the corresponding transmission image data are concealed according to an independent factor analysis using the key image data. And a control unit for separating and extracting concealed image data.

Preferably, the independent factor analysis is independent factor analysis by a fast fixed-point algorithm.

More preferably, the video data is video data encoded by an arbitrary video compression method.

More preferably, the image compression method is differential pulse code modulation.

More preferably, the key image data is the concealed image data.

More preferably, the key image data is image data mixed by linear matrix operation different from the image data.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a conceptual diagram of an image data service system according to an embodiment of the present invention.

Referring to FIG. 1, an image data service system according to an exemplary embodiment of the present invention includes an image data service server 100, an internet network 200, an inter-working function 300, and a mobile communication network 400. ), A first mobile communication terminal 500, and a second mobile communication terminal 600.

The image data service server 100 encrypts and transmits the prestored transmission image data according to a request of the first mobile communication terminal 500 or the second mobile communication terminal 600 by a linear mixing method and a differential pulse code modulation method ( After encoding by differential pulse code modulation (DPCM), the encrypted and encoded image data is transmitted to the first mobile communication terminal 500 or the second mobile communication terminal 600 through the Internet network 200.

The Internet network 200 is a network that transmits data using a TCP / IP protocol and transmits the image data service server 100 to the mobile communication network 400 through the IWF 300. The first mobile communication terminal 500 and the second mobile communication terminal 600 are connected to each other.

The IWF 300 serves to connect the mobile communication network 400 and the Internet network 200 to access the Internet through the mobile communication terminals 500 and 600.

The mobile communication network 400 may not only provide a mobile communication service between the first and second mobile communication terminals 500 and 600 and other mobile communication terminals (not shown), but also the first and second mobile communication terminals. (500, 600) serves to receive the Internet service through the IWF (300).

The first mobile communication terminal 500 transmits a delivery image data transmission request message to the image data service server 100, and the image is encrypted by mixing the hidden image data and the concealed image data to conceal the corresponding delivery image data. Then, the image data encoded by the differential pulse code modulation method is received. Thereafter, the transmitted image data are separated and extracted from the received image data according to independent factor analysis using prestored key image data.

The second mobile communication terminal 600 transmits a transfer video data transmission request message to the video data service server 100 like the first mobile communication terminal, and receives the encrypted and encoded video data. However, since the key image data is not included, the transmission image data cannot be separated and extracted according to independent factor analysis.

2 is a block diagram of an image data service server according to an embodiment of the present invention.

Referring to FIG. 2, the image data service server 100 according to an exemplary embodiment of the present invention includes a communication unit 120, a storage unit 140, and a central processing unit 160.

The communication unit 120 is controlled by the central processing unit 160, receives a transmission image data transmission request message, and the hidden image data for concealing the transmission image data and the transmission image data is mixed and encrypted. Transmit and receive data signals for transmitting video data encoded by differential pulse code modulation.

The storage unit 140 stores an operation program and a system program necessary for controlling the central processing unit 160, and particularly, the concealed image data for concealing the delivered image data, the delivered image data, and the delivered image data. And a program for mixing and encrypting the concealed image data.

The central processing unit 160 includes a control unit 162, an image data mixing unit 164, and an image data compression unit 166.

The controller 162 controls the overall operation of the image data service server 100.

The image data mixer 164 serves to generate encrypted image data by mixing the delivered image data and the concealed image data to conceal the corresponding delivered image data.

The concealed image data may have a high energy to effectively conceal the transmitted image data, and may use mosaic image data.

The method of mixing the image data should be a linear mixing method, and preferably, a method of multiplying and mixing the image data by a randomly generated matrix. When the image data are mixed by a randomly generated matrix, since the combination for generating the mixed image is mathematically infinite, it is impossible to extract the transfer image data from the mixed image data without separate key image data.

The image data compressor 166 receives the encrypted image data from the image data mixer 164 and outputs compressed image data encoded by differential pulse code modulation (DPCM). Do this.

The image signal input during differential pulse code modulation is quantized at a preset quantization level. The quantization level is an important factor that determines the degree of compression of the input image signal. The lower the quantization level, the higher the compression rate, but the higher the compression ratio, but the higher the quantization error of the compressed image data. There is a problem that cannot be done.

On the contrary, the higher the quantization level, the lower the quantization error of the compressed image data, so that the correct image can be recovered at the time of decoding. However, the compressed image data has a problem that the size of the compressed image data increases. In the case of the present invention, even when the compressed image data encoded by differential pulse code modulation (DPCM) is transmitted at an eight-level quantization level (3 bits / sample), the correlation is about 0.9 or more at the receiving end. The transmitted image data having coefficients can be separated and extracted by independent factor analysis.

The image data service server 100 may achieve the object of the present invention even if the encrypted image data is transmitted as it is without encoding the encrypted image data by differential pulse code modulation. However, when encoding the image data by the differential pulse coding method, there is an advantage in that the image data can be compressed and transmitted at a high rate. In particular, when used in conjunction with the independent factor analysis, the transmission image data received almost the same as the original transmission image data even if the image data is transmitted at a high rate compared to when using other compression coding methods together with the independent factor analysis. There is an advantage that can be recovered from the side. Since the differential pulse code modulation scheme is a well-known technology, detailed description thereof will be omitted in describing the present invention.

3 is a block diagram of a first mobile communication terminal according to an embodiment of the present invention.

Referring to FIG. 3, the first mobile communication terminal 500 according to an embodiment of the present invention includes an input unit 510, a display unit 520, a wireless communication unit 530, a storage unit 540, and a controller ( 550).

The input unit 510 includes a text key, a numeric key, and various function keys, and generates a key input signal corresponding to a key input by a user and transmits the generated key input signal to the controller 550. In particular, the user receives a key for the delivery image data to be received from the image data service server 100 and transmits a transmission image data transmission request message signal corresponding thereto to the controller 550.

The display unit 520 is a display device such as a liquid crystal display (LCD). The display unit 520 is controlled by the controller 550 to display the state of the mobile communication terminal 500 or the progress of the program. In particular, the transfer image data is displayed under the control of the controller 550.

The wireless communication unit 530 is controlled by the control unit 550, and transmits and receives a voice signal for a telephone call with a counterpart caller, and in particular, includes a differential image data including the transmission image data request message and the transmission image data. Transmits and receives a data signal for transmitting and receiving video data encoded by a pulse code modulation method.

The storage unit 540 stores an operation program and a system program necessary for the control of the controller 550, and in particular, performs separation of the transmission image data according to transmission, reception and decoding of the image data, and independent factor analysis. Various device drivers and programs and key image data are stored.

The control unit 550 controls the overall operation of the first mobile communication terminal 500, the mobile communication processing unit 552, image data determination unit 554, image data loading unit 556, and image data separation unit 558.

The mobile communication processing unit 552 is configured to operate using a known mobile communication technology as a module for performing a mobile communication service using a radio resource in a mobile communication terminal, and thus detailed description thereof will be omitted.

When any encrypted image data is received, the image data determination unit 554 determines whether the image data is decodable by independent component analysis (ICA).

The image data load unit 556 reads the predetermined key image data from the storage unit 540 and transmits the key image data to the image data separator 558 when the determination result is data that can be decoded by the independent factor analysis.

The image data separator 558 decodes the received image data according to a differential pulse code modulation scheme. In addition, the key image data is received and extracted from the decoded image data according to the independent factor analysis using the key image data to separate and extract the concealed image data for concealing the transferred image data. A method of separating and extracting the transmission image data according to the independent factor analysis will be described in detail below.

4 is a flowchart illustrating a method for processing delivery data security of an image data service server according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the central processing unit 160 of the image data service server 100 receives a transfer image data transmission request message from the first mobile communication terminal 500 (S100).

Thereafter, the central processor 160 reads the delivered image data and the concealed image data from the storage 140 (S120). The delivered image data is image data that a user of the mobile communication terminal 500 wants to receive. The concealed image data may be image data having higher energy than the delivered image data to conceal the transferred image data, and may be mosaic image data.

Thereafter, the central processing unit 160 generates encrypted image data by mixing the transferred image data and the concealed image data by matrix operation (S140).

v = As

Here, v denotes an encrypted image data matrix, A denotes a mixing matrix, and s denotes a matrix consisting of transmission image data and hidden image data. For details on Equation 1, see A. Hyvarinen and E. Oja, "A Fast Fixed-Point Algorithm for Independent Component Analysis," Neural Computation, 9, pp. 1483-1492, 1997.

FIG. 7A shows the transferred image data, FIG. 7B shows the concealed image data, and FIG. 7C shows the encrypted image data.

Thereafter, the central processing unit 160 encodes the encrypted image data by differential pulse code modulation to generate compressed compressed image data (S160). The encrypted video signal input during differential pulse code modulation is quantized to a preset quantization level. The quantization level may be, for example, 8 levels (3 bits / sample), 16 levels (4 bits / sample), 32 levels (5 bits / sample), or 64 levels (6 bits / sample), and 8 levels. Even in the case of encoding by the receiver, the receiver may separate and extract the image data faithful to the transmitted image data according to the independent factor analysis.

FIG. 7D illustrates compressed image data in which the encrypted image data shown in FIG. 7C is encoded and compressed according to the differential pulse code modulation scheme.

Thereafter, the central processing unit 160 transmits the compressed image data to the mobile communication terminal 500 through the communication unit 120 (S180).

5 is a security image extraction method of a mobile communication terminal according to an embodiment of the present invention.

Referring to FIG. 5, the controller 550 of the first mobile communication terminal 500 receives arbitrary encrypted image data from the image data service server 100 through the mobile communication network 400 (S200). 7D illustrates compressed image data received from the image data service server 100.

The controller 550 determines whether the received image data is decodable data by independent factor analysis (S220).

If the corresponding image data is data that can be decoded by independent factor analysis, the controller 550 decodes the encoded image data according to a differential pulse code modulation scheme to restore the image data received by matrix operation. (S240). FIG. 8A illustrates encrypted image data obtained by decrypting the image data of FIG. 7D according to a differential pulse code modulation scheme.

On the other hand, when the determination result of the S220, the image data is data that can not be decoded by independent factor analysis, the procedure is terminated.

The control unit 550 extracts the transfer image data from the encrypted image data according to independent factor analysis using the key image data stored in the storage unit 540 (S260), and ends the procedure. 8B shows key image data, and FIGS. 9A to 9D show transfer image data separated and extracted.

6 is a flowchart illustrating a method of separating and extracting transmission image data according to fast fixed point independent factor analysis according to an embodiment of the present invention.

The controller 550 of the first mobile communication terminal 500 images a matrix having a value obtained by subtracting an average value of the received image data from the received image data and a value obtained by subtracting an average value of the key image data from the preset key image data. The data x is set (S300).

Thereafter, the controller 550 generates image data v by performing data whitening on the image data x according to Equation 2 below (S310).

Where v and x are image data, and D and E are covariance matrices obtained by performing eigenvalue decomposition on R _xx = E [xx ^T ]. D is the eigenvalues of R _xx are located in the diagonal of the matrix, and E is the eigenvectors of R _xx are located in the column of the matrix.

Thereafter, the controller 550 sets a matrix having an arbitrary weight to a temporary weight value w (0) (S320).

Thereafter, the controller 550 normalizes the temporary weight value to a unit size according to Equation 3 below and sets the initial weight value w (i) to the initial weight value (S330).

Where w (0) is the temporary weight value, w (i) is the initial weight value, || w (0) || ₂ is the secondary norm of w (0).

Thereafter, the controller 550 sets the value obtained by substituting the initial weight value w (i) and the image data v subjected to data whitening into the following Equation 4 as an estimated weight value w (i + 1). (S340).

Where w (i) is the initial weight value, w (i + 1) is the estimated weight value, || w (i) || ₂ is the second norm of w (i), v is the image data, and E [] is the expectation operator.

Thereafter, the controller 550 normalizes the estimated weight value to a unit size according to Equation 5 below, and sets the estimated weight value to an estimated weight value (S350).

Where w (i + 1) is an estimated weight value and || w (i + 1) || ₂ is the secondary norm of w (i + 1).

Thereafter, the controller 550 determines whether | w ^T (i + 1) w (i) | is close to 1 (S360).

When the result of the S360 determination | w ^T (i + 1) w (i) | is close to 1, the controller 550 multiplies the estimated weight value w (i) by the image data x according to Equation 6 below. The value of the operation is set to the transferred image data y (S370), and the procedure ends.

y = w (i + 1) x

Where y is transmitted image data, w (i + 1) is an estimated weight value, and x is image data.

On the other hand, when the result of the determination in S360 | w ^T (i + 1) w (i) | does not approach 1, the controller 550 sets the estimated weight value w (i + 1) to the initial weight value w ( i) and the process moves to step S340.

For a detailed method of extracting and extracting transmission image data according to the fast fixed-point independent factor analysis shown in FIG. 6, see well-known papers A. Hyvarinen and E. Oja, "A Fast Fixed-Point Algorithm. for Independent Component Analysis, "Neural Computation, 9, pp. 1483-1492, 1997. Fast fixed-point algorithms converge faster than other independent factor analyzes, making them suitable for use in mobile handsets with relatively limited memory and processing power.

In addition to the independent factor analysis shown in FIG. 6, A.J. Bell and T.J. Sejnowski, "An information-maximization approach to blind separation and blind deconvolution," Neural Computation, vol. 7, pp. Of course, other independent factor analysis, such as the independent factor analysis described in 1129-1159, 1995, can be used in the present invention.

Table 1 is a table showing the simulation evaluation results for one embodiment of the present invention.

Quantization level Signal to Noise Ratio (SNR-DPCM) Correlation coefficient Entropy of transmitted image 64 33.4607 0.9975 5.8726 32 29.3906 0.9933 4.7086 16 23.7698 0.9784 3.7162 8 17.7464 0.9208 2.8268

This simulation uses a differential pulse code modulation system using a first order linear predictor and a probability density function optimized quantizer. The constants of the linear linear predictor were obtained using the Wiener-Hopf equation and the probability density function-optimized quantizer was designed using the k-means algorithm. The simulations were performed four times with 64, 32, 16, and 8 quantization levels, respectively.

Original image data stored in the image data service server 100 are illustrated in FIGS. 7A and 7B. FIG. 7A shows the transferred image data, FIG. 7B shows the concealed image data, and each image data has 540 x 578 = 312,120 pixels. The image data service server 100 generates two encrypted image data for each image using a random mixing matrix.

One of them is encoded according to the differential pulse code modulation scheme in the image data service server 100 and then transmitted to the mobile communication terminals 500 and 600, and the first mobile communication terminal 500 is the other encrypted image. The data is stored in advance. When the first mobile communication terminal 500 stores one of the two encrypted image data as key image data as in the simulation, a key for the other one of the two encrypted image data. Can only be used as image data. In contrast, unlike the simulation, when the first mobile communication terminal 500 stores the concealed image data as key image data, the first mobile communication terminal 500 may be used as key image data for all delivered image data.

FIG. 7C illustrates encrypted image data to be transmitted by the image data service server 100, and FIG. 7D illustrates image data obtained by encoding the image data illustrated in FIG. 7C according to a differential pulse code modulation scheme. .

In this simulation, it is assumed that the first mobile communication terminal 500 and the second mobile communication terminal 600 have received the image data shown in FIG. 7D. When the image data is transmitted through the internet network 200 or the mobile communication network 400, there may be a slight difference between the image data and the original data received due to the influence of noise. In order to prevent this, image data encoded by the differential pulse modulation method may be transmitted after being encoded using a binary coding method such as Huffman coding or error correcting coding.

The first mobile communication terminal 500 and the second mobile communication terminal 600 receive the image data shown in FIG. 7D, decode the received image data by differential pulse code modulation, and then display the image shown in FIG. 8A. Restore the data. The first mobile communication terminal 500 can accurately separate and extract the delivered image data from the image data shown in FIG. 8A using the key image data shown in FIG. 8B. On the contrary, since the second mobile communication terminal 600 does not have the key image data, the second mobile communication terminal 600 cannot extract the transferred image data.

9A to 9D show transmission image data recovered by independent factor analysis when quantization levels are encoded according to the differential pulse code modulation scheme at 64, 32, 16, and 8 levels, respectively. As the quantization level is higher, the transmission image data similar to the original transmission image data can be separated and recovered.

Referring to Table 1, the correlation coefficient between the original delivered video data stored in the video data service server 100 and the restored delivered video data restored by the first mobile communication terminal is 0.9208 and the compression ratio is about 19: 3. .

The quantization level, the signal-to-noise ratio, the correlation coefficient, and the entropy of the transmitted image determine the compression ratio of the original delivered image data stored in the image data service server 100 to the compressed image data transmitted from the image data service server 100. It is an important factor in determining.

When the differential pulse code modulation is used in conjunction with the independent factor analysis, even when the image data is transmitted at a high rate compared with the other compression coding method together with the independent factor analysis, the image data is almost the same as the original transmission image data. There is an advantage that the transmission image data can be recovered at the receiving side.

Although the present invention has been described with reference to a differential pulse code modulation method of a method of encoding and compressing data encrypted by a linear mixed method, it is a matter of course that the present invention can be easily implemented by employing another compression method.

The present invention is not limited to the embodiments described above, and various modifications and changes can be made by those skilled in the art, which are included in the spirit and scope of the present invention as defined in the appended claims.

According to the present invention as described above, it is possible to transmit and receive securely processed image data through a mobile communication terminal so that it is not possible to release it without a key image data, thereby transmitting image data without fear of hacking to the mobile communication terminal. There is.

In addition, according to the present invention as described above, using the differential pulse code modulation method and the independent factor analysis together, even if the transmitted video data is quantized and compressed after the 8-bit level, the receiving mobile terminal receives the transmitted video data. There is also an effect that can be correctly recovered by separation extraction.

In addition, according to the present invention as described above in the transmission and reception of the image data to the mobile communication terminal or between the mobile communication terminal to prevent exposure of the image data to an unauthorized third party to prevent information leakage as well as mobile image data There is also the effect that the service industry can be activated.

Claims (12)

An image data receiving step of determining whether the image data is decodable by independent component analysis (ICA) when any encrypted image data is received; A key image data loading step of reading preset key image data when the determination result is data decodable by the independent factor analysis; A transfer image data separation step of separating and extracting transfer image data to be delivered from the received image data and concealed image data for concealing the transfer image data according to the independent factor analysis using the key image data; Security processed image extraction method of a mobile communication terminal comprising a. The method according to claim 1, wherein the independent factor analysis is independent factor analysis by a fast fixed-point algorithm. The method of claim 1, wherein the image data is image data encoded by any image compression method, After the image data receiving step, An image data decoding step of decoding the received image data according to the image compression method; The security processed image extraction method of the mobile communication terminal further comprising. The method of claim 3, wherein the video compression method is differential pulse code modulation. The method of claim 1, wherein the key image data is the concealed image data. The method of claim 1, wherein the key image data is different from the received image data, and is image data mixed by linear matrix operation. A storage unit for storing key image data for decrypting any encrypted image data; If any encrypted image data is received, the key image data is read, and the transfer image data and the corresponding transfer image data to be transferred from the received image data according to independent factor analysis using the key image data. A control unit for separating and extracting concealed image data for concealing; Mobile communication terminal for extracting a security-processed image comprising a. 8. The mobile communication terminal of claim 7, wherein the independent factor analysis is independent factor analysis by a fast fixed-point algorithm. The method of claim 7, wherein the image data is image data encoded by an arbitrary image compression method, and the controller is configured to extract the security processed image, wherein the received image data is decrypted according to the image compression method. Mobile terminal. The mobile communication terminal of claim 9, wherein the video compression method is differential pulse code modulation. The mobile communication terminal of claim 7, wherein the key image data is the concealed image data. The mobile communication terminal of claim 7, wherein the key image data is image data mixed by a linear matrix operation different from the received image data.

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