KR20190036328A - Frame selective encryption method for video data - Google Patents

Abstract

The present invention relates to a frame selective encryption method for a video which elastically adjusts an encryption degree of an I frame by adapting to the amount of data of a P frame and a B frame while selecting only the I frame as an encryption target to encrypt with an image puzzling scheme for a video having the I frame, the P frame, and the B frame after compression coding. After a size of an image fragment and the number of times of shuffling are set to appropriately adjust a time required for encryption, the encryption degree of the I frame is further adjusted in accordance with the amount of added information of the P frame and the B frame which are dependent on the I frame.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of encrypting a frame,

The present invention compresses and encodes a moving picture having an I frame, a P frame, and a B frame so that only an I frame is selected as an encryption target and encrypted by an image puzzling method, And more particularly, to a frame selective video encryption method for flexibly adjusting the degree of encryption.

A method of encrypting data in various formats including images is divided into a plurality of subblocks by dividing the rewritten data into an array having a matrix form or a matrix form, .

The inventor of the present invention invented a technique for enhancing security by allowing a user to arbitrarily change the size of a sub-block and the number of times of changing the position of a free block (i.e., the number of shuffling) in order to improve the encryption technique of the puzzling method, Patent No. 10-1112157.

However, this encryption technique can secure security by appropriately selecting the size of the sub-block and the number of shuffling times. When applied to moving picture data (i.e., video data) implemented by continuous connection of image frames, This can be a time consuming problem.

That is, for video data having different resolutions such as HD, FULL HD, and UHD and having different frame rates such as 15, 20, 30, and 60, and supporting different image qualities, If the number of rings is selected as a uniform value or arbitrarily selected and used, it may be delayed by an amount of time required for encryption to process a moving image, for example, when providing a real-time streaming service.

On the other hand, the moving image data is typically compressed and coded using an I frame, a P frame, and a B frame, and at this time, only the I frame has a full image.

According to the registration number 10-0732056, only the I frame is encrypted in consideration of this compression coding structure. Thus, the time required for encryption can be shortened and the overhead can be reduced.

However, the time required for the encryption varies greatly depending on the difference in image quality supported by the moving image data, it is difficult to ensure proper encryption, and the moving image processing can not be stably handled.

KR 10-1112157 B1 Jan 21, 2012. KR 10-0732056 B1 2007.06.19.

Therefore, the object of the present invention is to provide a frame selective video encrypting method in which the encryption process is flexibly operated even for a moving picture with a difference in image quality supported, and the degree of encryption is adjusted according to the amount of data to enhance security .

In order to accomplish the above object, the present invention provides a shuffling process of dividing a frame image of a moving picture received by the encryption apparatus into a plurality of image fragments, then randomly selecting two image fragments and performing position exchange The method of claim 1, further comprising the steps of: (S20) setting an image size and a number of shuffling times; An I frame extracting step of extracting an I frame among the I, P and B frames in the moving image and obtaining the amount of data for the P frame and the B frame and resetting the number of shuffling according to the sum data amount of the P frame and the B frame, (S30); An encrypting step (S40) of generating an encrypted puzzled I frame in accordance with the size of the image fragment in which the image of the extracted I frame is set and the number of shuffling times that have been reset; And an I frame replacement step (S50) of inserting and replacing the puzzled I frame into the moving image.

In the I frame extracting step (S30) of the present invention, the number of shuffling times is increased as the amount of data to be summed in the P frame and the B frame increases.

In the I frame extracting step (S30) of the present invention, the number of times of shuffling according to the sum data amount of the P frame and the B frame is limited so as not to exceed the predetermined upper limit.

In addition, the operation condition setting step (S20) adjusts the encryption required time by varying the size of the image piece and the number of shuffling according to the number of pixels of the I frame image and the frame rate of the moving picture to be encrypted.

According to the present invention as described above, the security of the I frame is enhanced according to the amount of information of the P frame and the B frame, so that the security can be improved as the GOP having a large amount of information increases, Can be reduced.

Brief Description of Drawings FIG. 1 is a block diagram of a moving image transmission / reception system to which a frame selective moving picture encryption method according to an embodiment of the present invention is applied.
2 is a flowchart of a frame selective video encryption method according to an embodiment of the present invention;
3 is a diagram schematically illustrating a frame selective moving picture encryption method;
Figure 4 is an image drawing showing a varying image as it repeats shuffling.

The frame selective moving picture encryption method according to the present invention receives a moving picture having a coding structure composed of an I frame, a P frame and a B frame, encrypts only the I frame, and outputs the encrypted moving picture.

Here, the encryption includes a shuffling process of dividing an image in a data area of a frame into a plurality of image fragments and randomly selecting two image fragments to swap positions of two image fragments a predetermined number of times By providing a puzzle-like image repeatedly, encryption can be restored to the original image by knowing the size of the divided image fragments, the random sequence, and the number of shuffling.

According to the present invention, the increase in the number of times of shuffling is increased or decreased according to the sum data amount of the P frame and the B frame, thereby enhancing the security of a group of pictures (GOP) having a large amount of information.

According to an embodiment of the present invention, by setting the size and the number of shuffling times of the image piece that determines the required time for encryption to be variable according to the number of pixels of the I frame, There is no difference or the difference can be reduced.

According to an embodiment of the present invention, by using the size and shuffling frequency of the image fragments in accordance with the frame rate of the moving image, it is possible to prevent the difference in the time required for encryption for the moving images having different frame rates from each other, .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description of the embodiments of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

FIG. 1 is a configuration diagram of a moving picture transmission / reception system for implementing a frame selective moving picture encryption method according to an embodiment of the present invention.

FIG. 2 is a flowchart of a frame selective moving picture encryption method according to an embodiment of the present invention.

Referring to FIG. 1, a first terminal 1 for transmitting a moving picture coded with a frame divided into I (Intra) frame, P (Predictive) frame and B (Bi-directional predictive) The moving picture encrypted by the frame selective moving picture encryption method according to the embodiment of the present invention can be transmitted.

Here, the I frame, the P frame, and the B frame are obtained by compressing the consecutive frames in the GOP (Group of Pictures) unit on the moving picture data of the still moving picture image, and are obtained by a known compression coding technique. Description will be omitted and a coding structure of moving picture data shown in Fig. 3 will be briefly described for the sake of understanding of the present invention.

An I frame is a frame obtained from a GOP before coding, and is an independent frame having all image data in a frame taken like a normal image, and becomes a reference frame in a GOP. Such an I frame can be compressed and used as a still image, for example, by DCT conversion.

The P frame and the B frame refer to the I frame and have a conversion value called a motion vector, which is dependent on the I frame.

In other words, a P frame is a frame that is coded so as to be reproduced by supplementing only the difference from a reference I frame, and may be a reference of a P frame to be reproduced next.

The B frame is a frame coded with reference to the previous frame, the latter frame, or both of the front and back frames, and is disposed between the I frame and the P frame, or between the P frame and the next P frame.

The I, P, and B frames have a header for recording a code for identifying at least a frame type.

Therefore, even if only I frames are encrypted for security reasons, I frame, P frame and B frame, which are dependent on the I frame, can restore almost all of the videos impossible.

For this reason, it is possible to shorten the time required for encryption and effectively operate the encryption apparatus by encrypting I frames only after I, P, and B frames are identified by distinguishing them by a header.

Referring to FIG. 2, in the frame selective moving picture encryption method according to the present invention, an I frame extracting step (S30), an encrypting step (S40), and an I frame replacing step (S50) are performed to encrypt only I frames, The cryptographic apparatus 10 for encryption includes a cryptographic condition acquisition step S10 and an operation step S11 in order to adaptively encrypt and adaptively operate according to the image quality of the moving picture or the data amount of the P frame and the B frame, The encryption device 10 further includes a cryptographic condition acquisition unit 12 and an operation condition setting unit 13 for performing the condition setting step S20 first.

The encryption step S40 performed by the encryption unit 11 extracts only I frames from the moving image and divides the I frame image into a plurality of image fragments in order to encrypt the image with an image puzzling method capable of adjusting the encryption level, The image is encrypted with the puzzle image by changing the arrangement of the image fragments by repeating the shuffling process of selecting two image fragments at random and swapping two image fragments (i.e., exchanging positions).

FIG. 2 showing a flow chart of the frame selective video encrypting method, FIG. 3 schematically showing a frame selectable video encrypting method with the structure of the moving picture data and the exemplary image attached thereto, and FIG. 3 showing shuffling Will be described in detail with reference to FIG.

The encryption condition acquiring step (S10) acquires information related to image quality in the moving image to be encrypted in advance.

According to the embodiment of the present invention, the image quality related information to be acquired is the number of pixels of the I frame image indicating the resolution of the moving image and the frame rate indicating the number of frames per second.

Here, since the number of pixels of the I frame image affects the time required for encryption, and the frame rate affects the time allowed for encryption, it is obtained as an encryption condition before encryption, And reflects the encryption operation condition.

The operation condition setting step 20 variably sets the size of the image fragment and the number of shuffling according to the number of pixels and the frame rate of the I frame image obtained in the encryption condition acquiring step (S10).

The size and the number of shuffling of the image fragment have not only correlation with each other but also determine the time required for encrypting the I frame. In order to set the encryption required time to an appropriate level, the number of pixels of the I frame image and the frame rate rate).

Referring to the I frame image shown in FIG. 3, an I frame image extracted from a moving image is divided into image fragments having a size of a X b pixel, and then a process of randomly selecting two image fragments and shuffling is repeated At the time of shuffling, the number of shuffling must be sufficiently large to make it impossible to recognize what image is visible and to make it difficult to restore original image data as data.

However, the smaller the size of the image fragment, the larger the number of image fragments obtained by division, and the larger the number of image fragments, the larger the number of shuffling.

The inventor of the present invention could obtain the result of the following equation (1) showing the correlation between the number of images and the appropriate shuffling number by using a mathematical theory on probability, and by puzzling the number N of divided image pieces The correlation was verified from the images obtained. By appropriately adding and subtracting the results of the mathematical expressions and providing a rule or a data table for increasing the number of shuffling as the number of image fragments is increased, the appropriate shuffling frequency can be set according to the image size.

In Equation 1, k is an appropriate shuffling number, N is the number of divided image fragments, and? Is a probability that a specific image fragment is stochastically present at uniform probability regardless of the dividing position as the shuffling process is repeated Is the convergence rate to the stationary distribution.

In addition, the execution time of the program for performing the encrypting step (S40) is as follows. The larger the size of the image fragment, the smaller the number of divided image fragments, and the longer the time required for one-time shuffling, It is possible to save time by reducing the number of shuffling.

That is, the time required according to the size of the image fragments is not only an increase factor but also a reduction factor.

However, by reducing the size of the divided image fragments so that the execution time of the one-time shuffling becomes relatively short and the corresponding number of shuffling times is relatively increased, the size of the divided image fragments is increased, Can be relatively long, and the time required for puzzling (encryption) can be reduced as compared with a case where the number of shuffling operations is relatively reduced.

This means that execution of the program code required to exchange positions of a relatively large divided image fragment has a greater influence on the time required for puzzling, and the inventor of the present invention creates an encryption program to vary the size of the image fragment As a result of executing the encryption program by applying the appropriate shuffling frequency to the size of the image fragment, it was confirmed that the smaller the image size, the smaller the time required to encrypt the I frame image, that is, the encryption time.

Of course, as a result of writing a program, if you can reduce the amount of time required for encryption to reduce the number of shuffling by increasing the size of the image fragments, you can increase the size of the image fragments to reduce the time required for encryption, However, according to the program confirmed by the applicant of the present invention, the smaller the size of the image fragment, the smaller the time required for encryption.

Accordingly, in the embodiment of the present invention, in order to reduce the time required for the encryption (puzzling) to increase as the number of pixels of the I frame image increases, a rule or a lookup table for setting the size of the image fragment having a smaller number of pixels Respectively. As an example of a rule, the size of a segmented image fragment can use a rule that is inversely proportional to the number of I frame pixels.

However, if the number of divided image fragments is excessively large, the necessary pseudo random number becomes too large, which is greatly influenced by the performance and operation time of the pseudo random number generator. If the size of the image fragment is too large, reverse puzzling may be possible even when the puzzling process is not known.

The maximum value for the size of image fragments is determined according to the degree of difficulty of reverse puzzling, and the size of the image fragments is determined within a predetermined range. It is better to determine the rule or lookup table to set.

In addition, the operation condition setting step S20 resets the size of the image fragment set according to the number of pixels of the I frame image according to the frame rate.

The resetting method is a method of reducing the size of image fragments as the frame rate is larger. Accordingly, even when the frame rate is different, the difference in the time required for encryption can be reduced.

Of course, when the size of the image fragment is reset, the number of divided image fragments corresponding to the size of the reset image fragment is also changed, so the number of shuffling is also reset accordingly.

On the other hand, according to a commonly used moving picture, since the total number of pixels (or the number of pixels) of the I frame image and the frame rate are limited, the total number of pixels of the I frame image and the size of the image fragment corresponding to the frame rate, It is also good to use the number of times by using lookup table.

After the setting is completed as described above, the encryption unit 11 receives the moving image data, performs the I frame extraction step S30, the encryption step S40, and the I frame replacement step S50, .

As shown in FIG. 3, the I frame extracting step (S30) extracts an I frame, extracts a data amount for P frame and B frame, which are dependent on the I frame to be extracted, .

3 illustrates a closed GOP in which I, P, and B frames are generated by compressing only a frame within a GOP. Thus, the amount of data of P and B frames existing in the GOP is extracted following the extracted I frame. However, to support open GOP, the range is adjusted to include the frame appearing before the extracted I frame, but it is limited to the P and B frames existing in the open GOP.

The I frame extracting step S30 resets the number of shuffling operations by increasing the number of shuffling operations in accordance with the sum data amount of the P and B frames (S31).

Here, the re-setting of the number of shuffling is a method of increasing the number of times of increasing the number of shuffling as the amount of data to be summed in the P and B frames is larger, and is to be reset adaptively to each GOP of the screening.

This is because, even if the number of shuffling is determined according to the size of the divided image fragments as described above, the larger the amount of data of the P and B frames is, the larger the increase in the number of shuffling times is to increase the security for the I frame.

Of course, since the number of times of shuffling is directly controlled, the size of the set divided image piece is not modified.

On the other hand, as the number of shuffling times increases, the time required for encryption becomes longer. Therefore, the number of times of increasing shuffling times is limited so as not to exceed a predetermined upper limit.

Further, since the number of shuffling is increased at the time of encrypting the I frame in accordance with the amount of P and B frame information in the repetitive GOP, the delay time is increased by the number of times of increase. Therefore, it is preferable that the number of shuffling times set in the operation condition setting step (S20) is set to be slightly lower than a value determined according to Equation (1) in consideration of resetting of the number of shuffling times.

As shown in FIG. 3, the encrypting step S40 is a step of generating a puzzled I frame obtained by encrypting the extracted I frame by the puzzling method. The I frame image in the data area of the extracted I frame is obtained, An image dividing step (S41) of dividing each image fragment into a grid shape according to the size of the image fragment, and generating a random number sequence by randomly selecting the grid number, wherein a random number sequence is determined according to the seed A random number generation step S42 of generating a random number sequence of double the set shuffling number using a pseudo random number generator, and a random number generation step S42 of taking two random numbers in order of the random number sequence, A purging step S43 for repeating the shuffling process for shifting the image fragments by the number of shuffling times set for the shuffling process, and the purging step S43 obtained by the puzzling step S43 The puzzled I frame image is inserted into the data area of the I frame to replace the image before puzzling, and the seed value, the size of the image fragment, and the number of shuffling are recorded in the header of the I frame to be used for decoding And a puzzled I frame generation step (S44).

Here, the value of the seed value, the size of the image fragment, and the number of shuffling operations to be recorded in the header of the I frame are the same as the set values encrypted in accordance with the pre-appointment with the decryption apparatus 20 provided in the receiving- It is preferable to record with a code.

The puzzling step S43 will now be described with reference to FIG. 4, which is exemplarily illustrated by assuming that the number of divided image pieces is 63. A preexisting I frame image A is divided into 63 divided image pieces After splitting, shuffling is performed repeatedly after assigning order numbers a01, a02, ..., a63 to each image fragment.

When shuffling is performed, two pieces of image are randomly selected and then the positions are exchanged. Accordingly, as the number of times of shuffling increases, the number of image pieces moving from one position to another increases.

Since the image fragments are randomly selected every time shuffling is performed, the probability distribution that each image fragment or any one specific image fragment can exist at each divided position by repeating shuffling is a uniform probability And converge to a stationary distribution that may exist as a whole. Thus, by appropriately selecting the degree of convergence of Equation (1) and setting the appropriate number of shuffling times corresponding to the number of divided image pieces in advance, the shuffling is repeated so as to appropriately puzzle. Of course, rather than applying Equation 1 as it is, it is preferable to change the image size, the number of divisions, etc., and modify the puzzle to have a proper number of shuffling.

The I frame replacing step (S50) inserts the generated puzzled I frame into the moving image data to replace the I frame before puzzling, thereby outputting the moving image data encrypted with the I frame.

Then, the process proceeds to the I frame extracting step (S30) in order to encrypt the next I frame in the moving image data.

In the description of the embodiment of the present invention, in order to apply the moving picture data to the moving picture transmission / reception system which transmits the moving picture data from the first terminal 1 to the second terminal 2 via the communication path 3 of the communication network, The encrypted moving picture data output by the I frame replacement step S50 is transferred to the second terminal 2 by the communication module 1a of the first terminal 1. [

The second terminal 2 includes a decryption unit 20 for receiving encrypted video data transmitted through the communication path 3 and then decrypting the received encrypted video data through the communication module 2a.

After extracting only the I frame, the decoding apparatus 20 decodes the puzzled I frame image in the data area of the I frame according to the seed value, the size of the divided image fragment, and the number of shuffling operations recorded in the header, and outputs the decoded I By replacing the frame with the moving image data, the moving image data before encryption is restored.

The decoding of the puzzled I frame image follows the order of the encrypting step S40, but there is a difference in performing the reverse puzzling step instead of the puzzling step S43.

First, according to the size of the divided image fragment, the puzzle I frame image is divided into a grid shape, each image fragment is numbered, and a random number sequence of two times of the number of shuffling is generated according to the seed value.

Next, in the random number sequence, a shuffling process of taking a random number of two by two in reverse order and exchanging the position of the image pieces having two random numbers is repeated by the number of shuffling times to obtain an inverted puzzle I frame image.

Next, the restored I frame is obtained by replacing the puzzled I frame image by inserting the inverted puzzled I frame image into the data area of the I frame.

Next, the restored I frame is replaced with the received moving image data, and the moving image data is restored.

Meanwhile, it is natural that the present invention can be applied to various terminals such as a terminal that encrypts moving picture data and stores the moving picture data in a storage medium, or a terminal that transmits to another terminal through a wire / wireless communication network.

The size, shuffling frequency, and seed value of the image fragment used in the encryption may be recorded in the header of the moving image data or may be transmitted in a separate data packet without being recorded in the header of the I frame.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, . ≪ / RTI > Accordingly, such modifications are deemed to be within the scope of the present invention, and the scope of the present invention should be determined by the following claims.

1: first terminal 1b: communication module
2: second terminal 2b: communication module
3: Communication path
10: Encryption device 11:
12: Encryption condition acquisition unit 13: Operation condition setting unit
20: Decryption device

Claims (4)

After the encryption device 10 divides the frame image of the moving image input into a plurality of image pieces, the shuffling process of randomly selecting two image pieces and exchanging their positions is output as an encrypted moving image A frame selective video encryption method,
An operation condition setting step (S20) of setting the size and the number of shuffling of the image fragment;
An I frame extracting step of extracting an I frame among the I, P and B frames in the moving image and obtaining the amount of data for the P frame and the B frame and resetting the number of shuffling according to the sum data amount of the P frame and the B frame, (S30);
An encrypting step (S40) of generating an encrypted puzzled I frame in accordance with the size of the image fragment in which the image of the extracted I frame is set and the number of shuffling operations that have been reset; And
And an I frame replacement step (S50) of inserting and replacing a puzzled I frame into a moving image
Frame Selective Video Encryption Method.
The method according to claim 1,
In the I frame extracting step S30, the number of shuffling times is increased by increasing the amount of data to be summed in the P frame and the B frame.
3. The method of claim 2,
Wherein the number of shuffling times in the I frame extracting step (S30) is limited so that the number of times of increase in the number of shuffling times according to the sum data amount of the P frame and the B frame does not exceed a predetermined upper limit.
The method of claim 3,
The operation condition setting step S20 adjusts the size of the image fragment and the number of shuffling according to the number of pixels of the I frame image and the frame rate of the moving picture to be encrypted,
Frame Selective Video Encryption Method.

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