KR20070072297A - Method for encryption and decryption video and apparatus thereof - Google Patents

Abstract

A video encoding method, a video decoding method, and a video encoding apparatus are provided to improve compression efficiency without affecting compressed original video data and reduce errors generated when video data is transmitted and stored. A video encoding method includes a step of encoding an intra-frame of video data by using a predetermined method(210), and a step of adding a weight according to a predetermined public key to a motion vector generated by estimating the motion of an inter-frame of the video data to encode the inter-frame(220). The video encoding method further includes a step of compressing the encoded video data.

Description

Video encryption method, video decryption method and apparatus therefor {Method for encryption and decryption video and Apparatus}

1 illustrates a frame structure of a video.

2 is a flowchart illustrating a video encryption method according to the present invention.

3 is a flowchart illustrating a video decoding method according to the present invention.

4 is a detailed flowchart of FIG. 2.

5 shows a discrete time wavelet transform process applied to the present invention.

6 is a block diagram of a video encryption apparatus according to the present invention.

7 is a block diagram of a video decoding apparatus according to the present invention.

FIG. 8A illustrates an AC / DC coefficient encryption unit included in the intra encryption unit according to FIG. 6.

FIG. 8B illustrates a vector encryption unit included in the inter encryption unit according to FIG. 6.

FIG. 9A illustrates an AC / DC coefficient decoder included in the intra decoder according to FIG. 7.

FIG. 9B illustrates a vector decoder included in the inter decoder of FIG. 7.

The present invention relates to image processing, and more particularly, to a video encryption method, a video decryption method and an apparatus thereof.

Due to the rapid development of moving picture compression technology such as MPEG-4 and wired and wireless Internet technology, multimedia streaming services such as digital video library and video on demand service are widely used. It is true that the provision of such services makes it possible for many people to access various digital contents conveniently and easily, but it is also true that illegal use by those without proper permission is increased due to the nature of multimedia resources that can be copied without restriction. . If the illegal use of such digital content increases, the sound distribution order of the work is severely damaged, and the copyright holder who created the digital content suffers an irreversible economic loss.

Among various multimedia content encoding methods, MPEG is widely used as the de facto international standard for video processing such as digital multimedia broadcasting, video streaming, and multimedia data storage. However, it is not easy to apply encryption due to the fact that video, which is one of the essential features of MPEG encoding, is temporally and spatially related.

In the conventional MPEG-4 encryption method, an encryption method using DES and an encryption method in MPEG-4 video frames are widely used. Encryption using DES uses a bitstream after MPEG-4 image compression as a method of encrypting a part or all bits of an MPEG-4 bit stream. This method does not take advantage of the inherent characteristics of MPEG-4. In addition to the decoding process of MPEG-4, the encryption process using the DES causes the compression efficiency and the encryption performance to be degraded due to the excessive bit excess, which causes a large burden on the server due to excessive computation.

The encryption method in the I-frame in the still image attempts to shuffle or encrypt directly in the pixel domain of the image data.

However, in the conventional video encryption method, the original video signal is modified while directly encrypting the video, thereby affecting the compressed data during video compression, thereby reducing the compression efficiency and generating an error between transmissions of contents online. There is a problem that this is lowered.

Therefore, the technical problem to be achieved by the present invention is to minimize the compression bit sequence that can occur between the encryption process through the encryption of the screen information and the information between the screen in MPEG-4 compression without affecting the compressed original image data To increase the efficiency and to reduce the errors that can occur during transmission or storage between media to provide a high level of security.

According to an aspect of the present invention, there is provided a video encryption method comprising: encrypting an intra frame of a video by applying a predetermined method; And encrypting the inter frame by applying a weight according to a predetermined public key to a motion vector generated by predicting the motion of the inter frame of the video. The video encryption method according to the present invention preferably further comprises the step of compressing the encrypted video.

According to another aspect of the present invention, there is provided a video decoding method comprising: decrypting an intra frame of an encrypted video by applying a predetermined method; And decoding the intra frame by applying a reduction value according to a preset public key to a motion vector generated by predicting the motion of the inter frame of the encrypted video. The video decoding method according to the present invention preferably further comprises the step of decompressing the encrypted video.

According to an aspect of the present invention, there is provided a video encryption apparatus for discrete cosine transforming an intra frame of a video, and converting the intra frame by converting a DC coefficient code and an AC coefficient code using a preset public key. An intra encryption unit for encrypting a frame; And an inter encryption unit configured to encrypt the inter frame by applying a weight according to a predetermined public key to a motion vector generated by predicting the motion of the inter frame of the video.

The present invention proposes a double encryption method using discrete cosine transform coefficients and motion vectors in MPEG-4 of video. By applying intra frame information encryption and inter frame information encryption between screens at the same time, the image is distorted to prevent unauthorized users or devices from using it. . Also, by minimizing the excess compression bitstream that may occur during the encryption process, an error that may occur during transmission or storage between media is reduced without affecting the compressed original image data.

Hereinafter, a video encryption method, a video decryption method, and an apparatus thereof according to the present invention will be described in detail with reference to the accompanying drawings.

1 illustrates a frame structure of a video. The video has a continuous stream structure as shown in FIG. Each individual intra frame 100, 101 can come anywhere in the data stream and is used for random access of the data and encoded without reference to other images. Intra frames 100 and 101 are compressed in real time in MPEG. The intra frames 100 and 101 are divided into 8 × 8 blocks designated in a macroblock (not shown), and then encoded using a DC coefficient and an AC coefficient after using a discrete cosine transform (DCT) method. Calculate and transform using variable length coding. The inter frame 102 containing the information between the continuous first intra frame 100 and the second intra frame 101 is vectorized based on the information between the consecutive frames to encrypt the vector.

Encryption key Intra frame Inter frame 0 DC '= -DC MV = MV + Δα One AC '= -AC MV '= -MV ... ... ... i DCT Motion vector conversion

In Table 1, i is the number of macro blocks to be encrypted and is limited to the number of blocks in the screen. The cryptographic key can be generated by the service provider, and up to 64 bits of cryptographic key can be configured. Since the cipher key changes the method of discrete cosine transform coefficients of the macroblock and the motion vector cipher, unauthorized access is impossible with different encryption keys.

2 is a flowchart illustrating a video encryption method according to the present invention.

First, input an image to be encrypted (step 200).

Intra frame encryption is performed from the input image (step 210). This is a video encryption method using the code change of the discrete cosine transform coefficients. This not only effectively distorts the image but also causes error propagation in which the distortion of the image in the screen is transferred to the distortion of the image between the screens. In the present invention, the discrete cosine transform coefficient for an arbitrary macroblock is divided into a DC coefficient and an AC coefficient to convert a sign. The discrete cosine transform coefficients of the intra frame are encrypted by the public key. The DC coefficient and the AC coefficient of the intra frame cause sufficient image distortion with each code conversion alone. Therefore, the unauthorized person cannot see the normal video unless normal decryption is performed.

(수직값),

(수평값)를 변형함으로써 벡터의 각도를 변형시키거나 벡터의 부호를 변환하여 벡터의 방향을 반대로 전환시킨다. 이 방법은 P-프레임이나 B-프레임의 모든 움직임 벡터를 변형시킬 필요는 없다. MPEG-4 비디오에서는 움직임 보상과 예측방법을 사용하기 때문에 전 프레임의 임의의 매크로 블록에 대해 움직임 벡터를 변환할 경우 에러의 확산을 일으켜 영상의 왜곡을 일으킬 수 있다. 움직임 벡터의 위상각도 변화는 다음과 같다.The present invention encrypts an intra frame after encrypting an intra frame (step 220). In order to encrypt inter frames, motion between frames of an input image is predicted and motion vectors are generated accordingly. Of the generated motion vector to encrypt the generated motion vector

(Vertical value),

By modifying the (horizontal value), the angle of the vector is transformed or the sign of the vector is transformed to reverse the direction of the vector. This method does not need to transform all the motion vectors of the P-frame or B-frame. Since MPEG-4 video uses motion compensation and prediction methods, when motion vectors are transformed for arbitrary macro blocks of all frames, error may be spread and distortion of the image may occur. The phase angle change of the motion vector is as follows.

, 수평값을

라고 했을때,

는 움직임 벡터의 위상 각도이다. 그리고

는 매크로블록의 수이고,

는 매크로블록의 인덱스를 가르킨다. 이때

는 한계치

를 초과하는 각도를 가진다.The vertical value of the motion vector of the i macro block

, The horizontal value

When I say

Is the phase angle of the motion vector. And

Is the number of macroblocks,

Points to the index of the macroblock. At this time

Is the threshold

Has an angle exceeding

, 수평값이

로 변화하면, 위상각도는 다음과 같이 변화한다.According to the public key, the vertical value of the motion vector

, The horizontal value

The phase angle changes as follows.

The change in vertical or horizontal values in the motion vector can be determined by the service provider to be encrypted. The direction change of the motion vector is as follows.

In motion vector encryption, the phase angle transformation or direction transformation of a vector is determined by a public key. The motion vector encryption method for each macro block varies according to the public key, and an image may be encrypted according to a service provider.

3 is a flowchart illustrating a video decoding method according to the present invention.

The bitstream of the encrypted video is input (step 300). This bitstream is a compressed bitstream in MPEG-4 format.

After decompression, the intra frame is decoded (step 310). The encrypted intra frame is decrypted according to the public key.

After the intra frame is decoded, the inter frame is decoded (step 320). The image distorted by the encryption method is decrypted by the public key and then output.

4 is a detailed flowchart of FIG. 2.

First, the image to be encrypted is input (step 400).

The video signal is discrete cosine-converted for all macroblocks in the intra frame from the input video (step 410). The intra frame is converted into an AC frequency component and a DC frequency component through a discrete cosine transform.

The AC coefficient and the DC coefficient are encrypted from the preset public key (step 411). The AC and DC coefficients generated by the discrete cosine transform of the image generate sufficient image distortion with each code conversion from a predetermined public key. Therefore, the unauthorized person cannot see the normal video unless normal decryption is performed.

After encrypting the intra frame, the inter frame between both adjacent intra frames is encrypted. The present invention encrypts intra frames and inter frames simultaneously, thereby increasing compression efficiency and reducing errors to provide a high level of security.

In order to encrypt the inter frame, first, a motion of the inter frame is predicted (step 420). The motion of the inter frame is predicted by referring to the previous intra frame and the next intra frame, and a motion vector is generated therefrom.

The motion vector is generated, and the motion vector is encrypted from the preset public key (step 421). This modifies the angle of the vector by modifying the vertical and horizontal values of the motion vector, or reverses the direction of the vector by changing the sign of the vector. This method distorts the image by transforming the motion vector for any macroblock between adjacent frames without converting all motion vectors of the P-frame or B-frame.

After encrypting the inter frame, the video frame is compressed (430).

The encrypted frame is compressed, producing a compressed MPEG-4 bit stream.

Finally, the encrypted MPEG-4 bit string is output (step 440). The intra frame and the inter frame are encrypted by the public key, compressed, and then transmitted to the external client.

5 shows a discrete time wavelet transform process applied to the present invention.

,

,

)들을 제외한 웨이브릿 트리를 포함하여 그룹화되어 있다. Apply wavelet tree shuffling to encrypt the intra frame of the video. The image is divided into four levels to form thirteen sub-bands. Wavelet coefficients are values of high frequency components that have little energy.

,

,

Are grouped together, including the wavelet tree except).

,

, 그리고

의 값을 이용한다. 따라서, 트리들의 수는

,

, 그리고

에 존재하는 값들의 총 갯수와 같으므로 3×2² = 12개의 총 트리가 생성된다. 이 웨이브릿 트리는 미리 정해진 공개키에 의해 셔플링되어 암호화되게 된다.After 4-level conversion, the wavelet trees are subbanded

,

, And

Use the value of. Thus, the number of trees

,

, And

This is equal to the total number of values in, so 3 × 2 ² = 12 total trees are generated. This wavelet tree is shuffled by a predetermined public key and encrypted.

6 is a block diagram of a video encryption apparatus according to the present invention.

The video encryption system includes an intra encryption unit 600, an inter encryption unit 610, and a video compression unit 620.

First, the discrete cosine transform unit 601 performs discrete cosine transform on the input video frame.

The AC / DC coefficient generator 602 generates AC / DC coefficients from a discrete cosine transformed input video frame. The generated coefficients are partially encrypted according to a predetermined public key and the remaining coefficients are passed through the residual coefficient bypass unit 604.

The AC / DC coefficient encryptor 603 encrypts the AC coefficient and the DC coefficient component according to a predetermined public key. The AC coefficient and DC coefficient generated by the discrete cosine transform of the intra frame of the image cause sufficient image distortion even for each code conversion from the public key. Therefore, the unauthorized person cannot see the normal video unless normal decryption is performed.

After encryption by the intra encryption unit 600, the inter encryption unit 610 performs the encryption of the inter frame. That is, when video frames sequentially enter the intra encryption unit, relatively higher priority frames perform intra encryption, and lower priority frames perform intra encryption, and then enter the video compression unit. Since subframes have mutually different values, inter encryption is performed from this value.

In the inter encoder 610, the motion predictor 611 predicts motion from two adjacent frames.

The motion vector generator 612 generates a vector from the predicted motion.

The vector encryptor 613 transforms the vector generated by the motion vector generator 612 by changing the angle of the vector or reverses the direction of the vector by changing the sign of the vector by modifying the vertical value and the horizontal value of the motion vector. Distort the image.

The adder 615 adds the AC / DC coefficients encrypted by the AC / DC coefficient encryption unit 603, the vector encrypted by the vector encryption unit 613, and the residual coefficients bypassed from the residual coefficient bypass unit 604. The video is sent to the video compression unit 620.

The video compression unit 620 sequentially receives the encrypted video frame, compresses the image, and outputs the MPEG-4 bitstream.

7 is a block diagram of a video decoding apparatus according to the present invention.

The decompressor 700 decompresses the encrypted MPEG-4 bitstream and converts the encrypted image into a form that can be decrypted.

The intra decoder 710 decrypts the decompressed bitstream according to a predetermined public key.

After decoding the intra frame, the inter decoder 720 decodes the inter frame. The image distorted by the inter frame encryption method is decrypted by the public key and then output.

FIG. 8A illustrates an AC / DC coefficient encryption unit 800 included in the intra encryption unit 600 of FIG. 6.

AC coefficients and DC coefficients are generated by performing discrete cosine transform on the intra frame, and the generated AC coefficients and DC coefficients are converted into codes of the DC coefficients according to a public key predetermined by the AC / DC coefficient encryption unit 800. The code of the AC coefficients is switched 802 and the intra frame is encrypted 803.

FIG. 8B illustrates a vector encryptor 810 included in the inter encryptor 610 of FIG. 6.

An inter frame generates a motion vector by predicting a motion between adjacent frames. In the vector encrypting unit 810, the vertical value of the motion vector is weighted according to a predetermined public key (811), and the horizontal value of the motion vector is weighted (812) so that the inter frame is encrypted (813). .

FIG. 9A illustrates an AC / DC coefficient decoder 900 included in the intra decoder 710 of FIG. 7.

The intra frame encrypted by the AC / DC coefficient encryption unit 800 is reconverted (901) by the AC / DC coefficient decryption unit 900 again according to a predetermined public key, and the code of the AC coefficient is reconstructed. A transform 902 is performed to decode an intra frame (903).

FIG. 9B illustrates a vector decoder 910 included in the inter decoder 720 of FIG. 7.

The encrypted interframe subtracts a value equal to a value weighted by the vector encrypting unit 810 according to the predetermined public key in accordance with the predetermined public key. This value is defined as a subtraction value. That is, a subtracted value is added to the vertical value of the motion vector according to the public key (911), and a subtracted value is added to the horizontal value of the motion vector (912), and the intra frame is decoded (913).

Encryption method Time ratio Bit growth rate (%) Normal compression One 0 DC coefficient code conversion One 0 AC coefficient code conversion One 0 Motion vector code conversion One 0 Motion vector angle change 1.2 1.4 DC coefficient code conversion + motion vector angle change 1.5 1.4 AC coefficient code conversion + motion vector code conversion 0.5 1.2 Method according to the invention 1.9 2.2

Table 2 shows the comparison of compression time and compression rate during compression including the compression and encryption of the original image. As shown in Table 2, the bit excess rate after encryption in the intra encryption unit 600 and the inter encryption unit 610 does not exceed 4% or more than during normal compression. Referring to Table 2, it can be seen that the present invention is excellent in security while reducing the loss due to compression as the encryption calculation amount is small and does not increase greatly in compression time.

The present invention can be embodied as code that can be read by a computer (including all devices having an information processing function) in a computer-readable recording medium.

The computer-readable recording medium includes all kinds of recording devices in which data is stored which can be read by a computer system. Examples of computer-readable recording devices include ROM, RAM, CD-ROM, magnetic tape, floppy disks, optical data storage devices, and the like. Computer-readable recording media are distributed and distributed over networked computer devices. Computer readable code may be stored and executed in such a manner.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical details of the appended claims.

As described above, according to the present invention, by simultaneously applying the encryption of the intra frame and the encryption of the inter frame, there is an effect of providing a high level of security without affecting the compressed original image data.

 In addition, there is an effect of increasing the compression efficiency without affecting the compressed original image data by minimizing the excess of the compression bit string that may occur during the encryption process.

Claims (11)

Encrypting the intra frame by applying a predetermined method to the intra frame of the video; And And encrypting the inter frame by applying a weight according to a predetermined public key to a motion vector generated by predicting the motion of the inter frame of the video. The method of claim 1, Compressing a video comprising the encrypted intra frame and the encrypted inter frame. The method of claim 1, Encrypting by applying the predetermined method, Discrete cosine transforming the predetermined macroblock of the intra frame; And And encrypting the intra frame by converting a DC coefficient code and an AC coefficient code using the converted intra frame using the predetermined public key. The method of claim 1, Encrypting by applying the predetermined method, And applying wavelet tree shuffling according to the preset public key. Decrypting the intra frame of the encrypted video by applying a predetermined method; And And decoding the inter frame by applying a reduction value according to a preset public key to a motion vector generated by predicting the motion of the inter frame of the encrypted video. The method of claim 5, And decompressing the encrypted video. The method of claim 5, Decoding by applying the predetermined method, Inverse discrete cosine transforming the predetermined macroblock of the intra frame; And And converting the transformed intra frame into a DC coefficient code and an AC coefficient code using the preset public key to decode the intra frame. The method of claim 5, Decoding by applying the predetermined method, And applying wavelet tree shuffling according to the preset public key. A non-transitory computer-readable recording medium having recorded thereon a program for executing the method of claim 1. An intra encryption unit for discrete cosine transforming the intra frame of the video and converting the converted intra frame to a DC coefficient code and an AC coefficient code using a predetermined public key to encrypt the intra frame; And And an inter encryption unit configured to encrypt the inter frame by applying a weight according to a predetermined public key to a motion vector generated by predicting the motion of the inter frame of the video. The method of claim 10, And a video compressor for compressing a video including the encrypted intra frame and the encrypted interframe.

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