CN107911715B

CN107911715B - H.264/AVC video format compatible encryption method based on CAVLC coding

Info

Publication number: CN107911715B
Application number: CN201711174801.XA
Authority: CN
Inventors: 郑培嘉; 郭剑艇; 黄继武
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2017-11-22
Filing date: 2017-11-22
Publication date: 2021-04-16
Anticipated expiration: 2037-11-22
Also published as: CN107911715A

Abstract

The invention provides a compatible encryption method of H.264/AVC video format based on CAVLC coding, which directly processes a compressed code stream, firstly, grouping the compressed code stream according to the block information of the video, encrypting an interest block and a random block in the video, placing the encrypted blocks as additional information at the end of the code stream, then partially encrypting data in the rest blocks, and organizing the data into a new video with slightly smaller resolution; and adding additional information to obtain the encrypted code stream. The method encrypts time domain, space domain and structural information of the video, reduces side information leakage and strengthens the protection of video content. The method can provide special protection for the region of interest, can adapt to different application scenes, simultaneously reserves the capability of detecting and processing the encrypted video, and can provide help for applications such as video monitoring systems and cloud storage.

Description

H.264/AVC video format compatible encryption method based on CAVLC coding

Technical Field

The invention relates to the field of multimedia information security, in particular to an H.264/AVC video format compatible encryption method based on CAVLC coding.

Background

In recent years, with the development of multimedia technology, people pay more and more attention to video content and privacy protection related technologies. Compared with picture data, the video data has the characteristics of large volume, strong correlation between image frames and the like. Typically, video is compression encoded for ease of storage and transmission. This makes the encryption techniques on video different from the common encryption techniques, for example, video content is usually encrypted while maintaining format compatibility. How to take security, format compatibility, and other requirements of application scenarios into account is a challenge of video encryption technology.

For a compressed video code stream, the existing method mainly encrypts the spatial domain and time domain related parameters in the video code stream. However, such algorithms all present a risk of privacy leakage if considered from a security point of view. In particular, the structure of the encrypted media data itself is not much different from that before encryption. The structure of the media data itself (block order, frame order, etc.) is accompanied by a lot of side information. This unencrypted structure information is likely to cause privacy disclosure. Because the media data structure after compression coding is complex, the context often has high correlation, and the coding standards used by different media data formats are different; meanwhile, the problems of coding efficiency, encryption time and the like need to be considered, and encrypting the structural information of the media data is a difficult task. The spatial domain and time domain related parameters are encrypted, and global lightweight protection is provided; it cannot meet the requirements of different application scenarios for the controllable adjustment of the region of interest and special local protection. In addition, the encrypted video is often used in a scene such as a cloud storage system, and a certain processing capacity needs to be reserved for the encrypted video.

The compatible encryption method of the H.264/AVC video format based on the CAVLC coding encrypts time domain, space domain parameters and structural information of the H.264/AVC video according to the characteristics of the CAVLC coding; meanwhile, special protection is provided for the region of interest, and the protection capability of the encryption algorithm on the private content is improved; the method also reserves the capability of detecting and processing the encrypted video and considers two requirements of video processing and video content protection.

Disclosure of Invention

The invention provides a CAVLC-coding-based H.264/AVC video format compatible encryption method, which can efficiently encrypt CAVLC-coded H.264/AVC-coded videos.

In order to achieve the technical effects, the technical scheme of the invention is as follows:

an H.264/AVC video format compatible encryption method comprises the following steps:

s1: grouping videos according to the blocking information in the code stream;

s2: respectively encrypting the interested block and the random selection block;

s3: using partial encryption on the remaining blocks;

s4: the partial encrypted blocks generated at S3 are organized into a format-compatible encrypted video bitstream, followed by NALUs into which the encrypted blocks generated at S2 are packed.

Further, the specific process of step S1 is:

s11: the positions of blocks belonging to the interested area in the video are located, and the blocks are marked as interested blocks R, wherein Mp is used in R₁Recording position information;

s12: some blocks are randomly selected and denoted as randomly selected blocks S. In S, Mp is used₂The position information is recorded. In particular, the skip block in S replaces the block of interest in the corresponding R;

s13: the remaining blocks are denoted as O.

Further, the specific process of step S2 is:

s21: encrypting all bits in R by using AES-CFB;

s22: the data in S is partially encrypted, after which all bits are encrypted using AES-CFB.

Further, the specific process of step S3 is:

for each block in encryption O:

s31: encrypting its intra prediction mode IPM;

s32: encrypting a suffix of a motion vector residual MVD code word;

s33: encrypting the suffix of its non-zero coefficient and its sign;

further, the specific process of step S4 is:

s41: packaging the encrypted data in the R into NALU of type 22;

s42: packaging the encrypted data in the S into NALU of type 23;

s43: reorganizing the encrypted data in the O into a video segment, recording the video segment as NVB, and recalculating partial parameters in the parameter set in the NVB;

s44: marking the related original parameters in the NVB and the related parameter sets in the R, S as P, and packaging the P into NALU of type 17 after completely encrypting the P;

s45: these NALUs are placed behind the stream of NVBs to obtain the encrypted video stream.

Further, the method can select the region of interest to encrypt according to the requirement, and can utilize a part of keys to detect and process the encrypted video, and the specific process is as follows:

s51, decrypting the content in the NALU of NALU type 23 to obtain a partially encrypted randomly selected block

S52, decrypting the content in the NALU with the NALU type of 17 to obtain the partially encrypted original parameters

S53 according to Mp₂From

And partially encrypted residual block

And recovering the video with the original video structure. In this video, the region information where the block of interest is located has been replaced by a skip block for the detection process.

The corresponding decryption method comprises the following specific processes:

s61, sequentially decrypting the content in the NALU with the NALU type of 17 or 23 to obtain a random selection block S and an original parameter P;

s62, decrypting the content with NALU type 22 to obtain the interested block R;

s63, decrypting the content in the NVB to obtain the residual block O and other parameters;

s64 according to Mp₁，Mp₂And recovering the original video structure, and performing subsequent decoding work by using the decrypted data.

Compared with the prior art, the technical scheme of the invention has the beneficial effects that:

aiming at the H.264/AVC video coded by CAVLC, the method firstly encrypts the format compatible part of the video and then completely encrypts the interested region, thereby improving better protection for the content of the interested region. Meanwhile, the video structure information is encrypted, and the risk of video content leakage caused by side information leakage is reduced. In addition, the method can select different regions of interest according to different application scenes, and is more suitable for practical application expansion; meanwhile, by using a plurality of keys, the detection processing capacity of the encrypted video can be reserved under the condition that sensitive information is not leaked, so that help can be provided for applications such as a video monitoring system and cloud storage.

Drawings

FIG. 1 is a basic flow diagram of a process employing the present invention;

FIG. 2 is a block diagram of a method of implementing encryption in accordance with the present invention;

FIG. 3 is a block diagram of a key employing the method of the present invention;

fig. 4 is an example of a video frame encrypted using the method of the present invention.

Detailed Description

The drawings are for illustrative purposes only and are not to be construed as limiting the patent;

for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product;

it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.

Example 1

FIG. 1 is a flow chart of the compatible encryption of H.264/AVC video format based on CAVLC coding in the method of the present invention. As shown in fig. 2, the encryption implementation framework is to encrypt the interested block and the randomly selected block, use them as additional information, and place them after the residual block that is partially encrypted, so as to obtain an encrypted video code stream. The method comprises the following specific steps:

(1) grouping video data, specifically, grouping block data of a video according to the following mode:

selecting different detection algorithms according to different application scenes, such as face detection, positioning blocks belonging to interested areas in a video, and recording a set of the interested blocks as R; in addition, Mp is used in R₁And recording the position information corresponding to the interested block. In particular to

Mp₁Is a sequence composed of 0 and 1, where 1 represents that the block at the corresponding position in the video is the block of interest, and 0 represents that the block at the corresponding position in the video is the block of non-interest.

R may be represented as, for example, "Mp₁，……，0，r_iForm 0, … …', where 0 is a spacer, r_iRepresenting a block of interest.

Randomly selecting some blocks, and recording the set of the blocks as S; in S, with Mp₂Recording information of which set obtains the original video block; in order to restore the original video structure for detection processing under the condition of not leaking the content of the interesting block, a skip block is used for replacing the interesting block in the corresponding R in S; therefore, S contains both the block that is originally a skip and a skip block that is used to replace the block of interest. In particular, the amount of the solvent to be used,

Mp₂can be represented as a sequence consisting of 0, 1, where 1 indicates that the corresponding block is in S and 0 is vice versa.

An example of S may be "Mp₂，……，0，s_i0, skip, 0, … … ", where 0 is a spacer, s_iRepresenting a randomly selected block, skip being a skipped macroblock (replaced by another randomly selected block in the I-frame), skip being used to replace the block of interest in the corresponding position, enabling the video to use the recovered part side information for the detection processing operation.

And recording the set of residual blocks as O.

(2) Encrypting R and S:

firstly, for data in R, AES-CFB and a secret key K are utilized₃Each bit is encrypted to yield FE { R }, which is the bit of the bit streamThe middle FE { } means that all bits are encrypted by using AES-CFB;

② for the data in each block in S, using partial encryption algorithm (see step (3) for concrete method), secret key K₁Is encrypted to obtain

Then, the AES-CFB and the key K are reused₂Encrypting all the bits to obtain

(3) Partially encrypting O with a key of K₁The partial encryption method for CAVLC coding is as follows:

(ii) encrypting an Intra prediction mode IPM, wherein

The Intra — 16 × 16 encryption method is: the Intra _16 × 16 prediction modes are 4, and are coded in the last bit of the codeword of the macroblock type, so that the last bit of the codeword corresponding to the macroblock type mb _ type is encrypted;

the Intra — 4 × 4 encryption method is: there are 8 Intra _4 × 4 prediction modes, which are coded using the most likely mode MPM. The identifier is 1, indicating that the prediction mode is the most probable mode MPM. If the most likely mode MPM identifier is 0, then the three bits of the suffix are used to represent the difference between the prediction mode and MPM; encrypting these three bits does not affect format compatibility, so the three bits of this suffix are selected for encryption.

Secondly, encrypting a suffix of a motion vector residual MVD code word of each block in the O, specifically:

in H.264/AVC encoded by CAVLC, MVD is encoded using the exponential Golomb code EG 0. The exponential golomb code may be represented in the form of a "prefix 0 suffix," where the prefix consists of bits of all 1's, representing a group; the suffix indicates the offset of the encoded parameter in the group and the corresponding symbol information. The suffix of the encrypted EG0 codeword does not change format compatibility, and therefore, the suffix of the MVD codeword is selected for encryption.

Thirdly, encrypting the amplitude and the sign of the non-zero coefficient of each block in the O, specifically:

in h.264/AVC using CAVLC coding, the following form is used for a residual coefficient after coding such as transform, quantization, prediction, and the like:

the "number of non-zero coefficients, the number of trailing coefficients, the sign of trailing coefficients, the magnitude of non-zero coefficients other than trailing coefficients, the number of leading zeros of the last non-zero coefficient, and the number of leading zeros of each non-zero coefficient".

Where the amplitude of the non-zero coefficients are encoded using EG 0. Similarly, the suffixes of these EG0 codewords are the bits used for encryption. Further, bits used for encoding non-zero coefficients and trailing coefficient symbols are also bits that need to be encrypted.

(4) And (3) packaging the generated encryption blocks in the step (2), and reorganizing the generated encryption blocks and the generated part of encryption blocks into an encryption video code stream with compatible format.

Packing the data in R into NALU of type 22;

packing the data in S into NALU of type 23;

thirdly, reorganizing the data in the O into a video segment, recording the video segment as NVB, and recalculating partial parameters in the parameter set in the NVB, specifically the following types of parameters:

a. the height and width parameters of the video are replaced by the size of NVB;

b. replacing the parameter of the address information of the first macro block in the video slice header into the address in the NVB;

replacing the intra prediction mode IPM of the edge macro block in the NVB with a mode which does not need prediction from pixels beyond the range of the image in the NVB;

MVD is recalculated from the predicted motion vector PMV in NVB by the formula MV ═ PMV + MVD.

Recording the related original parameters in the NVB and the related parameter sets in the R, S as P, and packaging the parameters after complete encryption into NALU of type 17;

fifthly, the NALUs are placed behind the NVB code stream to obtain the encrypted video code stream.

(5) The method can select the region of interest to encrypt according to requirements. At the same time, a multi-level protection is provided for the video, and the key structure is shown in fig. 3. And recovering partial information except the region of interest by using the partial key for detecting the encrypted video. The flow of using partial key to restore original video structure information for processing is as follows:

utilizing secret key K₂Decrypting data in a NALU of NALU type 23 to obtain a partially encrypted randomly selected block

② utilizing secret key K₂Decrypting data in NALU with NALU type 17 to obtain partially encrypted original parameters

③ according to Mp₂From

And

and recovering the video with the original video structure for detection processing.

(6) The complete decryption process is the reverse process of encryption, and the specific flow is as follows:

utilizing secret key K₂、K₁Sequentially decrypting data with NALU types of 17 and 23 to obtain a random selection block S and an original parameter P;

② utilizing secret key K₃Decrypting the data with the NALU type of 22 to obtain R;

utilizing secret key K₁Decrypting the content in the NVB to obtain the residual block O and other parameters;

r according to Mp₁，Mp₂And recovering the original video structure, and performing subsequent decoding work by using the decrypted data.

The principle of the method of the invention is as follows:

the method encrypts all bits in the region of interest extracted by preprocessing, and partially encrypts other regions, thereby providing special protection for the region of interest. The method combines bit-by-bit encryption and partial encryption, and provides a multi-level key for video content, so that the method can detect and process by using partial keys under the condition of not leaking information of the region of interest. Meanwhile, the random selection block is added in the method, and the video block information is reorganized, so that the encrypted video code stream structure has great difference with the original video code stream structure, side information leakage can be better prevented, and the video content is protected.

The results of experiments carried out by the method of the invention are as follows:

taking a 352 × 288 video as an example, part of the results are shown in fig. 4:

wherein, the image on the left is the original video frame, and the image on the right is the encrypted video frame. It can be seen that our algorithm can protect video content well. The detailed results are shown in the following table:

wherein, each video segment for testing is 300 frames, JM18.6 reference code is adopted, IR is residual information, LSD is local variance, ES is encryption space. As can be seen from Table 1, the video IR encrypted by the method of the present invention is very small, and the LSD is very large, so that a good video content protection effect is achieved. Meanwhile, the ratio of the encryption space to the whole parameter space exceeds 62%, and compared with the existing encryption (20%), the method can better resist brute force cracking and protect video contents.

The same or similar reference numerals correspond to the same or similar parts;

the positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the present patent;

it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An H.264/AVC video format compatible encryption method based on CAVLC coding is characterized by comprising the following steps:

s1: grouping videos according to the blocking information in the code stream;

s3: using partial encryption on the remaining blocks;

s4: organizing the partial encryption blocks generated in S3 into a format-compatible encrypted video code stream, and then packaging the partial encryption blocks generated in S2 into a NALU;

the specific process of step S1 is:

s11: selecting different detection algorithms according to different application scenes, positioning blocks belonging to interested areas in the video, and recording a set of the interested blocks as R; in addition, Mp is used in R₁Recording the position information corresponding to the interested block;

s12: randomly selecting some blocks, and recording the set of the blocks as S; mp for S₂Recording position information; in addition, a skip block is used in S to replace a corresponding block in R for encrypted video processing operation;

s13: the remaining blocks are denoted as O.

2. The CAVLC-encoding-based h.264/AVC video format-compatible encryption method of claim 1, wherein said specific process of step S2 is:

s21: for the data in R, encrypting each bit in the R by using AES-CFB;

s22: and after partial encryption is carried out on the data in each block in the S, all bits are encrypted through AES-CFB.

3. The CAVLC-encoding-based h.264/AVC video format-compatible encryption method of claim 2, wherein said specific process of step S3 is:

s31: intra prediction mode IPM of data in encrypted O;

s32: encrypting a suffix of a motion vector residual MVD codeword of the data in O;

s33: trailing coefficient symbols, suffixes of non-zero coefficients and their symbols of the data in the encrypted O.

4. The CAVLC-encoding-based h.264/AVC video format-compatible encryption method of claim 3, wherein said specific process of step S4 is:

s41: packaging the encrypted data in the R into NALU of type 22;

s42: packaging the encrypted data in the S into NALU of type 23;

s43: organizing the encrypted data in the O into a new video, recording the new video as NVB, and recalculating partial parameters in a parameter set in the NVB;

s44: marking the original value of the parameter needing to be recalculated in the NVB and the related parameter set in R, S as P, and packaging the parameter P into NALU of type 17 after being completely encrypted;

s45: NALUs of types 17, 22 and 23 are placed after the stream of NVBs to generate an encrypted video stream.

5. A method for recovering side information for detection processing, which is to process the encrypted video bitstream generated by the CAVLC-based h.264/AVC video format compatible encryption method of claim 4, wherein said method for recovering side information for detection processing is:

s51, decrypting the data in NALU type 23 to obtain partially encrypted randomly selected block

S52 decrypting NALU type 17Data, obtaining partially encrypted original parameters

S53 according to Mp₂From

And

and recovering the video with the original video structure, wherein the video is used for detection processing,

is the remaining block of partial encryption.

6. A decryption method for decrypting an encrypted video stream generated by the CAVLC-encoding-based h.264/AVC video format-compatible encryption method of claim 4, wherein said decryption method is:

s61, decrypting the data in the NALU with the NALU types of 17 and 23 to obtain a random selection block S and an original parameter P;

s62, decrypting the data in the NALU with the NALU type of 22 to obtain an interested block R;

s63, decrypting the data in the NVB to obtain the residual block O and other parameters;

s64 according to Mp₁，Mp₂And recovering the original video structure, and continuously decoding by using the decrypted data.