CN104093029B - A kind of Video Encryption Algorithm based on new Spatiotemporal Chaotic Systems - Google Patents

A kind of Video Encryption Algorithm based on new Spatiotemporal Chaotic Systems Download PDF

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CN104093029B
CN104093029B CN201410349710.5A CN201410349710A CN104093029B CN 104093029 B CN104093029 B CN 104093029B CN 201410349710 A CN201410349710 A CN 201410349710A CN 104093029 B CN104093029 B CN 104093029B
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CN104093029A (en
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佟晓筠
李凌昊
王翥
张淼
刘杨
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Harbin Institute of Technology Weihai
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Abstract

A kind of H.264 Video Encryption Algorithm based on Spatiotemporal Chaotic Systems, belongs to the technical field of multimedia information present invention.It is difficult while meeting the low requirement of real-time, high security, complexity for H.264 Video Encryption Algorithm.The present invention is by designing complicated Spatiotemporal Chaotic Systems model, construct composite chaotic cryptographic algorithm, the safer encryption pseudo-random sequence for being difficult to be broken of design generation is simultaneously by selecting control extension technology, to frame in inter-frame forecast mode, many places critical data in residual error data scanning sequency and coding before CAVLC cataloged procedures coding is encrypted.Theory analysis and test result indicates that, inventive algorithm enciphering rate is fast, safe, influences small to compression ratio, while having accomplished to keep the non-destructive of video format, is with a wide range of applications and practical value.

Description

Video encryption algorithm based on new spatiotemporal chaotic system
Technical Field
The invention belongs to the technical field of multimedia information safety, and particularly relates to an H.264 video encryption algorithm based on a spatiotemporal chaotic system.
Background
With the continuous development and innovation of computer network technology and wireless mobile communication technology, digital media data (including images, sounds, videos and the like) are used more and more widely in people's lives, and therefore, multimedia video applications based on network transmission are also diversified, for example, in related fields such as video conferences, video on demand, video real-time monitoring systems and the like. As with other networks for transmitting data, if video data is transmitted in an open network without being encrypted, the video data can be easily attacked by people, such as data interception, information stealing, data tampering, data deletion, and the like. The security of video data is crucial for multimedia applications, which has become an obstacle to the development of current video technology. Therefore, how to implement a more effective video encryption technology while sufficiently ensuring the convenience of video services becomes a problem that needs to be solved urgently.
Currently, the mainstream video compression technology in the world is H.264/AVC which is a new generation video coding standard jointly established by ITU-T and ISO/IEC, and the technology is widely applied to many multimedia application fields, and designing an encryption algorithm based on the H.264 coding and decoding standard and not influencing the compression coding efficiency as much as possible is a very challenging and difficult work. H.264 video coding data has the characteristics of format particularity, large data volume, high real-time application processing capacity requirement and the like, so that the H.264 coding format needs to be specially considered when an encryption algorithm is designed, and traditional encryption algorithms such as DES, RSA and the like are increasingly not suitable for H.264 encryption. The main research on the encryption algorithm designed based on the h.264 coding format is as follows:
ahn et al encrypt and scramble the INTRA-prediction mode according to the property of the H.264 data coding format, and the method respectively randomly scrambles the INTRA-4 × 4 block and INTRA-16 × 16 block prediction modes in all I, P, B frames in the video, so that a high-efficiency real-time encryption algorithm is realized, and the algorithm hardly affects the compression ratio of the video data; spinsant et al propose to select a part of encryption algorithm, by selecting various parameters including quantization parameters, deblocking filter coefficients, intra-frame prediction modes, etc. in the process of encrypting H.264 video, or by encrypting all the parameters, the security of the encryption algorithm of this scheme is not very high, and the scheme can be generally only used for commercial use, such as pay television, etc.; people in Jian nations and the like of the joint fertilizer industry university select important parameters of an encryption part in the H.264 entropy coding CAVLC process, and encrypt an intra-frame prediction mode in the exponential Golomb coding process, so that the rapid H.264 encryption is realized on the premise of not influencing the compression ratio; wang Y et al, on the basis of the predecessors, designed an encryption algorithm with a controllable encryption effect for a non-zero coefficient amplitude, and implemented a video encryption scheme with a selectable encryption effect.
Through analysis, the existing video encryption algorithm designed based on H.264 has the contradiction among safety, instantaneity and compression ratio. The algorithm has high real-time performance, so that the safety is relatively low and the encryption safety requirement cannot be met; the algorithm with high security is low in encryption speed and large in influence on the compression ratio of video data, and is not suitable for practical application. On the basis of the previous research, the invention provides a video encryption algorithm based on a novel composite space-time chaotic system aiming at an H.264 coding and decoding format, the algorithm is designed and selected to generate a pseudo-random sequence flow by a more complex space-time chaotic system under the condition of extremely low loss of compression efficiency and compression ratio, and key data in a plurality of coding and decoding processes are selected for encryption, so that the encryption algorithm provides higher safety while ensuring real-time performance.
Disclosure of Invention
The invention aims to provide a video encryption algorithm based on a novel composite space-time chaotic system aiming at an H.264 coding and decoding format, under the condition of extremely low loss of compression efficiency and compression ratio, the algorithm designs and selects a more complex space-time chaotic system to generate a pseudo-random sequence flow, and selects key data in a plurality of coding and decoding processes to encrypt, so that the encryption algorithm provides higher safety while ensuring real-time performance, and the application field of the encryption algorithm is extremely wide.
The invention discloses a video encryption algorithm based on a novel composite space-time chaotic system aiming at an H.264 coding and decoding format, which comprises specific algorithm content and a specific implementation mode, and in the aspect of algorithm design, the invention innovatively adopts space-time chaos as a pseudo-random sequence generation model for encryption in the invention, constructs a new local equation, processes a user key, eliminates iteration influence of a chaos equation, and generates a pseudo-random sequence flow with high randomness and high safety; meanwhile, the invention provides a selective encryption control module, and the time-space chaos encryption module and the selective encryption control module are combined, so that the uncertainty of each encryption process is caused; on the basis of selecting traditional encryption positions such as an intra-frame prediction mode, an inter-frame block mode, a trailing coefficient sign bit and the like on the basis of selecting encryption positions and data, an encryption algorithm based on a scanning sequence of residual data blocks is designed and innovated, and on the premise of not influencing the characteristics of the original scanning sequence, the local scanning sequence is scrambled, so that encryption scrambling is performed. And finally, designing and implementing a specific operation mode according to the algorithm content, realizing an H.264 coding and decoding platform for quickly encrypting and decrypting the video, and ensuring high safety and operability of the platform.
The technical scheme adopted by the invention for solving the technical problems is as follows:
1. novel space-time chaos algorithm model
The one-dimensional coupling lattice model is adopted as follows:
Xn+1(i)=(1-)f(Xn(i))+/2[f(Xn(i+1))+f(Xn(i-1))](1)
where n is the time after discretization, i is the coordinates of the grid, representing the coupling strength (diffusion coefficient), and the periodic boundary condition is xn(0)=xn(L). Namely, the coupling mapping grid system is a dynamic system which discretizes time and space.
2. Video encryption algorithm based on new space-time chaos
The algorithm relates to two main modules, namely a selective encryption control module and a space-time chaos encryption module, and the overall design flow chart of the encryption algorithm is shown in figure 1.
The original video stream enters an encoder to be compressed and encoded, wherein mode data after intra-frame prediction mode selection and inter-frame block mode selection are selectively encrypted through a selective encryption control module, other encoding residual data enter a CAVLC entropy encoding process, and related encoding coefficients in the encoding process are selectively encrypted through a pseudo-random sequence stream generated by a space-time chaotic system through the selective encryption control module.
2.1 Selective encryption control Module design
In this block, we select the more common logistic equation to generate a stream of pseudo-random sequences. The pseudo-random sequence is used for judging when encrypting the positions, the data to be encrypted related to encryption is determined and selected according to the parity of the pseudo-random sequence, when the read value is 1, encryption operation is carried out on the current corresponding frame data, and on the contrary, if the read value is zero, the current corresponding frame data is selected to be not encrypted. As shown in fig. 2, the encryption selection control pseudo-random sequence generator uses formula (2) as a generation equation of the pseudo-random sequence:
xi=μxi-1(1-xi-1) (2)
wherein 4 is more than or equal to mu and more than or equal to 3.569946, x0The range of (1) is (0); here, in order to generate a binary random sequence for selection control, a mean threshold method is used herein to generate a sequence according to equation (3):
aver=∑xi/n
key[i]=0;if xi<aver;
key[i]=1;if xi>aver; (3)
wherein n isThe total length of the original floating point sequence, aver, is the average value of the generated original floating point sequence when the current sequence value xiWhen the value is less than aver, a one-bit binary sequence value key [ i ] is generated]Is equal to 0, when xiWhen the average is larger than aver, a one-bit binary sequence key [ i ] is generated]Equal to 1; the finally generated binary pseudorandom sequence key is used for selecting encryption control.
The positions to be encrypted comprise intra-frame prediction mode parameters, inter-frame block mode parameters and zigzag rearrangement residual data before CAVLC coding, wherein the trailing coefficient sign bit and the non-zero coefficient amplitude in the coding are five parts, and an encryption control module is added, so that on one hand, the data of each encryption operation is not increased, and the real-time performance of an encryption algorithm is ensured; on the other hand, due to the introduction of the selective encryption module, the scheme is changed into dynamic encryption, the encryption data of each encryption sub-process is different from the encryption effect, so that the encryption security of the algorithm is higher, and a better encryption effect can be obtained.
2.2 spatio-temporal chaos equation design and Performance analysis
On the basis of designing an encryption control module, the invention designs a space-time chaos encryption module based on a space-time chaos system, as shown in figure 3, the module inputs a secret key through a user, the secret key is sent into the space-time chaos system, a pseudorandom sequence stream with the length of 512 bits for encryption is generated through initial value acquisition, data truncation and transformation of a space-time chaos box, and a coupled mapping lattice system is a dynamic system which discretizes time and space but keeps continuous state variables. We select the neighboring spatiotemporal chaos model here:
Xn+1(i)=(1-)f(Xn(i))+/2[f(Xn(i+1))+f(Xn(i-1))](4)
wherein n is the discretized time, i is the iteration number, i represents the lattice space coordinate, i is greater than or equal to 0 and less than or equal to 15, i is the coupling strength, the value range is greater than or equal to 0 and less than or equal to 1, f (x) is the local chaotic mapping, and f (x) algorithm is selected as follows:
f(x)=8*x4-8*x2+1 (5)
as a local f (x) chaotic equation, the value range of x is (-1, 1).
Relevant data of the local chaos mapping formula (5) in the spatiotemporal chaos are tested to comprise Lyapunov indexes and approximate entropy indexes shown in the table 1, the table 2 and the table 3:
TABLE 1 local chaos mapping Lyapunov exponent comparison
TABLE 2 approximate entropy index comparison
TABLE 3 comparison of Lyapunov indexes of different local equations of spatio-temporal chaos (4)
It can be seen that, compared with the Logistic equation, the correlation performance of the local chaotic mapping equation (5) is better than that of the Logistic equation. The space-time chaos is a complex high-dimensional chaotic system, wherein a plurality of positive Lyapunov indexes can ensure the complexity of a generated chaotic sequence, and can effectively prevent an attacker from attacking the chaotic system by predicting the chaotic sequence. In addition, compared with a single chaotic mapping, because the lattices are mutually coupled, under the condition that the current state value of each lattice is known, the calculation of the value of the previous state of the lattice is more difficult, so that the system has better unidirectionality, the difficulty of attack by an attacker is greatly improved, and the safety of the encryption system is improved.
2.3 pseudo-random sequence generation algorithm based on spatio-temporal chaos
After a space-time chaos equation model is designed, the invention designs a pseudo-random sequence generation method for encryption operation, and a key sequence K with the length of 16BYTE input by a user is K0K1K2K3K4K5K6...K15
pk[i]=(k[i]+0.1)/256 (6)
Wherein k [ i ]]For the ith key, i is greater than or equal to 0 and less than or equal to 15, and then the initial values of 16 lattices are generated by using the formula (6), and are respectively represented by an array pk [ i ≦ i]Storing, then carrying in a space-time chaos equation (4) with the formula (5) as a local chaos mapping to iterate for 50 times, eliminating the influence of an initial value, and enabling a lattice value after each iteration to be composed of an array nkn[i]And (5) storing.
The pseudo-random sequence flow generated by the space-time chaotic system is used for carrying out encryption operations such as exclusive OR and the like on data to be encrypted, so how to generate a pseudo-random sequence with good enough randomness is an important factor for ensuring the safety of the video encryption algorithm. According to the document [14], the randomness of the sequence generated from the beginning of the spatio-temporal chaos model formula (4) is not very good, the distribution is not symmetric about 0, and in order to obtain a sequence with better balance, the following operations are performed:
firstly, according to the invention, the random number nk [ i ] generated by the space-time chaos]Subtracting one lattice sequence from another in the manner of equation (7) to obtain a new sequence nKn[i]The distribution is substantially symmetrical about 0.
nKn[i]=(nkn[i]-nkn[16-i+1])/2,i∈[0,7](7)
Wherein nKn[i]For the new sequence obtained after calculation, nk [ i]Is the sequence corresponding to the ith lattice.
After obtaining a new sequence, intercepting the data of the 9 th-24 th bit 2byte after the decimal point, generating a random sequence of 16x 2byte after each iteration twice because of 16 boxes, and obtaining the data of the tempLn[i]And (3) storing:
for better randomness, for tempLn[i]The sequence is subjected to F/G/H/I function transformation, and is specifically shown in formulas (8), (9), (10) and (11):
cnew=H(a,b,c,d)=[(a+b+c)+d]mod 256 (10)
separately convert tempLn[i]The loop is taken into four functions to obtain the value of tempLn[i]Storing, specifically calculating pseudo codes as follows:
for(i=0;i<4;i++)
{
tempLn[(4*i)%16]=F(tempLn[(4*i)%16],tempLn[(4*i+1)%16],tempLn[(4*i+2)%16],tempLn[(4*i+3)%16]);
tempLn[(4*i+1)%16]=G(tempLn[(4*i+1)%16],tempLn[(4*i+2)%16],tempLn[(4*i+3)%16],tempLn[(4*i)%16]);
tempLn[(4*i+2)%16]=H(tempLn[(4*i+2)%16],tempLn[(4*i+3)%16],tempLn[(4*i)%16],tempLn[(4*i+1)%16]);
tempLn[(4*i+3)%16]=I(tempLn[(4*i+3)%16],tempLn[(4*i)%16],tempLn[(4*i+1)%16],tempLn[(4*i+2)%16]);
}
and (3) performing iterative computation for multiple times through the process, and performing binarization processing through a formula (3), and finally obtaining a pseudorandom sequence with good randomness and the length of 512 bits for data encryption of the H.264 video.
2.4 coded encryption Algorithm design
(1) Predictive mode scrambling encryption
In the encrypted data, because the INTRA-frame prediction mode and the inter-frame block mode have fixed mode classification, for example, the 4X4 INTRA-frame prediction module is divided into 9 prediction modes, so that encryption disturbance cannot be directly performed, otherwise, the encoding mode is illegal, which results in abnormal decoding, the INTRA-frame prediction scrambling mode proposed by the document [7] is simple and effective, but because the security mainly depends on the fixed-length sequence used by the INTRA-frame prediction module, Friedman key guessing and known plaintext attack cannot be prevented under the condition of limited sequence length, the invention can not only enhance the resistance to cryptoanalysis by performing XOR operation on the INTRA-frame prediction mode by using the chaos-time-space system to generate the pseudo-random sequence in the INTRA-frame prediction mode, such as INTRA-4X 4 block, and the like in the INTRA-frame prediction mode, and generating the 3-bit random sequence by the chaos-time-space pseudo-time-random sequence generator and performing XOR operation on the INTRA, but also expands the key space. The encryption process is as follows:
uRandSeq=Sqa_Chaos_Generator(k,3);
wherein,for exclusive or operation, Sqa _ Chaos _ Generator is a spatio-temporal Chaos iteration function generated by formula (4), k is an initial value of Chaos iteration, 3 is a pseudo-random sequence of 3 bits obtained each time, uRandSeq is a pseudo-random sequence generated by the spatio-temporal Chaos iteration, mode and sumEncrp _ Mode is a value before and after the prediction Mode encryption, respectively.
Meanwhile, for the inter-frame block mode, since it supports 7 variable block sizes (16x16, 16x8, 8x16, 8x8, 8x4, 4x4), each variable block has a fixed motion vector, in order to prevent decoding errors caused by scrambling of the block mode, the scrambling process for the inter-frame mode is as follows:
table 4 interframe block mode encryption scheme
Whether a 1-bit pseudo-random sequence generated by a space-time chaotic pseudo-random sequence generator is zero or not is judged to judge whether a pair of block modes with the same motion vector are scrambled, as shown in table 4, a 16x8 mode is taken as an example, and if the 1-bit pseudo-random sequence is scrambled, the 1-bit pseudo-random sequence is scrambled into a corresponding block mode 8x16 with the same motion vector;
in the CAVLC coding process, as mentioned in the above section, on the premise of not guaranteeing that the original coding format of the video is damaged, the algorithm selects zigzag rearranged residual error data before coding, sign bits of trailing coefficients, non-zero coefficient amplitude values and the number of pre-zeros of each non-zero coefficient to perform encryption disturbance through an encryption control selection module by using a pseudo random sequence generated by a space-time chaotic system, so that the encryption safety is improved as much as possible while the sufficient and small data quantity is ensured to be encrypted as much as possible.
(2) Zigzag scanning order encryption of residual data
In the process of H.264 data coding, after DCT (discrete cosine transform) transformation and quantization are carried out, the energy of the obtained residual data is mainly concentrated in low-frequency and direct-current areas. After the coefficients are quantized, the low frequency and dc components have a small number of larger values and most of the components are zero, so that before entropy coding, in order to achieve more efficient coding, the residual coefficients can be subjected to zigzag scanning, i.e. zigzag scanning, according to the statistical characteristics from high to low, so as to achieve better coding efficiency, and the zigzag scanning rule is shown in fig. 4.
In the invention, residual data zigzag scanning is encrypted and scrambled, in order to prevent the characteristic after DCT coding from being seriously damaged after encryption scrambling, and the compression efficiency of entropy coding is greatly reduced, according to the graph shown in FIG. 5, the scanning direction of each diagonal line in the zigzag scanning process is scrambled, the reading direction of each diagonal line data after encryption scrambling is determined by the parity of a 1-bit pseudorandom sequence value generated by a space-time chaotic pseudorandom sequence generator every time, and a specific encryption method is shown in FIG. 5.
In fig. 5, taking 8 × 8 data block scanning as an example, the generated pseudo random sequence is K1101011100101, the scanning order of each diagonal line data is determined by the parity of the sequence value of each 1bit, and when the read sequence value is 1, the scanning order of the diagonal line of the corresponding data block is reversed, and finally, the scrambled residual data scanning order is as shown in the right 8 × 8 data block in fig. 5.
Therefore, on the premise of integrally ensuring that the data scanning sequence is still a reading rule from top left to bottom right, the specific scanning sequence is scrambled, and the encryption of residual data is realized on the basis of less operation and less influence on the compression efficiency.
(3) CAVLC encoding process encryption
In the CAVLC coding process, the number of trailing coefficients is between 0 and 3, so that the sign bit T1_ Signs of the encrypted trailing coefficients needs to be subjected to exclusive OR with a 3-bit pseudo-random sequence at most, the amplitude of non-zero coefficients except the trailing coefficients is divided into a prefix (level _ prefix) and a suffix (level _ suffix), and the coding process firstly adopts formulas (13) and (14) to convert signed levels into unsigned level codes:
levelCode=(level<<1)-2if level>0; (13)
levelCode=()level<<1)-1if level<0; (14)
the level _ prefix and level _ suffix values are calculated next:
level_prefix=levelCode/(1<<suffixLength); (15)
level_suffix=levelCode%(1<<suffixLength); (16)
the prefix and the suffix of the character string are obtained through table lookup to complete coding, and through experiments, if the levelCode value is encrypted, on one hand, the compression efficiency of the coding can be seriously influenced, and on the other hand, the encrypted data can be illegally decrypted.
TABLE 5 level _ prefix code word Table
Therefore, the invention carries out encryption operation aiming at the level _ prefix, influences the corresponding code table selection during coding by disturbing the level _ prefix, and the code table is shown as the table 5, thereby realizing the encryption of the nonzero coefficient amplitude value, and the encryption process is as follows:
uRandSeq=Spa_Chaos_Generator(k,4);
wherein,for exclusive or operation, Spa _ Chaos _ Generator is a spatio-temporal Chaos iteration function generated by formula (4), k is an initial chaotic iteration value, 4 is a 4-bit pseudo random sequence obtained each time, uRandSeq is a pseudo random sequence generated by the spatio-temporal Chaos iteration, and level _ prefix and Encrp _ level _ prefix are values before and after prefix encryption of non-zero coefficient amplitude values respectively.
3 safety analysis
The safety analysis in this section is used as the embodiment of the actual effect of the invention, and the beneficial effect of the invention can be seen visually through the actual data analysis.
(1) Visual security analysis
Three standard sequences of foreman, mobile and akiyo are selected for testing, and the original image and the encrypted image are respectively shown in a figure (6).
Due to scrambling of prediction modes between frames in an algorithm and encryption scrambling of a residual coefficient scanning sequence and a coding control coefficient in CAVLC in entropy coding, the background and main content information of a video before and after encryption are seriously scrambled and cannot be identified, a good encryption effect is achieved, and the visual security is high.
Fig. 7 shows the comparison between before and after encryption of P frames of I frames in two test sequences of foreman and mobile, and it is found through the comparison that the encryption algorithm of the present invention has a better encryption effect on video sequences in h.264 format, and because the encrypted data relates to the prediction mode and CAVLC entropy coding process, it has a contextual effect, and the encryption effect is diffused for P frames inter-frame prediction based on I frames, the encryption effect is better, and an image disturbance which is more unrecognizable is generated for the original video visually.
(2) Key security analysis
The encryption algorithm of the invention encrypts the coding coefficients in the intra-frame prediction mode, the inter-frame block mode, the residual error data scanning sequence and the CAVLC coding operation, and the key spaces of two keys input by a user are respectively 1014And 2128So that the key space of the final overall encryption algorithm is 1014+2128≈246+2128=2128Pseudo-random sequences with encryption length of 512 bits are generated, and meanwhile, due to the fact that the data volume of the video is large, the key sequences are reset, operated bit by bit and recycled, decryption is extremely difficult through exhaustive attack. Meanwhile, as the encryption algorithm of the invention is additionally provided with an encryption control module, the main encryption module adopts a space-time chaotic system and is provided withA more complex pseudo-random sequence chaotic generating system is selected, the randomness of the pseudo-random sequence used for encryption is improved, and the method has higher safety and anti-cracking performance.
(3) Video image peak signal-to-noise ratio (PSNR) and Mean Structural Similarity (MSSIM) analysis
The video data has the characteristics of large data volume and complex structure relative to the image data, so that the video encryption algorithm is different from the traditional image encryption algorithm in encrypting all pixel data, the video image is disturbed on the premise of encrypting a small amount of control parameter information as much as possible, the effect of visually identifying the original image information is achieved, all data are not encrypted, the encryption safety is reduced relative to the image encryption, but the difficulty of attack is still large due to the large data volume of the video. The peak signal-to-noise ratio (PSNR) and the average structure similarity (MSSIM) of the video frame images before and after the coding of the encryption algorithm are tested and analyzed.
1) Peak signal to noise ratio (PSNR) contrast analysis
The peak signal-to-noise ratio (PSNR) is used to measure the difference between two images or videos, where the PSNR is used to measure the difference between the encrypted compressed video data and the non-encrypted compressed video, which are decoded to obtain the reconstructed original video, where the larger the difference is, the smaller the PSNR value is, the better the encryption effect is, and the PSNR is defined as follows:
PSNR=10×lg(2552/MSE); (18)
MSE=1/wh∑∑(I(i,j)-J(i,j))2; (19)
where the image size is w × h, and I (I, J) and J (I, J) represent the pixel values of the (I, J) positions in the images I and J, respectively.
TABLE 6 analysis of MSE and PSNR values of compressed video reconstructed video streams before and after encryption
Table 6 shows MSE values and PSNR values between reconstructed video streams of compressed videos before and after encryption, and test results show that MSE values and PSNR values before and after encryption of three video streams are large, and PSNR values are very small, so that the video encryption algorithm has a better encryption effect than the conventional video encryption algorithm.
2) Mean Structural Similarity Index (MSSIM) comparative analysis
The Structural Similarity (SSIM) is another evaluation index for measuring the similarity of two images, combines with the Human Visual System (HVS), makes up for the deficiency of PSNR, is more suitable for evaluation tests for video encryption algorithms, and has more accurate measurement results. The SSIM index is defined as follows:
SSIM(x,y)=(2μxμy+c1)(2σxy+c2)/(μx 2y 2+c1)(σx 2y 2+c2) (20)
where x and y denote the blocks of the two images, μxAnd muyDenotes the mean value of x and y, respectively, σxAnd σyDenotes the variance, σ, of x and y, respectivelyxyIs covariance, c1=(k1L)2,c2=(k2L)2Where k is1=0.01,k2L is 0.03, gray scale.
The invention uses MSSIM to evaluate the quality of a frame of image extracted from video stream in the encryption algorithm:
MSSIM(X,Y)=1/n∑SSIM(xi,yi) (21)
wherein X, Y represent a plaintext image and a ciphertext image, respectively, XiAnd yiThe number of the ith blocks corresponding to the two images is n image blocks, the smaller the MSSIM is, the larger the difference between the two images is, namely, the better the encryption effect is.
Table 7 comparison analysis of MSSIM values of video stream image frames before and after encryption
Table 7 shows the results of testing the MSSIM values before and after encryption of different frame types in the foreman and mobile test sequences, which are two P-frame images before the first I-frame and the next I-frame, respectively.
Fig. 8 is a comparison value of MSSIM of images before and after encryption of 90 frames before the foremost for the foremost frames of images of the foremost frames of the series, as can be seen from the figure, the comparison value of MSSIM is only 0.245 before and after encryption of the images of the I frames of the first frame of the series, on the premise. With the fact that each P frame is obtained through predictive coding, encryption influence is diffused continuously, MSSIM values are reduced continuously, the MSSIM comparison value of the image before and after encryption is reduced to 0.126 before the next I frame (with the serial number of 94), and index data are good.
FIG. 9 is the MSSIM comparison value of the image before and after encryption of the first 15 frames of the Mobile test sequence, because the color change of the image of the sequence is fine and smooth, the diffusion effect of the encryption algorithm of the invention is more ideal, the MSSIM value before and after encryption is kept below 0.1 from the first frame, and the excellent encryption effect is obtained.
(4) Coding compression ratio analysis
The encryption algorithm improves a generation system of a pseudo-random sequence, adopts a more complex space-time chaotic system which is more difficult to break, and adds an encryption control module system to the generated pseudo-random sequence.
TABLE 8 compression ratio comparison before and after encryption
As shown in table 8, the compression ratio influence before and after encryption is very small and can be almost ignored, so the encryption scheme of the present invention has very little influence on the compression ratio of the original video coding, and has a wide application space in aspects of video real-time secure transmission, etc.
(5) Coding computational efficiency analysis
The encryption information aimed by the algorithm is encrypted and scrambled by the encoding information in the video encoding process, the combination of the encryption and encoding processes is ensured, the time delay of encryption processing is greatly reduced, the influence on the complexity is small, the whole encryption process mainly adopts XOR and judgment operation, and the data encoding efficiency is hardly influenced.
TABLE 9 comparison of encoding durations before and after encryption
Table 9 shows the time lengths of the encoded 100 frames before and after the encryption of the three test sequences, and it can be seen from the data in the table that the encoding time lengths before and after the encryption are not substantially increased, so that the scheme herein is very suitable for the application and implementation of the real-time secure transmission of h.264. In addition, the algorithm of the invention improves the encryption security and does not disturb the format information and the control information in the video stream data, so the algorithm of the invention can well ensure the code rate control and can realize the compatibility with the standard code stream format.
Description of the drawings:
FIG. 1 is a general design flow chart of the H.264 video encryption process based on spatiotemporal chaos according to the present invention;
wherein (1) is an encoded video stream to be encrypted; (2) is the H.264/AVC video coding compression start; (3) is an intra prediction mode; (4) is an inter block mode; (5) is a CAVLC entropy coding process; (6) is to select encryption control; (7) scrambling/encryption (8) is a space-time chaos encryption module; (9) is an encoded ciphertext stream; (10) is a user key input; (11) is an encryption selection control pseudo-random sequence generator; (12) is a space-time chaos pseudo-random sequence generator; (13) is to generate a pseudo-random sequence K1; (14) is to generate a pseudo-random sequence K2;
FIG. 2 is a flowchart of an embodiment of the encryption selection control module of the present invention;
wherein (1) is an encoded video stream to be encrypted; (2) is a prediction mode encoding; (3) is a residual coefficient; (4) is CAVLC entropy coding; (5) is an intra prediction mode coding CAVLC entropy coding process; (6) is an inter-frame block mode encoding; (7) is the zigzag residual coefficient scan order (8) is the trailing coefficient sign bit; (9) a non-zero coefficient magnitude; (10) is a user key input; (11) adding a selection encryption control pseudo-random sequence generator; (12) selecting an encryption control pseudorandom sequence stream; (13) is data to be encrypted;
FIG. 3 is a detailed flow chart of the spatiotemporal chaos encryption module according to the present invention;
wherein (1) is an intra prediction mode; (2) is an inter block mode; (3) is the user key K; (4) is a space-time chaos pseudo-random sequence generator; (5) is scrambling; (6) is CAVLC entropy coding; (7) is the Zigzag residual coefficient scan order; (8) is the trailing coefficient sign bit (TI _ Signs); (9) non-zero coefficient magnitude (Levels); (10) is encryption; (11) is an encoded ciphertext stream;
FIG. 4 is a zigzag scan rule for H.264 video coding;
FIG. 5 is a schematic diagram illustrating a scrambling process for zigzag data scanning according to the present invention;
wherein (1) is a space-time chaos pseudo-random sequence generator; (2) is k-1101011100101; (3) is encrypted scramble scan;
FIG. 6 is a comparison of pre-and post-encryption effects for three test video sequences in accordance with the present invention;
wherein, fig. 6(a) (b) (c) are effect diagrams before encryption of three test sequences, respectively; FIG. 6(d) (e) (f) shows the effect of the encrypted three test sequences;
FIG. 7 is a comparison of the effects of the present invention before and after encryption for different types of frames;
wherein, fig. 7(a) (b) (c) (d) are effect diagrams before encryption of the test sequence, respectively; FIG. 7(e) (f) (g) (h) are the effect diagrams after the corresponding test sequences are encrypted; (a) the frame type of (c) is an I frame, and the frame type of (b) (d) is a P frame;
fig. 8 is the encrypted MSSIM value of the frame 90 frames before the foreman test sequence according to the present invention;
FIG. 9 is an SSIM value after encryption for the first 15 frames of a mobile test sequence according to the present invention;
FIG. 10 is a diagram illustrating the effect of the present invention before encryption for a mobile test sequence;
FIG. 11 is a diagram illustrating the effect of encrypting a mobile test sequence according to the present invention;
Detailed Description
In order to better understand the technical solution of the present invention, the following further describes the embodiments of the present invention with reference to the accompanying drawings.
Firstly, building an H.264 video encryption-based environment, particularly realizing the invention in an H.264 related coder-decoder, building a coding encryption-decryption environment, and completing the early preparation of H.264 coding, compression and encryption as shown in figure 1;
secondly, as shown in fig. 1, user initial keys for selecting the encryption control module and the spatio-temporal chaotic encryption module are respectively input and sent into corresponding key generators to complete the initial setting of the encryption system, prepare an original video stream to be encoded and encrypted, such as mobile.
And thirdly, operating an encoder, sending the original video to be encrypted and encoded into the encoder, starting the encoder to execute an encoding and encrypting process, generating two pseudo-random sequence streams for selection and encryption by the system, and simultaneously executing the encryption scheme designed by the invention at the same time of the original video encoding process according to the graph shown in the figure 2 and the figure 3.
Fourthly, the encoder finishes the encoding and encrypting process, displays the encoding result, judges whether the encoding is correct or not, and displays data such as time, compression effect, compression ratio and the like;
and fifthly, checking the encoded and encrypted H.264 video, confirming whether the encoded and encrypted H.264 video can be played normally or not, playing the effect, testing various performance indexes of the encoded and encrypted H.264 video, and judging the encryption safety.
And sixthly, performing decryption operation, wherein the decryption operation is the inverse operation of the encryption operation because the encryption operation in the invention is selection and exclusive-or operation, sending the H.264 video to be decrypted and decoded into a decoder, inputting a corresponding correct user decryption key, sending the key into the decoder, preparing for decoding and decryption, operating the decoder, executing the decoding and decryption operation, obtaining the decrypted and decoded original video after the decoding is finished, and obtaining related performance data.
Testing an experimental test platform T264(ver0.14), a hardware platform of Intel Core22.66GHz and a memory of 4GB, wherein the test sequences are three standard sequences of a standard CIF sequence, foreman, mobile and akiyo, the three video sequences are 300 frames, and the ratio of the foreman sequence I to the P frame is 8: 292; the ratio of the mobile sequence I to the P frame is 19: 281; the akiyo sequence I: P frame ratio is 3: 297.
Taking a mobile sequence as an example, the input original video format is standard CIF, yuv format video, the file size is 11138kb, the video frame size is 176 × 144, the total number of coded frames is 100 frames, and the frame ratio of the sequence I, P is 19: 281; a T264 coding and decoding test platform is adopted, a hardware platform is Intel Core22.66GHz, a memory is 4GB, and a coding mode adopts a basic mode. The original video effects are shown in FIGS. 10-11 below:
inputting an initial key sequence, and selecting a control module initial key to be 0.4111; the initial key of the space-time chaos encryption module is 'linyer 8281862108'; sending the video data to an encoder for encryption encoding, wherein after the encoding is finished, the corresponding video effects are shown in table 11:
the encryption coding time length is 1.09 s; the unencrypted encoding time length is 1.07 s; the size of the video after encryption coding and compression is 529,461 bytes; the size of the compressed video is 533,070 bytes after the unencrypted encoding; PSNR values, MSE values and SSIM values of five frames of the encoded video data and the encoded video data without encryption are shown in tables 10 and 11:
table 10: PSNR and MSE values of video stream before and after encryption
Table 11 comparison analysis of MSSIM values of video stream image frames before and after encryption
Reference to the literature
[1]WANG L,WANG W,MA J,et al.Perceptual video encryption scheme formobile application based on H.264[J].The Journal of China Universities ofPosts and Telecommunications,2008,15:73-78。
[2]Van Wallendael G,Boho A,De Cock J,et al.Encryption for HighEfficiency Video Coding with video adaptation capabilities[C]//2013IEEEInternational Conference Consumer Electronics(ICCE),2013,59(3):31-32.
[3]ITU-T Rec.H1 264|ISO/IEC 14496-10:2005(E).Advanced Video Codingfor Generic Audiovisual Services[S].
[4]Lian S,Liu Z,Ren Z,et al.Secure advanced video coding based onselective encryption algorithms[J].IEEE Transactions Consumer Electronics,2006,52(2):621-629.
[5]Zhang J,He Y,Yang S,et al.Performance and Complexity JointOptimization for H.264Video Coding[C]//Proceedings of the InternationalSymposium on Circuit and System.China:IEEE,2003:888-891。
[6]Spinsante S,Chiaraluce F,Gambi E.Masking video information bypartial encryption of H.264/AVC coding parameters[C]//The 13th Europeansignal processing conference,Antalya,Turkey,2005.
[7]Ahn J,Shim H J,Jeon B,et al.Digital Video Scrambling Method UsingIntra Prediction Mode[C]//PCM 2004.South Korea:LNCS 3333,2004:386-393.
[8] Jiang Guo, Bao Xian Yu, Lihua Lei, etc. FVEA-H, a kind of medicine for H.264 [ J ]. The system simulation journal 2008, 20(16): 4363-.
[9] The new encryption scheme [ J ] electronic newspaper suitable for H.264 real-time video transmission, 2006, 34(11): 2099-.
[10]Wang Y,O'Neill M,Kurugollu F.A Tunable Encryption Scheme andAnalysis of Fast Selective Encryption for CAVLC and CABAC in H.264/AVC[J],IEEE Transactions on Circuits and Systems for Video Technology,2013,23(9),1476-1490.
[11]Shahid Z,Chaumont M,Puech W.Fast Protection of H.264/AVC bySelective Encryption of CAVLC and CABAC for I and P frames,IEEE Transactionson Circuits and Systems for Video Technology,May,2011,21(5):565-576.
[12]Van Wallendael G,Boho A,De Cock J,et al.Encryption for HighEfficiency Video Coding with video adaptation capabilities[C]//2013IEEEInternational Conference Consumer Electronics(ICCE),2013:31-32.
[13] Wangyun, Lechang soldiers, which wave, chaotic encryption algorithm and Hash function construction research, Beijing: electronics industry publishers, 2011.
[14] Pengjun, Li Shuming, Zhang Wei, etc. spatio-temporal chaos binary sequence based on coupled mapping lattice model and its performance analysis [ J ], computer science 2005, 32(2): 196-.

Claims (1)

1. An H.264 video encryption method based on a spatiotemporal chaotic system is realized by two steps:
firstly, determining a selective encryption control module, generating a pseudorandom sequence key stream by a logistic equation, determining whether to execute encryption operation according to parity of the generated key stream, and when the read value is 1, performing encryption operation on related video syntax data in a current corresponding frame, including an intra-frame prediction mode, an inter-frame block mode and a scanning sequence of residual error data before CAVLC (context-adaptive coding) coding process; on the contrary, if the value is zero, the video grammar data related to the current corresponding frame is not encrypted;
and secondly, performing space-time chaotic encryption on the frame image to be encrypted in the selective encryption control module, wherein the space-time chaotic encryption is performed in two steps:
(1) firstly, a key stream required by video encryption is generated by a space-time chaos pseudorandom sequence method, and the specific method comprises the following steps: the user inputs a key sequence K of 16BYTE length0K1K2K3K4K5K6...K15
pk[i]=(k[i]+0.1)/256 (1)
Wherein k [ i ]]For the ith key, i is more than or equal to 0 and less than or equal to 15, the initial values of 16 lattices are generated by using the formula (1), and the initial values are respectively expressed by an array pk [ i ≦ i]Storing, then carrying in a space-time chaos equation (2) taking the formula (3) as a local chaos mapping to iterate for 50 times, eliminating the influence of an initial value, and enabling a lattice value after each iteration to be composed of an array nkn[i]Storing;
Xn+1(i)=(1-)f(Xn(i))+/2[f(Xn(i+1))+f(Xn(i-1))](2)
f(x)=8*x4-8*x2+1 (3)
in the formula (2), n is discretized time, namely n is iteration times, i represents a lattice space coordinate, i is more than or equal to 0 and less than or equal to 15 and is coupling strength, the value range is more than or equal to 0 and less than or equal to 1, an f function is a formula (3), in the formula (3), the value range of x is (-1,1), and random numbers nk generated by the spatio-temporal chaos are subjected to the methodn[i]Subtracting one lattice sequence from another in the manner of equation (4) to obtain a new sequence nKn[i]The distribution thereof is substantially symmetrical about 0;
nKn[i]=(nkn[i]-nkn[16-i+1])/2,i∈[0,7](4)
wherein nKn[i]For the new sequence obtained after calculation, nkn[i]The sequence corresponding to the ith lattice is set as the sequence corresponding to the ith lattice, i is more than or equal to 0 and less than or equal to 15, after a new sequence is obtained, the data of the 9 th-24 th bit 2byte after the decimal point is intercepted, because 16 boxes are provided, a random sequence of 16x 2byte can be generated after each iteration, and the tempL is used for determining the sequence of the data of then[i]Storing;
for tempLn[]F/G/H/I function transformation is carried out on the sequence, and the specific implementation method is as follows:
tempLn[a]=F(tempLn[(4*i)%16],tempLn[(4*i+1)%16],tempLn[(4*i+2)%16],tempLn[(4*i+3)%16]);
tempLn[b]=G(tempLn[(4*i+1)%16],tempLn[(4*i+2)%16],tempLn[(4*i+3)%16],tempLn[(4*i)%16]);
tempLn[c]=H(tempLn[(4*i+2)%16],tempLn[(4*i+3)%16],tempLn[(4*i)%16],tempLn[(4*i+1)%16]);
tempLn[d]=I(tempLn[(4*i+3)%16],tempLn[(4*i)%16],tempLn[(4*i+1)%16],tempLn[(4*i+2)%16]);
wherein the F/G/H/I function is as follows:
H(a,b,c,d)=[(a+b+c)+d]mod 256
wherein i is the iteration number, and the value range is [0, 3]]The above steps can be described as: a, b, c, d are tempLn[i]In the first iteration, a, b, c, d are respectively subjected to F, G, H, I functions, wherein a is (4 × i)% 16, b is (4 × i + 1)% 16, c is (4 × i + 2)% 16, and d is (4 × i + 3)% 16, four new numbers can be sequentially generated, and the iteration is performed for four times, namely tempL can be obtainedn[i]All 16 numbers in the array are converted into a new sequence after function transformation;
performing iterative computation for multiple times through the process, and performing binarization processing through a formula (5), and finally obtaining a pseudorandom sequence with good randomness and the length of 512 bits for data encryption of the H.264 video;
aver=∑xi/n;
key[i]=0;if xi<aver;
key[i]=1;if xi>aver; (5)
wherein n represents the total length of the sequence, aver is the average value of the generated sequence, and when the current sequence value xiWhen the value is less than aver, a one-bit binary sequence value key [ i ] is generated]Is equal to 0, when xiWhen the average is larger than aver, a one-bit binary sequence key [ i ] is generated]Equal to 1;
(2) after the step (1) is finished, a key stream generated by a space-time chaos pseudorandom sequence method is used for video encryption, an intra-frame inter-frame prediction mode, a scanning sequence of residual data, a trailing coefficient sign bit and a non-zero coefficient amplitude are selected for encryption, wherein the intra-frame prediction mode, the trailing coefficient sign bit and the non-zero coefficient amplitude are encrypted by an exclusive OR method, an inter-frame block mode is encrypted by a random scrambling method, in the encryption method of the residual data, scrambling is selected for the scanning direction of each diagonal line in a zigzag scanning process, and the reading direction of each diagonal line data after encryption scrambling is determined through the parity of a 1-bit pseudorandom sequence value generated by a space-time chaos pseudorandom sequence generator each time;
and after the encryption control module is selected in the first step and the space-time chaos encryption in the second step, H.264 video encryption based on the space-time chaos system is completed.
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