CN102523441A - H.264 compressed domain bit plane encryption method based on bit sensitivity - Google Patents

Abstract

The invention discloses an H.264 compressed domain bit plane encryption method based on bit sensitivity, which includes the H.264 code stream bit sensitivity testing step, the bit plane forming step and the bit plane encryption step. The encrypted bits are guaranteed to be the most important data for video reestablishing quality in the compressed code stream according to bit sensitivity information and the principle of the bit plane of the H.264 compressed code stream, so that computing is low in complexity, executing speed is high and the requirements of instantaneity of video application can be met. Compared with the conventional compressed domain video encryption method, the H.264 compressed domain bit plane encryption method is more purposeful, capable of guaranteeing higher safety on the condition of identical encrypted data quantity and keeping compatibility of an H.264 standard encoder and the code stream form after encryption and keeping the compression ratio of the code stream before and after encryption and constant and the like.

Description

H.264 compression domain bit-planes encryption method based on the bit susceptibility

Technical field

The present invention relates to the video-encryption in the multi-media information security field, be specially a kind of H264 compression domain bit-planes encryption method based on the bit susceptibility.

Background technology

Extensive use along with multimedia communications systems such as ecommerce, video conference, video monitoring, tele-medicine and 3G smart mobile phones; Various potential safety hazards such as multimedia messages such as image, video exists in network transmission process and is stolen, malice is distorted, the multi-media information security problem becomes and becomes increasingly conspicuous.For example, in various commercial applications, multimedia messages is stolen and will brings enormous economic loss to supplier; In the tele-medicine process, the leakage of patient's personal information will cause privacy right for patients to be encroached on; Especially the leakage of confidential departments' information such as military affairs, national defence, diplomacy tends to cause negative effect difficult to the appraisal.Therefore, the safety that how to guarantee multimedia messages has fully and effectively become the problem that current field of multimedia communication is needed solution badly.

Video-encryption is a kind of effective means that can guarantee video information safety.Existing video encryption method generally can be divided into the video-encryption and the compressed domain video that combine with coding and encrypt.The former is meant certain link that AES is embedded into cataloged procedure, such as dct transform, quantification or entropy coding etc.This type encryption method tends to cause the system compresses performance decrease, also need to change the structure of video standard codec usually, so practicality is relatively poor.

The compressed domain video encryption is meant encrypts the code stream that generates behind the video coding.Simple effective method is to adopt traditional text AES such as RSA, DES or AES etc. directly whole code stream to be encrypted.But the data volume of video information is very huge, whole code streams is encrypted will cause the load of encryption excessive, therefore can not satisfy the real-time demand of Video Applications.In order to obtain the compromise between fail safe and the computation complexity, people have proposed the selective video encryption, only select in the enciphered video data and the maximally related part of visually-perceptible.At present, it all is selectively a certain category information in the compressed bit stream to be encrypted that most of compression domain are encrypted, and for example encrypts the code stream header, changes predictive mode or scramble DCT coefficient code word etc., to improve the efficient of encrypting.Yet these methods can not guarantee that all encrypted bits all are to the of paramount importance data of video reconstruction quality, and code stream form after also being difficult to guarantee to encrypt and standard codec are compatible.The more important thing is that encipher only code stream header or predictive mode can not provide enough fail safes.

The decline degree of caused video reconstruction quality when the bit that the bit susceptibility refers to a certain type code word in the compressed bit stream makes a mistake.The video reconstruction quality descends obviously more, explains that the type code word is important to the video reconstruction quality more, and the bit susceptibility is also just high more.Therefore, according to the bit susceptibility information of all kinds code word in the code stream, in ciphering process, can guarantee the most important code word of video reconstruction quality is encrypted by preferential, thereby improve the specific aim and the validity of encrypting.Yet in compressed bit stream H.264, except the importance difference of dissimilar code words to the video reconstruction quality, the bit of diverse location also often has nothing in common with each other to the importance of video reconstruction quality in the code word.Therefore, how to guarantee that bit important in each code word also is the problem that realizes that efficient compression territory encryption method must solve by preferential encryption.

Accompanying drawing 1 is that block size is 8 * 8 DCT coefficient bit plane formation sketch map.For each DCT piece of 8 * 8, at first according to from top to bottom, from left to right Zig-Zag scanning sequency forms an one-dimension array with 64 DCT coefficients.Then, write the absolute value of 64 coefficients as binary form, i bit extraction of each coefficient come out, and forms a bit-planes.Can find out that bit-planes is high more, then the corresponding bit in this plane is important to the video reconstruction quality more.If encrypt successively according to bit-planes order from high to low, promptly encrypt from higher bit plane MSB and begin, encrypt time higher bit plane MSB-1 again, by that analogy, just can guarantee that most important bit is by preferential encryption in each DCT coefficient.Therefore, the present invention utilizes the thought of this bit-planes, proposed a kind of based on the bit susceptibility, be applicable to the H.264 bit-planes encryption method of compressed bit stream.

Summary of the invention

The objective of the invention is to, proposed a kind of H.264 compression domain bit-planes encryption method based on the bit susceptibility.At first, the various dissimilar code word in the compressed bit stream is H.264 carried out the test of bit susceptibility, and all code words are classified, the most important code word of video reconstruction quality is encrypted by preferential guaranteeing according to test result.For code word to be encrypted, then encrypt successively according to bit-planes order from high to low, promptly at first encrypt higher bit plane MSB, encrypt time higher bit plane MSB-1 again, by that analogy, to guarantee that most important bit is encrypted by preferential in each code word.

The present invention adopts following technological means to realize:

A kind of H.264 compression domain bit-planes encryption method based on the bit susceptibility comprises that H.264 code stream bit susceptibility test, bit-planes form and the bit-planes encrypting step;

Step 1, carry out H.264 the test of code stream bit susceptibility;

Step 1.1, test condition is set, does not promptly launch H.264 codec fault-tolerant mode;

Step 1.2, change any one bit of intra prediction mode code word, the PSNR value of record reconstruction video at random;

Step 1.3, repeat above-mentioned test process 20 times, all PSNR values that record are got average, as the bit susceptibility information of intra prediction mode code word;

Step 1.4, repeating step 1.2～1.3 are tested the bit susceptibility information of all the other type code words in the code stream H.264.

Step 2, carry out H.264 the code stream bit-planes and form;

Step 2.1, obtain a coded slice in the code stream H.264, the bit number that record present encoding sheet is comprised;

Step 2.2, if the present encoding sheet be intracoded frame, then set up bit planes such as intra prediction mode, low frequency coefficient symbol and low frequency coefficient amplitude successively;

Step 2.3, if the present encoding sheet be inter-frame encoding frame, then set up bit planes such as motion vector symbol, motion vector magnitude and intra prediction mode successively.

Step 3, carry out H.264 the code stream bit-planes and encrypt;

Step 3.1, the encrypted bit number of initialization are zero (EncBits_num=0), and encryption threshold value (Threshold) is set;

Step 3.2, encrypt successively according to bit-planes order from high to low; For intracoded frame; To encrypted frame inner estimation mode bit-planes, low frequency coefficient sign bit plane etc. successively; For inter-frame encoding frame, will add dense motion vector sign bit plane, motion vector magnitude bit-planes etc. successively;

Step 3.3, accomplishing after a bit-planes encrypts, calculate the percentage (EncBits_pre) that EncBits_num and encrypted bit number account for the total bit number of code stream;

Step 3.4, judge whether EncBits_pre has arrived the encryption threshold value Threshold of initial setting up,, otherwise finish the ciphering process of present encoding sheet if EncBits_pre less than Threshold, then continues to encrypt next bit-planes;

Step 4, repeating step 2, step 3, all coded slice in having encrypted current H.264 code stream.

The present invention compared with prior art has following remarkable advantages and useful effect:

The present invention utilize the thought of bit susceptibility information and the bit-planes of compressed bit stream H.264 guarantee all encrypted bits all be in the compressed bit stream to the of paramount importance data of video reconstruction quality, so computation complexity is low, execution speed is fast.Compare with compressed domain video encryption method in the past; Encryption has more specific aim; Can under the identical condition of enciphered data amount, obtain higher fail safe, and the code stream form after can keeping encrypting compatible with standard codec H.264, encrypt before and after the compression ratio of code stream constant etc.Its advantage mainly shows:

1, computation complexity is low, execution speed is fast, can satisfy the real-time requirement of Video Applications.

2, encryption has more specific aim, can guarantee effectively that all encrypted bits all are to the of paramount importance data of video reconstruction quality in the compressed bit stream.

3, the code stream form after can keeping encrypting is with H.264 the standard codec is compatible, and the compression ratio of code stream is constant before and after encrypting.

4, can realize the encryption of multiple level of security through the data volume of controlling encrypted bit, therefore can satisfy the different demands of various multimedia application.

Description of drawings

Fig. 1 is 8 * 8 DCT coefficient bit plane formation sketch map for block size;

Fig. 2 forms sketch map for code stream bit-planes H.264;

Fig. 3 is code stream bit-planes encryption flow figure H.264.

Embodiment

Below in conjunction with Figure of description, specific embodiment of the present invention is explained:

1, relevant H.264 code stream bit susceptibility test;

As previously mentioned, H.264 comprise various dissimilar code words in the compressed bit stream, and the importance of video reconstruction quality is had nothing in common with each other.The purpose of bit susceptibility test is exactly in order to obtain in the code stream various dissimilar code words to the importance degree information of video reconstruction quality.In when, in order to embody more significantly in the code word bit mistake taking place to the influence of video reconstruction quality; We are not launching the test of having carried out the bit susceptibility under the situation of encoding and decoding fault-tolerant mode H.264; That is to say when a bit in the code word is destroyed; H.264 decoder is not revised or is hidden this mistake effect, in this case the quality of reconstruction video is tested.Test experiments adopts the standard video sequence of QCIF form, comprises Bus, Football, Foreman, Mobile etc., and the severe of content such as the color of these video sequences, texture and motion has nothing in common with each other.

For video-encryption; Consider that code words such as encrypting header, residual coding scheme CBP and quantization parameter QP can not guarantee the fail safe of video information; Can not keep the compatibility of encrypting back code stream form; Therefore we only select to comprise intra prediction mode code word (IntraPredMode), DCT coefficient code word and motion vector residual error code word to H.264 possibly encrypted code word carrying out the test of bit susceptibility in the compressed bit stream.Wherein, DCT coefficient code word can be divided into low frequency coefficient symbol (LowCoeffSign), low frequency coefficient amplitude (LowCoeffLevel), high frequency coefficient symbol (HighCoeffSign), high frequency coefficient amplitude (HighCoeffLevel) and hangover coefficient (TrailingOnes); Motion vector residual error code word also can be divided into motion vector residual error symbol (MVDSign) and motion vector residual error amplitude (MVDLevel).According to the difference of coded system, these code words can be divided into I frame and two kinds of situation of P frame again.

What table 1 provided is the bit susceptibility test result of different video sequence compressed bit stream.For the video reconstruction quality, we adopt the most general present objective evaluation criterion-Y-PSNR (PSNR, Peak Signal-Noise Ratio) to measure.From table, can find out; When the MVDSign code word generation bit mistake in IntraPredMode in the I frame and the P frame; It is the most obvious that mean P SNR value descends, slippage basically all more than 2dB, so these two types of code words be H.264 in the compressed bit stream to the of paramount importance data of video reconstruction quality.In addition, the PSNR value descends also comparatively obvious when IntraPredMode in LowCoeffSign in the I frame and the P frame and MVDLevel generation bit mistake.In contrast, when the bit mistake takes place the LowCoeffSign in code word LowCoeffLevel, HighCoeffSign, HighCoeffLevel, TrailingOnes and the P frame, can't cause the obvious decline of mean P SNR value.Therefore, can above-mentioned code word be divided into three types, that is:

1) IntraPredMode in the I frame, the MVDSign in the P frame;

2) LowCoeffSign in the I frame, IntraPredMode and the MVDLevel in the P frame;

3) LowCoeffSign in LowCoeffLevel, HighCoeffSign, HighCoeffLevel, TrailingOnes and the P frame.

2, relevant H.264 code stream bit-planes forms step;

After H.264 the bit susceptibility information of compressed bit stream was confirmed, the encryption of various dissimilar code words order also can be confirmed thereupon in the code stream, but can not guarantee that most important bit is encrypted by preferential in each code word.The present invention will encrypt according to bit-planes order from high to low according to the thought of bit-planes successively, is encrypted by preferential to guarantee bit important in the code word.

Accompanying drawing 2 is that the H.264 code stream bit-planes that the present invention proposes forms sketch map.For intra prediction mode, H.264 comprise two types fixed length code word in the code stream, be respectively " 1 " and " 0 * * * ".If the current block predictive mode equals the minimum value (most probable predictive mode) of adjacent block (left side piece and top piece) predictive mode, then IntraPredMode is " 1 "; Otherwise IntraPredMode is " 0 * * * ", wherein " * * * " be the difference of current block predictive mode and most probable predictive mode.Change any one bit in " * * * ", all will change the current block predictive mode.Therefore, " * * * " among all IntraPredMode extracted just can form a bit-planes, be called IPMMSB.

For the motion vector residual error, H.264 adopting has symbol index Columbus coding, and each code word can be expressed as [M Zeros] [1] [INFO], and wherein INFO is the information suffix of a M position.Therefore, the amplitude of motion vector residual error is Level=2 ^M+ INFO-1, and last bit of INFO is exactly the sign bit of motion vector residual error.It is thus clear that, last bit extraction of all motion vector residual error code words is come out just to have formed the MVDSign bit-planes, be called MVDSign MSB.In all the other bits of information suffix INFO, in general range marker position " 1 " near more bit is important more to the amplitude of motion vector residual error.Therefore; With flag bit " 1 " is starting point; The bit extraction of same position among all motion vector residual error codeword information suffix INFO is come out just to have formed a MVDLevel bit-planes, be called MVDLevelMSB, MVDLevel MSB-1, MVDLevel MSB-2 successively, by that analogy.

For the DCT residual error coefficient; Though H.264 adopted based on contextual self-adapting changeable long codes (CAVLC; Context-based Adaptive Variable Length Coding) controls selection, have symbol index Columbus coding that each DCT coefficient is carried out entropy coding but still adopt to code table VLC.Therefore, can adopt the mode similar to form the bit-planes of DCT coefficient code word with the motion vector residual error.

3, relevant H.264 code stream bit-planes encrypting step;

Bit-planes just can be encrypted according to bit-planes order from high to low after forming successively.Accompanying drawing 3 is H.264 code stream bit-planes encryption flow figure that the present invention proposes.For the I frame, incite somebody to action encryption IP M MSB, LowCoeffSign MSB, LowCoeffLevel (MSB, MSB-1, MSB-2, MSB-3......), HighCoeffSign MSB etc. successively; For the P frame, will encrypt MVDSign MSB, MVDLevel (MSB, MSB-1, MSB-2......), IPM MSB, LowCoeffSign MSB etc. successively.

Yet many multimedia application do not need to encrypt fully all bit-planes, only hope through in the ciphering multimedia data with the maximally related part of visually-perceptible, to obtain the compromise between fail safe and the computation complexity.For example for video request program or pay TV etc., only only need to encrypt IPM MSB and the MVDSign MSB in the P frame in the I frame.In general, the quantity of encrypted bit is many more in the compressed bit stream, just can guarantee the safety of multimedia messages more effectively.Therefore, the present invention recently determines whether to encrypt next bit-planes according to the percentage that encrypted bit number accounts for the total bit number of code stream.

What formula (1) was represented is the percentage that encrypted bit number accounts for the total bit number of code stream, and wherein EncBits_num is encrypted bit number, and NaluBits_num is the total bit number of code stream.If EncBits_pre less than preset threshold Threshold, then continues next bit-planes is encrypted, otherwise finish to encrypt.

$\mathrm{EncBits}\_\mathrm{pre}=\frac{\mathrm{EncBits}\_\mathrm{num}}{\mathrm{NaluBits}\_\mathrm{num}}---\left(1\right)$

The bit susceptibility test result of table 1 different video sequence compressed bit stream

Claims (2)

1. the H.264 compression domain bit-planes encryption method based on the bit susceptibility is characterized in that: comprise that H.264 code stream bit susceptibility test, bit-planes form and the bit-planes encrypting step;

Step 1, carry out H.264 the test of code stream bit susceptibility;

Step 1.1, test condition is set, does not promptly launch H.264 codec fault-tolerant mode;

Step 1.2, change any one bit of intra prediction mode code word, the PSNR value of record reconstruction video at random;

Step 1.3, repeat above-mentioned test process repeatedly, all PSNR values that record are got average, as the bit susceptibility information of intra prediction mode code word;

Step 1.4, repeating step 1.2～1.3 are tested the bit susceptibility information of all the other type code words in the code stream H.264;

Step 2, carry out H.264 the code stream bit-planes and form;

Step 2.1, obtain a coded slice in the code stream H.264, the bit number that record present encoding sheet is comprised;

Step 2.2, if the present encoding sheet be intracoded frame, then set up bit planes such as intra prediction mode, low frequency coefficient symbol and low frequency coefficient amplitude successively;

Step 2.3, if the present encoding sheet be inter-frame encoding frame, then set up bit planes such as motion vector symbol, motion vector magnitude and intra prediction mode successively;

Step 3, carry out H.264 the code stream bit-planes and encrypt;

Step 3.1, the encrypted bit number of initialization are zero, and the encryption threshold value is set;

Step 3.2, encrypt successively according to bit-planes order from high to low; For intracoded frame; To encrypted frame inner estimation mode bit-planes, low frequency coefficient sign bit plane etc. successively; For inter-frame encoding frame, will add dense motion vector sign bit plane, motion vector magnitude bit-planes etc. successively;

Step 3.3, accomplishing after a bit-planes encrypts, calculate the percentage that current encrypted bit number and encrypted bit number account for the total bit number of code stream;

Step 3.4, judge whether percentage that encrypted bit number accounts for the total bit number of code stream has arrived the encryption threshold value of initial setting up; If current encrypted bit number accounts for the percentage of the total bit number of code stream less than encrypting threshold value; Then continue to encrypt next bit-planes, otherwise finish the ciphering process of present encoding sheet;

Step 4, repeating step 2, step 3, all coded slice in having encrypted current H.264 code stream.

2. the H.264 compression domain bit-planes encryption method based on the bit susceptibility according to claim 1, it is characterized in that: the test process of described step 1.3 is 20 times.

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