CN102523441B - 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 bit susceptibility

Technical field

The present invention relates to the video-encryption in multi-media information security field, be specially a kind of H.264 compression domain bit-planes encryption method based on 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, the various potential safety hazards such as the multimedia messages such as image, video exists and is stolen in network transmission process, malice is distorted, multi-media information security problem becomes and becomes increasingly conspicuous.For example, in various commercial applications, multimedia messages is stolen and will brings huge economic loss to supplier; In 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 fully and effectively multimedia messages has 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 refers to certain link that cryptographic algorithm is embedded into cataloged procedure, such as dct transform, quantification or entropy coding etc.This class encryption method tends to cause the decline of system compresses performance, also conventionally need to change the structure of video standard codec, so practicality is poor.

Compressed domain video is encrypted and is referred to that the code stream to generating after Video coding is encrypted.Simple effective method is to adopt traditional text encryption algorithm directly whole code stream to be encrypted as RSA, DES or AES etc.But the data volume of video information is very huge, whole code streams are encrypted and will cause the load of encryption excessive, therefore can not meet the real-time demand of Video Applications.In order to obtain the compromise between fail safe and computation complexity, people have proposed selective video encryption, only select in enciphered video data and the maximally related part of visually-perceptible.At present, it is all selectively a certain category information in compressed bit stream to be encrypted that most of compression domain are encrypted, such as encrypting code stream header, changing predictive mode or scramble DCT coefficient code word etc., to improve the efficiency of encryption.Yet these methods can not guarantee that all encrypted bits are all to the of paramount importance data of video reconstruction quality, be also difficult to guarantee that code stream form and standard codec after encryption are compatible.The more important thing is, 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 bit susceptibility refers to a certain type code word in compressed bit stream makes a mistake.Video reconstruction quality declines more obviously, illustrates that the type code word is more important to video reconstruction quality, and bit susceptibility is also just higher.Therefore, according to the bit susceptibility information of all kinds code word in code stream, in ciphering process, can guarantee the most important code word of video reconstruction quality preferentially to be encrypted, thereby improve specific aim and the validity of encrypting.Yet in compressed bit stream H.264, except dissimilar code word is to the importance difference of video reconstruction quality, in code word, the bit of diverse location is also often different to the importance of video reconstruction quality.Therefore, how to guarantee that it is also to realize the problem that Efficient Compression territory encryption method must solve that bit important in each code word is preferentially encrypted.

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

Summary of the invention

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

The present invention adopts following technological means to realize:

A H.264 compression domain bit-planes encryption method based on bit susceptibility, comprises that H.264 code stream bit susceptibility test, bit-planes form and 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 enable H.264 codec fault-tolerant mode;

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

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

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

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

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

If step 2.2 present encoding sheet is intracoded frame, set up successively the bit-planes such as intra prediction mode, low frequency coefficient symbol and low frequency coefficient amplitude;

If step 2.3 present encoding sheet is inter-frame encoding frame, set up successively the bit-planes such as motion vector sign of the residues, motion vector residual error amplitude and intra prediction mode.

Step 3, carry out H.264 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, according to bit-planes order from high to low, encrypt successively, 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 encrypt successively motion vector sign of the residues bit-planes, motion vector residual error amplitude bit-planes etc.;

Step 3.3, completing after 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, if EncBits_pre is less than Threshold, continue to encrypt next bit-planes, otherwise finish the ciphering process of present encoding sheet;

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

The present invention compared with prior art, has following obvious advantage and useful effect:

The present invention utilize H.264 the bit susceptibility information of compressed bit stream and the thought of bit-planes guarantee all encrypted bits be all in 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 is mainly manifested in:

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

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

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

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

Accompanying drawing explanation

Fig. 1 is that block size is 8 * 8 DCT coefficient bit plane formation schematic diagram;

Fig. 2 forms schematic diagram 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 embodiments of the invention are illustrated:

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

As previously mentioned, H.264 in compressed bit stream, comprise various dissimilar code words, and different to the importance of video reconstruction quality.The object of bit susceptibility test is exactly in order to obtain the importance degree information of various dissimilar code words to video reconstruction quality in code stream.Impact on video reconstruction quality while there is bit mistake in order to embody more significantly in code word, we have carried out the test of bit susceptibility in the situation that not enabling H.264 encoding and decoding fault-tolerant mode, that is to say when a bit in 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 degree of the contents such as the color of these video sequences, texture and motion is different.

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 maintain the compatibility of code stream form after encrypting, therefore we only select, to H.264 may encrypted code word carrying out the test of bit susceptibility in compressed bit stream, to comprise intra prediction mode code word (IntraPredMode), DCT coefficient code word and motion vector residual error code word.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 sign of the residues (MVDSign) and motion vector residual error amplitude (MVDLevel).According to the difference of coded system, these code words can be divided into again I frame and two kinds of situations of P frame.

What table 1 provided is the bit susceptibility test result of different video sequence compaction code stream.For video reconstruction quality, we adopt the most general objective evaluation criteria-Y-PSNR (PSNR, Peak Signal-Noise Ratio) at present to measure.As can be seen from the table, during MVDSign code word generation bit mistake in the IntraPredMode in I frame and P frame, it is the most obvious that mean P SNR value declines, slippage substantially all more than 2dB, so this two classes code word be H.264 in compressed bit stream to the of paramount importance data of video reconstruction quality.When in addition, bit mistake occurs for the IntraPredMode in the LowCoeffSign in I frame and P frame and MVDLevel, PSNR value declines also comparatively obvious.When in contrast, bit mistake occurs the LowCoeffSign in code word LowCoeffLevel, HighCoeffSign, HighCoeffLevel, TrailingOnes and P frame, can't cause the obvious decline of mean P SNR value.Therefore, above-mentioned code word can be divided into three classes, that is:

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

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

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

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

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

Accompanying drawing 2 is that the H.264 code stream bit-planes that the present invention proposes forms schematic diagram.For intra prediction mode, H.264 in code stream, comprise the fixed length code word of two types, be respectively " 1 " and " 0 * * * ".If current block predictive mode equals the minimum value (most probable predictive mode) of adjacent block (Kuai He top, left side piece) predictive mode, 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 current block predictive mode.Therefore, " * * * " in all IntraPredMode extracted and just can form a bit-planes, be called IPM MSB.

For motion vector residual error, H.264 adopt and have symbol index Columbus coding, each code word can be expressed as [MZeros] [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.Visible, last bit extraction of all motion vector residual error code words has out just been formed to MVDSign bit-planes, be called MVDSignMSB.In all the other bits of information suffix INFO, in general range marker position " 1 " nearer bit is more important to the amplitude of motion vector residual error.Therefore, the flag bit " 1 " of take is starting point, the bit extraction of same position in all motion vector residual error codeword information suffix INFO has out just been formed to a MVDLevel bit-planes, be called successively MVDLevel MSB, MVDLevel MSB-1, MVDLevel MSB-2, by that analogy.

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

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 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 P frame, will encrypt successively MVDSign MSB, MVDLevel (MSB, MSB-1, MSB-2......), IPM MSB, LowCoeffSign MSB etc.

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

What formula (1) 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 is less than the threshold value Threshold of setting, continues next bit-planes to be encrypted, otherwise finish to encrypt.

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

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

Claims (2)

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

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

Step 1.1, test condition is set, described test condition is not for enabling H.264 encoding and decoding fault-tolerant mode;

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

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

Step 1.4, repeating step 1.2～1.3, test the bit susceptibility information of motion vector residual error code word in code stream H.264 and DCT coefficient code word;

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

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

If step 2.2 present encoding sheet is intracoded frame, set up successively intra prediction mode, low frequency coefficient symbol, low frequency coefficient amplitude, high frequency coefficient symbol, high frequency coefficient amplitude and hangover coefficient bit plane;

If step 2.3 present encoding sheet is inter-frame encoding frame, set up successively motion vector sign of the residues, motion vector residual error amplitude, intra prediction mode, low frequency coefficient symbol, low frequency coefficient amplitude, high frequency coefficient symbol, high frequency coefficient amplitude and hangover coefficient bit plane;

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

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

Step 3.2, according to bit-planes order from high to low, encrypt successively, for intracoded frame, to encrypted frame inner estimation mode bit-planes successively, low frequency coefficient sign bit plane, low frequency coefficient amplitude bit-planes, high frequency coefficient sign bit plane, high frequency coefficient amplitude bit-planes and hangover coefficient bit plane, for inter-frame encoding frame, to add successively dense motion vector sign of the residues bit-planes, motion vector residual error amplitude bit-planes, intra prediction mode bit-planes, low frequency coefficient sign bit plane, low frequency coefficient amplitude bit-planes, high frequency coefficient sign bit plane, high frequency coefficient amplitude bit-planes and hangover coefficient bit plane,

Step 3.3, completing after 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 the percentage that current encrypted bit number accounts for the total bit number of code stream is less than encryption threshold value, continue to encrypt next bit-planes, otherwise finish the ciphering process of present encoding sheet;

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

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

Images