Video data encryption transmission method based on secure multi-party computing

Abstract

The invention discloses a video data encryption transmission method based on secure multi-party computing, and belongs to the field of encryption transmission in digital video monitoring. The implementation method comprises the following steps: splitting video data into a plurality of key frame sequences according to a video coding format, encrypting each key frame sequence by using different symmetric keys to obtain encrypted frames, and splitting the symmetric keys into a plurality of sub-key frames by using a Shamir (t, n) threshold secret sharing scheme; after receiving, the terminal analyzes the encrypted frame into mapping from a timestamp to a local sequence number and mapping from the sequence number to encrypted data, and after receiving, the server analyzes the sub-key frame into mapping from the sequence number to a sub-key; when a user needs to decrypt encrypted video data of a part of time periods, a time period to be decrypted is analyzed into a serial number column at a terminal, the encrypted video data are acquired, a dynamic password required for generating a sub-key frame corresponding to an access serial number column is configured on a server, the sub-key frame is acquired from the server side through the dynamic password, and the sub-key frame is decrypted. And decrypting the encrypted video data of the partial time period.

Description

Technical Field

[0001] The invention relates to a video data encryption transmission method based on secure multi-party computing, and belongs to the field of encryption transmission in digital video monitoring. Background Art

[0002] With the rapid growth of video data, how to efficiently transmit and store video data while ensuring data privacy and security has become an important issue. In recent years, there have been frequent incidents of eavesdropping and theft of camera data in the public domain. Cameras, servers, and even terminals are likely to be hijacked by criminals. Since video data often contains a lot of sensitive privacy information, once this information is leaked, it will have a serious impact. Therefore, ensuring data security during the video transmission and storage process can avoid potential privacy leaks and prevent criminals from using this private information.

[0003] The current video data encryption transmission method is often achieved by exchanging AES keys through HTTPS. This type of transmission method can ensure resistance to eavesdropping attacks and man-in-the-middle attacks during the transmission process, and can ensure data security to a certain extent.

[0004] However, these video data encryption transmission methods have the following shortcomings:

[0005] (1) Insecurity of storage media: The encrypted transmission process of video data only ensures the security of the transmission process. However, after the transmission is completed and stored in the storage medium, the data is stored in plain text. Once the storage medium is eavesdropped, stolen or hijacked, the video data is still at risk of being stolen.

[0006] (2) Incompatible with the video data frame format: The traditional encryption transmission process segments the data stream according to fixed-length units, which may destroy the frame structure of the data stream during the segmentation process. Video data is divided into I frames, P frames, and B frames, of which I frames are key frames and are the key to decoding subsequent frames. If the segmentation process destroys the I frame, the data segment cannot be successfully decoded. Since there is a need to read encrypted video data in a local time period, which requires that each segment of video data can be decoded separately, it is necessary to adapt the video data frame format during the encryption process to support the need to extract encrypted video data in a local time period.

[0007] Based on the shortcomings of the above-mentioned existing methods, the present invention proposes a video data encryption transmission method based on secure multi-party computing, which solves the security problems in the video transmission and storage process. Different from the traditional secure multi-party computing scheme that encrypts and decrypts the entire bit stream, this scheme takes into account the particularity of the video data frame format, so that the encryption process adapts to the video frame format, which can improve efficiency and security, and at the same time support the need to extract encrypted video data in a local time period. And this method can overcome the insecurity of the storage medium. Only when the terminal and more than or equal to t servers (the value of t depends on the user's configuration parameters) are hijacked at the same time, the video data can be stolen.

[0008] In summary, the current digital video surveillance field lacks an encrypted video data transmission and storage method that ensures the security of storage media, supports the extraction of local time periods, and is compatible with video frame formats. Summary of the invention

[0009] Aiming at the problem that the video transmission process is easy to be eavesdropped and tampered, and the storage medium is easy to be stolen and hijacked during the video transmission process, the purpose of the present invention is to provide a video data encryption transmission method based on secure multi-party computing, which realizes the adaptation of the video frame format during the transmission and storage process by dividing the video frame sequence into key frame sequences, realizes the real-time encryption key distribution of each key frame sequence based on the Shamir threshold secret sharing scheme, reorganizes the serial number, timestamp and encrypted video data into encrypted frames and transmits them to the terminal, and transmits the serial number and the corresponding subkey to each intermediate server respectively, so as to realize the anti-eavesdropping and anti-tampering in the transmission process, and the anti-theft and anti-hijacking in the storage process.

[0010] The objective of the present invention is achieved through the following technical solutions:

[0011] The invention discloses a video data encryption transmission method based on secure multi-party computing. The method comprises the following steps: dividing video data into a plurality of key frame sequences according to a video coding format, encrypting each key frame sequence using different symmetric keys that meet cryptographic security requirements to obtain an encrypted frame, dividing the symmetric key into a plurality of subkey frames using Shamir's (t, n) threshold secret sharing scheme, separating the encrypted frame from the subkey at a sending end, transmitting the encrypted frame to a terminal, and transmitting each subkey frame to a corresponding server, thereby realizing the separate transmission and storage of encrypted data and a key; after receiving the encrypted frame, the terminal parses the encrypted frame into a mapping from a timestamp to a local sequence number and a mapping from a sequence number to encrypted data, and after receiving the encrypted frame, the server parses the subkey frame into a mapping from a sequence number to a subkey; when a user needs to decrypt encrypted video data of a part of a time period, the terminal parses the time period to be decrypted into a sequence number column and obtains the encrypted video data, and configures a server to generate a dynamic password required for accessing the subkey frames corresponding to the sequence number columns, obtains the subkey frame from the server end through the dynamic password, and decrypts the encrypted video data of the part of a time period in combination with Shamir's (t, n) threshold secret sharing scheme, thereby realizing the encrypted transmission of video data based on secure multi-party computing.

[0012] The present invention discloses a video data encryption transmission method based on secure multi-party computing, comprising the following steps:

[0013] Step 1: In the configuration phase of the video acquisition device, the number of servers n and the number of servers t required to recover the key are specified according to the user's actual hardware conditions and encryption level requirements, and the access methods of the servers and terminals are configured on the video acquisition device;

[0014] Step 2: according to the frame format characteristics of the video stream, the bit stream of the video data is split into I-frame key frames as units to obtain a key frame sequence, the timestamp of the video stream is parsed according to PTS and DTS, and the video stream is reorganized into a key frame sequence to achieve adaptation of the video frame format during transmission and storage, so as to facilitate the extraction of the local time period of the encrypted video data and improve the transmission efficiency;

[0015] Step 2.1, if there is no SPS frame and PPS frame before the I frame in the video stream, every time an I frame is collected, the bit stream from the I frame to the next I frame is called a key frame sequence; if there is an SPS frame or PPS frame before the I frame in the video stream, every time an SPS frame or PPS frame is collected, the bit stream from the SPS frame or PPS frame to the next SPS frame or PPS frame is called a key frame sequence;

[0016] Step 2.2: For each key frame sequence m k Assign a self-incrementing serial number k, which is the unique identifier of the key frame sequence;

[0017] Step 2.3: Extract the PTS and DTS corresponding to each key frame sequence, and parse the absolute time offset based on the time reference of the video stream itself, and use the offset as the timestamp T of the key frame sequence. k ;

[0018] Step 3: Encrypt the key frame sequence extracted from each step 2 to obtain encrypted data, and convert the encrypted data s k And the sequence number k and timestamp T obtained in step 2 k Combined into encrypted frame F k =(k, T k ,s k ) and then transmitted to the terminal, and the security of the transmission and storage process is improved by separating the encrypted frame from the encryption key;

[0019] Step 3.1: Generate a secure random number as the encryption key r for the key frame sequence k , the random number should be generated by a cryptographically secure pseudo-random number generator;

[0020] Step 3.2: Use the encryption key generated in step 3.1 to encrypt the key frame sequence based on the symmetric encryption algorithm to obtain the encrypted data s k , combine the sequence number, timestamp, and encrypted data into an encrypted frame F k =(k, T k ,s k );

[0021] Step 3.3: The video capture device transmits the encrypted frame to the terminal. The transmission process uses the TLS protocol for secure transmission. When the terminal receives the encrypted frame, it stores the mapping of timestamp to serial number locally. k →k, and the mapping from sequence number to encrypted data k→s k ;

[0022] Step 4: Use the key r generated in step 3.1 k The (t, n) threshold secret sharing scheme based on Shamir is split into several subkeys u k，i , subkey u k，i and sequence number k to form subkey frame G k，i =(k,u k，i ) and then transmitted to each server respectively, and the security of the transmission and storage process is improved by decomposing the encryption key for transmission and storage;

[0023] Step 4.1: Use Shamir's (t, n) threshold secret sharing scheme to split the key in step 3.1 into n subkeys u k，i , the values ​​of t and n correspond to the configuration of step 1, and the sequence number and each subkey are respectively composed of subkey frames G k，i =(k,uk，i Specifically, we first select a large prime number p based on the Miller-Rabin algorithm and Randomly pick t-1 numbers a 1 , a 2 , …, a t-1 , construct the polynomial f(x)=r+a 1 x+…+a t-1 x t-1 mod(p), where the number of pairs u k，i =(i, f(i)) is the i-th subkey, where i=1,…,n;

[0024] Step 4.2: The video capture device sends each sub-key frame G k , i is transmitted to the corresponding server i. The transmission process uses the TLS protocol for secure transmission. After the transmission is completed, the sender returns to step 2 to parse the next key frame sequence. When each server receives the encrypted frame, it stores the mapping from the sequence number to the subkey locally;

[0025] Step 5: Based on Step 3 and Step 4, the encryption process and the secure transmission process are implemented. After that, if the user wants to decrypt the encrypted data of a local time period in the terminal, the user inputs the time period to be decrypted in the terminal to obtain the corresponding sequence number column and the encrypted video data, and configures the server to generate a dynamic password required to access the sub-key frame corresponding to the sequence number column, and obtains the sub-key frame u from the server through the dynamic password. k，i , combined with Shamir's (t, n) threshold secret sharing scheme to decrypt the encrypted video data of part of the time period; the encrypted frame F k and the encryption key r k The combination successfully decrypts the local visual time period that needs to be extracted, realizing encrypted transmission of video data based on secure multi-party computing.

[0026] Step 5.1, the user specifies the local time period corresponding to the video data to be extracted on the terminal, and parses the sequence number column corresponding to the video data in the local time period through the mapping from the timestamp to the sequence number in step 3.3;

[0027] Step 5.2, configure the t-stage server to generate dynamic passwords required to access the subkeys corresponding to the video sequence numbers specified in step 5.1;

[0028] Step 5.3: The user uses a dynamic password at the terminal to obtain each subkey frame from the server in step 4.2, and recovers the encryption key r of each frame from the subkey frame based on Shamir's (t, n) threshold secret sharing scheme. k Specifically, for the subkey frame u k，i =(x i ,y i)=(i,f(i)), where i=1,…,t, then the original encryption key

[0029] Step 5.4: The encrypted frame F obtained from step 3.3 k and the encryption key r obtained in step 5.3 k Combination, successfully decrypt the visual local time period that needs to be extracted.

[0030] Beneficial effects:

[0031] 1. The video data encryption transmission method based on secure multi-party computing disclosed in the present invention assigns a unique corresponding encryption key to each key frame sequence. Since the generation process of the encryption key is independent, the video data encryption transmission system has forward security. Even if any key is stolen, it will not affect the security of other frames.

[0032] 2. The video data encryption transmission method based on secure multi-party computing disclosed in the present invention adapts the video frame format during the transmission and storage process, and can support the decryption of encrypted video data only in any local time period without destroying the previous and subsequent video data frame structures, thereby improving the convenience and security of the encrypted video data access process.

[0033] 3. The video data encryption transmission method based on secure multi-party computing disclosed by the present invention uses Shamir's (t, n) threshold secret sharing scheme. Each encryption key is split into n sub-keys and transmitted to the intermediate server. Even if the intermediate server is eavesdropped, stolen or hijacked, as long as the number of stolen or hijacked intermediate servers is less than t, the decryption key cannot be stolen.

[0034] 4. The video data encryption transmission method based on secure multi-party computing disclosed by the present invention only stores encrypted frames in the terminal. Even if the terminal is stolen or hijacked, the attacker cannot obtain the decryption key of the encrypted frame and cannot steal the original video data. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is an example diagram of the network topology and transmission mode in steps 1 to 4 of the application of the video data encryption transmission method based on secure multi-party computing in the digital surveillance video encryption transmission of the present invention;

[0036] Figure 2 It is an example diagram of the process of decrypting video data in step 5 of the application of the video data encryption transmission method based on secure multi-party computing of the present invention in the encrypted transmission of digital surveillance video;

[0037] Figure 3It is a schematic diagram of the process of splitting the video into key frame sequences in step 2 of the application of the video data encryption transmission method based on secure multi-party computing in the digital surveillance video encryption transmission of the present invention;

[0038] Figure 4 It is a flow chart of the transmission process and the decryption process in the application of the video data encryption transmission method based on secure multi-party computing of the present invention in the encryption transmission of digital surveillance video; DETAILED DESCRIPTION

[0039] The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments, and the technical problems solved by the technical solution of the present invention and the beneficial effects will be discussed. It should be noted that the described embodiments are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0040] Example 1

[0041] This embodiment is an application of a video data encryption transmission method based on secure multi-party computing in the encryption transmission of digital surveillance videos.

[0042] This embodiment requires that the system should have a surveillance camera, several independent key storage servers, and an encrypted data storage terminal. In this embodiment, the surveillance camera periodically transmits the subkey frame and the encrypted frame to the server and the terminal respectively, and the surveillance camera periodically transforms the key frame sequence into the subkey frame and the encrypted frame and transmits them to the server and the terminal. In the decryption stage, the terminal configures a dynamic password on at least t servers, and uses the dynamic password to request each subkey frame, uses each subkey frame to combine into a key, and combines the encrypted data to obtain the plaintext video data. Taking t=3 and n=5 as an example, the network topology and transmission method are as follows: Figure 1 As shown, the decrypted video data is as follows Figure 2 The following is an example of digital surveillance video encryption transmission using the video data encryption transmission method based on secure multi-party computing of the present invention:

[0043] Step I: Configuration phase of the video acquisition device. Taking a surveillance camera as a video acquisition device as an example, the number of servers n and the number of servers t required for recovering the key are specified according to the user's actual hardware conditions and encryption level requirements, requiring 1≤t≤n. In this embodiment, t=3 and n=5 are considered, and the access mode of the server and the terminal is configured to the video acquisition device.

[0044] Step II: according to the frame format characteristics of the video stream, the bit stream of the video data is split into units of key frames such as I frames to obtain a key frame sequence, the timestamp of the video stream is parsed according to PTS and DTS, and the video stream is reorganized into a key frame sequence, so as to adapt the video frame format during transmission and storage, facilitate the extraction of the local time period of the encrypted video data and improve the transmission efficiency;

[0045] Step II.1: If there is no SPS frame or PPS frame before the I frame in the video stream, whenever an I frame is acquired, the bit stream from the I frame to the next I frame is called a key frame sequence. Figure 3 As shown; if there is an SPS frame or a PPS frame before the I frame in the video stream, every time an SPS frame or a PPS frame is collected, the bit stream from the SPS frame or the PPS frame to the next SPS frame or the PPS frame is called a key frame sequence;

[0046] Step II.2: For each key frame sequence m k Assign a self-incrementing serial number k, which is the unique identifier of the key frame sequence;

[0047] Step II.3: Extract the PTS and DTS corresponding to each key frame sequence, and parse the absolute time offset based on the time reference of the video stream itself, and use the offset as the timestamp T of the key frame sequence. k ;

[0048] Step III: Encrypt the key frame sequence extracted from each step II to obtain encrypted data, and convert the encrypted data s k And the sequence number k and timestamp T obtained in step 2 k Combined into encrypted frame F k =(k, T k ,s k ) and then transmitted to the terminal, and the security of the transmission and storage process is improved by separating the encrypted frame from the encryption key;

[0049] Step III.1, for m k Generate a secure random number r k As an encryption key, the random number should be generated by a cryptographically secure pseudo-random number generator;

[0050] Step III.2: Use the encryption key generated in step III.1 to encrypt the key frame sequence based on the symmetric encryption algorithm to obtain the encrypted data s k , combine the sequence number, timestamp, and encrypted data into an encrypted frame F k =(k, T k ,s k );

[0051] Step III.3: The video capture device transmits the encrypted frame to the terminal. The transmission process uses the TLS protocol for secure transmission. The digital certificate required for TLS should be configured in step I. When the terminal receives the encrypted frame, it stores the mapping of timestamp to serial number locally. k →k, and the mapping from sequence number to encrypted data k→s k ;

[0052] Step IV: Use the key r generated in step III.1 k The (t, n) threshold secret sharing scheme based on Shamir is split into several subkeys u k，i , subkey u k，i and sequence number k to form subkey frame G k，i =(k,u k，i ) and then transmitted to each server respectively, and the security of the transmission and storage process is improved by decomposing the encryption key for transmission and storage;

[0053] Step IV.1: Use Shamir's (t, n) threshold secret sharing scheme to split the key in step III.1 into n subkeys u k，i , t The value of n corresponds to the configuration of step 1. The sequence number and each subkey are respectively composed of a subkey frame G k，i =(k,u k，i ). Specifically, firstly, a large prime number p is selected based on the Miller-Rabin algorithm, where p>r, and in a finite field Randomly pick t-1 numbers a 1 , a 2 , …, a t-1 , construct the polynomial f(x)=r+a 1 x+…+a t-1 x t-1 mod(p). In this embodiment, t=3, n=5, and f(x)=r+a. 1 x+a 2 x 2 mod(p), number of pairs u k，i =(i, f(i)) is the i-th subkey, where i=1,2,3,4,5;

[0054] Step IV.2: Combine the sequence number and subkey into subkey frame G k，i =(k,u k，i ), G k,1 , G k,2 , G k,3 , G k,4 , G k，5 Transmit to the 1st, 2nd, 3rd, 4th, and 5th servers respectively. The server IP address is the IP address a configured in step I. i The transmission process uses the TLS protocol for secure transmission. Each server receives the subkey frame G k，i After that, the mapping relationship k→u is stored locally k，i After the video data acquisition device has completed the transmission, repeat step II.1;

[0055] Step V, the terminal decodes the encrypted video file, specifically including the following sub-steps;

[0056] Step V.1: The user specifies the local time period corresponding to the video data to be extracted on the terminal By step III.3 T k →k mapping parses the sequence number column [k 1 , k 2 ];

[0057] Step V.2: Configure t=3 servers to generate dynamic passwords p required to access the subkeys corresponding to the video sequence numbers specified in step V1. 1 , p 2 , p 3 ;

[0058] Step V.3: The user uses the dynamic password p at the terminal 1 , p 2 , p 3 Obtain each subkey frame from step IV.2 from the server, and recover the encryption key r of each frame from the subkey frame based on Shamir's (t, n) threshold secret sharing scheme k Specifically, for the subkey frame u k，i =(x i ,y i )=(i,f(i)), where i=1,2,3, then the original encryption key For every k∈[k 1 , k 2 ] Repeat this operation to recover the key r k , k∈[k 1 , k 2 ];

[0059] Step V.4: User uses key r k Combine k→s from step III.4 k The obtained k , decrypted to get the original key frame sequence m k Since each key frame sequence does not need to refer to other frame images when decoding, the video head and tail information will not be lost due to unreasonable segmentation after decoding;

[0060] At this point, the digital surveillance video encryption transmission process is completed.

[0061] This embodiment discloses a video data encryption transmission method based on secure multi-party computing. The method ensures the security of the digital surveillance video encryption transmission process. Even if an attacker steals some of the data on the server and the terminal, the original video data cannot be decrypted. The flow charts of the transmission process and the decryption process in this embodiment are as follows: Figure 4 shown.

[0062] This embodiment comprehensively considers the frame structure of the video stream and the possible insecurity in the storage medium of the server and the terminal. Compared with the traditional HTTPS encryption strategy, it is more suitable for the transmission of video streams. At the storage level, even if the encrypted video data and part of the subkey are leaked, the attacker cannot steal the original data. This embodiment is particularly suitable for scenarios where the channel may be insecure, the storage medium may be insecure, and the confidentiality requirements are high.

[0063] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A video data encryption transmission method based on secure multi-party computing, characterized in that: The following steps are included: Step 1: In the configuration phase of the video acquisition device, the number of servers n and the number of servers t required to recover the key are specified according to the user's actual hardware conditions and encryption level requirements, and the access methods of the servers and terminals are configured on the video acquisition device; Step 2: according to the frame format characteristics of the video stream, the bit stream of the video data is split into I-frame key frames as units to obtain a key frame sequence, the timestamp of the video stream is parsed according to PTS and DTS, and the video stream is reorganized into a key frame sequence to achieve adaptation of the video frame format during transmission and storage, so as to facilitate the extraction of the local time period of the encrypted video data and improve the transmission efficiency; Step 3: Encrypt the key frame sequence extracted from each step 2 to obtain encrypted data, and convert the encrypted data s k And the sequence number k and timestamp T obtained in step 2 k Combined into encrypted frame F k =(k, T k ,s k ) and then transmitted to the terminal, and the security of the transmission and storage process is improved by separating the encrypted frame from the encryption key; Step 4: Use the key r generated in step 3.1 k The (t, n) threshold secret sharing scheme based on Shamir is split into several subkeys u k，i , subkey u k，i and sequence number k to form subkey frame G k，i =(k,u k，i ) and then transmitted to each server respectively, and the security of the transmission and storage process is improved by decomposing the encryption key for transmission and storage; Step 5: Based on Step 3 and Step 4, the encryption process and the secure transmission process are implemented. After that, if the user wants to decrypt the encrypted data of a local time period in the terminal, the user inputs the time period to be decrypted in the terminal to obtain the corresponding sequence number column and the encrypted video data, and configures the server to generate a dynamic password required to access the sub-key frame corresponding to the sequence number column, and obtains the sub-key frame u from the server through the dynamic password. k，i , combined with Shamir's (t, n) threshold secret sharing scheme to decrypt the encrypted video data of part of the time period; the encrypted frame F k and the encryption key r k The combination successfully decrypts the local visual time period that needs to be extracted, realizing encrypted transmission of video data based on secure multi-party computing.

2. A video data encryption transmission method based on secure multi-party computing as claimed in claim 1, characterized in that: Step 2 is implemented as follows: Step 2.1, if there is no SPS frame and PPS frame before the I frame in the video stream, every time an I frame is collected, the bit stream from the I frame to the next I frame is called a key frame sequence; if there is an SPS frame or PPS frame before the I frame in the video stream, every time an SPS frame or PPS frame is collected, the bit stream from the SPS frame or PPS frame to the next SPS frame or PPS frame is called a key frame sequence; Step 2.2: For each key frame sequence m k Assign a self-incrementing serial number k, which is the unique identifier of the key frame sequence; Step 2.3: Extract the PTS and DTS corresponding to each key frame sequence, and parse the absolute time offset based on the time reference of the video stream itself, and use the offset as the timestamp T of the key frame sequence. k .

3. A video data encryption transmission method based on secure multi-party computing as claimed in claim 2, characterized in that: Step 3 is implemented as follows: Step 3.1: Generate a secure random number as the encryption key r for the key frame sequence k , the random number should be generated by a cryptographically secure pseudo-random number generator; Step 3.2: Use the encryption key generated in step 3.1 to encrypt the key frame sequence based on the symmetric encryption algorithm to obtain the encrypted data s k , combine the sequence number, timestamp, and encrypted data into an encrypted frame F k =(k, T k ,s k ); Step 3.3: The video capture device transmits the encrypted frame to the terminal. The transmission process uses the TLS protocol for secure transmission. When the terminal receives the encrypted frame, it stores the mapping of timestamp to serial number locally. k →k, and the mapping from sequence number to encrypted data k→s k .

4. A video data encryption transmission method based on secure multi-party computing as claimed in claim 3, characterized in that: Step 4 is implemented as follows: Step 4.1: Use Shamir's (t, n) threshold secret sharing scheme to split the key in step 3.1 into n subkeys u k，i , the values ​​of t and n correspond to the configuration of step 1, and the sequence number and each subkey are respectively composed of subkey frames G k，i =(k,u k，i ); Specifically, firstly, a large prime number p is selected based on the Miller-Rabin algorithm, and then Randomly select t-1 numbers a1, a2, ..., a t-1 , construct the polynomial f(x)=r+a1x+…+a t-1 x t-1 mod(p), where the number of pairs u k，i =(i, f(i)) is the i-th subkey, where i=1,…,n; Step 4.2: The video acquisition device sends each sub-key frame G k，i Transmit it to the corresponding server i. The transmission process uses the TLS protocol for secure transmission. After the transmission is completed, the sender returns to step 2 to parse the next key frame sequence. When each server receives the encrypted frame, it stores the mapping from the sequence number to the subkey locally.

5. A video data encryption transmission method based on secure multi-party computing as claimed in claim 4, characterized in that: Step 5 is implemented as follows: Step 5.1, the user specifies the local time period corresponding to the video data to be extracted on the terminal, and parses the sequence number column corresponding to the video data in the local time period through the mapping from the timestamp to the sequence number in step 3.3; Step 5.2, configure the t-stage server to generate dynamic passwords required to access the subkeys corresponding to the video sequence numbers specified in step 5.1; Step 5.3: The user uses a dynamic password at the terminal to obtain each subkey frame from the server in step 4.2, and recovers the encryption key r of each frame from the subkey frame based on Shamir's (t, n) threshold secret sharing scheme. k ; For subkey frame u k，i =(x i ,y i )=(i,f(i)), where i=1,…,t, then the original encryption key Step 5.4: The encrypted frame F obtained from step 3.3 k and the encryption key r obtained in step 5.3 k Combination, successfully decrypt the visual local time period that needs to be extracted.

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