A method for safely transmitting hydrological and meteorological data to shipborne terminals based on Beidou

Abstract

The present application relates to the technical field of communication data transmission, and specifically to a method for safely transmitting hydrological and meteorological data to a shipboard terminal based on Beidou, the method comprising: obtaining each Beidou short message data of the hydrological and meteorological data in chronological order; extracting co-occurring characters according to the similarity of characters contained between adjacent Beidou short message data; synthesizing the local similarity, overall character similarity and position similarity of all co-occurring characters between each Beidou short message data and its adjacent Beidou short message data, obtaining the similar position coefficient of each Beidou short message data; obtaining the original key shift amount according to the similar position coefficient of each Beidou short message data, performing displacement adjustment on the original key, and obtaining an updated key; encrypting each Beidou short message data according to the updated key and then transmitting it. The present application can improve the security of transmitting hydrological and meteorological data to a shipboard terminal.

Description

Technical Field

[0001] The present application relates to the technical field of communication data transmission, and in particular to a method for securely transmitting Beidou-based hydrological and meteorological data to a ship-borne terminal. Background Art

[0002] The BeiDou satellite system has three major functions: two-way communication, rapid positioning and precise timing, which helps ensure the timeliness and accuracy of ships' acquisition of hydrological and meteorological data. However, since the basic information of the BeiDou satellite navigation system transmission standard, such as carrier frequency, modulation mode, spread spectrum code and transmission format, has been made public, the data transmission process of short messages is vulnerable to attacks by third-party adversaries, resulting in security risks such as data leakage and data tampering.

[0003] Existing technologies often use encryption algorithms to ensure the secure transmission of short messages. However, because the format of Beidou short messages is fixed, the data information structure in each short message is fixed, and there may be a large correlation between different short message data. This correlation makes it easier to infer the key when the short message encryption transmission process encounters an enemy attack, affecting the security of the transmission of hydrological and meteorological data to the shipborne terminal. Summary of the invention

[0004] In order to solve the above technical problems, the present application provides a method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal to solve the existing problems.

[0005] The method for safely transmitting Beidou-based hydrological and meteorological data to a shipboard terminal in this application adopts the following technical solution:

[0006] An embodiment of the present application provides a method for securely transmitting hydrological and meteorological data based on Beidou to a shipboard terminal, the method comprising the following steps:

[0007] S1, obtain the Beidou short message data of hydrological and meteorological data in chronological order;

[0008] S2, extracting co-occurring characters according to the similarity of characters contained in adjacent Beidou short message data; obtaining the local similarity of each co-occurring character according to the similarity of local characters at different positions in the adjacent Beidou short message data;

[0009] S3, comprehensively analyzing the local similarity and overall character similarity of all co-occurring characters between each Beidou short message data and its adjacent Beidou short message data, and obtaining a comprehensive similarity coefficient of each Beidou short message data;

[0010] S4, according to the position similarity of all co-occurring characters between each Beidou short message data and its adjacent Beidou short message data, obtain the character position repetition of each Beidou short message data; comprehensively obtain the similarity position coefficient of each Beidou short message data by combining the comprehensive similarity coefficient and the character position repetition of each Beidou short message data;

[0011] S5, obtain the original key during encrypted transmission, and obtain the original key shift amount according to the similar position coefficient of each Beidou short message data; adjust the original key according to the original key shift amount of each Beidou short message data to obtain the updated key; encrypt each Beidou short message data according to the updated key and then transmit it.

[0012] Further, the method for extracting co-occurring characters comprises:

[0013] The same characters that exist in each Beidou short message data and its previous Beidou short message data are recorded as co-occurring characters.

[0014] Furthermore, the method for obtaining the local similarity of each co-occurring character includes:

[0015] For each co-occurring character, obtain a set consisting of the character positions of the co-occurring characters in each Beidou short message data and the previous Beidou short message data of each Beidou short message data, respectively, recorded as a first set and a second set; wherein the character position represents the order of the characters appearing in the corresponding Beidou short message;

[0016] Obtain any two combinations of any element in the first set with any element in the second set; form a local character sequence of each character from all characters in a local neighborhood centered on the position of each character in the Beidou short message data; obtain the maximum value of the similarity between the local character sequences of two characters in all the two-by-two combinations as the local similarity of each co-occurring character.

[0017] Furthermore, the similarity between the partial character sequences of the two characters is the Jaccard index between the partial character sequences of the two characters.

[0018] Further, the method for obtaining the comprehensive similarity coefficient of each Beidou short message data includes: The comprehensive similarity coefficient of Beidou short message data is recorded as , :in, It is The Jaccard index between a Beidou short message data and the previous Beidou short message data; It is The number of co-occurring characters between a Beidou short message data and its previous Beidou short message data; It is The local similarity of co-occurring characters.

[0019] Further, the method for obtaining the character position repetitiveness of each Beidou short message data comprises: The character position repetition of a Beidou short message data is recorded as , ;in, It is The number of co-occurring characters of a Beidou short message data and its previous Beidou short message data, , They are The first set and the second set of co-occurring characters, The table is the intersection symbol, The union conforms.

[0020] Further, the method for obtaining the similar position coefficient of each Beidou short message data includes:

[0021] The product of the comprehensive similarity coefficient of each Beidou short message data and the character position repetition is used as the similarity position coefficient of each Beidou short message data.

[0022] Furthermore, the method for obtaining the original key shift amount includes: The original key shift amount of a Beidou short message data is recorded as , ; It is Similarity position coefficient of Beidou short message data, is the length of the original key, is a modular function, is the floor function.

[0023] Further, the original key is shifted and adjusted according to the original key shift amount of each Beidou short message data to obtain an updated key, including:

[0024] Starting from the third Beidou short message data, the original key is shifted left cyclically with the original key shift amount of each Beidou short message data as the number of times to obtain the updated key of each Beidou short message data.

[0025] Further, the encrypting and transmitting each Beidou short message data according to the updated key includes: using the updated key as the key in the symmetric encryption algorithm, encrypting each Beidou short message data, obtaining a ciphertext, and transmitting the ciphertext to the terminal.

[0026] This application has at least the following beneficial effects:

[0027] The present application analyzes the impact of the similarity between the Beidou short message data of the hydrological and meteorological data on the security level during encryption, calculates the comprehensive similarity coefficient according to the global similarity between the two adjacent Beidou short message data and the local similarity within the neighborhood of each character, measures the similarity between the two Beidou short messages, and provides a basis for the subsequent key update; then, combined with the position information of each character in the two adjacent Beidou short message data, the similar position coefficient is calculated to measure the position repeatability of each character in the data, further enhancing the analysis of the similarity characteristics of the data, which is helpful to adjust the complexity of the subsequent key update according to the similarity; finally, the shift amount is calculated and the dynamic key update is performed; in this way, the dynamic update of the key is realized when the encryption algorithm is used, thereby ensuring the security of the encryption system, and because the key update is based on the adjacent historical data, not a fixed rule, it further increases the difficulty of cracking, thereby improving the security of the transmission of hydrological and meteorological data to the shipborne terminal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 A flowchart of the steps of a method for securely transmitting Beidou-based hydrological and meteorological data to a ship-borne terminal provided in one embodiment of the present application;

[0030] Figure 2 A schematic diagram of left cyclic shift provided for one embodiment of the present application. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0033] The following is a detailed description of the specific scheme of the method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal provided by the present application in conjunction with the accompanying drawings.

[0034] An embodiment of the present application provides a method for securely transmitting hydrological and meteorological data to a shipboard terminal based on Beidou. Specifically, the following method for securely transmitting hydrological and meteorological data to a shipboard terminal based on Beidou is provided. Figure 1 , the method comprises the following steps:

[0035] S1, obtain the Beidou short message data of hydrological and meteorological data in chronological order.

[0036] A specific implementation scenario of an embodiment of the present invention is a Beidou-based hydrological and meteorological data transmission scenario. When using Beidou short messages to transmit hydrological and meteorological data to a shipborne terminal, it is necessary to first monitor the hydrological and meteorological data through various hydrological and meteorological monitoring stations, and then transmit the data monitored by each hydrological and meteorological monitoring station to a ground center station through a dedicated network. The ground center station encodes the hydrological and meteorological data to generate a Beidou short message and encrypts the Beidou short message. Then the ground center station sends the encrypted Beidou short message to the satellite, and transmits it to the shipborne terminal through the satellite's broadcast signal. When the shipborne terminal receives the encrypted Beidou short message, it decrypts it to obtain specific hydrological and meteorological data.

[0037] The focus of this application is to ensure the secure transmission of Beidou short messages, and the way to ensure secure transmission is through data encryption. The focus is whether a third party can break the system and crack the system key within polynomial time, so the focus is on the encryption process of Beidou short messages by the ground center station. The rest of the processes are well-known in Beidou short message transmission technology and will not be repeated. According to the provisions of the Beidou satellite data format protocol, all data should be transmitted in ASCII characters. The ground center station will encode the acquired Beidou short message data in ASCII code and then encrypt it.

[0038] S2, extracting co-occurring characters according to the similarity of characters contained in adjacent Beidou short message data; obtaining the local similarity of each co-occurring character according to the local character similarity of each co-occurring character at different positions in the adjacent Beidou short message data; and obtaining the comprehensive similarity coefficient of each Beidou short message data by comprehensively analyzing the local similarity and overall character similarity of all co-occurring characters between each Beidou short message data and its adjacent Beidou short message data.

[0039] The ground center station sends Beidou short message data to the satellite once a second, one frame at a time. Beidou short message data has a unified format, so that various types of data have a relatively fixed position distribution in each frame of data; and hydrological and meteorological data have a high degree of similarity. There are multiple repeated data between the Beidou short message data sent per second, that is, the content between different Beidou short message data has a high similarity. In general, due to the high similarity of different short message data, ASCII code is used for encoding, and the encoding space is small, which makes it more likely for the adversary to break the encryption system.

[0040] Therefore, in order to enhance the security of the encryption system, this embodiment updates the key each time the encryption is performed according to the data characteristics of the Beidou short message to reduce the possibility of the enemy breaking the encryption system. Under normal circumstances, the Beidou short message data of the meteorological data at adjacent moments have a high similarity, and the higher the similarity of the data, the easier it is for the enemy to break the encryption system through the correspondence between the plaintext and ciphertext of different rounds after symmetric encryption. First, this embodiment obtains the characters that exist in each Beidou short message data and the previous Beidou short message data at the same time; the same characters are regarded as a character type; each character type is recorded as a co-occurring character. For example, the co-occurring characters of data 1, 2, 2, 4 and data 3, 2, 5, 4 are 2 and 4.

[0041] If the overall similarity of the Beidou short message is low, but there is a high similarity in the local part, the adversary can also attack the local data part with high similarity through the selected ciphertext attack, and then infer the overall key. Therefore, when measuring the similarity between short messages at different times, it is necessary to comprehensively consider the similarity of the overall data and the similarity of the local data. Co-occurring characters may appear multiple times in a short message data. The local character distribution of the co-occurring characters can be obtained The local similarity of all co-occurring characters.

[0042] For each co-occurring character, obtain a set consisting of the character positions of the co-occurring characters in each Beidou short message data and the previous Beidou short message data of each Beidou short message data, respectively, and record them as the first set and the second set; wherein the character position represents the order of the characters appearing in the corresponding Beidou short message.

[0043] Get any two combinations of any element in the first set with any element in the second set; for example, any two combinations of the set {1, 2, 3} and the set {4, 5} include [1, 4], [1, 5], [2, 4], [2, 5], [3, 4] and [3, 5].

[0044] All characters in the local neighborhood centered on the position of each character in the Beidou short message data are used to form a local character sequence of each character; the maximum value of the similarity between the local character sequences of two characters in all the two-by-two combinations is obtained as the local similarity of each co-occurring character. In this embodiment, the local neighborhood contains a total of 5 characters, that is, the first two digits, the last two digits adjacent to the character and the character itself are taken, and the first two digits and the last two digits in the entire short message data are not involved in the calculation.

[0045] For example, The set of pairwise combinations of the positions of characters is ,in, Is a collection Middle elements, , They are co-occurring characters in , This embodiment uses the Jaccard index to calculate the similarity between two sequences. As other embodiments of the present application, the inverse of the Hamming distance may be used for calculation, which is not limited in the present application.

[0046] S3, comprehensively analyzing the local similarity and overall character similarity of all co-occurring characters between each Beidou short message data and its adjacent Beidou short message data, and obtaining a comprehensive similarity coefficient of each Beidou short message data.

[0047] The above calculation calculates the local similarity of characters. Further, based on the similarity between the encoded data of two adjacent rounds of Beidou short messages and the local similarity between the same code and the surrounding adjacent codes in different Beidou short messages, the comprehensive similarity coefficient of Beidou short message data is calculated to measure the similarity characteristics between two adjacent rounds of Beidou short message data.

[0048] Specifically, the The comprehensive similarity coefficient of Beidou short message data is recorded as , :in, It is The Jaccard index between a Beidou short message data and the previous Beidou short message data; It is The number of co-occurring characters between a Beidou short message data and its previous Beidou short message data; It is The local similarity of co-occurring characters.

[0049] It can be understood that when the similarity between two Beidou short message data is high, the Jaccard index between the Beidou short message data represents the overall similarity. When the overall similarity is high, the local similarity also exists. That is, and are both large, so the similarity coefficient Relative maximum; when the overall similarity is small but the local similarity is large, Smaller Large, and because the transmission length of Beidou short message is between 110 and 848 bits, and the value of the exponential function is greater than , so the similarity coefficient is also relatively large; so when the similarity of two Beidou short message data is high, the similarity coefficient Larger, and On the contrary, when the similarity between the two northern short messages is small, the similarity coefficient The purpose of the exponential function is to increase the weight of local similarity to avoid inaccurate measurement of the similarity between data due to a small similarity coefficient when the global similarity is small.

[0050] S4, according to the position similarity of all co-occurring characters between each Beidou short message data and its adjacent Beidou short message data, obtain the character position repetition of each Beidou short message data; and obtain the similarity position coefficient of each Beidou short message data by combining the comprehensive similarity coefficient and the character position repetition of each Beidou short message data.

[0051] Since Beidou short message data has a fixed format, each type of data has a relatively fixed position distribution in each Beidou short message data, and the characters in each type of data have relatively high similarity, so there are many characters in different short message data that have high repeatability in their positions. Based on the repeatability of the character positions, the adversary can use these characters to infer the key when attacking the system, thereby relatively reducing the difficulty of key attacks and threatening data security.

[0052] Therefore, in order to analyze the position repeatability of two Beidou short message data, encryption is performed according to the degree of repetition. In this embodiment, the similarity between the first set and the second set of all co-occurring characters in the Beidou short message data at each moment and the previous moment is used to obtain the similarity position coefficient at each moment, which is used to measure the repeatability of the character position in the two short message data.

[0053] The first The character position repetition of a Beidou short message data is recorded as , ;in, It is The number of co-occurring characters of a Beidou short message data and its previous Beidou short message data, , They are The first set and the second set of co-occurring characters, The table is the intersection symbol, The union conforms.

[0054] The higher the repetitiveness of the positions of the characters in the first set and the second set in the Beidou short message, the greater the intersection and union ratio of the character position sets. At this time, the higher the repetitiveness of the character positions, the greater the possibility that the adversary can infer the key through the Beidou short message data.

[0055] To sum up, the comprehensive similarity coefficient measures the similarity characteristics between two adjacent rounds of Beidou short message data, and the character position repetition represents the degree of arrangement repetition of co-occurring characters in two Beidou short message data. Therefore, this embodiment combines the comprehensive similarity coefficient and character position repetition of Beidou short message data to obtain the similarity position coefficient of Beidou short message data.

[0056] In this embodiment, The similarity coefficient of the Beidou short message data is recorded as , ;in, For the The character position repetition of the Beidou short message data is For the The comprehensive similarity coefficient of Beidou short message data.

[0057] It is understandable that when the possibility of the adversary inferring the key through the Beidou short message data is greater, it is necessary for the Beidou short message data to have greater similarity, or the position of the characters in the Beidou short message to have higher repetitiveness. The greater the similarity between the Beidou short message data, the higher the similarity coefficient. The larger the similarity coefficient is, the higher the repetitiveness of the character position in the Beidou short message is, the greater the intersection and union ratio of the character position set is; so the greater the possibility that the adversary can infer the key through the Beidou short message data is, the greater the similarity coefficient is. is larger, and the probability of inferring the key is On the contrary, when the possibility of the adversary inferring the key through the Beidou short message data is small, it means that the similarity of the data between the Beidou short messages is small, and the repetitiveness of the character positions is also small, so the similarity position coefficient Smaller.

[0058] S5, obtain the original key during encrypted transmission, and obtain the original key shift amount according to the similar position coefficient of each Beidou short message data; adjust the original key according to the original key shift amount of each Beidou short message data to obtain the updated key; encrypt each Beidou short message data according to the updated key and then transmit it.

[0059] According to the encryption mechanism of the AES encryption algorithm, both parties use the same key for encryption and decryption, so a secure channel is required for key transmission to ensure that only the two parties can obtain the key. However, due to the high cost of secure channel transmission, the two parties cannot frequently update the key, so in the original AES encryption algorithm, different rounds of encryption use the same key. This method is relatively safe for data sets with large data sets or data with low data similarity. Because the data size is relatively large, it takes a greater cost and time for the adversary to infer the key through known information. According to the basic principle of cryptographic attack, when the cost of the attack exceeds the value of the information itself, such a key attack is considered meaningless.

[0060] However, due to the small amount of data in Beidou short messages and the high data similarity, if the original AES encryption algorithm is still used and a fixed key is used for encrypted transmission, the possibility of the adversary breaking through will be greatly increased. According to the Kerckhoffs principle, all details of the cryptographic system are public, and the security of the encryption system only depends on the security of the key. That is to say, when the adversary cracks the key, he can obtain any transmitted information and tamper with it at will, which seriously affects the security of the data.

[0061] In this case, in view of the characteristics of Beidou short messages and the security of the encryption system, it is necessary to frequently replace the keys. If the key is updated using a secure channel, the burden on the encryption system will increase. Therefore, this embodiment uses similar position coefficients to set the displacement amount for key update, without having to use a secure channel every time, thereby ensuring the security of the encryption system and avoiding a heavy burden on the system.

[0062] Specifically, the shift amount during key update is calculated for subsequent key updates. The original key shift amount of a Beidou short message data is recorded as , ; It is Similarity position coefficient of Beidou short message data, is the length of the original key, is a modular function, is a round-down function. In this embodiment, the original key length of AES encryption is 128 bits.

[0063] It should be noted that since the calculation of the shift amount requires the use of the features between the first two encrypted transmissions of the Beidou short message data, the shift amount cannot be calculated for the first two transmissions, so the first two data transmissions still use the original key. Since the amount of data in the first two data transmissions is small, it is difficult for the adversary to infer the key only through the first two encrypted messages, and the subsequent keys are constantly changing according to the historical interaction information, and there is no regularity, which increases the difficulty of the adversary's attack and ensures the security of the encryption system.

[0064] The first two Beidou short message data are encrypted according to the original key. Starting from the encryption of the third Beidou short message data, the ground center station performs left circular shift according to the shift amount each time the Beidou short message is encrypted; specifically, Figure 2 As shown, the data {s1, s2, s3...sn} is shifted to the left circularly, (1) is the result of the original key being shifted to the left circularly once; (2) is the result of the original key being shifted to the left circularly twice. Starting from the third Beidou short message data, the original key is shifted to the left circularly by the shift amount of the original key of each Beidou short message data, and the updated key of each Beidou short message data is obtained; then each Beidou short message data and its updated key are used as input, and AES encryption is performed to obtain ciphertext, and the ciphertext is transmitted to the terminal; the ground center station then sends the ciphertext to the satellite, and transmits it to the shipboard terminal through the satellite broadcast signal; finally, after the shipboard terminal receives the ciphertext, the shift amount is calculated according to the Beidou short message text received in the first two rounds, and the shift is performed to obtain the current round key, and the current round key is used for decryption to obtain specific hydrological and meteorological data. AES encryption and decryption and Beidou satellite information transmission and release are well-known technical means, and the specific process is not repeated.

[0065] This application calculates the shift amount when updating the key in this round based on the characteristics of the information transmitted in the previous two rounds, and uses the updated key for AES encryption and decryption. In this way, the key needs to be updated in each round of encrypted transmission, and the historical interaction information is used to avoid the participation of the secure channel, thereby reducing the cost of key update; in addition, since each round of update is based on the information of the previous two rounds of interaction, rather than a fixed rule, the difficulty for the adversary to crack the key has been greatly improved, thereby ensuring the security of encrypted transmission.

[0066] Finally, by using each round of key updates, the risks brought by the fixed format and similar content of Beidou short message data are avoided, and the security of the encryption system is improved; at the same time, the key is updated by using the characteristics between short message data, avoiding the involvement of the secure channel. In this way, the security of Beidou short message data transmission is guaranteed, and the efficiency and overhead of the encryption system are guaranteed, realizing the optimization of the process of secure data transmission from Beidou to shipborne terminals.

[0067] Through the above description of the implementation method in combination with the accompanying drawings, technical personnel in the relevant field can understand that for the convenience and simplicity of description, only the division of the above-mentioned functional modules is used as an example. In actual applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above.

[0068] The above contents are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be covered by the protection scope of the present application.

Claims

1. A method for securely transmitting Beidou-based hydrological and meteorological data to a ship-borne terminal, characterized in that: The method comprises the following steps: S1, obtain the Beidou short message data of hydrological and meteorological data in chronological order; S2, extracting co-occurring characters according to the similarity of characters contained in adjacent Beidou short message data; obtaining the local similarity of each co-occurring character according to the similarity of local characters at different positions in adjacent Beidou short message data; S3, comprehensively analyzing the local similarity and overall character similarity of all co-occurring characters between each Beidou short message data and its adjacent Beidou short message data to obtain a comprehensive similarity coefficient of each Beidou short message data; S4, according to the position similarity of all co-occurring characters between each Beidou short message data and its adjacent Beidou short message data, obtain the character position repetition of each Beidou short message data; comprehensively obtain the similarity position coefficient of each Beidou short message data by combining the comprehensive similarity coefficient and the character position repetition of each Beidou short message data; S5, obtain the original key during encrypted transmission, and obtain the original key shift amount according to the similar position coefficient of each Beidou short message data; adjust the original key according to the original key shift amount of each Beidou short message data to obtain the updated key; encrypt each Beidou short message data according to the updated key and then transmit it.

2. The method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal according to claim 1, characterized in that: The method for extracting co-occurring characters comprises: The same characters that exist in each Beidou short message data and its previous Beidou short message data are recorded as co-occurring characters.

3. The method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal as claimed in claim 1, characterized in that: The method for obtaining the local similarity of each co-occurring character includes: For each co-occurring character, obtain a set consisting of the character positions of the co-occurring characters in each Beidou short message data and the previous Beidou short message data of each Beidou short message data, respectively, recorded as a first set and a second set; wherein the character position represents the order of the characters appearing in the corresponding Beidou short message; Obtain any two combinations of any element in the first set with any element in the second set; form a local character sequence of each character from all characters in a local neighborhood centered on the position of each character in the Beidou short message data; obtain the maximum value of the similarity between the local character sequences of two characters in all the two-by-two combinations as the local similarity of each co-occurring character.

4. The method for safely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal as claimed in claim 3, characterized in that: The similarity between the partial character sequences of the two characters is the Jaccard index between the partial character sequences of the two characters.

5. The method for safely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal as claimed in claim 1, characterized in that: The method for obtaining the comprehensive similarity coefficient of each Beidou short message data comprises: The comprehensive similarity coefficient of Beidou short message data is recorded as , :in, It is The Jaccard index between a Beidou short message data and the previous Beidou short message data; It is The number of co-occurring characters between a Beidou short message data and its previous Beidou short message data; It is The local similarity of co-occurring characters.

6. The method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal as claimed in claim 1, characterized in that: The method for obtaining the character position repetitiveness of each Beidou short message data comprises: The character position repetition of a Beidou short message data is recorded as , ;in, It is The number of co-occurring characters of a Beidou short message data and its previous Beidou short message data, , They are The first set and the second set of co-occurring characters, The table is the intersection symbol, The union conforms.

7. The method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal as claimed in claim 1, characterized in that: The method for obtaining the similar position coefficient of each Beidou short message data includes: The product of the comprehensive similarity coefficient of each Beidou short message data and the character position repetition is used as the similarity position coefficient of each Beidou short message data.

8. The method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal as claimed in claim 1, characterized in that: The method for obtaining the original key shift amount comprises: The original key shift amount of a Beidou short message data is recorded as , ; It is Similarity position coefficient of Beidou short message data, is the length of the original key, is a modular function, is the floor function.

9. The method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal as claimed in claim 1, characterized in that: The method of adjusting the original key according to the original key shift amount of each Beidou short message data to obtain an updated key includes: Starting from the third Beidou short message data, the original key is shifted left cyclically with the original key shift amount of each Beidou short message data as the number of times to obtain the updated key of each Beidou short message data.

10. The method for securely transmitting Beidou-based hydrological and meteorological data to a shipborne terminal according to claim 1, characterized in that: The method of encrypting each Beidou short message data according to the updated key and then transmitting it includes: using the updated key as the key in the symmetric encryption algorithm, encrypting each Beidou short message data, obtaining a ciphertext, and transmitting the ciphertext to the terminal.

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