Frequency conversion communication system with encryption function for complex sea surface environment

Abstract

The invention discloses a frequency conversion communication system with an encryption function for a complex sea surface environment. The frequency conversion communication system is used for coping with severe weather on the sea and network attacks and interferences of attackers. The system comprises a space satellite carrying node, a plurality of water surface nodes and an underwater controlled instrument, the space satellite carrying node is in two-way communication connection with the plurality of water surface nodes through high-frequency electromagnetic waves; the plurality of water surface nodes are in two-way communication connection with the underwater controlled instrument through extremely-low-frequency electromagnetic waves; very-low-frequency electromagnetic wave two-way communication is adopted among the water surface nodes. Wherein all communications adopt an encryption algorithm to confront network attacks. The characteristics of various different frequencies are utilized, the anti-interference capability of the communication process is enhanced by combining LDPC coding, and real-time communication in a complex sea surface environment is realized.

Description

Technical Field

[0001] The present invention belongs to the intersection field of communication technology and security, and in particular relates to a variable frequency communication system with encryption function for complex sea surface environments. Background Art

[0002] The frequency conversion communication system with encryption function for the complex environment of the sea surface is a communication system that combines encryption technology, coding technology and frequency conversion technology. Communication on the sea surface is affected by bad weather. A single communication method cannot cope with all situations. High-frequency electromagnetic waves lack penetration and cannot penetrate dense raindrops and thick clouds in heavy rain, resulting in high-frequency communication being unusable in bad weather. Very low frequency and extremely low frequency communications cannot achieve efficient voice communication due to their own low code rates. Existing communication technologies generally do not involve very low frequency and extremely low frequency communications, making it difficult to adapt to more complex communication environments. At the same time, for instruments performing underwater tasks, once the distance from the surface node is increased, a single frequency cannot meet the communication requirements.

[0003] On the other hand, eavesdropping may occur in a strong adversarial environment. Very low frequency and extremely low frequency communications are used to transmit simple instructions, which can be easily intercepted and replayed by malicious attackers, and are also easy to be eavesdropped. High frequency communications are used for complex instant messaging, but the lack of encryption can lead to information leakage, and the lack of authentication may also lead to impersonation attacks.

[0004] In the field of coding, the use of LDPC error correction codes can identify errors in the process of information transmission, thereby increasing the anti-interference ability of communication. Maritime communications in a strong confrontation environment are always facing strong interference, including noise generated by the natural environment and noise deliberately released by attackers. Appropriate coding methods can enhance the anti-interference ability of communication. How to choose a suitable coding method is also the focus of current scholars' research. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a variable frequency communication system with encryption function for complex sea environment. It is based on a miniaturized mechanical antenna, combines the high code rate of high frequency communication, the penetration and anti-interference ability of very low frequency and extremely low frequency communication, and strengthens the ability to resist eavesdropping and replay attacks. It speeds up the information transmission rate by compressing information, and further strengthens the anti-interference ability through error correction coding.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a variable frequency communication system with encryption function for complex sea surface environment. One of the differences between this communication system and traditional real-time voice communication is that the communication frequency includes very low frequency and extremely low frequency in addition to the commonly used high frequency communication. Therefore, the present invention also proposes a set of compression, error correction and encryption methods applicable to very low frequency and low frequency.

[0007] A variable frequency communication system with encryption function for complex sea surface environment, the system includes: a space satellite carrying node, multiple surface nodes, and underwater controlled nodes, wherein:

[0008] The space satellite-borne node communicates with the plurality of surface nodes via a two-way connection via high-frequency electromagnetic waves;

[0009] The multiple surface nodes communicate with the underwater controlled nodes via bidirectional connection via extremely low frequency electromagnetic waves;

[0010] The multiple surface nodes communicate with each other via bidirectional connection using very low frequency electromagnetic waves.

[0011] In the variable frequency communication system with encryption function facing the complex sea environment, high-frequency electromagnetic wave voice communication can be used between the multiple surface nodes and between the multiple surface nodes and the space satellite-borne nodes, and the multiple surface nodes and the underwater controlled nodes send instructions via extremely low frequency electromagnetic waves; very low frequency electromagnetic waves are used between the multiple surface nodes for simple communication or sending instructions.

[0012] In the variable frequency communication system with encryption function facing the complex environment of the sea surface, high frequency communication has strong anti-interference ability and extremely high information transmission rate; very low frequency communication can resist harsh environment, including extreme rainstorms and sea waves; and extremely low frequency communication has strong underwater penetration ability.

[0013] Optionally, in the variable frequency communication system with encryption function facing the complex sea environment, the extremely low frequency and very low frequency communications use SM4 to perform encryption operations before information is sent to counter eavesdropping, and the high-frequency electromagnetic wave bidirectional connection performs stream cipher encryption operations before information is sent.

[0014] Optionally, in the variable frequency communication system with encryption function for complex sea environment, extremely low frequency and even low frequency communications use OFB mode for encryption operation before information is sent to counter replay.

[0015] Optionally, in the variable frequency communication system with encryption function for complex sea surface environment, LDPC error correction coding is used before very low frequency communication encryption to enhance anti-interference capability.

[0016] Optionally, in the variable frequency communication system with encryption function for complex sea surface environment, very low frequency communication encryption uses arithmetic coding for data compression.

[0017] Optionally, in the variable frequency communication system with encryption function for complex sea surface environment, the very low frequency communication reduces the accuracy during sampling and quantization.

[0018] Optionally, in the variable frequency communication system with encryption function facing the complex sea environment, the generation of very low frequency signals in the communication is assisted by a miniaturized mechanical antenna.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention utilizes the characteristics of multiple different frequencies to achieve real-time communication in complex environments.

[0021] 2. The present invention combines the techniques in voice communication sampling, quantization and other steps with the coding theory in information theory to improve the information transmission rate; uses LDPC coding to enhance the anti-interference ability of the communication process; and uses the encryption mode under OFB to enhance the anti-eavesdropping and anti-replay characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the variable frequency communication system with encryption function for complex sea surface environment of the present invention;

[0023] Figure 2 This is the encryption and decryption flow chart corresponding to the present invention. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0025] It should be noted that the steps in the encryption algorithm flowchart shown in the attached figure can be executed in a computer system or slightly processed in a communication machine, and the logical order is shown in the flowchart.

[0026] like Figure 1As shown, in this embodiment, a variable frequency communication system with encryption function facing the complex environment of the sea surface is provided, including: a space satellite-mounted node (i.e., the satellite communication node shown in the figure), multiple surface nodes (i.e., the water communication node shown in the figure), and an underwater controlled node (i.e., the underwater communication node shown in the figure); the space satellite-mounted node is connected to the multiple surface nodes through high-frequency electromagnetic waves for two-way communication; the multiple surface nodes are connected to the underwater controlled nodes through extremely low-frequency electromagnetic waves for two-way communication; the multiple surface nodes use very low frequency two-way communication; the very low frequency electromagnetic wave frequency is about 3KHz, which is used for long-distance node communication in harsh environments, and only transmits key information and instructions and simple voice communication. The transmission of very low frequency signals in communication is assisted by miniaturized mechanical antennas. The high frequency band is used for communication between multiple surface nodes and the space satellite-mounted node, and the high and low frequency electromagnetic waves have a frequency of about 2-30MHz. Since the high frequency band has the characteristics of high bit rate, it can be used for real-time communication with the space satellite-mounted node as a relay node. Extremely low frequency can be used for simple information exchange between multiple surface nodes and instruments far away under the water surface. The frequency of the extremely low frequency electromagnetic wave is less than 30Hz. In particular, each node in the communication system includes encryption and encoding modules, decryption and decoding modules.

[0027] like Figure 2 As shown, the main part of the VLF communication encryption algorithm is the SM4 block encryption algorithm. The encryption adopts the OFB mode. Due to the use of random initialization vectors, the encrypted data of the same content in different conversations are also different. This method can effectively prevent replay attacks. In the same conversation, due to the use of the OFB encryption mode, the same encrypted content results are also different. If there is no high security requirement, the high-frequency communication can be converted into traditional stream cipher encryption.

[0028] The reasons for using SM4 for encryption in the present invention and the efficiency analysis are as follows: the encryption method used in traditional instant messaging is stream cipher. Taking GSM as an example, the symmetric encryption algorithm used is A5. Stream cipher is faster but less secure than symmetric cipher. SM4 encrypts 5M data on a computer with i7-12700h as CPU in less than 1s, and encrypts 36KB of data in less than 0.3 seconds (SM4 has a significant gap in efficiency and AES when processing small-scale data). As shown in Table 1, the encryption and decryption speed test results of SM4 on CPUi7-12700h are given; the very low frequency data transmission rate is 1000-10000bps. The data transmission efficiency during the communication process is mainly affected by the very low frequency communication. Using SM4 as a stream cipher, its rate will not affect the very low frequency communication. As shown in Table 2, the advantages and disadvantages of block ciphers and stream ciphers are compared; at the same time, since the very low frequency communication transmits key information, the use of symmetric encryption can maximize the security of the very low frequency communication. The traditional 3G information transmission rate is 100kbps, and SM4 encryption will not excessively reduce the communication rate in the high-frequency band.

[0029] Table 1

[0030]

[0031] Table 2

[0032]

[0033] The VLF cannot use conventional real-time voice communication. In order to adapt to the disadvantage of low information transmission rate of VLF communication, the present invention first compresses the voice communication.

[0034] The first step is to use the sampling quantization in conventional voice communication combined with a new de-duplication method to compress the information.

[0035] There are about 1,300 Mandarin Chinese pronunciations, which are replaced by special symbols, such as A1, A2, etc. The time of each pronunciation is recorded approximately (1 second is recorded as 1 second if it exceeds 1 second), with an accuracy of 0.1s. If the pronunciation duration is 0.3 seconds, it is recorded as There are about 13,000 different characters in total, and with the addition of 5 amplitudes, there are 70,000 characters.

[0036] Step 2: Use arithmetic coding to compress the information.

[0037] Let's take a simple example: for a string containing only three characters A, B, and C, , sort A, B, and C in descending order of probability. Then taking AABABCABAB as an example, according to the rules of arithmetic coding, the final binary code is 00101011001011.

[0038] In the actual encoding process, 70,000 different symbols can be sorted according to the probability of occurrence. Each symbol has its own corresponding interval, and then the corresponding decimal is found in the interval to perform the encoding. After the encoding is completed, the unified length of the original code is noted.

[0039] Decoding process: After converting the code into a binary decimal, find out which interval the binary decimal is in according to the uniform original code length, and then translate it into a certain code. In addition, in the encoding process, encoding a combination of multiple characters can get closer to the Shannon limit.

[0040] Finally, the coding efficiency is estimated. There are 70,000 different characters, and the average amount of information carried by each character is at most 16 bits. The data transmitted by very low frequency voice communication is much larger than this amount. Therefore, this communication method can be applied to very low frequency communication, and even more precise sampling and quantization methods can be used to improve the quality of voice communication.

[0041] Step 2: Error correction coding for 70,000 different pronunciations and different lengths. The maximum number of codewords with Hamming distance d of 3 and code length n of 40 in the binary domain The Gilbert-Varshamov bound is used for estimation:

[0042] (1)

[0043] Let q=2, d=3, n=40:

[0044] (2)

[0045] have to It is close to 100,000. It can be seen that the encoded length of these 70,000 different pronunciations is less than 40 bits. The very low frequency transmission rate can reach more than 1 kbps. There is a coding method that meets the requirements and can even widen the Hamming distance between codewords.

[0046] The specific coding may adopt LDPC error correction coding.

[0047] Constructed using recursive coding matrix:

[0048] ,

[0049] in, is a circulant submatrix generated by shifting the unit matrix;

[0050] The cyclic shift submatrix Q is defined as:

[0051] ,

[0052] This circulant submatrix has a very nice property:

[0053] ;now that: ,

[0054] In this way, the inverse of the matrix can be obtained by transposing the matrix, which greatly simplifies the calculation. Matrix, from which the check equation , we can get:

[0055] (3)

[0056] Then we have:

[0057] (4)

[0058] set up Using the above recursive algorithm, we can get the corresponding . The first A code word.

[0059] LDPC decoding uses a soft decision algorithm:

[0060] : The message sent by the check node to the bit node, that is, Time The probability that the check equation is true.

[0061] : The message sent from the bit node to the check node, that is, probability.

[0062] : No. The first The probability that a bit is 1.

[0063] : No. The set of column numbers whose row elements are 1.

[0064] : except column number No. The set of column numbers whose row elements are 1.

[0065] : No. The set of row numbers whose column elements are 1.

[0066] : except line numbers No. The set of row numbers whose column elements are 1.

[0067] Decoding steps:

[0068] 1 Initialization:

[0069] (5)

[0070] (6)

[0071] 2 Horizontal Steps:

[0072] (7)

[0073] (8)

[0074] 3 vertical steps:

[0075] (9)

[0076] (10)

[0077] in, is to make The constant.

[0078] 4 For all calculate:

[0079] (11)

[0080] (12)

[0081] in, is to make The constant.

[0082] For each bit, if Q(1)>Q(0), it is translated as 1, otherwise it is translated as 0. If all check equations are satisfied or the maximum number of iterations is reached, the decoding ends, otherwise jump to the first step.

[0083] The code rate of the LPDC coding used in the present invention is above 0.5, which means that this error correction coding will not affect the transmission rate too much on the basis of ensuring communication reliability, and the very low frequency data transmission rate is above 1 kbps.

[0084] In summary, the above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A variable frequency communication system with encryption function for complex sea surface environment, characterized in that: The system includes: a space satellite-mounted node, multiple surface nodes, and an underwater controlled node, wherein: The space satellite-borne node communicates with the plurality of surface nodes via a two-way connection via high-frequency electromagnetic waves; The multiple surface nodes communicate with the underwater controlled nodes via bidirectional connection via extremely low frequency electromagnetic waves; The multiple surface nodes communicate with each other using very low frequency electromagnetic waves in a two-way connection; Each node of the communication system includes an encryption and encoding module, a decryption and decoding module.

2. The frequency conversion communication system with encryption function for complex sea surface environment as claimed in claim 1, characterized in that: High-frequency electromagnetic waves are used for voice communication between the multiple surface nodes and the space satellite-borne nodes, and extremely low-frequency electromagnetic waves are used to send instructions to the multiple surface nodes and the underwater controlled nodes; very low-frequency electromagnetic waves are used to carry out simple voice communication or send instructions between the multiple surface nodes.

3. The frequency conversion communication system with encryption function for complex sea surface environment as claimed in claim 1, characterized in that: The extremely low frequency and very low frequency electromagnetic wave bidirectional connection communications use SM4 to perform encryption operations before information is sent, and the high frequency electromagnetic wave bidirectional connection performs stream cipher encryption operations before information is sent.

4. The frequency conversion communication system with encryption function for complex sea surface environment as claimed in claim 3, characterized in that: The encryption mode of the SM4 encryption operation is OFB.

5. The frequency conversion communication system with encryption function for complex sea surface environment as claimed in claim 3, characterized in that: The SM4 encryption operation is preceded by LDPC error correction coding.

6. The frequency conversion communication system with encryption function for complex sea surface environment as claimed in claim 4, characterized in that: The SM4 encryption operation uses arithmetic coding for data compression.

7. The frequency conversion communication system with encryption function for complex sea surface environment as claimed in claim 3, characterized in that: The very low frequency electromagnetic wave two-way connection communication reduces the accuracy when sampling and quantizing simple voice communication.

8. The frequency conversion communication system with encryption function for complex sea surface environment as claimed in claim 7, characterized in that: The transmission of the VLF signal is by means of a miniaturized mechanical antenna.

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