阅读说明：本技术 基于细胞自动机和dna编码的超长距传输方法及系统 (Ultra-long distance transmission method and system based on cellular automaton and DNA coding ) 是由 李志浩 黄红兵 唐先锋 倪鹏程 刘乐 杨鸿珍 赵建朋 张明熙 李印宜 江昕 席丽 于 2021-06-24 设计创作，主要内容包括：本发明公开了一种基于细胞自动机和DNA编码的超长距传输方法及系统,属于光纤通信技术领域,包括：利用细胞自动机生成一组伪随机二值序列；将伪随机二值序列作为明文DNA加密的碱基置乱序列,利用密钥序列对明文进行加密。本发明可提高通信系统的安全性能和防窃取能力。(The invention discloses a cell automaton and DNA coding-based ultra-long distance transmission method and system, belonging to the technical field of optical fiber communication and comprising the following steps: generating a group of pseudorandom binary sequences by using a cellular automaton; and (3) taking the pseudorandom binary sequence as a base scrambling sequence for encrypting the plaintext DNA, and encrypting the plaintext by using a key sequence. The invention can improve the safety performance and the anti-theft capability of the communication system.)

1. A method for ultra-long distance transmission based on cellular automata and DNA coding is used for encrypting a plaintext at a sending end of a coherent receiving system, and is characterized by comprising the following steps:

generating a group of pseudorandom binary sequences by using a cellular automaton;

and (3) taking the pseudorandom binary sequence as a base scrambling sequence for encrypting the plaintext DNA, and encrypting the plaintext by using a key sequence.

2. The cellular automata and DNA coding based over-length transmission method according to claim 1, further comprising, prior to the generating a set of pseudorandom binary sequences using cellular automata:

and generating the key sequence by adopting a fourth-order hyper-chaotic system.

3. The cellular automaton and DNA coding-based very long distance transmission method according to claim 2, wherein the fourth order hyper-chaotic system comprises four coupled first order autonomous ordinary differential equations, specifically:

wherein x, y, z and w are four state variables, and A, B, C, D, k are five common system parameters.

4. The cellular automata and DNA coding-based long-range transmission method according to claim 3, wherein the constant system parameter a is 35, B is 6, C is 12, D is 7, and k is 2.

5. The cellular automata and DNA coding-based very long distance transmission method according to claim 3, wherein the generation of the key sequence using the fourth order hyper-chaotic system is as follows:

where mod () represents a modulo operation, ceil () represents rounding up, and m represents a discrete time index.

6. The cellular automata and DNA coding based over-length transmission method according to claim 5, wherein the generating a set of pseudo-random binary sequences using cellular automata comprises:

respectively selecting an initial state ring and a state ring evolution rule by using a Key5 and a Key6, and iteratively updating the state of the cellular automata to obtain a bit sequence, wherein the Key5 and the Key6 are internal keys of the cellular automata;

controlling the iteration number of the cell generator by using the Key Key1, and constructing the pseudorandom binary sequence as follows:

basescramblingPRBS＝f(State^t⊕State^t+1)

wherein ≧ represents an exclusive-OR operation, f represents a State evolution rule, and the PRBS sequence is the pseudo-random binary sequence, State^tState of the cellular automaton at time t^t+1And the state quantity of the cellular automata at the t +1 moment.

7. The cellular automata-and-DNA-coding-based over-length transmission method according to claim 5, wherein the encrypting the plaintext using the key sequence using the pseudo-random binary sequence as a base scrambling sequence for plaintext DNA encryption comprises:

selecting a coding rule when the symbol data and the pseudorandom binary sequence are subjected to DNA coding by using the Key 2;

selecting a DNA operation rule by using the Key Key3 to complete the DNA operation;

and the Key4 is used for selecting a decoding rule to realize DNA decoding, so as to realize plaintext encryption.

8. An ultra-long distance transmission system based on cellular automata and DNA coding, which is used for encrypting a plaintext at a sending end of a coherent receiving system, and is characterized by comprising: pseudo-random binary sequence generation module and encryption module, wherein:

the pseudo-random binary sequence generating module is used for generating a group of pseudo-random binary sequences by using a cellular automaton;

the encryption module is used for taking the pseudorandom binary sequence as a base scrambling sequence for encrypting the plaintext DNA and encrypting the plaintext by using the key sequence.

9. The cellular automaton and DNA coding-based very long distance transmission system of claim 8, wherein the key sequence is generated using a fourth order hyper-chaotic system, the fourth order hyper-chaotic system comprising four coupled first order autonomous ordinary differential equations, specifically:

wherein x, y, z and w are four state variables, and A, B, C, D, k are five constant system parameters;

the four-order hyper-chaotic system is adopted to generate the key sequence as follows:

where mod () represents a modulo operation, ceil () represents rounding up, and m represents a discrete time index.

10. The cellular automata and DNA coding based over-length transmission system according to claim 9, wherein the pseudo-random binary sequence generating module comprises an iterative updating unit and a pseudo-random binary sequence constructing unit, wherein:

the iterative updating unit is used for respectively selecting an initial state ring and a state ring evolution rule by using a Key Key5 and a Key Key6, and iteratively updating the state of the cellular automata to obtain a bit sequence, wherein the Key Key5 and the Key Key6 are internal keys of the cellular automata;

the pseudo-random binary sequence construction unit is used for controlling the iteration number of the cell generating machine by using the Key Key1, and the pseudo-random binary sequence is constructed as follows:

basescramblingPRBS＝f(State^t⊕State^t+1)

wherein ≧ represents an XOR operation, f represents an iteration, the PRBS sequence is the pseudorandom binary sequence, State^tState of the cellular automaton at time t^t+1And the state quantity of the cellular automata at the t +1 moment.

Technical Field

The invention relates to the technical field of optical fiber communication, in particular to a super-long distance safe transmission method and system based on cellular automata and DNA coding.

Background

The ultra-long distance transmission is widely applied to the fields of energy internet, extra-high voltage, trans-regional power transmission and the like. In the transmission process, along with the great improvement of dispersion and polarization effect in an optical fiber link, the communication quality can be remarkably reduced, and the longer the relay distance is, the more remarkable the reduction of the communication quality is.

Orthogonal Frequency Division Multiplexing (OFDM) technology has been widely studied in optical communication systems with its high spectral efficiency and flexible modulation, and can effectively suppress the influence of chromatic dispersion and nonlinear effect of optical fiber links on optical communication systems. Meanwhile, the optical fiber network receives much attention due to its advantages of large transmission capacity, high speed, and the like. The orthogonal frequency division multiplexing technology is applied to the transmission of the ultra-long distance system, so that the damage to signals can be effectively reduced, and the transmission quality of communication is improved. The CO-OFDM system integrates the advantages of coherent optical communication technology and OFDM technology, has a series of characteristics of high spectrum efficiency, high transmission speed and capability of effectively solving the influence caused by dispersion, and is considered as one of core schemes of future optical communication systems.

In the ultra-long distance power communication system, the service carried by the OPGW overhead optical cable is very important, and even some confidential information is transmitted. However, the aerial optical cable is suspended at high altitude and exposed outside, many technologies are easily used for attacking the optical fiber link, such as optical fiber bending, splitting and evanescent coupling, the transmission of data faces a great safety problem, and once important information is leaked and maliciously used, great damage is brought to national economy. Most of the current research on coherent OFDM systems focuses on channel capacity and spectral efficiency, but neglects the security of the system. In optical transmission systems, the transmitted data is easily eavesdropped and physical interruptions can lead to reduced security. Therefore, in recent years, many researchers have proposed various encryption schemes to overcome this problem.

Today, many encryption schemes are implemented at the upper layers of the optical network, with high security risks and inconvenient key management. In contrast, the physical layer is transparent to the upper layer, and encryption operations can provide complete protection for the upper layer data, and can be directly combined with Digital Signal Processing (DSP) to reduce complexity, so that physical layer encryption has gained wide attention in research. In recent years, chaotic systems have been rapidly developed due to their sensitivity to initial values, and many physical layer encryption schemes have been proposed to encrypt data using digital chaos. Researches show that the safety of the OFDM system can be improved by chaotic encryption of a time frequency domain, the utilization of chaos combined with a pilot frequency assistance and constellation transformation technology, dimension coordination optimization and optimal blocking method, Brownian motion scrambling and other schemes.

However, these methods are limited to the symbol dimension or the subcarrier dimension, and do not include randomness of direct bit data, which reduces the security of data.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and enhance the safety of an optical communication network.

To achieve the above objects, in one aspect, the present invention provides a cellular automata and DNA coding-based ultra-long distance transmission method for encrypting a plaintext at a transmitting end of a coherent receiving system, including:

generating a group of pseudorandom binary sequences by using a cellular automaton;

and (3) taking the pseudorandom binary sequence as a base scrambling sequence for encrypting the plaintext DNA, and encrypting the plaintext by using a key sequence.

Further, before the generating a set of pseudo-random binary sequences by using the cellular automaton, the method further includes:

and generating the key sequence by adopting a fourth-order hyper-chaotic system.

Further, the fourth-order hyper-chaotic system comprises four coupled first-order autonomous ordinary differential equations, which are specifically as follows:

wherein x, y, z and w are four state variables, and A, B, C, D, k are five common system parameters.

Further, the system parameters a is 35, B is 6, C is 12, D is 7, and k is 2.

Further, the generation of the key sequence by using the fourth-order hyper-chaotic system is as follows:

where mod () represents a modulo operation, ceil () represents rounding up, and m represents a discrete time index.

Further, the generating a set of pseudo-random binary sequences by using the cellular automaton comprises:

respectively selecting an initial state ring and a state ring evolution rule by using a Key5 and a Key6, and iteratively updating the state of the cellular automata to obtain a bit sequence, wherein the Key5 and the Key6 are internal keys of the cellular automata;

controlling the iteration number of the cell generator by using the Key Key1, and constructing the pseudorandom binary sequence as follows:

wherein the content of the first and second substances,representing an exclusive-or operation, f representing a State evolution rule, the PRBS sequence being said pseudo-random binary sequence, State^tState of the cellular automaton at time t^t+1And the state quantity of the cellular automata at the t +1 moment.

Further, the encrypting the plaintext by using the key sequence with the pseudorandom binary sequence as the encrypted base scrambling sequence of the plaintext DNA comprises:

selecting a coding rule when the symbol data and the pseudorandom binary sequence are subjected to DNA coding by using the Key 2;

selecting a DNA operation rule by using the Key Key3 to complete the DNA operation;

and the Key4 is used for selecting a decoding rule to realize DNA decoding, so as to realize plaintext encryption.

In another aspect, a cellular automata and DNA coding based ultra-long distance transmission system for encrypting plaintext at a transmitting end of a coherent receiving system is used, comprising: pseudo-random binary sequence generation module and encryption module, wherein:

the pseudo-random binary sequence generating module is used for generating a group of pseudo-random binary sequences by using a cellular automaton;

the encryption module is used for taking the pseudorandom binary sequence as a base scrambling sequence for encrypting the plaintext DNA and encrypting the plaintext by using the key sequence.

Further, the key sequence is generated by adopting a fourth-order hyper-chaotic system, and the fourth-order hyper-chaotic system comprises four coupled first-order autonomous ordinary differential equations, which specifically comprise:

wherein x, y, z and w are four state variables, and A, B, C, D, k are five constant system parameters;

the four-order hyper-chaotic system is adopted to generate the key sequence as follows:

where mod () represents a modulo operation, ceil () represents rounding up, and m represents a discrete time index.

Further, the pseudo-random binary sequence generating module includes an iterative updating unit and a pseudo-random binary sequence constructing unit, wherein:

the iterative updating unit is used for respectively selecting an initial state ring and a state ring evolution rule by using a Key Key5 and a Key Key6, and iteratively updating the state of the cellular automata to obtain a bit sequence, wherein the Key Key5 and the Key Key6 are internal keys of the cellular automata;

the pseudo-random binary sequence construction unit is used for controlling the iteration number of the cell generating machine by using the Key Key1, and the pseudo-random binary sequence is constructed as follows:

wherein the content of the first and second substances,representing an exclusive-or operation, f representing an iteration, the PRBS sequence being said pseudo-random binary sequence, State^tIs at t timeState quantity, State of the cellular automaton^t+1And the state quantity of the cellular automata at the t +1 moment.

Compared with the prior art, the invention has the following technical effects: the invention uses the Pseudo Random Binary Sequence (PRBS) generated by the cellular automata as the base scrambling sequence for DNA encryption, combines the DNA coding technology to form the DNA encryption scheme assisted by the cellular automata, further enlarges the key space, enables the system to have better scrambling effect and randomness, enhances the randomness and encryption complexity, and improves the safety performance and the anti-theft capability of the communication system.

Drawings

The following detailed description of embodiments of the invention refers to the accompanying drawings in which:

FIG. 1 is a flow chart of a method of over-length transmission based on cellular automata and DNA encoding;

FIG. 2 is a diagram of a coherent OFDM system encryption scheme;

FIG. 3 is a schematic diagram of a cellular automaton;

FIG. 4 is a schematic diagram of base scrambling sequence generation using an automatic cellular machine;

FIG. 5 is a block diagram of a cellular automata and DNA coding based over-length transmission system;

FIG. 6 is a system block diagram of an experimental platform;

FIG. 7 is a graph of BER performance of transmission signals in various systems;

fig. 8 is a diagram of CCDF for PAPR under conventional unencrypted OFDM and the inventive encryption scheme.

Detailed Description

To further illustrate the features of the present invention, refer to the following detailed description of the invention and the accompanying drawings. The drawings are for reference and illustration purposes only and are not intended to limit the scope of the present disclosure.

As shown in fig. 1 to fig. 2, the present embodiment discloses a cellular automata and DNA coding-based ultra-long distance transmission method for encrypting plaintext at a transmitting end of a coherent receiver, including the following steps S1 to S2:

s1, generating a group of pseudo-random binary sequences by using a cellular automaton;

s2, the pseudo random binary sequence is used as a base scrambling sequence for encrypting the plaintext DNA, and the plaintext is encrypted by using the key sequence.

It should be noted that, in the coherent OFDM system encryption scheme based on Cellular Automaton (CA) and DNA coding proposed in this embodiment, data is encrypted by using CA to assist DNA coding by using bit randomness of CA, so that security of the system is improved, and the scheme also shows good performance in terms of high-speed and long-distance communication.

As a more preferable embodiment, in step S1: before generating a set of pseudo-random binary sequences by using the cellular automaton, the method further comprises the following steps:

and generating the key sequence by adopting a fourth-order hyper-chaotic system.

The embodiment utilizes the hyper-chaotic system to generate the key sequence with good randomness and unpredictability for encryption. It should be noted that the chaotic system has been widely used in physical layer encryption due to its high initial sensitivity and good randomness. In the chaotic encryption scheme, the sharing of an initial value between a sending end and a receiving end is an important factor of system safety, so that an illegal user is difficult to break through the chaotic encryption scheme, and the chaotic encryption scheme is the core for realizing a huge key space. With the development of technology, the low-dimensional chaotic system is easier to decipher, and in order to obtain higher security performance, the embodiment adopts a new hyper-chaotic system generated by introducing a new state variable in encryption, which is expressed as:

wherein, the hyperchaotic system comprises four coupled first-order autonomous ordinary differential equations, wherein x, y, z and w are four state variables, A, B, C, D, k is five ordinary system parameters,respectively, representing a differentiating operation.

As a more preferable technical solution, by using the lyapunov exponent, it can be proved that when a is 35, B is 6, C is 12, D is 7, and k is 2, the system exhibits hyper-chaotic behavior, and the hyper-chaotic system has good randomness in this state and is suitable for key generation.

As a further preferred technical solution, in this embodiment, four sets of random sequences with strong randomness are obtained through four different sets of parameters and initialization to generate a key, as shown in the following formula:

x_m+1,n+νx_m,n+1＝1-μ((1+ν)x_m,n)²

where m is a discrete time index, N is a lattice index, N is 1, 2. In this embodiment, if N is 4 and N is 1, four sets of keys generated by the hyper-chaotic system are as follows:

Key1＝mod(ceil(x(m)·10¹⁵),8)+1

Key2＝mod(ceil(y(m)·10¹⁵),8)+1

Key3＝mod(ceil(z(m)·ith),3)+1

Key4＝mod(ceil(w(m)·10¹⁵),8)+1

where mod () represents a modulo operation, ceil () represents rounding up, and m represents a discrete time index.

As a more preferable embodiment, in step S1: generating a group of pseudorandom binary sequences by using a cellular automaton, and comprising the following subdivision steps:

respectively selecting an initial state ring and a state ring evolution rule by using a Key5 and a Key6, and iteratively updating the state of the cellular automata to obtain a bit sequence, wherein the Key5 and the Key6 are internal keys of the cellular automata;

controlling the iteration number of the cell generator by using the Key Key1, and constructing the pseudorandom binary sequence as follows:

wherein the content of the first and second substances,representing an exclusive-or operation, f representing a State evolution rule, the PRBS sequence being said pseudo-random binary sequence, State^tState of the cellular automaton at time t^t+1And the state quantity of the cellular automata at the t +1 moment.

The cellular automata CA is a dynamic system whose time, space and state are discrete, CA evolves deterministically in discrete time steps, each cell takes its value from a finite set S, called the state set, which is named boolean when S ∈ {0,1 }.

As shown in fig. 3, a status ring is one of the state transition patterns of the CA, and different status rings correspond to different CA lengths. The state set chosen here is of boolean type 0, 1. The boundary condition of CA is set to be periodic, and when a cell is beyond the range of its spatial structure, the next cell cycle is entered. The periodic boundaries of the CA depend on its dimensions, and a one-dimensional CA is a circle made up of left and right boundaries. The state period of one-dimensional CA is 8, so in an 8-bit CA with a length matching the state period, there are 2⁸256 different global states.

The method utilizes a one-dimensional unified 1 x 8 cellular automaton with periodic boundary conditions to generate random numbers, and utilizes one of 8 rules to generate random numbers, wherein the rules show good generation number characteristics in the aspects of entropy, chi-square and the like. The 8 rules of the state ring are denoted by the rule number: 153. 30, 90, 165, 86, 105, 101 and 150. The key6 is used to determine the exact evolution rules, and the boolean expression for each CA rule is shown in table 1:

TABLE 1 Boolean expressions of evolution rules of cellular automata

It should be noted that, as shown in fig. 4, an 8-bit seed sequence generated by the Key5 is used as the initial state loop of the cellular automaton. According to the state loop rule selected by the Key6, the state of the CA is updated, and then a new bit sequence is obtained by performing exclusive or operation on the two sequences. The Key1 is then used to control the number of iterations of the state update and xor operations. On the basis of controlling the iteration number, a base scrambling PRBS with good randomness is constructed, and encryption is realized together with DNA coding.

As a more preferable embodiment, in step S2: the method for encrypting the plaintext by using the key sequence by using the pseudorandom binary sequence as the base scrambling sequence for encrypting the plaintext DNA comprises the following subdivision steps:

selecting a coding rule when the symbol data and the pseudorandom binary sequence are subjected to DNA coding by using the Key 2;

selecting a DNA operation rule by using the Key Key3 to complete the DNA operation;

and the Key4 is used for selecting a decoding rule to realize DNA decoding, so as to realize plaintext encryption.

It should be noted that the Key2 is used to select eight encoding rules when encoding DNA between symbol data and PRBS sequence, the Key3 is used to select a DNA operation rule to complete DNA operation, and the Key4 is used to select one of the eight decoding rules to achieve DNA decoding. Thus, the sending end of the CO-OFDM system completes encryption, and information is transmitted to the receiving end of the coherent receiver through the optical fiber channel. In addition, it should be noted that the encryption algorithm is reversible, and the corresponding decryption step is performed to derive the information by reversing the encryption process at the receiving end.

It should be noted that there are eight different reasonable rules for encoding/decoding DNA in this example, and the specific rules are shown in table 2:

TABLE 2 DNA coding and decoding rules

In the process of DNA coding, binary sequences are divided into two groups, namely each group has the length of two bits, the binary sequences of each group are mapped to DNA sequences of 'A', 'T', 'G' and 'C' respectively according to coding and decoding rules, one bit data stream can be coded into a DNA chain according to the coding and decoding rules, and then the DNA chain can be decoded back to bit data. The various specific rules for DNA manipulation are shown in Table 3:

TABLE 3 operating rules of DNA operations

As shown in fig. 5, the present embodiment discloses an ultra-long distance transmission system based on cellular automata and DNA coding, which is used for encrypting a plaintext at a transmitting end of a coherent receiver, and includes: a pseudo-random binary sequence generating module 10 and an encrypting module 20, wherein:

the pseudo-random binary sequence generating module 10 is configured to generate a set of pseudo-random binary sequences by using a cellular automaton;

the encryption module 20 is configured to encrypt the plaintext by using the key sequence, using the pseudorandom binary sequence as a base scrambling sequence for encrypting the plaintext DNA.

As a further preferred technical scheme, the key sequence is generated by adopting a fourth-order hyper-chaotic system, and the fourth-order hyper-chaotic system comprises four coupled first-order autonomous ordinary differential equations, specifically:

wherein x, y, z and w are four state variables, and A, B, C, D, k are five constant system parameters;

the four-order hyper-chaotic system is adopted to generate the key sequence as follows:

where mod () represents a modulo operation, ceil () represents rounding up, and m represents a discrete time index.

As a further preferred technical solution, the pseudo-random binary sequence generating module 10 includes an iterative updating unit and a pseudo-random binary sequence constructing unit, wherein:

the iterative updating unit is used for respectively selecting an initial state ring and a state ring evolution rule by using a Key Key5 and a Key Key6, and iteratively updating the state of the cellular automata to obtain a bit sequence, wherein the Key Key5 and the Key Key6 are internal keys of the cellular automata;

the pseudo-random binary sequence construction unit is used for controlling the iteration number of the cell generating machine by using the Key Key1, and the pseudo-random binary sequence is constructed as follows:

wherein the content of the first and second substances,representing an exclusive-or operation, f representing an iteration, the PRBS sequence being said pseudo-random binary sequence, State^tState of the cellular automaton at time t^t+1And the state quantity of the cellular automata at the t +1 moment.

In this embodiment, the effectiveness of the method provided by the present invention is verified by building an experimental platform as shown in fig. 6, and the performance of the transmission system of the encrypted signal and the original unencrypted signal in a Back-To-Back (BTB) system and an 80-km ssmf (standard single mode fiber) is analyzed, where both the transmitting end Tx and the receiving end Rx of the experimental platform are executed offline through software.

At the transmitting end Tx, the transmit data is processed offline. The IFFT/FFT size is 512, and 200 OFDM symbols with modulation format of 16QAM are generated using 256 subcarriers, 4 pilots, and 252 zero padding sequences. Subsequently, after IFFT and P/S conversion are performed on the encrypted data, a Cyclic Prefix (CP) of length 1/32 of the OFDM code length is added in order to prevent intersymbol interference (ISI). And then 20 symbols are used as training sequences to realize IQ imbalance compensation, and channel response is obtained.

After the off-line DSP of the transmitting terminal Tx is executed, the digital signal is transmitted to an Arbitrary Waveform Generator (AWG) to complete the process of converting discrete digital signals into continuous analog signals with a sampling rate of 80 Gsa/s. The bandwidth is 16GHz and 8bit quantization is used. An External Cavity Laser (ECL) with the line width smaller than 100kHz and the frequency deviation about 300kHz is used as a light source, an encrypted signal is modulated on an optical carrier by a single-bias IQ modulator, and the power of an input fiber is 0 dBm. The optical signal is transmitted through an 80-km SSMF, filtered by a Tunable Optical Filter (TOF). The received optical power of the receiving end can be adjusted by a Variable Optical Attenuator (VOA), and the receiving power is controlled to be-6 dBm in the experimental process. The coherent signal is received by an Integrated Coherent Receiver (ICR), and is recorded by using a Digital Storage Oscilloscope (DSO) with the sampling rate of 80Gsa/s, and the obtained digital signal is processed by software at a receiving end Rx in an off-line manner to obtain final data. After passing through this module, the bit error rate is calculated.

The receiving end Rx also performs operations offline through software, and performs operations of compensating fiber dispersion, frequency offset, and phase noise in the offline DSP. And then decrypting by using a correct key to obtain data transmitted by a transmitting end, and finally calculating the performances such as the error rate of the CO-OFDM system.

In this experiment, the error rate performance of the optical signal-to-noise ratio range of [18dB,30dB ] was tested, and a curve was drawn. As shown in fig. 7, there are five different curves in fig. 7, which represent BER performance of raw OFDM signals in a back-to-back system, BER performance of raw OFDM signals in an 80km SSMF system, BER performance of encrypted OFDM signals in a back-to-back system, BER performance of encrypted OFDM signals in an 80km SSMF system, and BER performance of an illegal data receiving user, respectively.

In the experimental system, the forward error correction code (FEC) was 3.8 × 10^-3The ordinate in the figure is-2.420. As can be seen from fig. 8, the remaining four curves are substantially coincident except the BER performance curve of the illegal receiving user, so we can conclude two conclusions: firstly, the experimental equipment can well compensate various damages of signals passing through an 80km optical fiber system in an Rx off-line DSP, so the BER performance of the experimental equipment is not greatly reduced when compared with a back-to-back system. Secondly, if the encryption scheme is added into the CO-OFDM system to be compared with the original OFDM signal, the BER performance of the original OFDM signal is not greatly influenced, and the BER performance curves of the two OFDM signals are basically not different and are approximately coincident. The BER of the illegal receiving users is stabilized at about 0.5 (the ordinate in the figure is log10(BER), namely about-0.3), which indicates that the users without authorized right keys can not recover data correctly,the scheme has high safety, can effectively resist illegal eavesdropping, and can be used as a physical layer encryption scheme of a CO-OFDM system.

In the CO-OFDM system, the index for evaluating the signal is mainly the PAPR performance of the signal in addition to the BER performance, and a large PAPR may cause many adverse effects on the power amplifier, so the PAPR performance of the signal is also analyzed in this experiment, the CCDF of the PAPR of both the original OFDM signal and the encrypted OFDM signal is analyzed, and is plotted as shown in fig. 8. The blue curve represents the complementary cumulative distribution function of the original unencrypted OFDM signal and the red curve represents the complementary cumulative distribution function of the OFDM signal under the encryption scheme. As can be seen from fig. 8, the CCDF of the encrypted signal is substantially coincident compared with the CCDF of the original signal, and there is no significant difference, which indicates that there is no difference in PAPR performance between the original unencrypted OFDM signal and the OFDM signal under the encryption scheme, and the encryption scheme does not cause loss in PAPR performance of the system. In summary, the present physical layer encryption scheme is an implementation of validity.

It should be noted that the scheme performs different operations based on the traditional DNA coding algorithm, and introduces the concept and model of the cellular automata. The key generation is based on the logistic hyper-chaotic system, and because the encryption scheme needs a plurality of groups of keys, a plurality of groups of keys with strong randomness are generated through a plurality of groups of chaotic state quantities with different parameters and initial values in the scheme, and the size of the total key space is also changed into 10¹³⁸The anti-brute force anti-cracking device is enough to resist brute force cracking and has great safety. Finally, the encryption scheme is verified through experiments, and results show that the scheme has practical feasibility and safety. And in the aspect of PAPR performance, the original PAPR performance of the signal cannot be damaged. The encryption and decryption operations of the scheme are respectively performed in offline DSPs of a sending end and a receiving end, so the scheme has the characteristic of easy operation, and in addition, the scheme can not have extra hardware requirements on a common CO-OFDM system, so extra cost burden can not be caused.

The key space of the present encryption scheme is analyzed because the key is emptyThe size of the space determines the security of the encryption system, with greater key space providing greater security. As four groups of different parameters and initial values are adopted in experimental verification to generate the key based on the logistic hyper-chaotic system, the size of the key space is determined by the hyper-chaotic system. Due to the sensitivity characteristics of the initial value and the parameter, the size of the key space controlled by the initial value and the parameter of the hyper-chaotic system is also the key space. The total key space size is (1 multiplied by 10) after calculation¹⁵)⁹×2⁸×8≈2×10¹³⁸It is sufficient to resist most of the exhaustive brute force attack modes.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.