阅读说明：本技术 一种低冗余的极化码量子噪声流物理层加密方法及系统 (Low-redundancy physical layer encryption method and system for polarization code quantum noise stream ) 是由 高明义 朱华清 邵卫东 于 2021-09-16 设计创作，主要内容包括：本发明公开了一种低冗余的极化码量子噪声流物理层加密方法及系统,包括：S1、产生一组混沌序列；S2、将明文信息与混沌序列进行异或加密；S3、对加密后的信息进行极化码编码,编码后的信息分为信息位和冻结位,冻结位上的信息为极化码编码产生的冗余信息；S4、利用交织器改变原来信息位和冻结位的位置,将信息位放在QAM信号的高位,把冻结位放在QAM信号的低位；S5、将信号经过映射后发送至接收端；S6、利用反交织器将信息位和冻结位还原；S7、进行极化码解码；S8、将解码后的密文与参数产生的混沌序列进行异或计算,得到发送端发送的明文信息。本发明减小了密文信息传输的长度,提高了传输效率,同时提高了系统的安全性。(The invention discloses a low-redundancy physical layer encryption method and system for a polarization code quantum noise stream, which comprises the following steps: s1, generating a group of chaotic sequences; s2, carrying out XOR encryption on the plaintext information and the chaotic sequence; s3, carrying out polarization code encoding on the encrypted information, wherein the encoded information is divided into an information bit and a freezing bit, and the information on the freezing bit is redundant information generated by the polarization code encoding; s4, changing the positions of the original information bit and the frozen bit by using the interleaver, placing the information bit at the high position of the QAM signal, and placing the frozen bit at the low position of the QAM signal; s5, mapping the signal and then sending the signal to a receiving end; s6, restoring the information bits and the frozen bits by using a reverse interleaver; s7, decoding the polarization code; and S8, carrying out XOR calculation on the decoded ciphertext and the chaotic sequence generated by the parameters to obtain plaintext information sent by the sending end. The invention reduces the length of ciphertext information transmission, improves the transmission efficiency and simultaneously improves the safety of the system.)

1. A low redundancy physical layer encryption method for a polar code quantum noise stream is characterized by comprising the following steps:

a sending end step:

s1, generating a group of chaotic sequences;

s2, carrying out XOR encryption on the plaintext information and the chaotic sequence;

s3, carrying out polarization code encoding on the encrypted information, wherein the encoded information is divided into an information bit and a freezing bit, and the information on the freezing bit is redundant information generated by the polarization code encoding;

s4, changing the positions of the original information bit and the frozen bit by using the interleaver, placing the information bit at the high position of the QAM signal, and placing the frozen bit at the low position of the QAM signal;

s5, mapping the signal and then sending the signal to a receiving end;

a receiving end step:

s6, restoring the information bits and the frozen bits by using a reverse interleaver;

s7, decoding the polarization code;

and S8, carrying out XOR calculation on the decoded ciphertext and the chaotic sequence generated by the parameters to obtain plaintext information sent by the sending end.

2. The low redundancy polarization code quantum noise stream physical layer encryption method of claim 1, wherein step S1 comprises: a chaotic sequence generator is utilized to generate a group of infinite-length chaotic sequences, and the generated chaotic sequences pass through a cutter to convert the values of the chaotic sequences from real values into binary values.

3. The low-redundancy polarization code quantum noise stream physical layer encryption method of claim 2, wherein the chaotic sequence generator adopts a logical mapping model as follows:

wherein n is the number of iterations; { x_nN represents an initial value x₀N iteration values generated after N iterations; μ is a bifurcation parameter.

4. The low redundancy polarization code quantum noise stream physical layer encryption method of claim 3, wherein n-1000, μ -1.9125, x₀＝0.61854654500112。

5. The low redundancy polarization code quantum noise stream physical layer encryption method of claim 1, wherein a two-step coding method is used for polarization code coding.

6. The low redundancy polarization code quantum noise stream physical layer encryption method of claim 1, wherein in step S7, the polarization code decoding is performed by a serial cancellation decoder.

7. The low-redundancy polarization code quantum noise stream physical layer encryption method of claim 1, wherein a key shared by a transmitting end and a receiving end comprises parameters for generating a chaotic sequence and an interleaver.

8. The utility model provides a low redundant polarization code quantum noise stream physical layer encryption system which characterized in that, includes sending end and receiving terminal, the sending end is equipped with:

a chaotic sequence generator for generating a set of chaotic sequences;

the exclusive-or encryption module is used for carrying out exclusive-or encryption on the plaintext information and the chaotic sequence;

the polarization code coding module is used for carrying out polarization code coding on the encrypted information, the coded information is divided into information bits and freezing bits, and the information on the freezing bits is redundant information generated by the polarization code coding;

the interleaver is used for changing the positions of the original information bits and the frozen bits, placing the information bits at the high bits of the QAM signals, and placing the frozen bits at the low bits of the QAM signals;

the receiving end is provided with:

a deinterleaver for restoring the information bits and the frozen bits;

the polar code decoding module is used for decoding the polar code;

and the exclusive OR calculation module is used for carrying out exclusive OR calculation on the decoded ciphertext and the chaotic sequence generated by the parameters to obtain plaintext information sent by the sending end.

9. The low redundancy polar-code quantum-noise stream physical layer encryption system of claim 8, further comprising a clipper for converting values of the chaotic sequence from real values to binary values.

10. The low redundancy polar-code quantum-noise stream physical layer encryption system of claim 8, wherein said polar-code decoding module performs polar-code decoding using a serial cancellation decoder.

Technical Field

The invention relates to the technical field of encryption, in particular to a low-redundancy physical layer encryption method and system for a polarization code quantum noise stream.

Background

With the rapid development of the fifth generation communication technology, people realize the interconnection of industries such as education, medical treatment, transportation and the like, meanwhile, the decryption capability of a computer is continuously developed, and the traditional encryption algorithm based on the computation complexity is easy to threaten. The physical layer of an optical network is most vulnerable to attacks such as illegal interception, interference, and also destruction of the physical infrastructure, etc. Therefore, protection of the physical layer in the transmission system is the most direct and effective method for improving system security, and information leakage can be prevented for the first time. It follows that the search for advanced physical layer encryption methods is significant to further improve the security of the communication system.

In recent years, many schemes have been proposed to enhance the security of the physical layer, and Quantum Noise Stream encryption (QNSC) is a classic physical layer encryption method. To prevent the information from being intercepted during transmission, the QNSC will hide the plaintext information in the quantum phase noise or the amplified spontaneous emission noise. In recent years, Masataka Nakazawa et al have enabled long distance transmission by combining the QNSC technique with the Quantum Key Distribution (QKD) technique. In the previous work, the QNSC is combined with the chaotic sequence, the original key length which is nearly infinite is reduced to three, and the complexity of key distribution is greatly reduced. However, in the case of ensuring the security of the system, the efficiency of information transmission may be reduced.

The forward error correction code is a channel code that can improve transmission performance. In 1948, the theory of aroma was proposed. In 2009 Arikan proposed a polarization code, which is a forward error correction code with lower complexity and based on channel polarization theory. Polar codes change the sequence of original information while improving transmission efficiency, and can enhance the security of transmission, so polar codes are often used for encrypted communication. In 2018, X.Lu and the like use a chaos sequence generated by a channel state to be distributed to frozen bits of a polarization code to promote solutionThe difficulty of the encryption. In 2019, y.xiao et al used two-dimensional Henon mapping to encrypt subcarrier data, which improves physical layer security, and after using a polarization code, BER was 10^-3A gain of about 7.4dB can be obtained compared to the conventional case at the level. However, the use of polar codes brings about great redundant data while reducing the error rate, which has been a hindrance to the more widespread use of polar codes.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a low-redundancy encryption method for a polarization code quantum noise stream physical layer, which has high transmission efficiency and high safety.

In order to solve the above problem, the present invention provides a low redundancy physical layer encryption method for a polar code quantum noise stream, which includes:

a sending end step:

s1, generating a group of chaotic sequences;

s2, carrying out XOR encryption on the plaintext information and the chaotic sequence;

s3, carrying out polarization code encoding on the encrypted information, wherein the encoded information is divided into an information bit and a freezing bit, and the information on the freezing bit is redundant information generated by the polarization code encoding;

s4, changing the positions of the original information bit and the frozen bit by using the interleaver, placing the information bit at the high position of the QAM signal, and placing the frozen bit at the low position of the QAM signal;

s5, mapping the signal and then sending the signal to a receiving end;

a receiving end step:

s6, restoring the information bits and the frozen bits by using a reverse interleaver;

s7, decoding the polarization code;

and S8, carrying out XOR calculation on the decoded ciphertext and the chaotic sequence generated by the parameters to obtain plaintext information sent by the sending end.

As a further improvement of the present invention, step S1 includes: a chaotic sequence generator is utilized to generate a group of infinite-length chaotic sequences, and the generated chaotic sequences pass through a cutter to convert the values of the chaotic sequences from real values into binary values.

As a further improvement of the present invention, the chaotic sequence generator adopts a logic mapping model as follows:

wherein n is the number of iterations; { x_nN represents an initial value x₀N iteration values generated after N iterations; μ is a bifurcation parameter.

In a further development of the invention, n is 1000, μ is 1.9125, x₀＝0.61854654500112。

As a further improvement of the invention, a two-step coding method is adopted for polarization code coding.

As a further improvement of the present invention, in step S7, the polar code decoding is performed using a serial cancellation decoder.

As a further improvement of the invention, the key shared by the sending end and the receiving end contains parameters for generating the chaotic sequence and the interleaver.

The invention provides a low-redundancy physical layer encryption system for a polar code quantum noise stream, which comprises a sending end and a receiving end, wherein the sending end is provided with:

a chaotic sequence generator for generating a set of chaotic sequences;

the exclusive-or encryption module is used for carrying out exclusive-or encryption on the plaintext information and the chaotic sequence;

the polarization code coding module is used for carrying out polarization code coding on the encrypted information, the coded information is divided into information bits and freezing bits, and the information on the freezing bits is redundant information generated by the polarization code coding;

the interleaver is used for changing the positions of the original information bits and the frozen bits, placing the information bits at the high bits of the QAM signals, and placing the frozen bits at the low bits of the QAM signals;

the receiving end is provided with:

a deinterleaver for restoring the information bits and the frozen bits;

the polar code decoding module is used for decoding the polar code;

and the exclusive OR calculation module is used for carrying out exclusive OR calculation on the decoded ciphertext and the chaotic sequence generated by the parameters to obtain plaintext information sent by the sending end.

As a further improvement of the invention, the device also comprises a clipper used for converting the value of the chaotic sequence from a real value to a binary value.

As a further improvement of the invention, the polar code decoding module utilizes a serial cancellation decoder to decode the polar code.

The invention has the beneficial effects that:

the low-redundancy polarization code quantum noise stream physical layer encryption method and system are based on the quantum noise stream encryption technology of the polarization code and the interleaver, and the interleaver is used for changing the position of the frozen bit redundancy information generated by the polarization code and used for QNSC encryption. The transmission length of the ciphertext information is reduced, and in the 16-4096QAM/QNSC signal, the ciphertext information length is changed to 1/3 of the original length. According to the error rate curve, for 16-4096QAM/QNSC signal, at 10^-2A BER of the order of 3.9dB gain. The invention not only improves the transmission efficiency, but also improves the safety of the system.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the content of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following preferred embodiments are described in detail with reference to the accompanying drawings.

Drawings

FIG. 1 is a basic flow diagram of a QNSC;

FIG. 2 is a schematic constellation diagram of the implementation principle of 16-64 QAM/QNSC;

FIG. 3 is a block flow diagram of a low redundancy polarization code quantum noise stream physical layer encryption method in a preferred embodiment of the invention;

FIG. 4 is a graph of bifurcation parameters versus chaotic system behavior in a preferred embodiment of the present invention;

FIG. 5(a) shows x in a preferred embodiment of the present invention₀＝0.61854654500112, a graph of autocorrelation functions of the chaotic sequence; FIG. 5(b) shows x in the preferred embodiment of the present invention₀0.61854654500112 and x'₀0.61854654500113 cross correlation function graph; FIG. 5(c) shows x in the preferred embodiment of the present invention₀0.61854654500112 and x'₀0.61854654500113 chaotic sequence curve;

FIG. 6(a) is the process of two symbols entering a symmetric memoryless channel in polar code encoding; FIG. 6(b) is a process of two symbols entering a combined channel in polar code encoding;

fig. 7 is a schematic encoding diagram of a systematic polar code when N is 8;

FIG. 8 is an experimental flow diagram of a QNSC technique based on a polar code and interleaver;

FIGS. 9(a) and (b) are the constellations of a 16-64QAM/QNSC signal before and after decryption, respectively, over a 30km fiber optic transmission;

FIGS. 10(a), (b), (c), (d) are plots of the error rate for the signals of 16-64QAM/QNSC, 16-256QAM/QNSC, 16-1024QAM/QNSC, 16-4096QAM/QNSC, respectively, without fiber and with 30km SSMF;

FIG. 11 is a histogram of plaintext length comparisons for 16QAM buried in 64QAM, 256QAM, 1024QAM, 4096QAM modulated signals using different encryption methods;

FIG. 12 is a line graph showing the relationship between the accuracy of the initial value of the chaotic sequence and the error rate in the present invention.

Detailed Description

The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.

QNSC is a highly secure encryption technology applied to a physical layer, and its principle is mainly to change the amplitude and phase state of an optical signal using noise in an optical communication system, such as amplified spontaneous emission noise and quantum noise. When the state of the optical signal is changed, the minimum euclidean distance between a constellation point and a constellation point on the constellation map is reduced, and as a result, the constellation point is more likely to shift during the transmission process of the information. For an illegal receiver, completely wrong information is obtained, but for a legal receiver with a secret key, even if the signal state is changed greatly, plaintext information hidden in noise can still be calculated through the secret key. Fig. 1 shows a basic flow diagram of the QNSC.

First, a random sequence is generated by a Linear Feedback Shift Register (LFSR). The sending end Alice and the receiving end Bob share the seed key. Data B is a random sequence generated by a seed key, called the base state data information, used for data scrambling. The information that Alice has prepared to send in advance is data X ═ X (X)_I,X_Q). If the directly transmitted data X is a normal QAM signal, it is easily captured by an eavesdropper. Therefore, the data X and the data B are jointly coded to obtain scrambled ciphertext data S ═ (S)_I，S_Q)＝(X_I⊕B_I，X_Q⊕B_Q). Assuming that data X and data B are composed of m and n I/Q bits, respectively, per symbol, encrypted data S is composed of m + n I/Q bits. And after the ciphertext is mapped, transmitting the ciphertext to a receiving end Bob by an optical fiber. After the signal is detected, Bob uses the shared secret key to obtain data B, decodes the data and obtains correct plaintext information.

The constellation shown in fig. 2 is a 16QAM signal that is hidden in a 64QAM signal and is encrypted by QNSC, which is denoted as 16-64 QAM/QNSC. For a 64QAM signal, each symbol consists of 3I/Q bits, respectively. According to the mapping rule of the QNSC, the higher the position of the modulated ciphertext, the less the influence of noise. Therefore, in order to protect plaintext information while ensuring the effectiveness of information transmission, the 16QAM signal is hidden in the 64QAM signal, occupying the two high bits of the QAM signal. The remaining 1I/Q bit is the base state information, which is used to scramble the information. For example, in fig. 2, a ═ I, (Q) ═ 101, 010, where the upper bits (10, 01) of the QAM signal contain plaintext information that actually needs to be transmitted. The low-order QAM signal (1, 0) has strengthened the interference effect of noise to the encrypted signal, make the plain text information hide in the noise difficult to be cracked by the eavesdropper. The more bits of the ground state information, the higher the system security.

The present invention utilizes a decoding method of sharing the base state information when decoding the QNSC encrypted signal. As shown in fig. 2, a general QAM signal is decoded according to a conventional constellation decision line. When QNSC encryption is used, a transmission signal is very sensitive to noise, and the decoding mode easily causes misjudgment of points near a decision line. The shared basis state information-based decoding method used by the present invention reduces the probability of such false positives. The principle is as follows: since the base state information is generated by a key shared by the receiver and the sender, the value and the index of the base state information are both known. From this, in fig. 2, we can determine 16 points (the points indicated by hatching in fig. 2) of the same ground state information on the constellation from the ground state information of the point a. For example, point B ═ (111,110) and point a have the same ground state information (1, 0). The receiver can determine the base state information according to its index every time it receives a symbol, and then the correct position of the signal on the constellation diagram must be at one of the 16 shaded points in fig. 2. The minimum value of the Euclidean distances from the received symbol to 16 points corresponding to the basic state information is calculated to be used as the correct position of the symbol. The judgment method greatly improves the effectiveness of QNSC encryption transmission.

As shown in fig. 3, a preferred embodiment of the present invention discloses a low-redundancy physical layer encryption method for a polar code quantum noise stream, where the encryption method includes:

a sending end step:

s1, generating a group of chaotic sequences; the method comprises the following steps: a chaotic sequence generator is utilized to generate a group of infinite-length chaotic sequences, and the generated chaotic sequences pass through a cutter to convert the values of the chaotic sequences from real values into binary values.

The chaotic system is mainly divided into three types, namely a continuous chaotic system, a discrete chaotic system and a hyperchaotic system, wherein the sequence value of the discrete chaotic system is generated by a discrete chaotic mapping system. For the conventional QNSC technology, the quantum noise for hiding the plaintext information is randomly generated, and the required key is very complicated. In order to reduce the complexity of the key, the chaotic sequence generator in this embodiment adopts the following logic mapping model:

wherein n is the number of iterations; { x_nN represents an initial value x₀N iteration values generated after N iterations; μ is a bifurcation parameter.

FIG. 4 is a diagram showing the relationship between the bifurcation parameters and the chaotic system behavior in the preferred embodiment of the present invention, and it can be clearly seen that when μ e [1.4,2 ]]Then the system will enter the chaotic state completely. One feature of the chaotic sequence that is very important is the extreme sensitivity to the parameter, and in order to represent the extreme sensitivity of the chaotic sequence to the parameter, in one embodiment, the parameter is set to be n-1000, μ -1.9125, and x₀0.61854654500112, the value of the initial value x0 was slightly changed to x 'for comparison'₀0.61854654500113. Such slight differences are imperceptible and the chaotic sequences they produce are compared separately, and the other parameter values remain unchanged.

FIG. 5(a) shows x in a preferred embodiment of the present invention₀0.61854654500112, a graph of the autocorrelation function of the chaotic sequence; FIG. 5(b) shows x in the preferred embodiment of the present invention₀0.61854654500112 and x'₀0.61854654500113 cross correlation function diagram. It can be seen that when τ ≠ 0, the value of the autocorrelation is close to 0, and the value of the cross-correlation function of two chaotic sequences with different initial values is close to 0 regardless of the value of τ. Therefore, this result proves that the generated chaotic sequence has strong randomness, which makes the encryption system more reliable. FIG. 5(c) is a representation of x0 ═ 0.61854654500112 and x 'in a preferred embodiment of the invention'₀0.61854654500113 for a chaotic sequence. It can be seen that the iteration of the chaotic sequence enters two completely different tracks, which indicates that an illegal receiving end is possible to crack information except under the condition of possessing a key with extremely high accuracy, otherwise the cracked information is completely wrong. Therefore, the transmitting end only needs to pass n, mu, x₀The three parameters can generate a group of infinite-length chaotic sequences to add plaintext informationThe structure of the secret key is simplified, and meanwhile, the chaotic sequence can effectively resist selective plaintext attack, so that the encrypted information is more reliable.

After that, the generated chaotic sequence is subjected to a clipper, as shown in formula (2), a proper threshold value xi is set, and in general, the value of xi is set to be 0, and after the chaotic sequence is subjected to the clipper, the value of the chaotic sequence is converted from a real value to a binary value for encrypting information.

And S2, carrying out exclusive or encryption on the plaintext information and the chaotic sequence.

S3, carrying out polarization code encoding on the encrypted information, wherein the encoded information is divided into an information bit and a freezing bit, and the information on the freezing bit is redundant information generated by the polarization code encoding;

if the binary symmetric channel is specifically combined and split, then the split bit channel will have polarization phenomenon: the channel capacity of one part of bit channels tends to be 1, and the channel capacity of the other part of bit channels tends to be very small and tends to be 0, wherein the former is called as 'good channel', the latter is called as 'bad channel', and the phenomenon is more obvious when the number of channels tends to be infinite. This is the polarization of the channel and is the basic principle of polarization codes.

In the case where there is no memory at the source side, and the channel is unchanged for a period of time and also has no memory, when N symbols are continuously transmitted on a channel W (y | u), it can be understood that the N symbols have passed through the channelComprises the following steps:

as shown in fig. 6(a), it is a process of sending two symbols to a symmetric memoryless channel by a sending end, and we have:

W(y₀,y₁|u₀,u₁)＝W(y₀|u₀)W(y₁|u₁) (4)

as shown in figure 6(b) of the drawings,representing an exclusive or operation, when two channels are combined in a particular way, the channel at this time can be represented as:

this is the basic unit of channel combining. The transmitted information { u0, u1} is defined asLikewise, channel coded information may be obtainedThe process of channel coding can be formulated as:

G₂is to generate a matrix. On the basis of the above, can be composed of W₂To obtain W₄Two Ws under the condition of obtaining N channels by successive recursion_N/2W formed by combination_NA channel. Generating the matrix G arbitrarily_NCan be represented by the following sub-formula:

represents the inner product of Kronecker, B_NIs a bit flip permutation momentThe number of the arrays is determined,the Bhattacharyya parameter is used as a basis for measuring the quality of the information channel, and is defined as an integral function:

wherein σ²Is the variance of an additive white gaussian noise channel, W (y |0), W (y |1) is the channel transition probability. The polar code can be regarded as a linear block code, assuming that c is a code word of N bits long, the input code word can be divided into two parts, one part is composed of K bits of information bits u_AAnother part consisting of frozen bits u_A ^cThe value on the frozen bit is typically 0. The codeword can be represented as follows:

in the systematic polar code, the information bits and the frozen bits can be constructed by a two-step coding method or a recursive method according to the above equation. The systematic polarization code used in the present invention is a two-step coding method. Fig. 7 is a schematic diagram of coding a systematic polar code when N is 8, and the coding process is composed of two parts. In the figure the lighter information representation is located on the frozen bits and the darker information representation is located on the information bits. The input code word is coded according to the expression mode, after the first section of coding is finished, the bits on the information bit are not changed, the bits on the frozen bit are all changed into zero, and then the coding is continued according to the same mode. When the encoding is completed, it can be seen that the bit information on the information bits is identical to that before encoding, but the information on the frozen bits is already different from the original.

S4, changing the positions of the original information bit and the frozen bit by using the interleaver, placing the information bit at the high position of the QAM signal, and placing the frozen bit at the low position of the QAM signal;

s5, mapping the signal and then sending the signal to a receiving end;

a receiving end step:

s6, restoring the information bits and the frozen bits by using a reverse interleaver;

the key shared by the sending end and the receiving end comprises parameters for generating the chaotic sequence and the interleaver, and according to the parameters, the receiving end can construct the de-interleaver to restore the positions of the information bit and the frozen bit, and then the decoder of the system polarization code is used for SC decoding.

S7, decoding the polarization code;

in the decoding stage, the present invention uses a Successive Cancellation (SC) decoder. For i ∈ {1, 2., N }, the value of the ith symbol needs to be calculated according to the current received signal and the previous i-1 signals, unless the ith channel is a frozen channel, the original frozen information can be directly obtained, and the decoding algorithm of the receiving end is expressed as;

computingThe log likelihood ratio calculation formula is:

when i belongs to A^CWhen the channel is in a frozen state, the information of the frozen bit is shared by the receiver and the sender, so that the information can be directly obtained; when i belongs to a, the channel is represented as a frozen channel, and a decision function is needed:

and S8, carrying out XOR calculation on the decoded ciphertext and the chaotic sequence generated by the parameters to obtain plaintext information sent by the sending end.

The preferred embodiment of the invention also discloses a low-redundancy physical layer encryption system of the polar code quantum noise stream, which comprises a sending end and a receiving end, wherein the sending end is provided with:

a chaotic sequence generator for generating a set of chaotic sequences;

the exclusive-or encryption module is used for carrying out exclusive-or encryption on the plaintext information and the chaotic sequence;

the polarization code coding module is used for carrying out polarization code coding on the encrypted information, the coded information is divided into information bits and freezing bits, and the information on the freezing bits is redundant information generated by the polarization code coding;

the interleaver is used for changing the positions of the original information bits and the frozen bits, placing the information bits at the high bits of the QAM signals, and placing the frozen bits at the low bits of the QAM signals;

the receiving end is provided with:

a deinterleaver for restoring the information bits and the frozen bits;

the polar code decoding module is used for decoding the polar code;

and the exclusive OR calculation module is used for carrying out exclusive OR calculation on the decoded ciphertext and the chaotic sequence generated by the parameters to obtain plaintext information sent by the sending end.

The system also comprises a clipper used for converting the value of the chaotic sequence from a real value to a binary value.

The polar code decoding module utilizes a serial cancellation decoder to decode the polar code.

The method steps involved in the system are the same as those in the above method embodiments, and are not described herein again.

To verify the effectiveness of the invention:

fig. 8 is a flow chart of an experiment of the QNSC encryption technology based on polarization code and interleaver in an OFDM-PON system according to the present invention.

The signal is generated at the transmitting end by a data signal processing process. The resulting signal enters the random waveform generator at a sampling rate of 50 GS/s. The hermitian matrix in the random signal processing process generates real-valued time domain signals, and digital-to-analog conversion is realized in the random waveform generator. The electrical signal from the random waveform generator was modulated by a Mach-Zehnder modulator and a continuous wave laser into an optical signal at 1550.116nm and transmitted over a 30km Standard Single Mode Fiber (SSMF). Before the optical signal enters the receiving end, we use a variable optical attenuator and an erbium-doped fiber amplifier to change the received optical power. Another variable optical attenuator after this is used to adjust the optical power to ensure proper response of the photo-detector. The optical signal is converted into an electrical signal after passing through the photodetector. Finally, a real-time oscilloscope with a sampling rate of 50GS/s is used for collecting the signals and restoring the signals with the aid of offline digital signal processing. It is noted that in this experiment, the total number of carriers is 512, the number of data carriers is 128, and the carriers are located from 129 th to 256 th of the total number of carriers. To reduce the effect of the beat frequency, we set the first 128 of the total carriers to null carriers. On the other hand, the chaotic sequence is mainly generated by three main parameters n, μ, x0, corresponding to values of 1200,1.9125,0.61854654500112, respectively. Fig. 9(a) and (b) show the constellation of the 16-64QAM/QNSC signal before and after decryption, respectively, in a 30km fiber transmission. The 16QAM signal is hidden in the 64QAM constellation. Under the influence of spontaneous radiation noise of the amplifier, plaintext information is difficult to crack by an eavesdropper.

In one embodiment, the code length N of each module polarization code is set to 256, the number of information bits is K, and K/N represents the code rate. In this experiment, we tried to let the redundant bits generated by the polarization code in each case all be used as a scrambling of the signal by the QNSC. For example, for 16-256QAM/QNSC, there are 4I/Q bits of the transmitted 256QAM signal, and the plaintext information that we need to transmit is the 16QAM signal, occupying 2I/Q bits. That is, the plaintext information and the redundant information each account for half of the bit number, so for a 16-256QAM signal, we try to set the code rate to 50%. Similarly, for 16-64QAM/QNSC signals, we set the code rate to be about 66.6%. This allows the redundant information generated by the polar code to be used for scrambling as much as possible, rather than being left unused. In practical situations, the code rate can be set according to the requirement. For ease of comparison, we set the length of the plaintext information to be approximately 32000 bits.

As shown in fig. 10, each type of signal employs a method of combining conventional QNSC technology with polarization codes and a method improved herein, respectively. As shown in fig. 10, the curve of the five-pointed star point represents the case of error correction directly with the polarization code using the QNSC technique. The curve of the circular points represents the encryption of a signal using the polar code and interleaver based QNSC technique proposed herein.

As can be seen from FIG. 10, the BER is at 10^-5～10^-4The BER performance of the two methods does not differ much. However, as the received optical power is reduced and the noise is gradually increased, the bit error rate curve of the QNSC direct-plus-polarization code is rapidly increased. In contrast, the proposed scheme makes the rising trend of the bit error rate curve become moderate. Because in the newly proposed scheme the plaintext information is located in information bits which are put to the upper bits of the QAM signal by the interleaver. Then the plaintext information is less affected by noise during transmission. In addition, when decoding, the error rate is also reduced to a certain extent by making a decision based on the shared ground state information. This effect is more pronounced at higher QAM orders of the signal. In FIG. 10(d), a gain of about 3.9dB is achieved when the BER is at the 10-2 level. Because the code rates of the four signals are different, the bit error rates of the four signals are not compared.

The invention has the greatest advantage of reducing redundancy to a great extent. We set the length of the plaintext information to be about 32000 bits in the experiment. When the code rate of the polar code or the encryption technology is changed, the length of the ciphertext information is also changed. Table 1 shows a comparison of cipher text lengths for different modulation format signals using different encryption techniques. The plaintext information length and code rate of the same modulation signal are the same.

Encryption method used	Code rate (K/N)	Length of transmitting plaintext information
			16-64QAM/QNSC+polar	0.656	73728
16-64QAM/QNSC+polar+interleaver	0.656	49152
			16-256QAM/QNSC+polar	0.5	131072
16-256QAM/QNSC+polar+interleaver	0.5	65536
			16-1024QAM/QNSC+polar	0.39	204800
16-1024QAM/QNSC+polar+interleaver	0.39	81920
			16-4096QAM/QNSC+polar	0.328	294912
16-4096QAM/QNSC+polar+interleaver	0.328	98304

TABLE 1

Fig. 11 is a clear text length comparison histogram of 16QAM modulated signals hidden at 64QAM, 256QAM, 1024QAM, 4096QAM using different encryption methods. It can be seen intuitively that the scheme provided by the invention can reduce the ciphertext length of actual transmission. This is because the present invention uses the redundancy created by the polarization code for scrambling the information, which can sufficiently redundancy the information. And as the modulation order increases, the proportion of reduction of redundant information becomes more significant. In fig. 11, when the system transmits 16-4096QAM/QNSC signals, a large amount of redundant information is generated by directly using the polar code error correction. In this case, the actual transmitted ciphertext message is original 1/3 using the proposed scheme of the present invention. This is because the interleaver converts the redundant information generated by the polarization code into positions for encrypting plaintext information, making full use of the redundant information.

In practice, the attacks suffered by a communication system are mainly from eavesdroppers, of which an exhaustive search attack is the most common attack method. In an exhaustive search attack, an eavesdropper attempts to explore all possible keys in the key space until the correct key is found.

A security evaluation is made below for the proposed QNSC algorithm based on polar codes and interleavers. The proposed encryption algorithm has strong security, and can be comprehensively considered from two aspects of complexity of a chaotic sequence and an interleaver and concealment of QNSC.

For the complexity of the chaotic sequence, three initial values mu, n, x of the chaotic sequence are mainly constructed₀To decide, we focus on the key { μ, x } pair₀Precision of precision changes such as { mu +. DELTA.mu, x }₀+△x₀And quantitatively calculating the enhancement of the chaos sequence on the security of the encryption algorithm. These two parameters are chosen because they require a high degree of accuracy and have a large impact on the complexity of the calculation. As shown in fig. 11, if there is a slight deviation (10)^-16～10^-15) This results in erroneous decoding, which again demonstrates the extremely high sensitivity of the chaotic sequence to the initial values. Thus, the key space s₁Can be up to 10¹⁶×10¹⁵＝10³¹. On the other hand, we use an interleaver in the encryption algorithm, and if the illegal receiver does not know the correct interleaving order, the ciphertext still cannot be cracked. Therefore, the complexity of the interleaver also has an enhanced effect on the security of the encryption algorithm. The complexity of the interleaver is related to the number of source bits K that we encode per module polar code, since the interleaver mainly reorders the information bit order. If the number of information bits is K in the polar code encoding, the key space is denoted s₂＝2^K。

We evaluate the concealment of QNSC using the security level Q. As shown in equation (13), 1/Γ represents a probability that an encrypted constellation point is not transferred to another constellation point, which may be called a detection accuracy probability. M is the QAM repetition in the I/Q data. Where M is 2^m. m represents the number of bits of each ground state information, s ═ s₁×s₂Representing the size of the exhaustive computational key space.

The low-redundancy polarization code quantum noise stream physical layer encryption method and system are based on the quantum noise stream encryption technology of the polarization code and the interleaver, and the interleaver is used for changing the position of the frozen bit redundancy information generated by the polarization code and used for QNSC encryption. The transmission length of the ciphertext information is reduced, and in the 16-4096QAM/QNSC signal, the ciphertext information length is changed to 1/3 of the original length. According to the error rate curve, for 16-4096QAM/QNSC signal, at 10^-2A BER of the order of 3.9dB gain. The invention not only improves the transmission efficiency, but also improves the safety of the system.

The above embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.