JP2008079297A - Data transmitter and data receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide data communication equipment improved in security against wiretapping relating to private communication using Y-00 protocols. <P>SOLUTION: In a data transmitter 101, a multi-level code generating part 111 generates a multi-level code sequence 12 the signal level which varies substantially like a random number from key information 11. A multi-level processing part 112 generates a multi-level signal 13 having a plurality of levels corresponding to a combination of information data 10 and the multi-level code sequence 12. A level converting part 113 divides the plurality of levels of the multi-level signal 13 into several groups, allocates one level to a plurality of levels included in each of the groups in an overlapped manner, and converts the multi-level signal 13 into a converted multi-level signal 21. A modulating part 114 modulates the converted multi-level signal 21 and outputs the signal as a modulated signal 14. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus that performs secret communication that prevents illegal eavesdropping and interception by a third party. More specifically, the present invention relates to an apparatus that performs data communication by selecting and setting a specific encoding / decoding (modulation / demodulation) scheme between authorized senders and receivers.

  Conventionally, in order to perform communication only between specific persons, original information (key information) for encoding / decoding is shared between transmission / reception, and information data to be transmitted based on the original information ( In general, a configuration that realizes secret communication by mathematically calculating / reversing a plaintext) is employed.

  On the other hand, in recent years, several encryption schemes that actively use physical phenomena in the transmission path have been proposed. One of them is a method called Y-00 protocol that performs cryptographic communication using quantum noise generated in an optical transmission line. One example of a transmission / reception apparatus using the Y-00 protocol is disclosed in Patent Document 1.

  FIG. 25 is a block diagram showing a configuration example of a conventional transmission / reception apparatus using the Y-00 protocol. In FIG. 25, the transmission unit 901 includes a first multilevel code generation unit 911, a multilevel processing unit 912, and a modulation unit 913. The reception unit 902 includes a demodulation unit 915, a second multi-level code generation unit 914, and an identification unit 916. The transmission unit 901 and the reception unit 902 share the first key information 91 and the second key information 96 having the same contents in advance. The first multi-level code generation unit 911 is based on the first key information 91 and is a multi-level code sequence that is a multi-level pseudo-random number sequence having M values from “0” to “M−1”. 92 is generated.

  The multi-level processing unit 912 synthesizes the information data 90 and the multi-level code sequence 92 and generates a signal having a level corresponding to the combination of the levels of the information data 90 and the multi-level code sequence 92 as the multi-level signal 93. . Specifically, the multi-level processing unit 912 generates a multi-level signal 93 that is an intensity modulation signal using the signal format shown in FIG. That is, the multi-level processing unit 912 divides the signal strength of the multi-level code sequence 92 into 2M levels, sets these levels to two combinations of M, and sets the information data 90 “1” at one level of each combination. Assign “0” and “1” to the other level. The multi-value processing unit 912 assigns “0” and “1” so that levels corresponding to “0” and “1” of the information data 90 are evenly distributed in the entire 2M levels. In the example of FIG. 26, “0” and “1” are assigned alternately.

  The multi-level processing unit 912 selects one combination from among the M level combinations of the multi-level code sequence 92 based on the value of the input multi-level code sequence 92. Next, the multi-level processing unit 912 selects one level of the combination of the multi-level code sequence 92 selected earlier based on the value of the information data 90, and generates a multi-level signal 93 having the selected level. In Patent Document 1, the first multi-level code generation unit 911 is a “transmission pseudo-random number generation unit”, the multi-level processing unit 912 is a “modulation method designation unit”, a “laser modulation drive unit”, and a modulation unit 913. Is a “laser diode”, a demodulator 915 is a “photo detector”, a second multi-level code generator 914 is a “reception pseudo-random number generator”, and an identification unit 916 is a “determination circuit”.

  FIG. 27 is a schematic diagram for explaining a signal form used in a conventional transmission / reception apparatus. Examples of signal changes when M = 4 are shown in FIGS. For example, when the value of the information data 90 changes as “0111” (see FIG. 27A) and the value of the multilevel code string 92 changes as “0321” (see FIG. 27B), the multilevel signal 93 Changes as shown in FIG. The modulation unit 913 converts the multilevel signal 93 into a modulation signal 94 that is a light intensity modulation signal, and transmits the modulated signal 94 via the optical transmission path 910.

  The demodulator 915 photoelectrically converts the modulated signal 94 transmitted via the optical transmission path 910 and outputs it as a multilevel signal 95. The second multi-level code generation unit 914 generates a multi-level code sequence 97 that is the same multi-value pseudo-random number sequence as the multi-level code sequence 92 based on the second key information 96. Based on the value of the multilevel code sequence 97, the identification unit 916 determines which one of the signal level combinations shown in FIG. 27 is used for the multilevel signal 95, and sets the two signal levels included in the combination to 2 Identify the value.

  Specifically, as shown in FIG. 27E, the identification unit 916 sets an identification level based on the value of the multi-level code sequence 97, and determines whether the multi-level signal 95 is larger (upper) than the identification level. Or small (bottom). In this example, the identification unit 916 identifies “lower, lower, upper, lower”. Next, when the multi-level code sequence 97 is an even number, the identification unit 916 determines that the lower side is “0”, the upper side is “1”, and the odd number is “1”, and the upper side is “0”. , And output as information data 98. In this example, since the multilevel code sequence 97 is “even, odd, even, odd”, the information data 98 is “0111”. The multilevel signal 95 contains noise, but by appropriately selecting the signal strength, it is possible to suppress the occurrence of errors in binary identification to a level that can be ignored.

  Next, assumed wiretapping will be described. An eavesdropper attempts to decrypt the information data 90 or the first key information 91 from the modulated signal 94 without having the key information shared by the sender and the receiver. An eavesdropper does not have key information when performing binary identification similar to that of an authorized receiver, and therefore needs to try to identify all possible values of key information. Such a method is not practical when the length of the key information is sufficiently long because the number of trials increases exponentially with respect to the length of the key information.

  Therefore, as a more efficient method, it is conceivable that the eavesdropper attempts to decrypt the information data 90 or the first key information 91 from the modulated signal 94 using an eavesdropping reception unit 903 as shown in FIG. In the eavesdropping reception unit 903, the demodulation unit 921 demodulates the modulation signal 94 obtained by branching from the optical transmission path 910 and reproduces the multilevel signal 95. The multi-level identifying unit 922 multi-levels the multi-level signal 81 and outputs the obtained information as a reception sequence 82. The decryption processing unit 923 performs decryption processing on the reception sequence 82 and attempts to specify the information data 90 or the first key information 91. When such a decryption method is used, the wiretap receiving unit 903 can identify the first key information 91 in one trial from the obtained reception sequence 82 if the reception sequence 82 can be identified in multiple values without error. Decoding can be performed.

However, when the demodulating unit 921 performs photoelectric conversion, shot noise is generated and superimposed on the multilevel signal 81. It is known that this shot noise is always generated by the principle of quantum mechanics. Here, if the interval between the signal levels of the multilevel signal (hereinafter referred to as the step width) is sufficiently smaller than the level of the shot noise, the multilevel signal 81 received due to the identification error can be various other than the correct signal level. The possibility of taking multiple multi-levels cannot be ignored. Therefore, since an eavesdropper needs to perform a decoding process in consideration of the possibility that the correct signal level is a value other than the signal level obtained by the identification, there is no identification error (the first multi-level code is generated). Compared with a stream cipher using the same random number generator as that used for the unit 911), the number of trials required for the decryption process, that is, the calculation amount increases, and as a result, the security against eavesdropping is improved.
JP 2005-57313 A

  However, since the probability distribution of the signal level on which the shot noise is superimposed follows the Poisson distribution, when the eavesdropper identifies the multilevel signal 81 in a multilevel manner, the probability that each multilevel signal level is identified becomes non-uniform and is distributed. The spread of is also reduced. For example, as shown in FIG. 28, when the transmitted multi-level signal level is “4”, the probability distribution of the multi-level level obtained by multi-level identification by the eavesdropper is “4” which is the correct level. Next, adjacent levels “3” and “5” appear with a high probability. Further, the probability of being identified at other levels ("2" or less and "6" or more) is a value that can be almost ignored. Therefore, since the eavesdropper only needs to consider the possibility of being identified by these three multilevel signal levels, the amount of calculation required for the decryption process does not increase sufficiently.

  Further, an eavesdropper can obtain a part of the information data 90 (plain text) (for example, header information commonly used for a certain electronic file format) and a corresponding modulation signal 94 (cipher text). Using this as a clue, it may be possible to try to specify key information from the value of the multilevel code string 92 and to attempt to decrypt the remaining information data using the obtained key information. Such an eavesdropping method is called a known plaintext attack. In this case, since the information data values “1” and “0” are alternately assigned to the multi-level signal level, the possible values of the multi-level signal level for each information data value are Every other line is equivalent to the case where the step width is substantially doubled. Therefore, the probability that an eavesdropper can identify the correct multi-level signal level is further increased, and the multi-level signal level can be uniquely specified in practice. In such a state, the effect of increasing the number of trials required for the decoding process cannot be obtained at all.

  On the other hand, if the step width is made smaller, the probability of taking the multilevel level other than the correct level and the adjacent level becomes a value that cannot be ignored, and it is possible to further increase the calculation amount required for the decoding process. However, this requires extremely large multi-level numbers (thousands to tens of thousands), resulting in very small step widths. As a result, extremely precise accuracy is required for multi-level control. Is done. Therefore, there has been a problem that the hardware configuration becomes complicated and the cost is increased.

  Therefore, an object of the present invention is to solve the above-described problem, and without complicating the hardware configuration, effectively increases the amount of calculation required for the decryption process, and safety against eavesdropping. It is an object of the present invention to provide a data transmission device and a reception device that can improve the performance.

  The present invention is directed to a data transmitting apparatus that encrypts information data using predetermined key information and performs secret communication with a receiving apparatus. In order to achieve the above object, a data transmitting apparatus according to the present invention includes a multi-level code generation unit that generates a multi-level code sequence whose signal level changes substantially randomly from key information, information data, and multi-level code. A multi-level signal modulation unit that generates a signal having a plurality of signal levels based on the column, modulates the generated signal in a predetermined modulation format, and outputs the modulated signal as a modulation signal; The multi-level signal modulation unit divides signals having a plurality of levels corresponding to combinations of information data and multi-level code strings into a plurality of groups, and overlaps one level with a plurality of levels included in each group. Thus, a signal having a plurality of signal levels is generated.

  Preferably, the multilevel signal modulation unit combines the information data and the multilevel code sequence, and generates a multilevel signal having a plurality of levels corresponding to combinations of the information data and the multilevel code sequence. And a level converter that converts the multilevel signal into a converted multilevel signal by dividing the multilevel signal into a plurality of groups and allocating one level to a plurality of levels included in each group. And a modulation unit that modulates the converted multilevel signal in a predetermined modulation format and outputs the modulated signal. The converted multilevel signal is a signal having the same symbol rate as the multilevel signal and having a multilevel number smaller than the multilevel number of the multilevel signal.

  Preferably, the multilevel signal is expressed by a plurality of bits. In such a case, the level conversion unit includes a D / A conversion unit that selects a part of the bits of the multilevel signal, performs digital / analog conversion on the selected bits, and generates a converted multilevel signal.

  The level conversion unit further includes a selection random number generation unit that generates pseudo-random numbers using predetermined selection key information, and a bit selection unit that selects some bits of the multilevel signal based on the pseudo-random numbers. It may be a configuration. In such a case, the D / A conversion unit performs digital / analog conversion on the bit selected by the bit selection unit, and generates a converted multilevel signal.

  The multilevel signal is expressed by a plurality of bits. In such a case, the level conversion unit receives a part of the bits of the multi-level signal and performs a logical operation on the input bit, thereby converting the bit conversion signal having a smaller number of bits than the input number of bits. And a D / A converter that performs digital-to-analog conversion on the bits of the multilevel signal that are not input to the bit conversion circuit, and generates a multilevel signal after conversion.

  The level conversion unit calculates an exclusive OR of a random number generation unit that generates a conversion random number that is a binary random number, any one bit of the multi-level signal, and the conversion random number, and performs the calculation. The configuration may further include an exclusive OR circuit that outputs the result to the D / A converter.

  The multi-level signal modulation unit combines the multi-level code conversion unit that converts the multi-level code sequence into the converted multi-level code sequence and the inverted signal, and the information data, the converted multi-level code sequence and the inverted signal. A multi-level processing unit that generates a multi-level signal having a plurality of levels corresponding to a combination of information data, a converted multi-level code sequence and an inverted signal, and modulates the multi-level signal in a predetermined modulation format, And a modulation unit that outputs the signal. The converted multi-level code sequence is a signal having the same symbol rate as the multi-level code sequence and having a multi-level number smaller than the multi-level number of the multi-level code sequence. The inverted signal is a binary signal having the same bit rate as the symbol rate of the multilevel code sequence.

  The multilevel processing unit calculates an exclusive OR of the information data and the inverted signal, and synthesizes the calculation result and the converted multilevel code string to generate a multilevel signal.

  The multi-level code conversion unit converts a multi-level code sequence into a converted multi-level code sequence by allocating one level to a plurality of levels included in the multi-level code sequence.

  The multi-level code string is expressed by a plurality of bits. In such a case, the multi-level code conversion unit outputs a part of the bits of the multi-level code sequence as a converted multi-level code sequence and outputs any one bit of the multi-level code sequence as an inverted signal.

  In addition, the multi-level code conversion unit selects a part of the multi-level code string based on the pseudo-random number and a selection random number generation unit that generates pseudo-random numbers using predetermined selection key information, It may be configured to include a bit selection unit that outputs as a value code string and outputs any one bit of the multi-level code string as an inverted signal.

  The multi-level code string is expressed by a plurality of bits. In such a case, the multi-level code conversion unit receives a part of the bits of the multi-level code string and performs a logical operation on the input bits, thereby having a smaller number of bits than the input number of bits. A bit conversion circuit that converts the signal into a signal and outputs the converted signal as a bit conversion signal, outputs the remaining bits of the multilevel code sequence and the bit conversion signal as a converted multilevel code sequence, Any one bit of the value code string is output as an inverted signal.

  The multi-level code conversion unit receives a random number generation unit that generates a conversion random number that is a binary random number, and any one bit of the multi-level code string, and the input one bit and the conversion random number And a bit operation circuit that outputs the operation result as one input bit.

  The multi-level signal modulation unit calculates an exclusive OR of the multi-level code conversion unit that converts the multi-level code string into an inverted signal, the information data and the inverted signal, and outputs the calculation result as a binary conversion signal. A signal conversion unit; and a modulation unit that modulates the binary conversion signal in a predetermined modulation format and outputs the modulated signal. The inverted signal and the binary conversion signal are binary signals having the same bit rate as the symbol rate of the multilevel code sequence.

  The multi-level code string is expressed by a plurality of bits. In such a case, the multilevel code conversion unit outputs any one bit of the multilevel code string as an inverted signal.

  The present invention is also directed to a data receiving apparatus that receives information data encrypted using predetermined key information and performs secret communication with the transmitting apparatus. In order to achieve the above object, the data receiving apparatus of the present invention includes a multi-level code generation unit that generates a multi-level code sequence in which the signal level changes from the key information in a substantially random manner, and the modulation received from the transmitting apparatus. A demodulator that demodulates the signal and outputs a signal having a plurality of levels corresponding to the combination of the information data and the multilevel code string, and reproduces the information data from the output signal of the demodulator based on the multilevel code string A signal reproduction unit. The signal reproduction unit identifies the output signal of the demodulation unit using, as an identification level, a signal having the same symbol rate as the multilevel code sequence and having a multilevel number smaller than the multilevel number of the multilevel code sequence.

  Preferably, the signal reproduction unit converts the multi-level code sequence into a multi-level code sequence after conversion into a converted multi-level code sequence and an inverted signal according to a predetermined rule, and a multi-level based on the converted multi-level code sequence. An identification unit that binary-identifies the signal, and a data inversion unit that calculates an exclusive OR of the output signal and the inverted signal of the identification unit and outputs the calculation result as information data. The converted multi-level code sequence is a signal having the same symbol rate as the multi-level code sequence and having a multi-level number smaller than the multi-level number of the multi-level code sequence. The inverted signal is a binary signal having the same bit rate as the symbol rate of the multilevel code sequence.

  The multi-level code conversion unit converts a multi-level code sequence into a converted multi-level code sequence by allocating one level to a plurality of levels included in the multi-level code sequence.

  The multi-level code string is expressed by a plurality of bits. In such a case, the multi-level code conversion unit selects a part of the bits of the multi-level code sequence, performs digital / analog conversion on the selected bits, and generates a converted multi-level code sequence. And one of the bits not selected by the D / A conversion unit in the multi-level code string is output as an inverted signal.

  Further, the multi-level code conversion unit includes a selection random number generation unit that generates a pseudo-random number using predetermined selection key information, and a bit selection unit that selects some bits of the multi-level code sequence based on the pseudo-random number. The structure which has further may be sufficient. In such a case, the D / A conversion unit performs digital / analog conversion on the bit selected by the bit selection unit to generate a converted multi-level code string. The bit selection unit outputs one of the unselected bits of the multilevel code string as an inverted signal.

  The multi-level code string is expressed by a plurality of bits. In such a case, the multi-level code conversion unit receives a part of bits of the multi-level code string, converts the input bits by a logical operation, and reduces the number of bits smaller than the input number of bits. D / A conversion for digital / analog conversion of a bit conversion circuit that outputs a bit conversion signal having a bit and a bit conversion signal that is not input to the bit conversion circuit of the multi-level code string and generates a converted multi-level code string Part.

  Preferably, the signal reproduction unit includes a multi-level code conversion unit that converts the multi-level code string into an inverted signal, an identification unit that binarizes the multi-level signal based on a predetermined identification level, and an output signal of the identification unit And a data inverting unit for calculating the exclusive OR of the signal and the inverted signal and outputting the calculation result as information data. The inverted signal is a binary signal having the same bit rate as the symbol rate of the multilevel code sequence.

  As described above, according to the present invention, even when the noise level is not sufficiently large with respect to the step width of the multilevel signal, the eavesdropper can change the value of the pseudo random number sequence used on the transmission side based on the received signal level. It becomes impossible to specify one. Therefore, compared to the case where an eavesdropper can uniquely specify the value of the pseudo random number sequence, the number of trials of the decryption process for identifying the encryption key information, that is, the amount of calculation required for the decryption process increases. Therefore, it is possible to improve safety against eavesdropping without complicating the hardware configuration.

  These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a configuration example of a data communication apparatus 1 according to the first embodiment of the present invention. In FIG. 1, the data communication device 1 has a configuration in which a data transmission device (hereinafter referred to as a transmission unit) 101 and a data reception device (hereinafter referred to as a reception unit) 201 are connected via a transmission line 110. is there. The transmission unit 101 includes a first multi-level code generation unit 111, a multi-level processing unit 112, a level conversion unit 113, and a modulation unit 114. The reception unit 201 includes a demodulation unit 211, a second multi-level code generation unit 212, a multi-level code conversion unit 213, an identification unit 214, and an inversion unit 215. For the transmission line 110, a metal line such as a LAN cable or a coaxial cable, or an optical waveguide such as an optical fiber cable is used. The transmission path 110 is not limited to a wired cable such as a LAN cable, and may be a free space capable of propagating a radio signal.

  First, the transmission unit 101 and the reception unit 201 share the first key information 11 and the second key information 16 having the same contents in advance. In the transmission unit 101, the first multi-level code generation unit 111 generates and outputs a multi-level code sequence 12 that is a multi-level pseudo-random number sequence using the first key information 11 as an initial value. The signal form of the multi-level code string 12 may be either a multi-level serial signal or a binary parallel signal. The multilevel processing unit 112 synthesizes the information data 10 and the multilevel code sequence 12 according to a predetermined procedure, as in the prior art example described with reference to FIG. A signal having a level corresponding to the combination is generated as the multilevel signal 13.

  The level conversion unit 113 converts the multilevel signal 13 into a converted multilevel signal 21 and outputs it. Here, the converted multilevel signal 21 has the same symbol rate as the multilevel signal 13 and has a multilevel number smaller than the multilevel number of the multilevel signal 13. Details of the multi-value processing unit 112 and the level conversion unit 113 will be described later. The modulation unit 114 modulates the converted multilevel signal 21 in a predetermined modulation format, and sends the modulated signal 14 to the transmission line 110 as the modulation signal 14.

  In the reception unit 201, the demodulation unit 211 demodulates the modulated signal 14 transmitted via the transmission path 110 and reproduces the converted multilevel signal 33. Similar to the first multi-level code generator 111, the second multi-level code generator 212 generates a multi-level code string 17 that is a multi-value pseudo-random number sequence using the second key information 16 as an initial value. And output. The multi-level code conversion unit 213 generates a converted multi-level code sequence 31 and an inverted signal 32 from the multi-level code sequence 17 and outputs them.

  Here, the converted multi-level code sequence 31 is a signal having the same symbol rate as the multi-level code sequence 17 and having a multi-level number smaller than the multi-level number of the multi-level code sequence 17. Further, the inverted signal 32 is a binary signal having the same bit rate as the symbol rate of the multilevel code string 17. Details of the multi-level code conversion unit 213 will be described later. The identification unit 214 identifies (binary determination) the converted multilevel signal 33 based on the converted multilevel code string 31, and outputs the identification result. The inversion unit 215 performs an exclusive OR operation on the output signal of the identification unit 214 and the inversion signal 32 and outputs the calculation result as information data 18.

  Further, in FIG. 1, a receiving device assumed to be used by an eavesdropper is shown as an eavesdropping reception unit 301. However, the eavesdropping reception unit 301 is only shown for explaining the effect of this embodiment on eavesdropping, and is not included in the configuration of the data communication apparatus 1. The configuration and operation of the wiretap receiving unit 301 are the same as those described with reference to FIG. The effect on wiretapping of this embodiment will be described later.

  Next, the signal point arrangement of the multilevel signal 13 and the converted multilevel signal 21 and the setting of the inverted signal 32 in this embodiment will be described with reference to FIG. FIG. 2 is a schematic diagram for explaining the signal point arrangement in the first embodiment of the present invention. In FIG. 2, the value of the multi-level code string 12 is expressed in binary (decimal notation in parentheses). As shown in FIG. 2A, the multilevel signal 13 is assigned one level for each combination of the multilevel code string 12 and the information data 10. On the other hand, in the converted multilevel signal 21, one level is assigned to a plurality of combinations of the multilevel code string 12 and the information data 10.

  Here, the combination of the multilevel code sequence 12 and the information data 10 is expressed as (multilevel code sequence 12, information data 10). In the example of FIG. 2, the converted multilevel signal 21 includes (0000, 0), (0001, 1), (0010, 0), (0011, 1), (0100, 0), (0101, 1). , (0110, 0), and (0111, 1) are assigned one level L1 redundantly. That is, the level conversion unit 113 converts the multilevel signal 13 into the converted multilevel signal 21 by allocating one level to a plurality of levels of the multilevel signal 13.

  As described above, the transmission unit 101 generates a signal in which some information of the multi-level code sequence 12 is intentionally deleted, and transmits the signal to the reception unit 201. In the reception unit 201, the multilevel code conversion unit 213 divides the levels of the multilevel code sequence 17 into a plurality of groups in the same manner as the transmission unit 101, and one level is provided for the plurality of levels included in each group. The multi-level code sequence 17 is converted into a post-conversion multi-level code sequence 31. The value of the inverted signal 32 is set to the same value as the least significant bit of the multilevel code string 17.

  In the transmission unit 101, the multi-level processing unit 112, the level conversion unit 113, and the modulation unit 114 may be collectively referred to as a multi-level signal modulation unit. In the receiving unit 201, the multi-level code converting unit 213, the identifying unit 214, and the inverting unit 215 may be collectively referred to as a signal reproducing unit.

  Next, the signal form used in this embodiment will be described with reference to FIG. FIG. 3 is a schematic diagram for explaining signal forms used in the data communication apparatus 1 according to the first embodiment of the present invention. In FIG. 3, it is assumed that the information data 10 and the value of the multi-level code sequence 12 in each time slot (t1 to t4) are the values shown in FIGS. 3 (a) and 3 (b). At this time, the level of the converted multi-level signal 21 changes to “L1, L2, L2, L4” as shown in FIG. 3C from the relationship shown in FIG. The modulation unit 114 modulates the converted multilevel signal 21 and transmits it as the modulated signal 14.

  On the other hand, in the receiving unit 201, the multilevel code conversion unit 213 generates a converted multilevel code sequence 31 having the same value as the most significant bit of the multilevel code sequence 17 (see FIG. 3E). In addition, the multi-level code conversion unit 213 generates an inverted signal 32 having the same value as the least significant bit of the multi-level code string 17 (see FIG. 3F). As shown in FIG. 3G, the identification unit 214 binary-identifies the converted multilevel signal 33 obtained by demodulating the modulated signal 14 using the converted multilevel code string 31 as an identification level. The inverting unit 215 calculates an exclusive OR of the output signal (see FIG. 3 (h)) of the identifying unit 214 and the inverted signal 32, and outputs the calculation result as information data 18 (see FIG. 3 (i)). ).

  Next, the effect on wiretapping of this embodiment will be described. Here, it is assumed that an eavesdropper attempts a known plaintext attack using the eavesdropping reception unit 301. In the eavesdropping reception unit 301, the demodulation unit 311 demodulates the modulation signal 14 obtained by branching from the transmission path 110 and reproduces the converted multilevel signal 33. The multi-level identifying unit 312 can specify the level of the converted multi-level signal 33, but cannot specify the combination of the multi-level code sequence 12 and the information data 10 assigned in duplicate. For example, in the time slot t1 shown in FIG. 3, the multilevel identifying unit 312 can know that the level of the converted multilevel signal 33 is L1, but there are eight ways corresponding to L1 shown in FIG. Which combination is correct among the combinations of the multi-level code string 12 and the information data 10 cannot be specified.

Therefore, the eavesdropper can narrow down the possibility of the value of the multi-level code sequence 12 by comparing the converted multi-level signal 33 with the value of the information data 10 obtained in advance. However, there is still a possibility that the multi-level code sequence 12 takes four values. That is, as shown in FIG. 3 (j), the values of some bits of the reception sequence 42 are unknown. In the subsequent time slots, there is still a possibility that the reception sequence 42 takes four values. Here, when the symbol length of the multi-level signal 41 required for the decryption process is X, the possibility of multi-level signal 41 possible values of the symbol length is 4 ^X. Since an eavesdropper needs to perform decryption processing on all 4 ^X patterns, the number of decryption processing attempts, that is, the amount of calculation required for the decryption processing increases. That is, the safety against eavesdropping is improved as compared with the case where the value of the reception sequence 42 is uniquely determined.

  2 and 3, the multi-level code sequence 12 has a multi-level number of 16 (the number of bits is 4), and the number of multi-level code sequences 12 to be overlapped with the level of one converted multi-level signal 21 (hereinafter, 8) is described as an example, but different values may be used. Here, the larger the duplication number, the greater the number of attempts by the eavesdropper for decryption processing. However, the overlap number needs to be set so as not to exceed the multi-level number of the multi-level code string 12.

  In FIG. 2, the multilevel signal 13 (or converted multilevel signal 21) is arranged so that the value of the multilevel code string 12 increases as the level of the multilevel signal 13 (or converted multilevel signal 21) increases. The correspondence relationship between the post-multilevel signal 21) and the multi-level code sequence 12 is not limited to this, and any multi-level code sequence 12 of each level of the multi-level signal 13 (or the converted multi-level signal 21) can be obtained. It is also possible to associate values. Furthermore, although the value of the inversion signal 32 is set to the same value as the least significant bit of the multilevel code sequence 17, it can also be set to the same value as other bits.

  In FIG. 3, the step width (in this embodiment, the distance between signal points of the converted multi-value signal 33 is referred to as the step width) is described as being larger than the noise level. By setting it small, it is possible to have an effect of causing an error in multi-level identification of an eavesdropper. An error in multi-level identification of an eavesdropper means that, for example, the eavesdropper mistakenly identifies “L1” even though the level of the converted multi-level signal 21 is “L2” on the transmission side. In this case, since the eavesdropper needs to perform the decoding process in consideration of the value of the multi-level code string 12 corresponding to the adjacent level of the converted multi-level signal 21, the number of trials of the decoding process further increases.

  Next, a specific configuration of the multi-value processing unit 112 and the level conversion unit 113 will be described. FIG. 4 is a block diagram illustrating a first configuration example of the multi-value processing unit 112 and the level conversion unit 113 according to the first embodiment of the present invention. In the configuration of FIG. 4, the multilevel code string 12 and the multilevel signal 13 take the form of parallel signals, and the converted multilevel signal 21 takes the form of a multilevel serial signal. The multi-value processing unit 112 includes an exclusive OR circuit 121. The exclusive OR circuit 121 performs an exclusive OR operation on the least significant bit A of the multilevel code string 12 and the information data 10 and outputs the operation result as the most significant bit of the multilevel signal 13. Each bit of the multilevel code string 12 is output as it is as a bit other than the most significant bit of the multilevel signal 13.

  The level conversion unit 113 includes a digital / analog conversion unit (hereinafter referred to as a D / A conversion unit) 131. Some bits of the multilevel signal 13 input to the level conversion unit 113 are not used, and the remaining bits are input to the D / A conversion unit 131. The D / A converter 131 performs digital / analog conversion on the input bits and outputs the converted multilevel signal 21. In FIG. 4, the configuration is such that the least significant bit A of the multi-level code string 12 is input to the exclusive OR circuit 121, but the bits not used by the level conversion unit 113 (A to C in the figure). Any bit may be input to the exclusive OR circuit 121 as long as it exists.

  FIG. 5 is a block diagram showing a second configuration example of the multi-level processing unit 112 and the level conversion unit 113 according to the first embodiment of the present invention. Also in the configuration of FIG. 5, the multi-level code sequence 12 and the multi-level signal 13 are in the form of parallel signals, and the converted multi-level signal 21 is in the form of a multi-level serial signal. The configuration and function of the multi-value processing unit 112 are the same as those in FIG. The level conversion unit 113 includes a D / A conversion unit 131 and a bit conversion circuit 132. Some bits of the multilevel signal 13 are input to the bit conversion circuit 132. The bit conversion circuit 132 outputs a bit conversion signal 25 that is a binary signal having the same bit rate as the symbol rate of the multilevel signal 13.

  The value of the bit conversion signal 25 is determined by a logical operation using each bit input to the bit conversion circuit 132. That is, the bit conversion circuit 132 converts the input bits by a logical operation, and outputs a bit conversion signal having a number of bits smaller than the number of input bits. Bits that are not input to the bit conversion circuit 132 of the multilevel signal 13 and the bit conversion signal 25 are input to the D / A conversion unit 131. The D / A conversion unit 131 performs digital / analog conversion on the bits of the multilevel signal 13 that are not input to the bit conversion circuit 132 and the bit conversion signal 25 and outputs the converted multilevel signal 21. In FIG. 5, although the least significant bit of the multi-level code string 12 is input to the exclusive OR circuit 121, the bits (A to D in the figure) input to the bit conversion circuit are used. For example, arbitrary bits may be input to the exclusive OR circuit 121.

  Next, a specific configuration of the multilevel code conversion unit 213 will be described. FIG. 6 is a block diagram illustrating a first configuration example of the multi-level code conversion unit 213 according to the first embodiment of the present invention. In the configuration of FIG. 6, the multi-level code sequence 17 takes the form of a parallel signal, and the converted multi-level code sequence 31 takes the form of a multi-level serial signal. The multi-level code conversion unit 213 includes a D / A conversion unit 231. Of the multi-level code string 17 input to the multi-level code converter 213, the remaining bits excluding some bits are input to the D / A converter 231. The D / A conversion unit 231 performs digital / analog conversion on the input bits and outputs the converted multi-level code string 31. Further, the least significant bit (A in the figure) of the multilevel code string 17 is output as it is as the inverted signal 32. The inversion signal 32 can be arbitrarily selected from bits (A to C in the figure) that are not input to the D / A conversion unit 231 in the multi-level code string 17. It is necessary to select a bit having the same arrangement as the bit input to the sum circuit 121.

  FIG. 7 is a block diagram showing a second configuration example of the multi-level code conversion unit 213 according to the first embodiment of the present invention. Also in the configuration of FIG. 7, the multi-level code sequence 17 takes the form of a parallel signal, and the converted multi-level code sequence 31 takes the form of a multi-level serial signal. The multi-level code conversion unit 213 includes a D / A conversion unit 231 and a bit conversion circuit 232. Some bits of the multilevel code string 17 are input to the bit conversion circuit 232. The bit conversion circuit 232 outputs a bit conversion signal 34 that is a binary signal having the same bit rate as the symbol rate of the multilevel code sequence 17. The value of the bit conversion signal 34 is determined by a logical operation using each bit input to the bit conversion circuit 232. That is, the bit conversion circuit 232 converts the input bits by a logical operation, and outputs a bit conversion signal 34 having a number of bits smaller than the number of input bits.

  Bits that are not input to the bit conversion circuit 232 in the multilevel code string 17 and the bit conversion signal 34 are input to the D / A conversion unit 231. The D / A conversion unit 231 performs digital / analog conversion on the bits of the multilevel code string 17 that are not input to the bit conversion circuit 232 and the bit conversion signal 34, and outputs the converted multilevel code string 31. Also, in the multi-level code string 17, the bit (the least significant bit in the example of FIG. 6) having the same arrangement as the bit input to the exclusive OR circuit 121 on the transmission side is output as it is as the inverted signal 32. The inverted signal 32 can be arbitrarily selected from the bits (A to D in the figure) input to the bit conversion circuit 232 in the multi-level code string 17. It is necessary to select bits having the same arrangement as the bits input to the circuit 121.

  Note that the configurations of the multi-level processing unit 112, the level conversion unit 113, and the multi-level code conversion unit 213 shown in FIGS. 4 to 7 are merely examples, and setting of bits that are not used or the bit conversion circuits 132 and 232 are not included. As long as the input bits are unified between the transmission side and the reception side, it is possible to arbitrarily set other than the above.

  4 to 7 can be replaced with another element having the same function. Furthermore, components other than the D / A converters 131 and 231 are not limited to hardware, and their functions may be realized by software processing.

  Further, the receiving unit used by the authorized receiver can use a receiving unit having the same configuration as the conventional one instead of the configuration of the receiving unit 201 shown in FIG. 1 as long as the signal-to-noise ratio can be degraded. When a reception unit having the same configuration as the conventional one is used, signal level degradation corresponding to a difference in discrimination level between the reception unit 201 of the present embodiment and the reception unit having the same configuration as the conventional one (that is, signal-to-noise ratio degradation) Is equivalent to Therefore, if the deteriorated signal-to-noise ratio is within the range of the specification of the receiving unit, the receiving unit having the same configuration as the conventional one can be used.

  As described above, according to the first embodiment of the present invention, even when the noise level is not sufficiently large with respect to the step width of the converted multilevel signal 33, the eavesdropper can uniquely identify the received sequence. As compared with, the number of attempts of decryption processing by an eavesdropper can be increased. Therefore, it is possible to improve safety against eavesdropping without complicating the hardware configuration.

(Second Embodiment)
FIG. 8 is a block diagram showing a configuration example of the data communication apparatus 2 according to the second embodiment of the present invention. In FIG. 8, the data communication device 2 has a configuration in which a data transmission device (hereinafter referred to as a transmission unit) 102 and a data reception device (hereinafter referred to as a reception unit) 201 are connected via a transmission line 110. is there. The transmission unit 102 includes a first multi-level code generation unit 111, a multi-level processing unit 112a, a modulation unit 114, and a multi-level code conversion unit 115. Since the configuration and operation of the receiving unit 201 are the same as those described in the first embodiment, description thereof is omitted. Further, although the wiretap receiving unit 301 is not illustrated in FIG. 8, it is assumed that the wiretap attempts to wiretap using the method described in the first embodiment.

  The first multi-level code generation unit 111 generates and outputs a multi-level code string 12 that is a multi-level pseudo-random number sequence using the first key information 11 as an initial value. The signal form of the multi-level code string 12 may be either a multi-level serial signal or a binary parallel signal. The multi-level code conversion unit 115 generates a converted multi-level code sequence 22 and an inverted signal 23 from the multi-level code sequence 12 and outputs them. Here, the converted multi-level code sequence 22 is a signal having the same symbol rate as the multi-level code sequence 12 and a multi-level number smaller than the multi-level number of the multi-level code sequence 12. Further, the inverted signal 32 is a binary signal having the same bit rate as the symbol rate of the multilevel code sequence 12. The multi-level processing unit 112 generates a multi-level signal 13 having a level corresponding to each combination of signal levels based on the information data 10, the converted multi-level code sequence 22, and the inverted signal 23 according to a predetermined procedure. . The modulation unit 114 modulates the multilevel signal 13 in a predetermined modulation format, and sends the modulated signal 14 to the transmission line 110 as the modulation signal 14.

  In the transmission unit 102, the multi-level processing unit 112a, the modulation unit 114, and the multi-level code conversion unit 115 may be collectively referred to as a multi-level signal modulation unit. In the receiving unit 201, the multi-level code converting unit 213, the identifying unit 214, and the inverting unit 215 may be collectively referred to as a signal reproducing unit.

  Next, the relationship among the signal point arrangement of the information data 10, the multi-level code sequence 12, the converted multi-level code sequence 22, the inverted signal 23, and the multi-level signal 13 in the present embodiment will be described with reference to FIG. . FIG. 9 is a schematic diagram for explaining signal point arrangement in the second embodiment of the present invention. In FIG. 9, the value of the multi-level code string 12 is represented in binary (decimal notation in parentheses). The multi-level code conversion unit 213 divides the values of the multi-level code sequence 12 into several groups, and assigns the value of the converted multi-level code sequence 22 to each group. In the example of FIG. 9, the multi-level code conversion unit 213 includes the values “0111”, “0110”, “0101”, “0100”, “0011”, “0010”, “0001”, “ The value “0” of the converted multi-level code sequence 22 is assigned to 0000, and the value “1” of the converted multi-level code sequence 22 is assigned to the values of other multi-level code sequences 12. Further, the multilevel code conversion unit 213 assigns the value “1” or “0” of the inverted signal 23 to each value of the multilevel code string 12. However, the value of the inversion signal 23 is assigned equally within each group. In the example of FIG. 9, the multilevel code conversion unit 213 assigns the same value as the least significant bit of the multilevel code sequence 12 as the value of the inverted signal 23.

  Subsequently, the multi-level processing unit 112a determines the signal level of the multi-level signal 13 from the converted multi-level code sequence 22, the inverted signal 23, and the value of the information data 10. However, the multi-level number of the multi-level signal 13 is twice the multi-level number of the converted multi-level code sequence 22. First, the multilevel processing unit 112a assigns two signal levels to each value of the converted multilevel code sequence 22. At this time, the multi-level processing unit 112a assigns a half of the signal level side (hereinafter referred to as the upper half) to one signal level, and a half of the signal level side to the other level. (Hereinafter referred to as the lower half). The difference between these signal levels is constant regardless of the value of the converted multi-level code sequence 22.

  Next, the multi-value processing unit 112a obtains an exclusive OR (XOR) of the information data 10 and the inverted signal 23. If the obtained exclusive-OR is “1”, the upper half signal level is multi-valued. Assigned to the signal 13, and in the case of “0”, the lower half signal level is assigned to the multilevel signal 13. The modulation signal 14 obtained by modulating the multilevel signal 13 obtained in this way has the same signal format as in the first embodiment. Therefore, the receiving unit 201 can demodulate the modulated signal 14 in the same procedure as in the first embodiment. The effect on wiretapping is the same as that described in the first embodiment.

  In FIG. 9, the multilevel code string 12 has been described with the multilevel number being 16 (the number of bits is 4) and the overlapping number being 8. However, this is merely an example, and different values may be used. Here, the larger the duplication number, the greater the number of attempts by the eavesdropper for decryption processing. However, the overlap number needs to be set so as not to exceed the multi-level number of the multi-level code string 12. Further, the relationship among the information data 10, the multi-level code sequence 12, the converted multi-level code sequence 22, the inverted signal 23, and the multi-level signal 13 shown in FIG. 9 is merely an example, and has different correspondences. It doesn't matter. However, even in that case, it is necessary to evenly distribute the value of the inverted signal 23 in the group of the multi-level code sequence 12 assigned to the same value of the converted multi-level code sequence 22.

  Next, specific configurations of the multilevel processing unit 112a and the multilevel code conversion unit 115 will be described. FIG. 10 is a block diagram illustrating a first configuration example of the multi-value processing unit 112a and the level conversion unit 113 according to the second embodiment of the present invention. In the configuration of FIG. 10, the multilevel code sequence 12 and the converted multilevel code sequence 22 take the form of parallel signals, and the multilevel signal 13 takes the form of a multilevel serial signal. The multi-level code conversion unit 115 outputs the remaining bits obtained by removing some bits from the multi-level code sequence 12 as the converted multi-level code sequence 22, and the least significant bit (A in the figure) of the multi-level code sequence 12 Is output as an inverted signal 23 as it is. The multi-value processing unit 112 a includes an exclusive OR circuit 121 and a D / A conversion unit 122.

  The exclusive OR circuit 121 performs an exclusive OR operation on the information data 10 and the inverted signal 23 and outputs the operation result. The D / A converter 122 receives the output signal of the exclusive OR circuit 121 as the most significant bit and each bit of the converted multi-level code string 22 as a bit other than the most significant bit. The D / A conversion unit 121 performs digital / analog conversion on the input bits and outputs the result as the multilevel signal 13. In FIG. 10, the least significant bit of the multi-level code sequence 12 is used as the inverted signal 23, but any other bits (A to C in the figure) that are not used as the converted multi-level code sequence 22 are also selected. It doesn't matter.

  FIG. 11 is a block diagram illustrating a second configuration example of the multi-value processing unit 112a and the level conversion unit 113 according to the second embodiment of the present invention. Also in the configuration of FIG. 11, the multi-level code sequence 12 and the converted multi-level code sequence 22 are in the form of parallel signals, and the multi-level signal 13 is in the form of a multi-level serial signal. The multilevel code conversion unit 115 includes a bit conversion circuit 133. The bit conversion circuit 133 receives a part of the bits of the multilevel code sequence 12 and outputs a binary signal having the same bit rate as the symbol rate of the multilevel code sequence 12. The value of the output signal of the bit conversion circuit 133 is determined by a logical operation using each bit input to the bit conversion circuit 133.

  The output signal of the bit conversion circuit 133 is output as a converted multi-level code sequence 22 together with the remaining bits of the multi-level code sequence 12 not input to the bit conversion circuit 133. The multi-level code conversion unit 115 outputs the least significant bit (A in the figure) of the multi-level code sequence 12 as it is as the inverted signal 23. The configuration of the multi-value processing unit 112 is the same as that in FIG. In FIG. 11, the least significant bit of the multilevel code sequence 12 is used as the inverted signal 23, but any other bit (A to D in the figure) input to the bit conversion circuit 133 can be arbitrarily selected. It doesn't matter.

  FIG. 12 is a block diagram showing a third configuration example of the multi-value processing unit 112a and the level conversion unit 113 according to the second embodiment of the present invention. In the configuration of FIG. 12, the multi-level code sequence 12 takes the form of a parallel signal, and the converted multi-level code sequence 22 and the multi-level signal 13 take the form of a multi-level serial signal. The multilevel code conversion unit 115 includes a D / A conversion unit 122. The remaining bits obtained by removing some bits from the multi-level code sequence 12 are input to the D / A converter 122. The D / A converter 122 performs digital-to-analog conversion on the input bits, outputs the converted bits as the multi-level code sequence 22, and outputs one of the other bits of the multi-level code sequence 12 (in the example of FIG. The lower bits are output as the inverted signal 23 as it is.

  The multi-value processing unit 112 includes an exclusive OR circuit 121 and an adding unit 123. The exclusive OR circuit 121 performs an exclusive OR operation on the information data 10 and the inverted signal 23 and outputs the operation result. The adder 123 adds the output signal of the exclusive OR circuit 121 and the converted multi-level code string 22 and outputs the result as a multi-level signal 13. In FIG. 12, the least significant bit of the multi-level code sequence 12 is used as the inverted signal 23, but any other bits (A to C in the figure) that are not used as the converted multi-level code sequence 22 are also selected. It doesn't matter. Although not shown, an amplifier or an attenuator may be provided on the input side of the adder 123 in order to adjust the output level of the exclusive OR circuit 121 and the signal level of the converted multilevel code sequence 22. Good.

  Further, although not shown, as an example of the configuration of the multilevel processing unit 112 and the multilevel code conversion unit 115, a bit conversion circuit is provided in the multilevel code conversion unit 115 in the configuration of FIG. It can also take a configuration.

  Note that the configurations of the multilevel processing unit 112 and the multilevel code conversion unit 115 shown in FIGS. 10 to 12 are merely examples, and the setting of bits that are not used or the setting of bits input to the bit conversion circuits 132 and 232 is as follows. As long as the transmission side and the reception side are unified, any other setting can be set.

  10 to 12 can be replaced with another element having the same function. Furthermore, the components other than the D / A converter 122 and the adder 123 are not limited to hardware, and their functions may be realized by software processing.

  As described above, according to the second embodiment of the present invention, as with the first embodiment, even when the noise level is not sufficiently large with respect to the step width of the multilevel signal 15, the eavesdropper can decrypt the noise level. The number of processing trials can be increased. Therefore, it is possible to improve safety against eavesdropping without complicating the hardware configuration.

(Third embodiment)
FIG. 13A is a block diagram illustrating a configuration example of the data communication device 3 according to the third embodiment of the present invention. In FIG. 13A, the data communication device 3 has a configuration in which a data transmission device (hereinafter referred to as a transmission unit) 103 and a data reception device (hereinafter referred to as a reception unit) 201 are connected via a transmission line 110. is there. The overall configuration of the data communication apparatus 3 according to the third embodiment is basically the same as that described with reference to FIG. 1 in the first embodiment. The transmission unit 103 differs from the first embodiment only in the internal configuration of the level conversion unit 113a. In the present embodiment, only differences from the first embodiment will be described, and description of functional blocks that operate in the same manner as in the first embodiment will be omitted.

  FIG. 13B is a block diagram showing an example of the configuration of the level conversion unit 113a according to the third embodiment of the present invention. In FIG. 13B, the level conversion unit 113 includes a D / A conversion unit 131, a random number generation unit 134, and an exclusive OR circuit 135. The random number generator 134 generates and outputs a conversion random number 26 that is a binary random number. As the conversion random number 26, either a physical random number generated based on a physical phenomenon or a pseudo-random number generated mathematically based on an initial value is used. When using a pseudo-random number, the initial value is not disclosed to anyone other than the sender. The exclusive OR circuit 135 performs an exclusive OR operation of the least significant bit (D in the figure) other than the unused bits (A to C in the figure) of the multilevel signal 13 and the conversion random number 26. And output the calculation result. The D / A converter 131 performs digital / analog conversion on the input bits and outputs the converted multilevel signal 21.

  Next, the signal form used in this embodiment will be described with reference to FIG. FIG. 14 is a schematic diagram for explaining a signal form used in the data communication apparatus 3 according to the third embodiment of the present invention. The signal form shown in FIG. 14 is an example in the case where the multilevel code string 12 has a multilevel number of 16 (5 bits) and the overlap number is 8. When the information data 10 and the multi-level code string 12 have the values shown in FIGS. 14A and 14B, the multi-level signal 13 has the values shown in FIG. 14C. Here, consider a case where the conversion random number 26 takes the value shown in FIG.

  The level conversion unit 113a does not use the lower 3 bits of the multilevel signal 13, but uses only the upper 3 bits (bits surrounded by a dotted line in FIG. 14C). The exclusive OR circuit 135 performs an exclusive OR operation on the third bit from the top of the bits surrounded by the dotted line and the conversion random number 26 and outputs the operation result. The D / A conversion unit 131 determines the level of the converted multilevel signal 21 by performing digital / analog conversion on the upper 2 bits of the multilevel signal 13 and the output signal of the exclusive OR circuit 135. On the receiving side, information data is reproduced by the same method as in the first embodiment (see FIGS. 14F to 14K).

  Next, the effect on wiretapping of this embodiment will be described. Here, it is assumed that an eavesdropper attempts a known plaintext attack using the eavesdropping reception unit 301. As in the first embodiment, the eavesdropping reception unit 301 cannot narrow down the possibility of the value of the multi-level code sequence 12 (four possibilities remain in the case of FIG. 14), and a part of the reception sequence 42 The bit value of is unknown. Further, in the present embodiment, in the time slot in which the value of the conversion random number 26 is “1”, another bit of the reception sequence 42 (exclusive OR with the conversion random number 26 of the multilevel signal 13 is obtained. Corresponding to the bit on which the operation is performed, an error also occurs in the case of FIG. 14 (l) (second bit from the top). Since the eavesdropping reception unit 301 does not have the information of the conversion random number 26, this bit is also uncertain for the eavesdropper. Therefore, there is a possibility that the value of the multi-level code sequence 12 takes twice the value when the conversion random number 26 is not used, that is, eight values. Thus, since the number of values that the multi-level code sequence 12 can take further increases, the number of decoding process trials can be further increased as compared with the first embodiment.

  In FIG. 14, the multi-level code string 12 has been described with the multi-level number of 16 (5 bits) and the overlap number of 8 as an example, but this is only an example, and different values may be used. In addition, the bits of the multi-level signal 13 input to the exclusive OR circuit 135 are bits that are not used (A to C in the figure) and other than the most significant bit, and an arbitrary bit is used. Is also possible.

  Further, the configuration of the level conversion unit 113a shown in FIG. 13B conforms to the configuration shown in FIG. 4. However, the level conversion unit 113a according to the present embodiment uses the configuration shown in FIG. It is also possible to use a configuration in which a random number generator and an exclusive OR circuit are added to the configuration shown in (1). Further, as the overall configuration of the transmission unit 103 illustrated in FIG. 13A, the same configuration as the transmission unit 102 (see FIG. 8) of the second embodiment is used, and a random number generation unit and an exclusive unit are included in the multilevel code conversion unit 115. The same effect can be obtained even if a configuration to which a logical OR circuit is added is used. In these configurations, each block may be replaced with another element having the same function, or components other than the digital / analog converter 131 may be replaced with software processing.

  As described above, according to the third embodiment of the present invention, it is possible to further increase the amount of calculation required for the decryption process by the eavesdropper than in the first embodiment and improve the safety against eavesdropping. .

(Fourth embodiment)
This embodiment corresponds to a special case of the first or second embodiment, that is, a case where the multi-value number and the overlap number of the multi-value code string 12 are matched.

  FIG. 15 is a block diagram illustrating a configuration example of the data communication device 4 according to the fourth embodiment of the present invention. In FIG. 15, the data communication device 4 has a configuration in which a data transmission device (hereinafter referred to as a transmission unit) 104 and a data reception device (hereinafter referred to as a reception unit) 204 are connected via a transmission line 110. is there. The transmission unit 104 includes a first multi-level code generation unit 111, a modulation unit 114, a multi-level code conversion unit 115a, and a signal conversion unit 116. The reception unit 204 includes a demodulation unit 211, a second multi-level code generation unit 212, a multi-level code conversion unit 213a, an identification unit 214, and an inversion unit 215.

  In the transmission unit 104, the first multi-level code generation unit 111 generates and outputs a multi-level code sequence 12 which is a multi-level pseudo-random number sequence using the first key information 11 as an initial value. The signal form of the multi-level code string 12 may be either a multi-level serial signal or a binary parallel signal. The multi-level code conversion unit 115a generates and outputs an inverted signal 23 from the multi-level code string 12. The signal conversion unit 116 performs an exclusive OR operation between the information data 10 and the inverted signal 23 and outputs the operation result as a binary conversion signal 24. The modulation unit 114 modulates the binary conversion signal 24 in a predetermined modulation format, and sends the modulated signal 14 to the transmission line 110 as the modulation signal 14.

  In the reception unit 204, the demodulation unit 211 demodulates the modulated signal 14 transmitted via the transmission path 110 and reproduces the binary conversion signal 35. Similar to the first multi-level code generator 111, the second multi-level code generator 212 generates a multi-level code string 17 that is a multi-value pseudo-random sequence using the second key information 16 as an initial value. And output. The identification unit 214 identifies the binary conversion signal 35 (binary determination) and outputs the identification result. The identification level of the identification unit 214 is basically a fixed value, but is not limited to this when the signal level of the binary conversion signal fluctuates for some reason. That is, the identification unit 214 has a function of adjusting the identification level to an optimum value. The multilevel code conversion unit 213a generates and outputs an inverted signal 32 from the multilevel code sequence 17. The inverting unit 215 calculates an exclusive OR of the output signal of the identifying unit 214 and the inverted signal 32 and outputs the calculation result as information data 18.

  Further, in FIG. 15, a receiving device assumed to be used by an eavesdropper is shown as an eavesdropping reception unit 301. However, the eavesdropping reception unit 301 is only shown for explaining the effect on the eavesdropping of the present embodiment, and is not included in the configuration of the data communication device 4. The configuration and operation of the wiretap receiving unit 301 are the same as those described with reference to FIG.

  In the transmission unit 104, the signal conversion unit 116, the modulation unit 114, and the multi-level code conversion unit 115a may be collectively referred to as a multi-level signal modulation unit. In the receiving unit 204, the multi-level code converting unit 213a, the identifying unit 214, and the inverting unit 215 may be collectively referred to as a signal reproducing unit.

  Next, a signal setting method in the present embodiment will be described with reference to FIGS. 16 and 17. FIG. 16 is a diagram illustrating an example of the relationship between the multi-level code sequence 12 and the inverted signal 23 in the fourth embodiment of the present invention. The inverted signal 23 is a binary signal having the same bit rate as the symbol rate of the multilevel code sequence 12. Here, the value of the inverted signal 23 is set to the same value as the least significant bit of the multilevel code sequence 12. FIG. 17 is a diagram showing a relationship among the information data 10, the inverted signal 23, and the binary conversion signal 24 in the fourth embodiment of the present invention. The value of the binary conversion signal 24 is determined by an exclusive OR operation between the information data 10 and the inverted signal 23. In the first embodiment, the binary converted signal 24 obtained in this way has a plurality of levels obtained by combining the information data 10 and the multilevel code string 12 with the level of one converted multilevel signal 21. This is equivalent to allocating the same number of multi-level code strings 12 as the multi-level number (16 in this case).

  Next, the signal form used in this embodiment will be described with reference to FIG. FIG. 18 is a schematic diagram for explaining a signal form used in the data communication apparatus 4 according to the fourth embodiment of the present invention. In FIG. 18, it is assumed that the information data 10 and the multi-level code sequence 12 in each time slot (t1 to t4) have the values shown in FIGS. 18 (a) and 18 (b). At this time, the binary conversion signal 24 takes the value shown in FIG. 18D from the relationship shown in FIGS. The modulation unit 114 modulates the binary conversion signal 24 and transmits it as the modulation signal 14.

  On the other hand, in the reception unit 204, the multi-level code conversion unit 213a generates the inverted signal 32 based on the same procedure as that of the transmission unit 104 (see FIG. 18E). The identification unit 214 sets the identification level according to the fixed identification level, and binary-identifies the binary conversion signal 35 obtained by demodulating the modulation signal 14. The inversion unit 215 performs an exclusive OR operation on the output signal of the identification unit 214 and the inversion signal 32, and outputs the calculation result as information data 18 (see FIG. 18 (f)).

  Next, the effect on wiretapping of this embodiment will be described. Here, it is assumed that an eavesdropper attempts a known plaintext attack using the eavesdropping reception unit 301. In the eavesdropping reception unit 301, the demodulation unit 311 demodulates the modulation signal 14 obtained by branching from the transmission path 110 and reproduces the binary conversion signal 35. The multi-level identifying unit 312 can specify the value of the binary conversion signal 35 but cannot specify the combination of the multi-level code sequence 12 and the information data 10. Therefore, the eavesdropper can narrow down the possibility of the value of the multilevel code string 12 by comparing the binary conversion signal 35 with the value of the information data 10 obtained in advance. However, the multi-level code sequence 12 still has a possibility of taking 8 values (corresponding to half of the multi-level number of the multi-level code sequence 12).

  That is, as shown in FIG. 18 (g), the value of the bit of the reception sequence 42 is unknown except for one (the least significant bit in the example of FIG. 18). In the subsequent time slots, the multi-level code sequence 12 still has a possibility of taking eight values. Therefore, since the eavesdropper needs to perform a decoding process on all patterns that may have the value of the multi-level code sequence 12, it is compared with the case where the eavesdropper can uniquely identify the value of the reception sequence 42. Thus, the number of decryption processing trials, that is, the amount of calculation required for the decryption processing increases. Therefore, safety against eavesdropping is improved.

  In FIGS. 16 to 18, the multi-level code string 12 is described with the multi-level number 16 being 16 (the number of bits is 4), but this is only an example, and different values may be used.

  Next, specific configurations of the multi-level code conversion unit 115a and the signal conversion unit 116 will be described. FIG. 19 is a block diagram illustrating a configuration example of the multi-level code conversion unit 115a and the signal conversion unit 116 according to the fourth embodiment of the present invention. In the configuration of FIG. 19, the multilevel code sequence 12 takes the form of a parallel signal. The multilevel code conversion unit 115a outputs the least significant bit (A in the figure) of the multilevel code string 12 as the inverted signal 23 as it is. The signal conversion unit 116 includes an exclusive OR circuit 141, performs an exclusive OR operation on the information data 10 and the inverted signal 23, and outputs the operation result as a binary conversion signal 24. The multi-level code converter 213a on the reception side can also be realized by the same configuration as the multi-level code converter 115a on the transmission side.

  Note that the configurations of the multi-level code conversion unit 115a and the signal conversion unit 116 shown in FIG. 19 are merely examples, and settings of unused bits are not limited to those described above as long as they are unified between the transmission side and the reception side. Can also be set arbitrarily. The inverted signal 23 is configured such that the least significant bit of the multilevel code sequence 12 is output as it is, but any other bit of the multilevel code sequence 12 can be used. Alternatively, the value of the inverted signal 23 may be determined by a logical operation of all or some of the bits of the multi-level code sequence 12. Furthermore, it is also possible to separately prepare an encryption key that is secretly shared between the sender side and the receiver side, and to set the above bits based on this encryption key.

  19 can be replaced with another element having a similar function. Furthermore, each component is not limited to hardware, and its function may be realized by software processing.

  As described above, according to the fourth embodiment of the present invention, it is possible to increase the amount of calculation required for the decryption process by an eavesdropper even when a binary modulated signal is used. Therefore, it is possible to improve safety against eavesdropping without complicating the hardware configuration.

(Fifth embodiment)
In this embodiment, in the second embodiment, a separate encryption key is secretly shared between the sender side and the receiver side, and the multilevel signal level to be duplicated is set based on this encryption key. It is an example.

  FIG. 20 is a block diagram illustrating a configuration example of the data communication apparatus 5 according to the fifth embodiment of the present invention. In FIG. 20, the data communication device 5 has a configuration in which a data transmission device (hereinafter referred to as a transmission unit) 105 and a data reception device (hereinafter referred to as a reception unit) 205 are connected via a transmission line 110. is there. The transmission unit 105 includes a first multi-level code generation unit 111, a multi-level processing unit 112a, a modulation unit 114, and a multi-level code conversion unit 115b. The receiving unit 205 includes a demodulating unit 211, a second multi-level code generating unit 212, a multi-level code converting unit 213b, an identifying unit 214, and an inverting unit 215. In FIG. 20, although the wiretap receiving unit 301 is not described, it is assumed that the wiretap attempts to wiretap using the method described in the first embodiment.

  In the present embodiment, functional blocks other than the multi-level code conversion unit 115b and the multi-level code conversion unit 213b are the same as those described in the second embodiment, and thus description thereof is omitted. Hereinafter, differences from the second embodiment will be described.

  In the present embodiment, the transmission unit 105 and the reception unit 205 have the third key information 41 and the fourth key information 42 having the same contents in advance separately from the first key information 11 and the second key information 16. Share it. Based on the third key information 41, the multi-level code conversion unit 115b randomly selects a bit output as the multi-level code sequence 22 and a bit output as the inverted signal 23 from the bits constituting the multi-level code sequence 12. select. Similarly to the multi-level code conversion unit 115b, the multi-level code conversion unit 213b, based on the fourth key information 42, outputs the bits to be output as the multi-level code sequence 31 from the bits constituting the multi-level code sequence 17. A bit to be output as the inverted signal 32 is selected at random.

  Next, the relationship among the multilevel code sequence 12, the converted multilevel code sequence 22, and the inverted signal 23 in the present embodiment will be described with reference to the example of FIG. FIG. 21 is a diagram illustrating a corresponding pattern of the multi-level code sequence 12, the converted multi-level code sequence 22, and the inverted signal 23 according to the fifth embodiment of the present invention. In FIG. 21, the value of the multi-level code string 12 is expressed in binary (decimal notation in parentheses). In the present embodiment, a plurality of these correspondence patterns (four types in the example of FIG. 21) are prepared. In each corresponding pattern, the value of the multi-level code sequence 12 is divided into several groups, and the value of the converted multi-level code sequence 22 is assigned to each group. In each group, the values of the inversion signal 23 are assigned so as to be evenly distributed. This can be realized by the following procedure.

  First, the multi-level code conversion unit 115b on the transmission side generates a pseudo random number using the third key information 41, and selects one of a plurality of corresponding patterns based on the value. Then, based on the selected corresponding pattern and the value of the multilevel code sequence 12, the values of the converted multilevel code sequence 22 and the inverted signal 23 are determined. That is, one of the bits constituting the multi-level code sequence 12 (shown in bold in FIG. 21) is selected, the value of the converted multi-level code sequence 22 is determined from the value, and the multi-level code sequence 12 One of the remaining bits (displayed in italics in FIG. 21) is selected, and the value of the inverted signal 23 is determined from the value. Note that the corresponding patterns other than those shown in FIG. 21 are conceivable, but are omitted here. Next, the multi-level processing unit 112a uses the same method as described with reference to FIG. 9 to calculate the signal of the multi-level signal 13 from the converted multi-level code sequence 22, the inverted signal 23, and the value of the information data 10. Determine the level.

  On the other hand, in the multilevel code conversion unit 213b on the reception side, similarly to the multilevel code conversion unit 115b on the transmission side, pseudo random numbers are generated using the fourth key information 42, and a plurality of correspondences are generated based on the value. Select one of the patterns. Then, based on the values of the selected corresponding pattern and the multi-level code sequence 17, the values of the converted multi-level code sequence 31 and the inverted signal 32 are determined.

  By determining the multi-level signal level in this way, each value of the converted multi-level code sequence 22, and further, for each multi-level signal level, the value of each bit constituting the multi-level code sequence 12 is , “0” and “1” correspond to each other. For example, in the example of FIG. 21, the value “0” (corresponding to the multilevel signal levels L1 and L3) of the converted multilevel code sequence 22 is changed from the value (decimal notation) “0” of the multilevel code sequence 12. All values up to “14” correspond to the value “1” of the converted multi-level code sequence 22 (corresponding to the multi-level signal levels L2 and L4) from the values “1” to “1” of the multi-level code sequence 12. All values up to 15 "correspond. Considering this in binary notation, the value of each bit constituting the multilevel code sequence 12 is “0” and “1” for both the values “0” and “1” of the converted multilevel code sequence 22. There is a possibility that both will respond. From the viewpoint of an eavesdropper, when the decryption processing unit 313 performs the process of converting the key information into binary numbers, “0” and “1” cannot be specified for all bits. It may contain errors. Therefore, since the decryption must be performed in consideration of these possibilities, the amount of calculation is further increased and the safety is improved as compared with the first and second embodiments.

  In FIG. 21, the multi-level code string 12 has been described with the multi-level number of 16 (the number of bits is 4) and the overlap number of 8. However, this is merely an example, and different values may be used. Further, the relationship among the multi-level code sequence 12, the converted multi-level code sequence 22, and the inverted signal 23 shown in FIG. 21 is merely an example, and may have a different correspondence relationship. However, even in that case, it is necessary to evenly distribute the value of the inverted signal 23 in the group of the multi-level code sequence 12 assigned to the same value of the converted multi-level code sequence 22.

  Next, a specific configuration example of the transmission-side multilevel code conversion unit 115b will be described. FIG. 22 is a block diagram illustrating a configuration example of the multi-level code conversion unit 115b. In the configuration of FIG. 22, the multilevel code sequence 12 and the converted multilevel code sequence 22 are in the form of parallel signals. The selection random number generator 151 is based on the third key information 41, and is a multi-value or binary signal whose symbol rate is equal to that of the multi-value code string 12 (and the multi-value signal 13) and whose value changes in a substantially random manner. A selection random number 43 is generated. Here, the multi-value number of the selection random number 43 is set to be equal to the number of corresponding patterns of the multi-value code string 12, the inverted signal 23, and the converted multi-value code string 22. The bit selection unit 152 receives the multi-level code string 12 and the selection random number 43. Based on the value of the selection random number 43, the bit selection unit 152 selects and outputs bits to be used as the converted multi-level code sequence 22 and the inverted signal 23 from the bits constituting the multi-level code sequence 12.

  Subsequently, a specific configuration example of the multilevel code conversion unit 213b on the reception side will be described. FIG. 23 is a block diagram illustrating a configuration example of the multilevel code conversion unit 213b. Referring to FIG. 23, selection random number generator 251 generates selection random number 44 having the same value as selection random number 43 based on third key information 41. Similarly to the bit selection unit 152, the bit selection unit 252 uses the converted multi-level code sequence 31 and the inverted signal 32 from the bits constituting the multi-level code sequence 17 based on the value of the selection random number 44. Select a bit and output.

  Note that the configurations of the multilevel code converters 115b and 213b shown in FIGS. 22 and 23 are merely examples, and other configurations may be used as long as the same functions can be realized. Furthermore, components other than the D / A conversion unit 231 are not limited to hardware, and their functions may be realized by software processing.

  In addition, the same concept as that of the present embodiment can be applied to the configuration of the first embodiment described with reference to FIG. FIG. 24 is a block diagram illustrating a configuration example of the level conversion unit 113b when applied to the configuration in the first embodiment. Referring to FIG. 24, level conversion unit 113b includes D / A conversion unit 131b, selection random number generation unit 151b, and bit selection unit 152b. Based on the third key information 41, the selection random number generator 151b is a multi-level or binary signal whose symbol rate is equal to that of the multi-level code sequence 12 (and the multi-level signal 13) and whose value changes in a substantially random manner. A selection random number 43 is generated. The bit selection unit 152 receives the multilevel signal 13 and the selection random number 43. Based on the value of the selection random number 43, the bit selection unit 152b selects and outputs a bit to be used from among the bits constituting the multilevel signal 13. However, the D / A converter 131b shown in this example always selects the most significant bit constituting the multilevel signal 13 because the most significant bit constituting the multilevel signal 13 includes the information data 10. Shall. The D / A conversion unit 131b performs digital / analog conversion on the bits selected by the bit selection unit 152b to generate the converted multi-level code sequence 21.

  As described above, according to the fifth embodiment of the present invention, it is possible to further increase the amount of calculation required for the decryption process by the eavesdropper than in the first and second embodiments, and to improve safety against eavesdropping. It becomes possible.

  Although the present invention has been described in detail above, the above description is merely illustrative of the present invention in all respects and is not intended to limit the scope thereof. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention.

  The data communication apparatus according to the present invention is useful as a secure secret communication apparatus that does not receive eavesdropping / interception.

1 is a block diagram showing a configuration example of a data communication device 1 according to a first embodiment of the present invention. The schematic diagram for demonstrating signal point arrangement | positioning in the 1st Embodiment of this invention The schematic diagram for demonstrating the signal form used with the data communication apparatus 1 which concerns on the 1st Embodiment of this invention. The block diagram which shows the 1st structural example of the multi-value processing part 112 and the level conversion part 113 which concern on the 1st Embodiment of this invention. The block diagram which shows the 2nd structural example of the multi-value processing part 112 and the level conversion part 113 which concern on the 1st Embodiment of this invention. The block diagram which shows the 1st structural example of the multi-value code conversion part 213 which concerns on the 1st Embodiment of this invention. The block diagram which shows the 2nd structural example of the multi-value code conversion part 213 which concerns on the 1st Embodiment of this invention. The block diagram which shows the structural example of the data communication apparatus 2 which concerns on the 2nd Embodiment of this invention. The schematic diagram for demonstrating signal point arrangement | positioning in the 2nd Embodiment of this invention The block diagram which shows the 1st structural example of the multi-value processing part 112a and the level conversion part 113 which concern on the 2nd Embodiment of this invention. The block diagram which shows the 2nd structural example of the multi-value processing part 112a and the level conversion part 113 which concern on the 2nd Embodiment of this invention. The block diagram which shows the 3rd structural example of the multi-value processing part 112a and the level conversion part 113 which concern on the 2nd Embodiment of this invention. The block diagram which shows the structural example of the data communication apparatus 3 which concerns on the 3rd Embodiment of this invention. The block diagram which shows an example of a structure of the level conversion part 113a which concerns on the 3rd Embodiment of this invention. The schematic diagram for demonstrating the signal form used with the data communication apparatus 3 which concerns on the 3rd Embodiment of this invention. The block diagram which shows the structural example of the data communication apparatus 4 which concerns on the 4th Embodiment of this invention. The figure which shows an example of the relationship between the multilevel code sequence 12 and the inversion signal 23 in the 4th Embodiment of this invention. The figure which shows the relationship between the information data 10, the inversion signal 23, and the binary conversion signal 24 in the 4th Embodiment of this invention. The schematic diagram for demonstrating the signal form used with the data communication apparatus 4 which concerns on the 4th Embodiment of this invention. The block diagram which shows the structural example of the multilevel code converter 115a and the signal converter 116 which concern on the 4th Embodiment of this invention. The block diagram which shows the structural example of the data communication apparatus 5 which concerns on the 5th Embodiment of this invention. The figure which shows the corresponding | compatible pattern of the multilevel code sequence 12, the converted multilevel code sequence 22, and the inversion signal 23 which concern on the 5th Embodiment of this invention. The block diagram which shows the structural example of the multi-level code conversion part 115b which concerns on the 5th Embodiment of this invention. The block diagram which shows the structural example of the multi-value code conversion part 213b which concerns on the 5th Embodiment of this invention. The block diagram which shows the structural example of the level conversion part 113b which concerns on the 5th Embodiment of this invention. Block diagram showing a configuration example of a conventional transmission / reception device using the Y-00 protocol Schematic diagram for explaining signal point arrangement in a conventional transmission / reception apparatus using the Y-00 protocol Schematic diagram for explaining signal forms used in a conventional transceiver Schematic diagram for explaining the probability distribution of multi-levels identified by an eavesdropper

Explanation of symbols

101-105 data transmission device (transmission unit)
201, 204, 205 Data receiving device (receiving unit)
301 wiretapping reception unit 111 first multi-level code generation unit 112, 112a multi-level processing unit 113, 113a level conversion unit 114 modulation unit 115 multi-level code conversion unit 116 signal conversion unit 121, 135 exclusive OR circuit 123 addition unit 131,231 D / A conversion unit 132,232 bit conversion circuit 134 random number generation unit 151,251 selection random number generation unit 152,252 bit selection unit 211 demodulation unit 212 second multi-level code generation unit 213, 213a multi-level code Conversion unit 214 Identification unit 215 Inversion unit 311 Demodulation unit 312 Multi-level identification unit 313 Decoding processing unit

Claims (25)

A data transmitting device that encrypts information data using predetermined key information and performs secret communication with a receiving device,
A multi-level code generator for generating a multi-level code sequence in which the signal level changes in a substantially random manner from the key information;
A multi-level signal modulator that generates a signal having a plurality of signal levels based on the information data and the multi-level code string, modulates the generated signal in a predetermined modulation format, and outputs the modulated signal as a modulation signal;
The multi-level signal modulator is
By dividing a signal having a plurality of levels corresponding to a combination of the information data and the multi-level code string into a plurality of groups, and assigning one level to a plurality of levels included in each group. A data transmission device that generates a signal having the plurality of signal levels. The multi-level signal modulator is
A multi-level processing unit that combines the information data and the multi-level code sequence, and generates a multi-level signal having a plurality of levels corresponding to a combination of the information data and the multi-level code sequence;
A level converter that converts the multilevel signal into a converted multilevel signal by dividing the multilevel signal into a plurality of groups and assigning one level to a plurality of levels included in each group. When,
The data transmission device according to claim 1, further comprising: a modulation unit that modulates the converted multilevel signal in a predetermined modulation format and outputs the modulated signal as a modulation signal.   The converted multilevel signal is a signal having the same symbol rate as the multilevel signal and having a multilevel number smaller than the multilevel number of the multilevel signal. The data transmission device described. The multilevel signal is expressed by a plurality of bits,
The level conversion unit includes a D / A conversion unit that selects a part of the bits of the multilevel signal and performs digital / analog conversion on the selected bits to generate the converted multilevel signal. The data transmission device according to claim 2. The level converter is
A selection random number generator for generating pseudo-random numbers using predetermined selection key information;
A bit selection unit that selects some bits of the multilevel signal based on the pseudo-random number;
5. The data transmission apparatus according to claim 4, wherein the D / A conversion unit digital-analog-converts the bit selected by the bit selection unit to generate the converted multilevel signal. 6. The multilevel signal is expressed by a plurality of bits,
The level converter is
A bit conversion circuit that receives a part of bits of the multi-level signal and outputs a bit conversion signal having a bit number smaller than the input bit number by performing a logical operation on the input bit;
A D / A conversion unit that performs digital / analog conversion on the bit that is not input to the bit conversion circuit of the multilevel signal and the bit conversion signal, and generates the converted multilevel signal. The data transmission device according to claim 2. The level converter is
A random number generator for generating a conversion random number that is a binary random number;
An exclusive OR circuit that calculates an exclusive OR of any one bit of the multilevel signal and the random number for conversion, and outputs the operation result to the D / A converter; The data transmission device according to claim 4, wherein the data transmission device is characterized by: The level converter is
A random number generator for generating a conversion random number that is a binary random number;
An exclusive OR circuit that calculates an exclusive OR of any one bit of the multilevel signal and the random number for conversion, and outputs the operation result to the D / A converter; The data transmission device according to claim 6, wherein the data transmission device is characterized by: The multi-level signal modulator is
A multi-level code conversion unit that converts the multi-level code sequence into a converted multi-level code sequence and an inverted signal;
The information data, the converted multi-level code sequence and the inverted signal are combined, and a multi-level signal having a plurality of levels corresponding to a combination of the information data, the converted multi-level code sequence and the inverted signal is obtained. A multi-value processing unit to be generated;
A modulation unit that modulates the multilevel signal in a predetermined modulation format and outputs the modulated signal as a modulation signal;
The converted multi-level code sequence is a signal having the same symbol rate as the multi-level code sequence and having a multi-level number smaller than the multi-level number of the multi-level code sequence,
The data transmission apparatus according to claim 1, wherein the inverted signal is a binary signal having a bit rate equal to a symbol rate of the multilevel code sequence.   The multi-level processing unit calculates an exclusive OR of the information data and the inverted signal, synthesizes the calculation result and the converted multi-level code string, and generates the multi-level signal. The data transmission apparatus according to claim 9, wherein the data transmission apparatus is characterized by   The multi-level code conversion unit converts the multi-level code sequence into the converted multi-level code sequence by allocating one level to a plurality of levels included in the multi-level code sequence. The data transmission device according to claim 9, wherein: The multi-level code sequence is represented by a plurality of bits,
The multi-level code conversion unit outputs some bits of the multi-level code sequence as the converted multi-level code sequence and outputs any one bit of the multi-level code sequence as the inverted signal. The data transmission device according to claim 11, wherein: The multi-level code converter is
A selection random number generator for generating pseudo-random numbers using predetermined selection key information;
Based on the pseudo-random number, a part of the bits of the multi-level code sequence is selected and output as the converted multi-level code sequence, and any one bit of the multi-level code sequence is output as the inverted signal. The data transmission device according to claim 12, further comprising a bit selection unit. The multi-level code sequence is represented by a plurality of bits,
The multi-level code converter is
A part of the bits of the multi-level code string is input, and the input bit is subjected to a logical operation to be converted into a signal having a bit number smaller than the input bit number, and the converted signal is converted into a bit. It has a bit conversion circuit that outputs as a conversion signal,
The remaining bits of the multi-level code sequence and the bit converted signal are output as the converted multi-level code sequence, and any one bit of the multi-level code sequence is output as the inverted signal. The data transmission device according to claim 11. The multi-level code converter is
A random number generator for generating a conversion random number that is a binary random number;
Any one bit of the multi-level code string is input, the exclusive OR of the input one bit and the conversion random number is calculated, and the calculation result is output as the input one bit The data transmission device according to claim 12, further comprising a bit operation circuit that performs the operation. The multi-level code converter is
A random number generator for generating a conversion random number that is a binary random number;
Any one bit of the multi-level code string is input, the exclusive OR of the input one bit and the conversion random number is calculated, and the calculation result is output as the input one bit 15. The data transmission device according to claim 14, further comprising a bit operation circuit that performs the operation. The multi-level signal modulator is
A multi-level code converter that converts the multi-level code string into an inverted signal;
A signal converter that calculates an exclusive OR of the information data and the inverted signal, and outputs the calculation result as a binary conversion signal;
A modulation unit that modulates the binary conversion signal in a predetermined modulation format and outputs the modulated signal as a modulation signal;
The data transmission apparatus according to claim 1, wherein the inverted signal and the binary conversion signal are binary signals having the same bit rate as a symbol rate of the multilevel code sequence. The multi-level code sequence is represented by a plurality of bits,
The data transmission apparatus according to claim 17, wherein the multi-level code conversion unit outputs any one bit of the multi-level code string as the inverted signal. A data receiving device that receives information data encrypted using predetermined key information and performs secret communication with a transmitting device,
A multi-level code generator that generates a multi-level code sequence in which the signal level changes from the key information in a substantially random manner;
A demodulator that demodulates the modulated signal received from the transmitter and outputs a signal having a plurality of levels corresponding to a combination of the information data and the multilevel code sequence;
Based on the multi-level code sequence, comprising a signal reproduction unit for reproducing the information data from the output signal of the demodulation unit,
The signal reproduction unit uses the signal having the same symbol rate as the multilevel code sequence and a multilevel number smaller than the multilevel number of the multilevel code sequence as an identification level, and outputs the output signal of the demodulation unit A data receiving apparatus characterized by identifying. The signal reproduction unit is
A multi-level code conversion unit that converts the multi-level code sequence into a converted multi-level code sequence and an inverted signal according to a predetermined rule;
An identification unit for binary-identifying the multilevel signal based on the converted multilevel code sequence;
A data inversion unit that calculates an exclusive OR of the output signal of the identification unit and the inverted signal, and outputs the calculation result as the information data,
The converted multi-level code sequence is a signal having the same symbol rate as the multi-level code sequence and having a multi-level number smaller than the multi-level number of the multi-level code sequence,
The data receiving apparatus according to claim 19, wherein the inverted signal is a binary signal having the same bit rate as the symbol rate of the multilevel code sequence.   The multi-level code conversion unit converts the multi-level code sequence into the converted multi-level code sequence by allocating one level to a plurality of levels included in the multi-level code sequence. 21. The data receiving apparatus according to claim 20, wherein The multi-level code sequence is represented by a plurality of bits,
The multi-level code converter is
A D / A converter that selects some of the bits of the multi-level code sequence, digital-analog converts the selected bits, and generates the converted multi-level code sequence;
The data receiving apparatus according to claim 21, wherein one of the bits not selected by the D / A converter in the multilevel code string is output as the inverted signal. The multi-level code converter is
A selection random number generator for generating pseudo-random numbers using predetermined selection key information;
A bit selection unit that selects some bits of the multi-level code sequence based on the pseudo-random number;
The D / A conversion unit performs digital / analog conversion on the bits selected by the bit selection unit, and generates the converted multi-level code string,
The data receiving apparatus according to claim 22, wherein the bit selection unit outputs one of the unselected bits of the multi-level code string as the inverted signal. The multi-level code sequence is represented by a plurality of bits,
The multi-level code converter is
A bit conversion circuit that receives a part of bits of the multi-level code string, converts the input bits by a logical operation, and outputs a bit conversion signal having a bit number smaller than the input bit number; ,
A D / A converter that digital-analog converts a bit that is not input to the bit conversion circuit of the multi-level code string and the bit-converted signal, and generates the converted multi-level code string; The data receiving device according to claim 22. The signal reproduction unit is
A multi-level code converter that converts the multi-level code string into an inverted signal;
An identification unit for binary-identifying the multilevel signal based on a predetermined identification level;
A data inversion unit that calculates an exclusive OR of the output signal of the identification unit and the inverted signal, and outputs the calculation result as the information data,
The data receiving apparatus according to claim 19, wherein the inverted signal is a binary signal having the same bit rate as the symbol rate of the multilevel code sequence.

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