WO2018092313A1 - Communication device, communication system and communication method - Google Patents

Abstract

A communication device (1-1) according to the present invention is provided with: a receiver (15) which receives first coded text from a communication device (1-2) serving as a communication partner; a coder (11) which generates second coded text by performing coding using first plaintext to be transmitted at a first time, and second plaintext that is plaintext obtained by decoding the first coded text transmitted from the communication device (1-2) at a second time earlier than the first time; a transmitter (12) which transmits the second coded text to the communication device (1-2); and a decoder (16) which generates the second plaintext by decoding the first coded text using the first plaintext transmitted at the second time.

Description

COMMUNICATION DEVICE, COMMUNICATION SYSTEM, AND COMMUNICATION METHOD

The present invention relates to a communication device, a communication system, and a communication method that perform bidirectional communication while suppressing information leakage and tampering.

In the communications field, information security needs to be strengthened to prevent information leakage and tampering. Information security is to ensure confidentiality, integrity, and availability. In the OSI (Open Systems Interconnection) reference model, the function of enhancing the confidentiality of information is mainly handled by the transport layer of the fourth layer. In the future, in order to improve confidentiality, cross-layer processing in which encryption is performed in a plurality of layers is required. Especially in the physical layer, confidentiality is regarded as important, and it is a problem to improve the confidentiality of data in order to prevent an attack from an eavesdropper on the transmission path. Hereinafter, the original data to be transmitted, that is, data that has not been encrypted or encoded is referred to as plain text.

An encryption algorithm called AES (Advanced Encryption Standard) used in a common key cryptosystem is widely used as a technique for improving the secrecy of a transmission path. However, since AES is an encryption algorithm for unidirectional transmission among communication modes, during bidirectional transmission, the plain text is transmitted in both the forward direction and the opposite direction, which is the reverse direction of the forward direction. AES must be applied. Encryption algorithms other than AES are also intended for unidirectional transmission as in AES, and during bidirectional transmission, a common encryption scheme is applied in each of the forward and opposite directions.

In the common key cryptosystem, since the secret key is used while being updated between the transmitter and the receiver in order to ensure confidentiality, the management of the secret key at the time of bidirectional transmission is complicated.

As a technique for solving the complexity of secret key management, which is a problem in the common key cryptosystem, Patent Document 1 discloses that a ciphertext is generated from a signature generated from plaintext and a sender-side secret key on the transmission side. A method has been proposed in which the original plaintext can be restored by decrypting the signature on the receiver side using the private key on the receiver side.

Japanese Patent Application Laid-Open No. 10-083138

Using the technique described in Patent Document 1, management of the secret key is simplified. However, the technique described in Patent Document 1 is a technique for unidirectional transmission, and encryption is necessary in each of the forward direction and the opposite direction during bidirectional transmission. Common key cryptosystems can be broadly classified into two types: block cryptosystems and stream cryptosystems. The block cipher system is a system that guarantees secrecy by the amount of calculation required for decryption because the length of the secret key is shorter than the plaintext length. The stream encryption method is a method in which the length of the secret key is equal to or longer than the plaintext length, and complete secrecy is guaranteed by a one-time pad. The stream encryption method is a method with high encryption strength that guarantees complete secrecy, but generally the hardware circuit scale is larger than that of the block encryption method.

In recent years, both high confidentiality and reduction in hardware circuit scale have been demanded. For this reason, it is required to reduce the hardware circuit scale while ensuring confidentiality.

This invention is made in view of the above, Comprising: Obtaining the communication apparatus which can suppress the increase in a hardware circuit scale after ensuring the secrecy of a bidirectional transmission path in bidirectional | two-way transmission. Objective.

In order to solve the above-described problems and achieve the object, a communication device according to the present invention includes a receiver that receives a first encoded text from a communication device of a communication partner, and a first that is transmitted at a first time. And a second plaintext obtained by decoding the first encoded text transmitted from the communication device of the communication partner at a second time before the first time. And an encoder for generating a second encoded sentence. In addition, the communication device decodes the first encoded text using the transmitter that transmits the second encoded text to the communication device of the communication partner and the first plaintext that is transmitted at the second time. And a decoder for generating two plaintexts.

The communication apparatus according to the present invention has an effect that it is possible to suppress an increase in the hardware circuit scale while ensuring the secrecy of the bidirectional transmission path in bidirectional transmission.

The figure which shows the structural example of the communication system concerning Embodiment 1. FIG. The figure which shows the concept of the encoding method of Embodiment 1. FIG. The figure which shows an example of data transmission by the encoding of Embodiment 1 FIG. 11 is a sequence diagram illustrating an example of a procedure until the encoded transmission according to the first embodiment is started. The figure which shows the form of the bidirectional | two-way transmission of 1: 1 node of Embodiment 1. The figure which shows the form of bidirectional | two-way transmission of 1: N (N is an integer greater than or equal to 2) of Embodiment 1 The figure which shows the form of the bidirectional | two-way transmission which passes through several nodes of Embodiment 1. The figure which shows the structural example of the communication system concerning Embodiment 2. FIG. The figure which shows the concept of the encoding and encryption method of Embodiment 2. The figure for demonstrating the encryption in the 1st method of Embodiment 2, and an encoding procedure. The figure for demonstrating the encryption in the 2nd method of Embodiment 2, and an encoding procedure. The figure which shows the relationship between the signal point of the quaternary phase modulation signal of Embodiment 3, and the bit value allocated to each signal point The figure which shows the relationship between the signal point of the 16 value phase amplitude modulation signal of Embodiment 3, and the bit value allocated to each signal point The figure which shows the relationship between the signal point of the quaternary phase modulation signal of Embodiment 3, and the bit value allocated to each signal point The figure which shows the relationship between the signal point of the polarization multiplexing 16 value phase amplitude modulation signal of Embodiment 3, and the bit value allocated to each signal point FIG. 4 is a diagram showing a concept of a block encryption method in Embodiment 3 using both the encoding method described in Embodiment 1 and a multi-level phase amplitude modulation method. The figure which shows the frequency arrangement | positioning of the signal comprised from n subchannels of Embodiment 3. FIG. 11 is a diagram illustrating a concept of a block encryption method according to the third embodiment using both the encoding method described in the first embodiment and the multi-channel multilevel phase amplitude modulation method. The figure which shows the calculation amount which an eavesdropper needs for a cryptanalysis with respect to the bit block size of Embodiment 3 FIG. 10 is a diagram illustrating a configuration example of a communication device when a stream data pad method is applied to a multi-level phase amplitude modulation signal using multi-channel according to the third embodiment. The figure which shows the structural example of the control circuit of Embodiment 1 to Embodiment 3.

Hereinafter, a communication device, a communication system, and a communication method according to an embodiment of the present invention will be described in detail based on the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram of a configuration example of a communication system according to the first embodiment of the present invention. As shown in FIG. 1, a communication system 100 according to the present embodiment includes a communication device 1-1 and a communication device 1-2.

As shown in FIG. 1, a communication device 1-1 as a first communication device includes a control unit 10, an encoder 11, a transmitter 12, memories 13, 14, a receiver 15, and a decoder 16. The communication device 1-2, which is the second communication device, has the same configuration as that of the communication device 1-1. The communication device 1-1 and the communication device 1-2 can perform bidirectional communication via the transmission path 2. The transmission path 2 may be a wired transmission path including an optical transmission path or a wireless transmission path. In communication from the communication device 1-1 to the communication device 1-2, the communication device 1-1 is a transmission device, and the communication device 1-2 is a reception device. In communication from the communication device 1-2 to the communication device 1-1, the communication device 1-2 is a transmission device, and the communication device 1-1 is a reception device. Hereinafter, when the communication device 1-1 and the communication device 1-2 are shown without distinction, they are referred to as the communication device 1.

The control unit 10 controls each unit in the communication device 1. The encoder 11 performs encoding based on plaintext that is data to be transmitted and data stored in the memory 13. Further, the encoder 11 stores the plaintext used for encoding, that is, the plaintext to be transmitted, in the memory 14 which is the first memory. The memory 14 stores the plain text used for encoding in the encoder 11. The transmitter 12 transmits the encoded data to the opposite device via the transmission path 2. The receiver 15 receives data from the opposite device and outputs it to the decoder 16. The decoder 16 decrypts the data input from the receiver 15 using the data stored in the memory 14 to obtain plain text, and stores the plain text obtained by the decryption in the memory 13. The memory 13 as the second memory stores the plain text obtained by the decryption. In the configuration example of FIG. 1, the opposite device, that is, the communication partner device for the communication device 1-1 is the communication device 1-2, and the opposite device, that is, the communication partner device for the communication device 1-2 is the communication device 1-1. .

Next, a general common key cryptosystem will be described before describing the encoding of the present embodiment. In communication using a common common key cryptosystem, an encryption device generates a ciphertext by performing encryption using a plaintext and a secret key in a transmission apparatus. Specifically, the encryptor of the transmission apparatus using a general common key cryptosystem encrypts the plaintext D _tA (t) using the secret key K _A (t) and encrypts the ciphertext Y shown in the following formula (1). Generate _A. Note that t indicates time, D _tA (t) indicates plaintext encoded by encoding at time t, and K _A (t) indicates a secret key used for encoding at time t.

The decryptor of the receiving apparatus using a general common key cryptosystem restores the transmitted plaintext D _tA (t) by decrypting the ciphertext Y _A using the secret key K _A (t).

When bidirectional communication is performed using a general common key cryptosystem, encryption and decryption as described above are performed in the forward direction and the opposite direction, respectively. That is, assuming that the above-described processing is processing performed in the forward direction, in the opposite direction transmission, the encryptor of the transmission device encrypts the plaintext D _tB (t) using the secret key K _B (t), and The ciphertext Y _B shown in equation (2) is generated.

The decryptor of the receiving device in the opposite direction transmission decrypts the ciphertext Y _B by using the secret key K _B (t) to restore the transmitted plain text D _tB (t). As described above, when a general common key cryptosystem is used, it is necessary to use a secret key. In order to ensure confidentiality, the secret key is used while being updated between the transmitting device and the receiving device, so that the management of the secret key at the time of bidirectional transmission is complicated in a general common key cryptosystem.

On the other hand, the communication system according to the present embodiment does not require management of a secret key by performing encoding using the characteristics of bidirectional communication, and increases the hardware circuit scale while ensuring secrecy. Suppress. FIG. 2 is a diagram showing the concept of the encoding method of the present embodiment. The encoding method according to the present embodiment will be described with reference to FIGS. In FIG. 2, the communication device 1-1 shown in FIG. 1 is shown on the left side, and the communication device 1-2 shown in FIG. 1 is shown on the right side. Hereinafter, the direction from the communication device 1-1 to the communication device 1-2 is referred to as a forward direction, and the direction from the communication device 1-2 to the communication device 1-1 is referred to as a facing direction.

In the communication device 1-1 that is a transmission device in forward transmission, the encoder 11 calculates an exclusive OR of the plaintext D _tA (t) and the plaintext D _rB (t−Δt) stored in the memory 13. By doing so, the encoded sentence Y ′ _A shown in Expression (3) is calculated. The transmitter 12 of the communication device 1-1 transmits Y ′ _A via the transmission path 2 to the communication device 1-2 that is a reception device in forward transmission. The plaintext D _rB (t-Δt) is the plaintext D _tB (t-Δt) encoded by the communication device 1-2 which is the receiving device in the forward transmission at the time t-Δt. Plain text obtained by being received and decrypted. Δt is the time for which each memory holds data. The transmission time from the communication apparatus 1-2 to the communication apparatus 1-1, obtained by adding the processing time in the communication apparatus 1-1 and the communication apparatus 1-2 times When T _h, Delta] t is the T _h or more values Any value can be set. A method of setting Δt will be described later. Here, it is assumed that the time required for encoding is negligible, and the time when D _tA (t) and D _tB (t) are encoded and the time when they are transmitted are the same. That is, the plain text encoded at time t is transmitted as the encoded text at time t.

In the communication device 1-2 which is a receiving device in forward transmission, the receiver 15 receives Y ′ _A, and the receiver 15 gives the received Y ′ _A to the decoder 16. The decoder 16 calculates the exclusive OR of the encoded text Y ′ _A and the plain text D _tB (t−Δt) stored in the memory 13 to obtain the transmitted plain text D _tA (t). Restore. The plain text D _tB (t−Δt) is plain text encoded by the communication device 1-2 at the time t−Δt, and is stored in the memory 13 by the encoder 11. The plaintext D _rB (t-Δt) is received and restored by the communication device 1-1 after the plaintext D _tB (t-Δt) used for encoding by the communication device 1-2 is encoded. is there. Therefore, the plaintext D _rB (t-Δt) and the plaintext D _tB (t-Δt) match. Therefore, D _tA (t) is restored by exclusive OR of the encoded text Y ′ _A and the plain text D _tB (t−Δt).

Similarly, in transmission in the opposite direction, in the communication device 1-2 which is a transmission device, the encoder 11 _excludes the plaintext D _tB (t) and the plaintext D _rA (t−Δt) stored in the memory 13. By calculating the logical OR, the encoded sentence Y ′ _B shown in Expression (4) is calculated. The transmitter 12 of the communication apparatus 1-2 through the transmission path 2 transmits the Y _'B the opposing direction communication device 1-1 is a receiving apparatus in the transmission of.

In the communication device 1-1 that is a receiving device in transmission in the opposite direction, when the receiver 15 receives Y ′ _B , it inputs it to the decoder 16. The decoder 16 calculates the exclusive OR of the encoded text Y ′ _B and the plain text D _rA (t−Δt) stored in the memory 14, thereby _{obtaining the} transmitted plain text D _tB (t). Restore.

As described above, the receiver 15 of the communication device 1-1 is a first receiver that receives Y ′ _B that is the first encoded text from the communication device 1-2. The encoder 11 of the communication device 1-1, which is the first encoder, transmits the first plaintext D _tA (t) to be transmitted at time t, which is the first time, and the second plaintext before the first time. Encoding using D _rB (t-Δt), which is the second plaintext obtained by decoding the first encoded text transmitted from the communication device 1-2 at time t-Δt, which is time To generate a second encoded sentence Y ′ _A. The transmitter 12 of the communication device 1-1 that is the first transmitter transmits Y ′ _A to the communication device 1-2. The decoder 16 of the communication device 1-1 serving as the first decoder decodes the first encoded text Y ′ _B using the first plaintext D _tA (t−Δt) transmitted to t−Δt. To generate the second plaintext D _rB (t).

The receiver 15 of the communication device 1-2 is a second receiver that receives Y ′ _A that is the second encoded text from the communication device 1-1. The encoder 11 of the communication device 1-2, which is the second encoder, transmits the second plaintext D _tB (t) transmitted at time t and the second plaintext D _tB (t) transmitted from the communication device 1-1 at time t-Δt. and D _rA (t-Δt) of the encoded sentences is first plaintext obtained by decoding, to generate a first encoded sentences Y _'B by carrying out the coding using. The transmitter 12 of the communication device 1-2 which is the second transmitter transmits Y ′ _B to the communication device 1-1. The decoder 16 of the communication device 1-2 as the second decoder decodes the second encoded text Y ′ _A using the second plaintext D _tB (t−Δt) transmitted to t−Δt. To generate a first plaintext D _rA (t).

FIG. 3 is a diagram illustrating an example of data transmission by encoding according to the present embodiment. FIG. 3 shows an example in which each plaintext is composed of 6 bits. Six numerical values such as 110111 indicate examples of 6-bit data values. In the example shown in FIG. 3, it is assumed that 110111 is stored in the memory 13 of the communication device 1-1 as plain text _DrB (t-Δt) received and restored by communication in the opposite direction. As shown in FIG. 3A1, the encoder 11 of the communication device 1-1 exclusively uses 101100, which is plain text D _tA (t), and 110111, which is D _rB (t−Δt), in forward communication. A logical sum is calculated and 011011 is obtained as the encoded sentence Y ′ _A. The encoded text Y ′ _A is transmitted in the forward direction as shown in FIG.

It is assumed that 110111 that is a plaintext D _tB (t−Δt) transmitted from the communication device 1-2 in the past is stored in the memory 14 of the communication device 1-2. Decoder 16 of the communication device 1-2, as shown in FIG. 3 (A3), calculates an exclusive OR of the 110111 is a code-text Y _'A 011011 plaintext D _tB (t-Δt) performs decoding by, obtaining 101100 as D _rA (t) is a plaintext received in the forward communications. Since D _rA (t) is the reconstructed D _tA (t), the communication apparatus 1-2 determines 101100, which is the plaintext D _tA (t) transmitted from the communication apparatus 1-1, by the above processing. Can be restored.

Further, it is assumed that 010101 is stored in the memory 13 of the communication device 1-2 as the plain text _DrA (t-Δt) received and restored by communication in the opposite direction. In the communication in the opposite direction, the encoder 11 of the communication device 1-2, as shown in FIG. 3 (B1), 110011 which is plaintext D _tB (t) and 010101 which is plaintext D _rA (t−Δt). The exclusive OR is calculated and 100110 is obtained as the encoded sentence Y ′ _B. The encoded text Y ′ _B is transmitted in the opposite direction as shown in FIG. 3 (B2).

It is assumed that 010101 is stored in the memory 14 of the communication device 1-1 as the plaintext D _tA (t−Δt) transmitted from the communication device 1-1 in the past. Decoder 16 of the communication apparatus 11, as shown in FIG. 3 (B3), calculates an exclusive OR of the 010101 is a code-text Y _'B 100110 plaintext D _tA (t-Δt) Thus, decryption is performed, and 110011 is obtained as _DrB (t) which is a plaintext received in the opposite communication. Since D _rB (t) is the restored D _tB (t), the communication apparatus 1-1 has received 110011, which is the plaintext D _tB (t) transmitted from the communication apparatus 1-2, through the above processing. Can be restored.

Next, the procedure until the above-described encoded transmission is started will be described. FIG. 4 is a sequence diagram illustrating an example of a procedure until the encoded transmission of the present embodiment is started. Hereinafter, the mode in which the communication apparatus 1-1 and the communication apparatus 1-2 perform the above-described encoded transmission is referred to as an encoded transmission mode. Before the start of the sequence shown in FIG. 4, it is assumed that the communication device 1-1 and the communication device 1-2 are not performing the above-described encoded transmission.

First, the control unit 10 of the communication device 1-1 transmits a notification ACK for starting the encoded transmission mode to the communication device 1-2 via the transmitter 12 (step S1). When the control unit 10 of the communication apparatus 1-2 receives the notification ACK of the start of the encoded transmission mode via the receiver 15, the control unit 10 transmits a RES, which is a response indicating that the notification is accepted, via the transmitter 12. To the communication device 1-1 (step S2).

Next, the control unit 10 of the communication apparatus 1-1 determines whether data is transmitted between the communication apparatus 1-1 and the communication apparatus 1-2 in order to determine the time Δt for holding the plaintext during transmission in the opposite direction in the memory. Using the MEA, which is a signal for measuring the time spent for one round trip, the time spent for one round trip of data between the communication device 1-1 and the communication device 1-2 is measured (step S3). ). That is, the communication device 1-1 stores the time when the MEA is transmitted, and stores the time when the response to the MEA is received. Then, the difference between the time when the response to the MEA is received and the time when the MEA is transmitted is calculated as the time spent for one round trip. As the MEA, any signal may be used as long as the reception device returns a response as soon as it is received. The signal for measurement may be any signal.

Next, the control unit 10 of the communication device 1-1 determines the calculated time spent for one round trip as the memory retention time, and transmits the memory retention time information storing the memory retention time to the communication device 1-2. (Step S4). As a result, the memory holding time is shared between the communication device 1-1 and the communication device 1-2. When receiving the memory retention time information, the control unit 10 of the communication device 1-2 transmits RES, which is a response indicating that the notification has been received, to the communication device 1-1 (step S5). The control unit 10 of the communication device 1-1 and the communication device 1-2 controls the memory 13 and the memory 14 so that the data retention time in the memory 13 and the memory 14 becomes the above-described memory retention time. As a result, the oldest data stored in each memory becomes data at a time before the current time t by the memory holding time Δt. Note that the memory holding time can be set to an arbitrary value equal to or longer than the time spent for one round trip.

Next, the control unit 10 of the communication device 1-1 transmits a data transmission start notification to the communication device 1-2 (step S6). When receiving the notification of the start of data transmission, the control unit 10 of the communication device 1-2 transmits RES, which is a response indicating that the notification has been received, to the communication device 1-1 (step S7).

Next, in the forward transmission, the communication device 1-1 generates a ciphertext by encoding a plaintext by using a predetermined fixed secret key or a secret key generated by higher layer processing as an initial vector. Then, the ciphertext is transmitted to the communication device 1-2 (step S8). At the start of encoded transmission, the plaintext received by the transmission in the opposite direction is not stored in the memory 13. For this reason, in step S8, the communication apparatus 1-1 performs encoding using the above-described initial vector instead of the plain text received in the memory 13 by transmission in the opposite direction. The communication device 1-1 stores the transmitted plain text in the memory 14. The plaintext at the start of data transmission refers to the first frame when the plaintext is transmitted in units of frames, and in the case of stream transmission, refers to the arbitrarily set bits from the start of transmission.

The communication device 1-2 decrypts the encoded text received by the forward transmission using the same secret key as that used by the communication device 1-1 for encoding, and stores the decrypted text in the memory 13. Further, as described above, the communication device 1-2 encodes and transmits the plaintext to be transmitted in the opposite direction using the plaintext stored in the memory 13 (step S9). The communication device 1-1 decodes the encoded text received by the transmission in the opposite direction using the plain text stored in the memory 14. Further, the communication device 1-1 encodes and transmits the plain text to be transmitted in the forward direction using the plain text stored in the memory 13 (step S10). The communication device 1-2 decodes the encoded text received by the forward transmission using the plain text stored in the memory 14. Further, the communication device 1-2 encodes and transmits the plain text to be transmitted in the opposite direction using the plain text stored in the memory 13 (step S11). Thereafter, step S10 and step S11 are repeated until the end of encoded transmission.

Note that the encoding method described in the present embodiment can be applied without depending on the network form. For example, a bidirectional transmission form of 1: 1 node as shown in FIG. 5 similar to FIG. 1 may be used, or both 1: N (N is an integer of 2 or more) nodes as shown in FIG. It may be in the form of bidirectional transmission. Moreover, the form of bidirectional transmission via a plurality of nodes as shown in FIG. 7 may be used. The communication device 1-2 to the communication device 1-5 illustrated in FIG. 6 have the same configuration as the communication device 1-1. The communication devices 3-1 to 3-3 shown in FIG. 7 are not particularly limited in configuration as long as the communication devices have a relay function.

As described above, the present embodiment uses the fact that the communication apparatuses 1-1 and 1-2 perform bidirectional communication, that is, the communication apparatuses 1-1 and 1-2 are also transmitting apparatuses and are in the reverse direction. Utilizing the fact that it is also a receiving device in transmission, the transmitted plaintext is stored in the memory 13 and encoding is performed using the plaintext obtained by restoring the received data. That is, the plaintext received in the past is used as a key for encryption, and the plaintext transmitted in the past is used as a key for decryption. As a result, the communication devices 1-1 and 1-2 can decrypt the received data using the plaintext transmitted by the communication devices 1-1 and 1-2. Also, since the plaintext used for decryption by the decoder is information that can only be obtained by the communication partner, confidentiality can be ensured. Furthermore, since the processing can be realized by a circuit that performs exclusive OR with the memory, it can be realized by simple hardware.

Embodiment 2. FIG.
FIG. 8 is a diagram illustrating a configuration example of a communication system according to the second exemplary embodiment of the present invention. As shown in FIG. 8, the communication system 100a of the present embodiment includes a communication device 1a-1 and a communication device 1a-2.

As shown in FIG. 8, the communication device 1a-1 includes an encryptor 17 that is an encoder according to the present embodiment instead of the encoder 11 according to the first embodiment, and instead of the decoder 16 according to the first embodiment. Except for the provision of the decoder 18, it is the same as the communication apparatus 1-1 of the first embodiment. Components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant description is omitted. The configuration of the communication device 1a-2 is the same as that of the communication device 1a-1. Hereinafter, the direction from the communication device 1a-1 as the first communication device to the communication device 1a-2 as the second communication device is referred to as the forward direction, and from the communication device 1a-2 to the communication device 1a-1. The direction is called the facing direction.

In this embodiment, the encoding method described in Embodiment 1 and the common key encryption method are used in combination. FIG. 9 is a diagram showing the concept of the encoding and encryption method of the present embodiment. In the present embodiment, the encryptor 17 of the communication device 1a-1 includes the plaintext D _tA (t), the plaintext D _rB (t−Δt) stored in the memory 13 of the communication device 1a-1, and the secret key K _A ( A coded sentence transmitted in the forward direction is generated by exclusive OR with t). The decoder 18 of the communication device 1a-2 performs exclusive OR of the encoded text transmitted in the forward direction, the plaintext D _tB (t−Δt) stored in the memory 14 and the secret key K _A (t). By calculating, the plaintext D _tA (t) transmitted from the communication device 1a-1 is restored.

Similarly, in the opposite direction transmission, the encryption device 17 of the communication device 1a-2 performs the plaintext D _tB (t), the plaintext D _rA (t−Δt) stored in the memory 13 of the communication device 1a-2, and the secret key K. A coded sentence transmitted in the opposite direction is generated by exclusive OR with _B (t). The decoder 18 of the communication device 1a-1 performs an exclusive OR operation between the encoded text transmitted in the opposite direction, the plaintext D _tA (t−Δt) stored in the memory 14, and the secret key K _B (t). By calculating, the plaintext D _tB (t) transmitted from the communication device 1a-2 is restored. _A method for generating and updating a secret key K _A (t) and a secret key K _B (t), which are common secret keys between the communication device 1-1 and the communication device 1-2, is a common common key encryption method. Although the method may be used, the memory holding time described in Embodiment 1 may be used as a secret key. As described in the first embodiment, the memory holding time is shared between the communication device 1-1 and the communication device 1-2. For this reason, the memory retention time can be used as the above-described common secret key.

Specific implementation forms when the encoding system and the common key encryption system described in Embodiment 1 are used in combination include the following two forms of the first method and the second method. FIG. 10 is a diagram for performing an encryption and encoding procedure in the first method. The first method shown in FIG. 10 is a scheme in which the transmitting device encodes the plaintext to be transmitted using the plaintext received from the opposite device after encrypting with the secret key.

As shown in (A11) of FIG. 10, in forward transmission, the encryptor 17 of the communication device 1a-1 transmits plaintext D _tA (t) transmitted in the forward direction with 001010 which is the secret key K _A (t). Is encrypted by an exclusive logical operation to generate a ciphertext 100110. Thereafter, as shown in FIG. 10 (A12), the encryptor 17 of the communication device 1a-1 performs an exclusive OR operation between the ciphertext ₁₀₀₁₁₀ and the plaintext _DrB (t−Δt) ₁₁₀₁₁₁ received in the communication in the opposite direction. Is obtained as an encoded sentence. This encoded text is transmitted in the forward direction as shown in FIG. 10 (A13).

As shown in (A14) of FIG. 10, the decoder 18 of the communication device 1a-2 exclusively receives the received encoded text 010001 and the plain text D _tB (t−Δt) 110111 transmitted in the opposite direction. Decrypt by logical operation. Thereafter, as shown in (A15) of FIG. 10, a decoder 18 of the communication device 1a-2 is decoded by an exclusive logical operation between the result of decryption 100110 and a secret key K _A (t) 001010 To obtain plain text D _rA (t) 101100 received in the forward direction. D _rA (t) is the same as D _tA (t) transmitted in the forward direction.

Further, in the transmission of the opposite direction, as shown in (B11) of FIG. 10, the encryptor 17 of the communication device 1a-2 is plaintext D _tB to transmit at 010101 and opposing direction is the private key K _B (t) ( The ciphertext 100110 is generated by encrypting 110011 that is t) by an exclusive logical operation. Thereafter, as shown in FIG. 10 (B12), the exclusive logical sum of the encryptor 17 of the communication device 1a-2 is a plaintext D _rA received by the communication ciphertext 100110 and forward (t-Δt) 100011 000101 is generated as an encoded sentence. This encoded text is transmitted in the opposite direction as shown in FIG. 10 (B13).

As shown in (B14) of FIG. 10, the decoder 18 of the communication device 1a-1 exclusively uses the received encoded text 00101 and the plaintext D _tA (t−Δt) 1000011 transmitted in the forward direction. Decrypt by logical operation. Thereafter, as shown in (B15) of FIG. 10, the decryptor 18 of the communication device 1a-2 decrypts the result of the decryption by the exclusive logical operation of 100110 as the decrypted result and 010101 as the secret key K _B (t). _And plaintext D _rB (t) 110011 received in the opposite direction is obtained. D _rB (t) is the same as D _tB (t) transmitted in the forward direction.

FIG. 11 is a diagram for performing encryption and encoding procedures in the second method. The second method shown in FIG. 11 is a method in which the transmitting device performs an exclusive logical operation on a secret key and a plaintext received in the past used as a kind of key in advance and then performs an exclusive logical operation on the plaintext.

In the second method, as shown in (A21) of FIG. 11, in the transmission of the forward, encryptor 17 of the communication device 1a-1 is a received in the opposing direction of the communication plaintext D _rB (t-Δt) An exclusive logical operation of a certain 110111 and a secret key K _A (t) 001010 is performed to generate 111101 as an encryption key. Next, as shown in (A22) of FIG. 11, the encryptor 17 of the communication device 1a-1 performs exclusive logic on the encryption key 111101 and the plaintext D _tA (t) 101100 transmitted in the forward direction. An encoded sentence 010001 is generated by encoding by calculation. This encoded text is transmitted in the forward direction as shown in FIG. 11 (A23).

As shown in (A21 ′) of FIG. 11, the decryptor 18 of the communication device 1a-2 has 110111 as the plaintext D _tB (t−Δt) transmitted in the opposite direction and 000010 as the secret key K _A (t). And 111101 is generated as an encryption key. As shown in (A24) of FIG. 11, the decryptor 18 of the communication device 1a-2 decrypts the encryption key 111101 and the received encoded text 010001 by an exclusive logical operation, and sequentially The plaintext D _rA (t) 101100 received in the direction is obtained. D _rA (t) is the same as Dt _A (t) transmitted in the forward direction.

Also in the opposite direction, as shown in FIG. 11, when the communication device 1a-2 transmits the plaintext D _tB (t) 110011, (B21) to (B24) and (B21 ′) are changed as in the forward direction. As a result, the communication device 1a-1 _obtains the plaintext D _rB (t) 110011 received in the opposite direction.

As described above, in the present embodiment, the encoding method described in the first embodiment and the common key cryptosystem are used in combination. Thereby, it is possible to improve confidentiality as compared with the first embodiment.

Embodiment 3 FIG.
The coding schemes of the first and second embodiments can be considered as a stream type scheme, but in this embodiment, a scheme for further improving the cryptographic strength by using together with the block type cryptographic scheme. Will be explained. As a specific method, a rule such as assigning each bit information in the bit block included in the received symbol to which bit information in the transmission bit block is assigned to the reference table. And the confidentiality of the data in a transmission line can be improved by sharing the information of a reference table between a transmitter and a receiver. Further, when the bit block size is increased, the possible combinations of received data assigned to transmission data are increased and the key space is expanded, so that the confidentiality of data is improved.

As a method for increasing the bit block size, there is a form using a modulation technique or a signal processing technique. As a method for increasing the bit block size using a modulation technique, there is a multi-valued method using a phase amplitude modulation method. That is, there is a method of transmitting the encoded text after performing multi-value amplitude phase modulation. Further, as a technique for increasing the bit block size using a signal processing technique, there is a method of sub-channeling using a plurality of carriers, that is, a method of transmitting a coded sentence using a plurality of frequencies.

When mapping symbols to bit blocks during modulation, the modulation process is performed using bit numbers b _{i, j} (i = 1, 2,..., M) (j = 1, 2,..., N) in the bit blocks. It can be expressed by an m × n matrix as an element. m is the number of bit blocks and n is the number of subchannels. i indicates the number of a bit block resulting from the modulation scheme, and j is a number indicating a subchannel.

FIG. 12 is a diagram showing the relationship between the signal points of the quaternary phase modulation signal on the IQ plane and the bit values assigned to the signal points. FIG. 13 is a diagram showing the relationship between the signal points of the 16-level phase amplitude modulation signal on the IQ plane and the bit values assigned to the signal points. In FIG. 12 and FIG. 13, in the bit numbers b _{i, j} , j is fixed and the description is omitted and shown as b _i . In addition, i is 1, 2,.

In optical communications, polarization multiplexing technology that puts information on polarization is used. FIG. 14 is a diagram illustrating the relationship between the signal points of the quaternary phase modulation signal and the bit values assigned to the signal points. FIG. 15 is a diagram illustrating a relationship between signal points of the polarization multiplexed 16-level phase amplitude modulation signal and bit values assigned to the signal points. In FIG. 14 and FIG. 15, i = 1, 2,... In order from the most significant bit of the X polarization, and the bit number following the least significant bit of the X polarization is the most significant bit of the Y polarization. The bit number i is determined so that the bit number increases from the most significant bit to the lower bit of the polarization.

FIG. 16 is a diagram showing a concept of a block encryption method using both the encoding method described in the first embodiment and the multi-level phase amplitude modulation method. FIG. 16 shows an example in which the encoding method and the 16-level phase amplitude modulation method are used in combination.

As shown in (A31) of FIG. 16, in forward transmission, the transmitting apparatus _converts 0111, which is plaintext _DrB (t−Δt) received in transmission in the opposite direction, into a bit string according to a reference table held in advance. Bit string conversion based on rules. In the example shown in FIG. 16, a rule for converting the first and third upper bits is used. As shown in (A32) of FIG. 16, the transmitting device, code statements coded by an exclusive logical operation 1011 and a plaintext D _tA sent in 1101 and forward is a data bit string conversion (t) 0110 is generated as follows. As shown in (A33) of FIG. 16, the encoded text 0110 is modulated by the 16-value phase amplitude modulation method and transmitted in the forward direction.

The receiving apparatus in the forward transmission receives the modulated signal, demodulates the analog signal, and calculates 0110 which is an encoded sentence. Then, as shown in (A34) of FIG. 16, the receiving apparatus decodes the encoded text 0110 and the plain text D _tB (t−Δt) 1101 transmitted in the opposite direction by performing an exclusive logical operation. , 1011 which is the plaintext D _rA (t) received in the forward transmission is obtained. As shown in (A35) of FIG. 16, the receiving device converts 1011 as plain text _DrA (t) into 1011 according to the bit string conversion rule of the same reference table as the reference table used by the transmitting device and stores it in the memory. Store. The plaintext D _rA (t) stored here is subjected to an exclusive logical operation with the plaintext that is bit-string converted and transmitted in the opposite transmission when encoding in the opposite direction transmission is performed later. That is, the plaintext D _rA (t) is used in the FIG. 16 (B31). In the transmission in the opposite direction, (B31) to (B36) are performed as in the forward transmission.

FIG. 17 is a diagram showing a frequency arrangement of a signal composed of n subchannels. In order from the subchannel on the low frequency side, j is set to 1, 2,. FIG. 18 is a diagram showing the concept of a block encryption method using both the encoding method described in the first embodiment and the multichannel multilevel phase amplitude modulation method. The multi-channel multi-level phase amplitude modulation method is a method in which subchannelization and multi-level phase amplitude modulation method are combined. In the example shown in FIG. 18, a case where a 2-subchannel 16-value phase amplitude modulation method is applied is shown.

As shown in (A41) of FIG. 18, in forward transmission, the transmission device converts 01111001, which is plaintext _DrB (t−Δt) received in transmission in the opposite direction, into a bit string by a reference table that is held in advance. Bit string conversion based on rules. In the example shown in FIG. 18, it is assumed that a rule for converting the first upper bit of the first subchannel and the first lower bit of the second subchannel is used. As shown in (A32) of FIG. 18, the transmission apparatus encodes 11111000 which is data after bit string conversion and 10110110 which is plaintext D _tA (t) transmitted in the forward direction by an exclusive logical operation. 01101110 is generated as As shown in (A43) of FIG. 18, the encoded text 01101110 is modulated by the 2-subchannel 16-value phase amplitude modulation method and transmitted in the forward direction.

The receiving device in the forward transmission receives the modulated signal, demodulates the analog signal, and calculates 11111000 which is an encoded sentence. Then, as shown in (A44) of FIG. 18, the receiving apparatus decodes the encoded text 11111000 and the plaintext D _tB (t−Δt) 11111000 transmitted in the opposite direction by performing an exclusive logical operation. , 10110110, which is the plaintext D _rA (t) received in the forward transmission. Receiving apparatus, as shown in (A45) of FIG. 18, in accordance with the bit string conversion rule of the same reference table and the reference table transmitting device is used, by converting 10110110 a plaintext D _rA (t) to 00110111 in the memory Store. In the transmission in the opposite direction, (B41) to (B46) are performed as in the forward transmission.

For example, in the case of a quaternary phase modulation system using 5 subchannels, (m, n) is (2, 5), and the bit block size is 10 bits.

For example, in the case of a polarization multiplexing quaternary phase modulation system using 5 subchannels, (m, n) is (4, 5), and the bit block size is 20 bits.

FIG. 19 is a diagram showing the amount of calculation that an eavesdropper needs to decrypt for the bit block size. In FIG. 19, the horizontal axis indicates the bit block size, and the vertical axis indicates the calculation time. In FIG. 19, the calculation time for the bit block size in AES is shown as a characteristic 501, and the calculation time for the bit block size of the present embodiment is shown as a characteristic 502. For example, when the encryption strength equivalent to commercially available 256-bit AES is realized by the method of this embodiment, the bit block size may be 60 bits.

FIG. 20 is a diagram illustrating a configuration example of the communication apparatus 200 when the stream data pad method is applied to a multi-level phase amplitude modulation signal using multi-channel. The communication device 200 includes a transmission device 5, a reception device 6, and a data processing unit 70. The data processing unit 70 includes a first memory 71, a second memory 72, a reference table processing unit 73, and a hard decision unit 74.

The 1: nDeMUX (demultiplexer) 51 of the transmission device 5 branches n bits of serial data to be transmitted into n bits for each bit, and branches to 1: mDeMUX (demultiplexer) 52-1 to 52-n. Output each data. 1: The mDeMUXs 52-1 to 52-n branch the input data every m bits. 1: Data output from the mDeMUXs 52-1 to 52-n is stored in the first memory 71. Further, the data stored in the second memory 72 is bit string converted by the reference table processing unit 73. 1: Data output from mDeMUXs 52-1 to 52-n are encoded by performing an exclusive logical operation on the result of bit string conversion, and input to signal point map units 53-1 to 53-n. .

Signal point map units 53-1 to 53-n assign signal points to the input data, and output the data after assigning the signal points to digital filters 54-1 to 54-n, respectively. The digital filters 54-1 to 54-n shape the frequency shape of the input data and output it to the n: 1 MUX (multiplexer) 56. The n: 1 MUX 56 multiplexes the input data and outputs the multiplexed data to a DAC (Digital to Analog Converter) 57. The DAC 57 converts the input data into an analog signal and outputs it to the driver 58. The driver 58 amplifies the input analog signal and outputs it to the modulator 59. The modulator 59 modulates the input signal and outputs it as a transmission signal.

In the receiving device 6, the receiver 61 receives the transmitted signal and outputs it to an ADC (Analog to Digital Converter) 62. The ADC converts the input signal into a digital signal and outputs it to the 1: nDeMUX 63. 1: nDeMUX 63 branches the signal into n and outputs the branched signals to digital filters 64-1 to 64-n, respectively. Each of the digital filters 64-1 to 64-n corresponds to one subchannel, and performs filtering so as to transmit the signal of the corresponding subchannel and outputs the filtered signals to the equalizers 65-1 to 65-n. The equalizers 65-1 to 65-n perform processing for compensating for the influence of the transmission path on the data received from the digital filters 64-1 to 64-n, and the processed data is processed by the data processing unit 70. Output to. The hard decision unit 74 of the data processing unit 70 makes a hard decision on the input signal, restores the original bit value, and outputs it to the reference table processing unit 73. The reference table processing unit 73 performs bit string conversion using the reference table, and stores the converted value in the second memory 72.

The data output from the equalizers 65-1 to 65-n is subjected to an exclusive logical operation with data obtained by rearranging the data stored in the second memory 72 by the reference table processing unit 73. The result of this exclusive logical operation is received by m: 1 MUX 66-1 to 66-n. m: 1 MUX 66-1 to 66-n combine the received data and output as received data.

As described above, in the present embodiment, the example in which at least one of the modulation technique and the signal processing technique is used in combination with the encoding of the first embodiment has been described. Thereby, confidentiality can be further improved as compared with the first embodiment.

Of the constituent elements described in the first to third embodiments, each other than the receiver, transmitter, and memory is realized by a processing circuit. The processing circuit may be an analog circuit or a digital circuit. The processing circuit may be dedicated hardware or a control circuit including a processor. Note that the encoder, the encryptor, and the decoder that perform the encoding according to the present invention can be realized by an exclusive OR circuit. When at least a part of the constituent elements described in the first to third embodiments is realized by a control circuit, the control circuit has, for example, the configuration shown in FIG.

FIG. 21 is a diagram illustrating a configuration example of the control circuit. The control circuit 300 includes a processor 301 and a memory 302. The processor 301 is a CPU (Central Processing Unit), a microprocessor, or the like. When at least some of the components described in the first to third embodiments are realized by a control circuit, each unit realized in the control circuit executes a program stored in the memory 302 by the processor 301 Is realized. The memory 302 is also used as a storage area when a program is executed by the processor 301.

The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1-1 to 1-5, 1a-1, 1a-2, 200 communication device, 5 transmission device, 6 reception device, 10 control unit, 11 encoder, 12 transmitter, 13, 14 memory, 15 receiver, 16 , 18 Decryptor, 17 Encryptor, 70 Data processing unit, 100, 100a communication system.

Claims (11)

A receiver for receiving a first encoded text from a communication device of a communication partner;
Obtained by decoding the first plaintext transmitted at the first time and the first encoded text transmitted from the communication device of the communication partner at the second time before the first time A second plaintext, and an encoder that performs encoding using and generates a second encoded text;
A transmitter for transmitting the second encoded text to the communication partner communication device;
A decoder for decoding the first encoded text using the first plaintext transmitted at the second time to generate the second plaintext;
A communication apparatus comprising: A first memory in which the first plaintext is stored;
A second memory in which the second plaintext is stored;
The communication apparatus according to claim 1, further comprising: The encoder is configured to decode the first plaintext transmitted at the first time and the first encoded text transmitted from the communication device of the communication partner at the second time. The communication apparatus according to claim 1, wherein the second encoded text is generated by performing encoding using two plaintexts and a secret key shared with the communication apparatus of the communication partner. The encoder is configured to decode the first plaintext transmitted at the first time and the first encoded text transmitted from the communication device of the communication partner at the second time. The communication apparatus according to claim 2, wherein the second encoded text is generated by performing encoding using a plaintext of 2 and a secret key common to the communication apparatus of the communication partner. The time that the first memory holds the first plaintext and the time that the second memory holds the second plaintext are the same memory holding time, and the memory holding time is the secret key The communication apparatus according to claim 4, wherein the communication apparatus is used as a communication apparatus. The encoder performs first encoding using the first plaintext to be transmitted at the first time and the secret key, and at the second time and the result of the first encoding. 6. The second encoding using the second plaintext obtained by decoding the first encoded text transmitted from a communication apparatus of a communication partner is performed. The communication apparatus as described in any one. The encoder uses the second plaintext obtained by decrypting the first encoded text transmitted from the communication device of the communication partner at the second time, and the first using the secret key. The second encoding using the result of the first encoding and the first plaintext to be transmitted at the first time is performed. The communication apparatus as described in any one. The communication apparatus according to any one of claims 1 to 7, wherein the second encoded text is subjected to multi-level phase amplitude modulation and transmitted. The communication apparatus according to any one of claims 1 to 8, wherein the second encoded text is transmitted using a plurality of frequencies. A communication system comprising a first communication device and a second communication device that is a communication device of a communication partner of the first communication device,
The first communication device is:
A first receiver for receiving a first encoded text from the second communication device;
Obtained by decoding the first plaintext transmitted at the first time and the first encoded text transmitted from the second communication device at the second time prior to the first time A first encoder that performs encoding using the second plaintext to generate a second encoded text;
A first transmitter for transmitting the second encoded text to the second communication device;
A first decoder for decoding the first encoded text received from the second communication device using the first plaintext transmitted at the second time to generate the second plaintext; ,
With
The second communication device is:
A second receiver for receiving a second encoded text from the first communication device;
A second plaintext transmitted at the first time, and a second plaintext obtained by decoding the second encoded text transmitted from the first communication device at the second time, A second encoder that performs encoding using and generates the first encoded sentence;
A second transmitter for transmitting the first encoded text to the first communication device;
A second decoder for decoding the second encoded text received from the first communication device using the second plaintext transmitted at the second time to generate the first plaintext; ,
A communication system comprising: A communication method in a communication system comprising a first communication device and a second communication device that is a communication device of a communication partner of the first communication device,
In forward transmission, which is a direction from the first communication device to the second communication device,
The first plaintext transmitted by the first communication device at a first time, and the first encoded text transmitted from the second communication device at a second time before the first time. A first plaintext obtained by decoding the first plaintext, and a first step of generating a second encoded text by performing encoding using
A second step in which the first communication device transmits the second encoded text to the second communication device;
The second communication device decodes the second encoded text received from the first communication device by using the second plaintext transmitted at the second time and decodes the first plaintext. A fourth step of generating;
Including
In opposite direction transmission, which is a direction from the second communication device to the first communication device,
The second plaintext transmitted by the second communication device at the first time and the second encoded text transmitted from the first communication device at the second time are obtained by decoding. A second step of generating the first encoded text by performing encoding using the second plaintext received,
A sixth step in which the second communication device transmits the first encoded text to the first communication device;
The first communication device decodes the first encoded text received from the second communication device using the first plaintext transmitted at the second time, and the second plaintext is decoded. A seventh step of generating;
A communication method comprising:

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