JP2017046268A - Communication device, transmission device, and reception device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication device that safely communicates data without impairing a real-time property in a control field.SOLUTION: A transmission port 12 of a transmission unit 4 in a transmission side communication device 2A transmits a communication frame data in which an encoded electronic signature including clocking counter information, a check code, a sequence number, and a random number is added to control communication data. An information extraction unit of a reception unit in a reception side communication device 2B decodes the electronic signature extracted from the communication frame data received by the reception port, and extracts the clocking counter information, check code, sequence number, and random number from the decoded electronic signature. A determination unit checks the extracted clocking counter information, check code, and sequence number, and permits a control device 3 to take in the control communication data if it determines that the communication frame data is normal.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a communication device, a transmission device, and a reception device suitable for performing secure control communication in a control system such as a plant.

  In recent years, in the control field, plant control solutions that fuse information and control, such as IoT (Internet Of Things), have been attracting worldwide attention. Nowadays, the application of this plant control solution is expanding especially in the field of FA (Factory Automation) and PA (Process Automation).

  The technology used for the plant control solution is considered to drastically improve the operation efficiency and the production efficiency of the plant control. On the other hand, since the outside of the plant and the plant control system are more closely coupled than before by passing through the information network, there is a concern that a new security hole may be generated in the network.

  Conventionally, in the information processing field, a technology that protects information as a property by using encryption technology represented by AES (Advanced Encryption Standard) or the like against a security attack from a malicious third party has been used. .

  For example, Patent Literature 1 discloses a method for outputting a frame using a common key from a random number generated based on timekeeping information as an authentication method between communication devices.

JP 2007-221204 A

  By the way, the network used in the control system mostly transmits process input / output values, which are quantified physical phenomena that change every moment, as control communication data. Is not necessarily required. For example, the valve opening / closing information is not highly confidential. On the other hand, in control transmission, it is essential that each communication device can transmit and receive data in real time.

  However, since the technology disclosed in Patent Document 1 realizes security by encoding and decoding information (random numbers) in a form that is difficult to decipher mathematically, it takes a lot of time for processing by a computer. As a result, it has been difficult to divert the encryption technology disclosed in Patent Document 1 as it is to a control system where real-time performance is important. Further, in the technique disclosed in Patent Document 1, even if an attacker makes an attack by acquiring a data frame and impersonating, an effective countermeasure is not disclosed in Patent Document 1.

  The present invention has been made in view of such a situation, and an object thereof is to communicate data safely without impairing real-time performance.

A communication apparatus according to the present invention includes a transmission unit having an electronic signature generation unit and a transmission port, and a reception unit having a reception port, an information extraction unit, and a determination unit.
The electronic signature generation unit of the transmission unit includes a first check code generated based on control communication data received from the control device, a first sequence number indicating a transmission order of communication frame data, and a random number in predetermined units. An electronic signature is generated by converting a block composed of a set of bit sequences separated and rearranged in a predetermined order by an encoder.
The transmission port transmits communication frame data obtained by adding an electronic signature to control communication data to another communication device.
The reception port of the reception unit extracts an electronic signature from communication frame data received from another communication device.
The information extraction unit extracts the first check code, the first sequence number, and the random number in the reverse order from the predetermined order from the block obtained by reversely converting the electronic signature by the decoder.
The determination unit compares the extracted first check code with the second check code generated from the control communication data of the communication frame data, the extracted first sequence number, and the communication frame data of the previous period. When the communication frame data is determined to be normal based on the result of comparison with the second sequence number added to, the control device allows the control communication data to be captured.

According to the present invention, the electronic signature added to the communication frame data includes a random number, and the reception unit can quickly detect tampering with the communication frame data. For this reason, when invalid communication frame data is detected, only effective control communication data can be captured by taking measures such as discarding the communication frame data.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a system configuration diagram of a communication system according to a first exemplary embodiment of the present invention. It is a schematic block diagram of two communication apparatuses which concern on the 1st Example of this invention. It is a block diagram which shows the internal structural example of the transmission part which concerns on the 1st Example of this invention. It is a block diagram of the communication frame data which concerns on the 1st Example of this invention. It is a time chart which shows the flow of the signal in each signal path of the transmission part which concerns on the 1st Example of this invention. It is a block diagram which shows the internal structural example of the receiving part which concerns on the 1st Example of this invention. It is explanatory drawing which shows the example of the state transition of the authentication determination circuit based on the 1st Example of this invention. It is explanatory drawing which shows the example of the state transition of the authentication determination circuit based on the 2nd Example of this invention. It is a system configuration | structure figure of the communication system which concerns on the modification of embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same function or configuration are denoted by the same reference numerals, and redundant description is omitted.

[1. First Embodiment]
FIG. 1 is a system configuration diagram of the communication system 1.

  The communication system 1 includes a plurality of communication devices 2A to 2M connected to a network N. The communication devices 2A to 2M can communicate with each other. In the example of FIG. 1, the communication device 2A transmits communication frame data to the communication device 2B via the network N, and the communication device 2A receives communication frame data from the communication device 2E via the network N. Has been. Although FIG. 1 shows an example in which the network N is a ring network connection form, the network N may be another connection form.

  FIG. 2 is a schematic configuration diagram of the two communication devices 2A and 2B.

  The communication device 2A has a function of transmitting communication frame data to other communication devices and receiving communication frame data from other communication devices.

The communication device 2A includes a control device 3, a transmission unit 4, and a reception unit 5.
The control device 3 of the communication device 2A outputs communication frame data including control communication data to the communication device 2B to the transmission unit 4, and receives control communication data received by the reception unit 5 from the communication device 2B.
The transmission unit 4 of the communication device 2A encrypts the communication frame data input from the control device 3 by a predetermined process, and transmits the communication frame data to the communication device 2B via the network N. The control communication data includes, for example, a command for controlling plant equipment and a process input / output value from the plant.
The receiving unit 5 of the communication device 2A decrypts the encrypted communication frame data received from the communication device 2B, and outputs control communication data to the control device 3 if the result of checking the decrypted communication frame data is normal. To do.

The communication device 2B includes a control device 3, a transmission unit 4, and a reception unit 5, similarly to the communication device 2A.
The control device 3 of the communication device 2B outputs communication frame data including control communication data to the transmission unit 4, and receives the control communication data received by the reception unit 5 from the communication device 2A.
The transmission unit 4 of the communication device 2B encrypts the communication frame data input from the control device 3 by a predetermined process, and transmits the communication frame data to the communication device 2A via the network N.
The receiving unit 5 of the communication device 2B decrypts the encrypted communication frame data received from the communication device 2A, and outputs the control communication data to the control device 3 if the result of checking the decrypted communication frame data is normal. To do.

  Next, configuration examples and operation examples of the transmission unit 4 and the reception unit 5 will be described. First, the transmission unit will be described.

FIG. 3 is a block diagram illustrating an internal configuration example of the transmission unit 4.
The transmission unit 4 extracts a circuit (electronic signature generation unit 6) that generates an electronic signature and a circuit (transmission port 12) that transmits the electronic signature by adding the electronic signature to communication frame data from the components of the communication device 2A. It is a thing.

First, the configuration of each unit of the transmission unit 4 will be described.
The transmission unit 4 includes a frame transmission control circuit 11, a transmission port 12, a time counter circuit 13, a check code generation circuit 14, a frame sequence number generation circuit 15, a random number generator 16, a block generation unit 17, a multiplexer 18, a conversion table 19, A PS conversion circuit 20 is provided. In the present embodiment, each component other than the transmission port 12 in the transmission unit 4 is collectively referred to as an electronic signature generation unit 6.

  The frame transmission control circuit 11 takes in communication frame data including control communication data from the control device 3 through the signal path d1. The frame transmission control circuit 11 transmits predetermined signals to the time counter circuit 13, the check code generation circuit 14, the frame sequence number generation circuit 15, the random number generator 16, the block generation unit 17, the multiplexer 18, and the PS conversion circuit 20. Then, each part is controlled.

Here, the configuration of communication frame data will be described.
FIG. 4 is a frame format showing a configuration example of communication frame data.

  The communication frame data according to the present embodiment includes header information (communication header f1, IP header f2, UDP header f3), control communication data f4 received from the control device 3, electronic signature f5, and FCS (Frame Check Sequence) f6. Consists of each field. The header information is provided in common for each communication frame data to be transmitted, and is generated by the frame transmission control circuit 11. Also, the mounting location of the electronic signature f5 in the communication frame data is not limited. The electronic signature f5 includes encoded time counter information f11, a check code f12, a sequence number f13, and a random number f14. In the following description, the communication header f1, the IP header f2, the UDP header f3, and the control communication data f4 may be collectively referred to as “frame information”.

The check code f12 is generated using the header information and the control communication data f4 as a check range. The reason for the check range is that the purpose of the check code is to detect that the control communication data has been tampered with.
FCS f6 is generated using the frame information and electronic signature f5 as a check range. The reason for this check range is that the purpose of the FCS is to detect garbled communication frame data, and the garbled data of the electronic signature f5 is also included in the object.
In the following description, the header information and the control communication data f4 without the electronic signature f5 and FCS f6 may also be referred to as communication frame data.

The description of FIG. 3 will be continued again.
The electronic signature generation unit 6 separates the check code f12 generated based on the control communication data f4 received from the control device 3, the sequence number f13 indicating the transmission order of the communication frame data, and the random number f14 in predetermined units. . Then, an electronic signature f5 is generated by converting the blocks d8 to d10 composed of the bit number sequence set obtained by rearranging these pieces of information in a predetermined order using the conversion table 19.

  The time counter circuit 13 generates time counter information f11 in the transmission unit 4 by a time measuring operation and outputs it to the signal path d4. The time counter information f11 generated by the time counter circuit 13 is synchronized with the time counter information timed by other communication devices. It is possible to synchronize the time counter circuit 13 to the time counter circuit 37 when the time counter circuit 37 shown in FIG. 6 to be described later is synchronized with another communication device.

The check code generation circuit 14 (an example of a first check code generation unit) generates a check code f12 from the header information received from the frame transmission control circuit 11 and the control communication data f4, and outputs the check code f12 to the signal path d5.
The frame sequence number generation circuit 15 (an example of a sequence number generation unit) generates a sequence number f13 indicating the transmission order of communication frame data and outputs it to the signal path d6. The sequence number f13 is a value (n) obtained by incrementing the sequence number (n-1) of the communication frame data transmitted in the previous cycle by "1".

  The random number generator 16 (an example of a random number generation unit) generates a random number f14 and outputs it to the signal path d7. The electronic signature encoding method according to the present embodiment is realized using a random number f14. As a method for the random number generator 16 to generate a random number, for example, an M-sequence (LFSR) or a pseudo-random number generation method using Xorshift is used. In addition, for example, a generation method based on a ring oscillator type true random number using metastability of a flip-flop as described in Japanese Patent No. 4982750 may be used, and the method is not limited to one method. However, as the electronic signature encoding method, an inexpensive method that does not impair high speed when transmitting communication frame data is adopted.

  The block generation unit 17 extracts the unit fixed length bits separated from the time counter information f11, the check code f12, the sequence number f13, and the random number f14 in units of single bits or in units of multiple bits. Then, the block generation unit 17 generates a plurality of blocks d8 to d10 including a bit number sequence set obtained by rearranging the separated unit fixed length bits.

The multiplexer 18 (an example of a selection circuit) sequentially selects any one of the plurality of blocks d8 to d10 generated by the block generation unit 17 and outputs the selected blocks to the conversion table 19.
The conversion table 19 (an example of an encoder) converts and encodes a plurality of blocks d8 to d10 that are sequentially input from the multiplexer 18.
A PS (Parallel / Serial) conversion circuit 20 converts the encoded bit sequence set into serial data to generate an electronic signature f5, and outputs the electronic signature f5 to the transmission port 12.
As described above, the multiplexer 18, the conversion table 19, and the PS conversion circuit 20 are used as an encoding unit 21 that converts a plurality of blocks d8 to d10 using the conversion table 19 to generate an electronic signature f5.

  The transmission port 12 adds the electronic signature f5 and the FCS f6 generated by the transmission port 12 to the communication frame data (header information and control communication data f4) received from the frame transmission control circuit 11. The transmission port 12 transmits the communication frame data to the communication device 2B through the network N.

Next, the operation of each unit of the transmission unit 4 will be described with reference to the time chart of FIG.
FIG. 5 is a time chart showing a signal flow in each signal path of the transmission unit 4.

The communication frame data transmission process of the communication device 2A is started in response to a transmission request made from the control device 3 to the transmission unit 4.
The frame transmission control circuit 11 issues a check code generation control signal d3 to the check code generation circuit 14 (FIG. 5B) while capturing the communication frame data via the signal path d1 of the communication frame data (FIG. 5A). Upon receiving the check code generation control signal d3, the check code generation circuit 14 generates a check code f12 based on the frame information (FIGS. 4 and 5D).

  The check code generation circuit 14 generates the check code f12 using a CRC (Cyclic Redundancy Check) that requires less circuit resources, but may generate the check code f12 by a method other than CRC. The generation and check range of the check code f12 covers the communication header f1 to the control communication data f4 as shown in FIG.

  While the check code generation circuit 14 is generating the check code f12, the frame transmission control circuit 11 causes the transmission port 12 to transmit frame information to the network N (FIG. 5K).

  When the input of the control communication data f4 to the transmission port 12 is completed after the transmission port 12 transmits the frame information, the frame transmission control circuit 11 issues an increment of the frame sequence number and a latch control signal d2 ( FIG. 5C). The frame sequence number generation circuit 15 increments the current frame sequence number by “1” at the timing at which the increment of the frame sequence number and the latch control signal d2 are input (FIG. 5F). Then, the frame sequence number generation circuit 15 sends the incremented frame sequence number to the signal path d6 of the frame sequence number.

  The time counting operation of the time counter circuit 13 is always performed (FIG. 5E). Therefore, the time counter information timed by the time counter circuit 13 always flows through the signal path d4 of the time counter information. Similarly, the operation in which the random number generator 16 generates a random number is always performed (FIG. 5G). For this reason, the random number generated by the random number generator 16 always flows through the signal path d7 of the random number information.

  When a communication request is generated and the frame sequence number increment and the latch control signal d2 are issued, the block generation unit 17 obtains the time counter information, check code, frame sequence number, and random number flowing through the signal paths d4 to d7. get. Then, the block generator 17 separates these pieces of information in units of 1 bit or more. Further, the block generation unit 17 generates a bit number sequence in which the separated time counter information, check code, frame sequence number, and random number are rearranged, and a plurality of blocks d8˜ Divide into d10.

  The plurality of blocks d8 to d10 are required to store time counter information, check code, frame sequence number, and random number, respectively, at least 1 bit. If this requirement can be satisfied, there is no upper or lower limit to the bit length of the block. The greater the number of random bits per block, the greater the complexity of irregular changes in the encoded code, which will be described later.

Each of the plurality of blocks d8 to d10 includes an arbitrary 1 bit of the signal path d4 of the clock counter information, an arbitrary 1 bit of the signal path d5 of the check code, an arbitrary 1 bit of the signal path d6 of the frame sequence number, and a random number It is composed of 3 bits (6 bits in total) of the information signal path d7.
Arbitrary bits constituting the plurality of blocks d8 to d10 are irreversible codes and cannot be decoded unless they are arranged in the same manner on the transmission side and the reception side. As long as reversibility can be maintained, arbitrary bits may be used in a plurality of blocks. As the number of patterns in which the plurality of blocks d8 to d10 can change irregularly increases, the generation pattern of the encoded code observed in the network N increases and the encryption strength of the communication frame data can be further increased.

  Subsequently, the frame transmission control circuit 11 activates the selection control signal d12 of the plurality of blocks d8 to d10 (FIG. 5H). As a result, the frame sequence number generation circuit 15 latches the current states of the N blocks d8 to d10 in accordance with the increment of the frame sequence number and the latch control signal d2.

  Then, the multiplexer 18 switches the order of the plurality of blocks d8 to d10 to be input, and outputs the plurality of blocks d8 to d10 to the conversion table 19. A plurality of blocks d8 to d10 are encoded by the conversion table 19, respectively. The plurality of encoded blocks d8 to d10 are output from the conversion table 19 to the PS conversion circuit 20 through the signal path d14 of the selected encoded code (FIG. 5I).

  The conversion table 19 is a so-called “common key”. The relationship between the input and the output of the conversion table 19 does not need to have mathematical regularity, and may be an irregular value. However, the data converted by the conversion table 19 needs to have reversibility. That is, the data output from the conversion table 19 needs to be able to restore the original input data by inverse conversion. By storing such a conversion table 19 in a rewritable storage unit such as a RAM (Random Access Memory) or a flash ROM (Read Only Memory), it is possible to cope with periodic content changes. As a result, even if the information in the conversion table 19 leaks to the outside, it is possible to minimize the loss of data due to an attack from the outside by quickly switching the conversion table 19.

  Next, the frame transmission control circuit 11 activates the parallel / serial conversion control signal d13 of the encoded code (FIG. 5J). The PS conversion circuit 20 converts each of the plurality of encoded blocks d8 to d10 from parallel data to serial data. Each of the plurality of blocks d8 to d10 converted into serial data is sequentially sent to the transmission port 12 as an electronic signature f5. The electronic signature f5 is also sent to the frame transmission control circuit 11, and the frame transmission control circuit 11 generates FCS f6.

  The transmission port 12 adds each of the plurality of blocks d8 to d10 converted to serial data as an electronic signature f5 to the end of the communication frame data received from the frame transmission control circuit 11. Next, the transmission port 12 adds the FCS f6 generated by the frame transmission control circuit 11 to the end of the electronic signature f5 using the frame information of the communication frame data and the electronic signature f5 as a check range. Then, the transmission port 12 transmits the communication frame data to which the electronic signature f5 and FCS f6 are added to the destination communication device 2B via the network N.

Next, a configuration example and an operation example of the reception unit 5 of the communication device 2B will be described.
FIG. 6 is a block diagram illustrating an internal configuration example of the receiving unit 5.

  The receiving unit 5 includes a circuit (reception port 31) that extracts the electronic signature f5 from the received communication frame data, and a circuit that decrypts the electronic signature f5 and extracts each piece of information (information extraction unit) among the components of the communication device 2B. 7) and a circuit for determining information (determination unit 8). By decoding the electronic signature f5, the time counter information f11, the check code f12, the sequence number f13, and the random number f14 are extracted from the communication frame data.

  The reception unit 5 includes a reception port 31, a frame reception control circuit 32, an SP (Serial / Parallel) conversion circuit 33, an inverse conversion table 34, a demultiplexer 35, and a bit extraction unit 36. The receiving unit 5 includes a time counter circuit 37, a check code generation circuit 39, a sequence number previous cycle storage circuit 41, a first storage circuit 43, and a second storage circuit 44. In this embodiment, these circuits are collectively referred to as an information extraction unit 7.

  The receiving unit 5 includes a first determination circuit 38, a second determination circuit 40, a third determination circuit 42, a fourth determination circuit 45, and an authentication determination circuit 46. In the present embodiment, the first determination circuit 38, the second determination circuit 40, the third determination circuit 42, the fourth determination circuit 45, and the authentication determination circuit 46 are collectively referred to as the determination unit 8.

  The reception port 31 receives the communication frame data transmitted by the communication device 2A via the network N, outputs the communication frame data to the frame reception control circuit 32, and SP-converts the electronic signature f5 extracted from the communication frame data. Output to the circuit 33.

  The frame reception control circuit 32 transmits the communication frame data received by the reception port 31 to the control device 3 through the signal path d21. The frame reception control circuit 32 transmits predetermined data and signals to the SP conversion circuit 33, the inverse conversion table 34, the demultiplexer 35, the bit extraction unit 36, the time counter circuit 37, the check code generation circuit 39, and the determination circuit. Control each part.

  The information extraction unit 7 checks the check code f12 and the sequence number f13 in the reverse order from the predetermined order performed by the digital signature generation unit 6 of the transmission unit 4 from the blocks d27 to d29 obtained by reverse conversion of the electronic signature f5 by the reverse conversion table 34. , And a random number f14.

At this time, the SP conversion circuit 33 converts the electronic signature f5 input from the reception port 31 into parallel data.
The inverse conversion table 34 (an example of a decoder) decrypts the electronic signature f5 converted into parallel data.
The demultiplexer 35 (an example of a distribution circuit) distributes the electronic signature f5 decrypted by the inverse conversion table 34 to a plurality of blocks d27 to d29 composed of a bit number sequence set.
As described above, the SP conversion circuit 33, the inverse conversion table 34, and the demultiplexer 35 are used as a decoding unit 30 that performs inverse conversion of the electronic signature f5 by the inverse conversion table 34 and decodes it into a plurality of blocks d27 to d29.

  The bit extraction unit 36 extracts one or more arbitrary bits each having a unit fixed length from the blocks d27 to d29, rearranges the arbitrary bits in a predetermined order, and counts time counter information f11, check code f12, sequence number f13 and random number f14 are extracted. The extracted time counter information f11, check code f12, sequence number f13, and random number f14 are output to signal paths d30, d31, d32, and d33, respectively.

  Then, when the determination unit 8 determines that the communication frame data is normal based on the comparison result of the time counter information, the check code, and the sequence number, the determination unit 8 permits the control device 3 to capture the control communication data. Specifically, the determination unit 8 performs the following comparison.

The time counter circuit 37 (an example of the second time counter information generation unit) outputs the time counter information (an example of the second time counter information) generated by the time measurement operation to the first determination circuit 38.
The first determination circuit 38 (an example of the current cycle difference determination unit) compares the time counter information measured by itself with the time counter information timed by another communication device. For example, the first determination circuit 38 determines that the difference between the time counter information generated by the time counter circuit 37 and the time counter information f11 extracted from the blocks d27 to d29 by the bit extraction unit 36 is a predetermined error (second It is determined whether or not it is within a range of (example of error). Then, the first determination circuit 38 outputs the determination result to the authentication determination circuit 46.

The check code generation circuit 39 (an example of a second check code generation unit) secondly determines a check code (an example of the second check code) generated based on the frame information of the communication frame data received by the reception port 31. Output to the circuit 40.
The second determination circuit 40 (an example of a check code determination unit) determines whether or not the check code of the communication frame data has been tampered with. For example, the second determination circuit 40 determines the difference between the check code generated by the check code generation circuit 39 and the check code f12 extracted from the blocks d27 to d29 by the bit extraction unit 36, and authenticates the determination result. Output to the circuit 46.

The sequence number previous cycle storage circuit 41 (an example of the sequence number storage unit) stores the sequence number f13 of the previous cycle decoded from the electronic signature f5 in the reception process of the previous cycle, and the sequence number f13 of the previous cycle is stored in the first cycle. 3 is output to the determination circuit 42.
The third determination circuit 42 (an example of a sequence number determination unit) determines whether the sequence numbers added to the communication frame data of the previous cycle and the current cycle match or do not match. For example, the third determination circuit 42 extracts the sequence number f13 extracted from the communication frame data of the previous cycle stored in the sequence number previous cycle storage circuit 41 and the communication frame data of the current cycle by the bit extraction unit 36. A difference from the sequence number f13 is determined. Then, the third determination circuit 42 outputs the determination result to the authentication determination circuit 46.

The first storage circuit 43 (an example of a first time counter information storage unit) stores time counter information f11 extracted from communication frame data in the current cycle.
The second storage circuit 44 (an example of a second time counter information storage unit) stores time counter information f11 extracted from the communication frame data of the previous cycle.
The clock counter information f11 of the previous period stored in the first storage circuit 43 is shifted and stored in the second storage circuit 44 when the reception port 31 receives the next communication frame data. The first memory circuit 43 stores the current period clock counter information f11 extracted from the blocks d27 to d29.

  The fourth determination circuit 45 (an example of the inter-period difference determination unit) determines whether or not the difference between the previous period and the current period clock counter information f11 is within the range of an allowable error (an example of the first error). . For example, in the fourth determination circuit 45, the difference between the current period time counter information f11 stored in the first memory circuit 43 and the previous period time counter information f11 shifted to the second memory circuit 44 is an allowable error. It is determined whether it is within the range, and the determination result is output to the authentication determination circuit 46.

  The authentication determination circuit 46 (an example of an authentication determination unit) authenticates the electronic signature f5 based on the determination results input from the first determination circuit 38, the second determination circuit 40, the third determination circuit 42, and the fourth determination circuit 45. Then, it is determined whether or not the control communication data f4 is captured. The authentication determination circuit 46 permits the control device 3 to capture the control communication data f4 when the permission determination is made, and discards the communication frame data when the control communication data f4 is determined not to be permitted. A detailed example of the authentication process of the electronic signature f5 performed by the authentication determination circuit 46 will be described later with reference to FIG. Then, the authentication determination circuit 46 outputs the determination result to the control device 3. The control device 3 takes in the control communication data from the communication frame data based on the determination result.

In order for the determination unit 8 to authenticate that it is communication frame data transmitted by the regular communication device 2A, it is necessary to satisfy all of the following three requirements (1) to (3).
(1) The receiving unit 5 compares the time counter information f11 extracted from the communication frame data with the time counter information timed by its own time counter circuit 37 to obtain a time counter information difference, and this difference is determined in advance. Within the specified tolerance.
(2) The check code f12 extracted from the communication frame data matches the content of the check code calculated based on the frame information of the received communication frame data.
(3) The sequence number f13 of the current cycle is not the same as the sequence number f13 attached to the communication frame data of the previous cycle.
Note that the random number f14 extracted by the bit extraction unit 36 is a decoy (囮) implemented for the purpose of increasing the encryption strength on the network N, and is discarded.

An example of communication frame data reception processing performed by the reception unit 5 will be described below.
The frame reception control circuit 32 starts reception processing of communication frame data when the reception port 31 starts receiving communication frame data, and issues a check code generation control signal d23 to the check code generation circuit 39. . Upon receiving the check code generation control signal d23, the check code generation circuit 39 generates a check code f12 based on the frame information of the communication frame data received from the frame reception control circuit 32 through the signal path d21. When the input of the control communication data f4 is completed, the frame reception control circuit 32 cancels the check code generation control signal d23 and completes the generation of the check code f12 by the check code generation circuit 39.

  Subsequently, when the electronic signature f5 is input to the reception port 31, the electronic signature f5 is output to the frame reception control circuit 32 and the SP conversion circuit 33. When the frame reception control circuit 32 activates the serial / parallel conversion control signal d24 of the encoded code, the SP conversion circuit 33 converts the encoded code (electronic signature f5) into parallel data. Then, the SP conversion circuit 33 sequentially inputs the encoded code converted into the parallel data into the inverse conversion table 34 (an example of a decoder). The encoded code converted into parallel data and input to the inverse conversion table 34 is decoded into a bit sequence set.

  When the encoded code is decoded into the bit number sequence set, the frame reception control circuit 32 activates a distribution control signal d25 for distributing the bit number sequence set into blocks. A distribution control signal d25 is supplied to the demultiplexer 35 (an example of a distribution circuit). The demultiplexer 35 distributes and stores the decoded bit sequence set into a plurality of N blocks d27 to d29.

  When the storage of the bit sequence set in the plurality of blocks d27 to d29 is completed, the frame reception control circuit 32 issues the bit extraction signal d26 to the bit extraction unit 36 and issues the authentication determination execution signal d22 to the determination circuit. The bit extraction unit 36 extracts arbitrary bits corresponding to the time counter information f11, the check code f12, and the sequence number f13 through the signal paths d30, d31, and d32 from the plurality of blocks d27 to d29 according to the bit extraction signal d26. Note that the bit corresponding to the random number f14 extracted through the signal path d33 is discarded.

  The determination circuit that has received the authentication determination execution signal d22 from the frame reception control circuit 32 performs the following determination processing. Depending on the results of these determination processes, the state of the authentication determination circuit 46 changes as shown in FIG.

Next, a method of synchronizing the time counter information generated by the time counter circuit 37 performed between the communication device 2B (self device) and the communication device 2A (other device) will be described.
In the embodiment of the present invention, authentication by electronic signature cannot be performed in a so-called unsynchronized state where synchronization is not performed between the communication devices 2A and 2B.

  However, if the digital signature authentication cannot be performed on the communication frame data itself that transfers information used to synchronize the time counter information, the security risk that the information used to synchronize the time counter information is impersonated by an attacker. There is. For this reason, it is necessary to perform digital signature authentication for information used to synchronize time counter information. Therefore, in the present embodiment, the receiving unit 5 that is out of synchronization and in an incomplete synchronization state authenticates the electronic signature f15 by the following determination method.

  As a premise of this determination method, a communication device (for example, the communication device 2A) serving as a master of time counter information needs to transmit communication frame data at a predetermined arbitrary cycle. The communication frame data to be transmitted may be dedicated for synchronization or may be obtained by diverting normal communication frame data.

  When receiving the communication frame data from the communication device 2A, the reception unit 5 in the incomplete synchronization state extracts the time counter information f11 decoded through the SP conversion circuit 33, the inverse conversion table 34, the demultiplexer 35, and the bit extraction unit 36. To do. Similarly, after the check code f12 extracted from the communication frame data is determined by the second determination circuit 40 and the sequence number f13 is determined by the third determination circuit 42, the time counter information f11 is temporarily stored in the first storage circuit 43. The

  Next, when receiving the communication frame data of the current cycle (n + 1 cycle) from the communication device 2A, the receiving unit 5 performs the decoding process again, extracts the time counter information f11 from the communication frame data of the current cycle, and checks the check code. Check f12 and sequence number f13. When the following first and second requirements are satisfied, the information extraction unit 7 stores the time counter information f11 of the current period (n + 1 period) in the first memory circuit 43 and is stored in the first memory circuit 43. The clock counter information f11 of the previous period (n period) is shifted and stored in the second memory circuit 44. The first requirement is that the check code f12 extracted from the communication frame data matches the check code generated from the frame information of the communication frame data. The second requirement is that the sequence number f13 extracted from the communication frame data is different from the sequence number f13 of the previous cycle stored in the sequence number previous cycle storage circuit 41.

  Then, the fourth determination circuit 45 calculates the difference between the previous cycle and the current cycle time counter information f11 stored in the first storage circuit 43 and the second storage circuit 44, respectively, as an allowable error (first error in the frame transmission interval time). Compared with the range of (example). The fourth determination circuit 45 determines that the time counter circuit 37 may be synchronized with the time counter circuit of another communication device if the difference is within the allowable error range of the frame transmission interval time. Then, the time counter circuit 37 synchronizes the time counter information timed by the time counter circuit 37 to the time counter information f11 by copying the time counter information f11 of the current period stored in the first memory circuit 43 to itself. It becomes possible to do.

  FIG. 7 is an explanatory diagram illustrating an example of state transition of the authentication determination circuit 46.

As described above, the time counter circuit 37 of the receiving unit 5 transitions between the synchronization incomplete state (asynchronous state) and the synchronous state with the master communication device. Then, if the time counter circuit 37 is in an incomplete synchronization state, the authentication determination circuit 46 has two authentication steps (first and second authentication steps) until the time counter circuit 37 transitions from the synchronization incomplete state to the synchronization state. ) Is required.
The reason why the authentication determination circuit 46 requires two authentication steps as described above is as follows.
In control communication,
When communication frame data is exposed to disturbance such as transient noise generated in the network N, a phenomenon (uncertainty) in which a part of the communication frame data is temporarily lost may occur. When the uncertainty occurs, the authentication determination circuit 46 may discard the communication frame data of the current cycle that should be normally determined due to the frame loss of the previous cycle due to transient noise. . The operation of discarding the communication frame data in the current cycle in this way is not only unnecessarily weakening the transient error tolerance in communication, but also cannot be allowed because communication frame data cannot be continuously transmitted and received. . Therefore, if the time counter circuit 37 is in an incomplete synchronization state, the reception unit 5 uses the first memory circuit 43 and the second memory circuit 44 to generate the time counter generated by the time counter circuit 37 between the master communication devices. A synchronization process for synchronizing counter information is performed. In this synchronization process, the authentication determination circuit 46 of the receiving unit 5 employs a two-step authentication step. In the first authentication step, if both the second determination circuit 40 and the third determination circuit 42 are OK determination and the fourth determination circuit 45 is NG determination, the state of the authentication determination circuit 46 is changed from the authentication non-determination 53 to the state. This is a process for authenticating the transition to the authentication intermediate determination OK51. In the second authentication step, if the second determination circuit 40, the third determination circuit 42, and the fourth determination circuit 45 are all OK, the state of the authentication determination circuit 46 is changed from the authentication non-determination 53 to the authentication determination OK 52. It is a process of authenticating
In the following, in the incomplete synchronization state in which the time counter information generated by the other communication device serving as the master and the time counter information generated by the time counter circuit 37 of the receiver 5 are not synchronized, the authentication determination circuit 46 The state transition that transitions to the synchronous state will be described.

  In the present embodiment, the state of the authentication determination circuit 46 is divided into a time counter synchronization incomplete state 50 and a time counter synchronization state 60. In the time counter synchronization incomplete state 50, the authentication determination circuit 46 transitions between the authentication intermediate determination OK51, the authentication determination OK52, the authentication not determination 53, and the authentication determination NG54. In the time counter synchronization state 60, the authentication determination circuit 46 transitions between the authentication determination OK 61, the authentication not determined 62, and the authentication not determined 63 states.

  First, the description will be started from the unauthenticated determination 53 in the initial state where the time counter information is incomplete. The authentication non-determination 53 is in the time counter synchronization incomplete state 50, and at this time, the first determination circuit 38 that performs the allowable error determination of the time counter information generated by the time counter circuit 37 does not function.

  The second determination circuit 40 compares the decoded check code f12 input through the signal path d31 with the check code generated from the communication frame data by the check code generation circuit 39, and determines whether the check codes match. Is determined (second determination process). The second determination circuit 40 outputs an OK determination to the authentication determination circuit 46 if the check codes match, and outputs an NG determination if they do not match. If the check codes do not match, it means that the attacker may have rewritten the frame information.

  The third determination circuit 42 compares the decoded sequence number f13 of the current cycle input through the signal path d32 with the sequence number f13 of the previous cycle stored in the sequence number previous cycle storage circuit 41. Then, the third determination circuit 42 determines whether or not these sequence numbers do not match (third determination process). The third determination circuit 42 outputs an OK determination to the authentication determination circuit 46 if the sequence numbers do not match, and outputs an NG determination if they match. Matching sequence numbers means that the attacker has stolen communication frame data on the network N and received communication frame data that may have been copied.

  In the fourth determination circuit 45, the difference between the time counter information stored in the first memory circuit 43 and the time counter information stored in the second memory circuit 44, which is input through the signal path d30, is within an allowable error range. Is determined (fourth determination process). The fourth determination circuit 45 outputs an OK determination to the authentication determination circuit 46 if the time counter information difference is within the allowable error range, and outputs an NG determination if the difference is outside the range. That the difference in the time counter information is outside the allowable error range means that the received communication frame data is not received at regular intervals, and the control communication data cannot be used. In the initial state, the time counter information is stored in the first memory circuit 43, but nothing is stored in the second memory circuit 44. Therefore, the fourth determination circuit 45 outputs an NG determination.

  If the second determination circuit 40 and the third determination circuit 42 determine that the check code and sequence number determination results are OK, respectively, and the fourth determination circuit 45 determines that the time counter information is NG, the state of the authentication determination circuit 46 is Then, the process proceeds from the authentication non-determination 53 to the authentication intermediate determination OK 51 (first authentication step). If the second determination circuit 40 or the third determination circuit 42 determines that either the check code or the sequence number is NG, the state of the authentication determination circuit 46 transitions to the authentication determination NG54. At this time, the authentication determination circuit 46 discards the received communication frame data.

After the transition to the authentication intermediate determination OK 51, the authentication determination circuit 46 outputs the authentication determination report signal d 34 to the first storage circuit 43 and the second storage circuit 44. When the authentication determination report signal d34 is input, the time counter information stored in the first memory circuit 43 is shifted to the second memory circuit 44.
After the time counter information is shifted, the received communication frame data is discarded, and the state of the authentication determination circuit 46 returns to the authentication non-determination 53 again.

  If the state of the authentication determination circuit 46 is the authentication determination NG 54, the time counter information stored in the first storage circuit 43 is not shifted to the second storage circuit 44. The reason for this is that either the second determination circuit 40 or the third determination circuit 42 determines NG, and it is clear that the received communication frame data was transmitted by a malicious third party (attacker). Because there is. For this reason, the second storage circuit 44 should not be overwritten with the time counter information stored in the received communication frame data, and the received communication frame data is discarded, and the state of the authentication determination circuit 46 is not authenticated. Return to 53.

  When the receiving unit 5 receives the communication frame data of the next cycle, the same reception process as when the communication frame data is received in the current cycle is performed. As a result, the fourth determination circuit 45 makes a difference between the time counter information of the current cycle newly stored in the first memory circuit 43 and the time counter information of the previous cycle stored in the second memory circuit 44 after being shifted. Can be compared.

  Then, the fourth determination circuit 45 outputs an OK determination to the authentication determination circuit 46 if the difference of the time counter information is within the allowable error range. At the same time, if the second determination circuit 40 and the third determination circuit 42 also output OK determination to the authentication determination circuit 46, the state of the authentication determination circuit 46 transitions from the authentication non-determination 53 to the authentication determination OK 52 (second authentication). Step). The authentication determination circuit 46 then outputs an authentication determination report signal d34 to the control device 3 in an OK manner. Thereby, the control device 3 can fetch the control communication data f4 of the communication frame data from the frame reception control circuit 32.

  The authentication determination report signal d34 is also input to the time counter circuit 37. Thereby, the time counter information timed by the time counter circuit 37 is rewritten with the value of the time counter information f11 extracted from the received communication frame data. Thereby, the communication device 2A on the transmission side and the communication device 2B on the reception side complete the synchronization of the time counter information.

  When the communication frame data reception process and the time counter information synchronization process are completed, the state of the authentication determination circuit 46 transitions to the authentication non-determination 62 in the time counter synchronization state 60. In the subsequent reception process, not the fourth determination circuit 45 but the first determination circuit 38 operates and takes over the authentication process.

  In the first determination circuit 38, the time counter information f11 decoded from the received communication frame data input through the signal path d30 is compared with the time counter information output from the time counter circuit 37, and an error in the time counter information is detected. It is determined whether it is within the allowable error range.

  If all the determination results of the first determination circuit 38, the second determination circuit 40, and the third determination circuit 42 are OK at the timing when the authentication determination execution signal d22 is issued by the frame reception control circuit 32, the authentication determination circuit 46 The state changes from authentication not determined 62 to authentication determination OK 61. Then, the authentication determination circuit 46 outputs the authentication determination report signal d34 to the control device 3, thereby simultaneously performing the communication frame data reception process and the time counter circuit 37 synchronization process. Further, the control device 3 can fetch the control communication data f4 of the communication frame data from the frame reception control circuit 32.

  If at least one of the determination results of the first determination circuit 38, the second determination circuit 40, and the third determination circuit 42 is NG, the state of the authentication determination circuit 46 transitions to the authentication determination NG 63 when the authentication is not determined 62, and the authentication The determination circuit 46 discards the received communication frame data.

  As long as normal communication continues, the time counter circuit 37 periodically receives the authentication determination report signal d34 from the authentication determination circuit 46, and synchronizes the time counter information. However, when the reception of the authentication determination report signal d34 is delayed so that the deviation of the time counter information becomes unacceptable, the time counter circuit 37 outputs the time counter synchronization timeout occurrence signal d35 to the authentication determination circuit 46. When receiving the time counter synchronization timeout occurrence signal d35 from the time counter circuit 37, the state of the authentication determination circuit 46 changes from the authentication non-determination 62 to the authentication non-determination 53 of the time counter synchronization incomplete state 50. As a result, the clock counter information is synchronized again.

  According to the communication system 1 according to the first embodiment described above, the electronic signature f5 is generated using the random number f14 every time communication frame data is transmitted. Since the random number f14 has nothing to do with the control communication data f4 of the communication frame data, the contents of the electronic signature f5 appearing on the network N change irregularly. For this reason, it is possible to make it difficult to decrypt the electronic signature f5 by eavesdropping by a third party.

  Further, it is possible to cope with the risk that the attacker captures the communication frame data and continuously issues the communication frame data captured by impersonation to the communication device to stagnate the operation of the control system. In this case, the time counter in the electronic signature f5 stored in the communication frame data is continuously received by the receiving unit 5 in a frozen state. For this reason, the receiving unit 5 can determine that the time counter information in the frozen state is out of the allowable error range by comparing the time counter information, and discard the communication frame data.

  Further, there is a case where the attacker captures the communication frame data at high speed within the allowable error range of the time counter information, and falsifies the control communication data f4 while leaving only the electronic signature f5. Even in this case, the receiving unit 5 can discard the communication frame data because the check code f12 does not match.

  In addition, when an attacker operating at high speed continuously issues communication frame data captured locally for the purpose of overloading, the sequence number f13 appears to be frozen without being incremented. The communication frame data can be discarded by the check.

  The above authentication process is performed on communication frame data that has passed the FCS check. For this reason, detecting communication frame data whose authentication is discarded may determine that there is a possibility that a third party who has artificially intervened illegally exists.

  Therefore, the system administrator considers that a security attack has been received if the detection of the authentication cancellation state frequently occurs per unit time. Then, any one of the communication devices 2A to 2M suspected of being attacked is disconnected from the control system, and a decrementing operation corresponding to the communication device, switching of the operating system, or temporarily stopping the control system itself is taken. be able to.

  In addition, the present embodiment can be realized with a simple and small-scale hardware resource, and can be easily implemented in an FPGA (Field Programmable Gate Array) or the like. Although the functions according to the present embodiment can be implemented by software, if hardware, normal frame processing and authentication processing can be performed in parallel, so there is no time overhead. In addition, since the function of the authentication determination circuit 46 can be implemented in the layer 2 or lower referred to in the OSI reference model when realized by hardware, even if there is an overload attack, processing in the layer 3 or higher is not compressed. , Has the characteristics.

  As a method for adding a signature to an electronic document, there is a method using a time stamp service of an electronic document standardized by ISO / IEC18014. In this service, a time-stamping authority (TSA) generates a time-stamp token that combines a hash value and a time stamp of an electronic document, and issues the time-stamping certificate to guarantee the reliability of the electronic document creation date. This service is similar to the operation according to the present embodiment in that “time keeping” is used to generate the electronic signature f5. However, the receiving unit 5 according to the present embodiment uses the expiration date of the received data. Is different from the authentication judgment condition. That is, the feature of the present invention is that the time signature is given to the effectiveness of the electronic signature f5. For example, by including the time counter information f11 encoded in the electronic signature f5, the communication frame data received at a timing outside the allowable range of the time counter information f11 is discarded. As a result, the control device 3 does not capture communication frame data including old control communication data, and the control device 3 does not perform erroneous processing.

  In addition, the authentication process according to the present embodiment has a security requirement to prevent “control stoppage and stagnation” and “control runaway” that are direct risks of the control system. This authentication process can protect the control system from an “overload access attack” and a “spoofed access attack (data alteration)” from a malicious third party without impairing real-time performance. Further, the control system can be protected by adding an electronic signature f5 with time information randomized by random numbers to the frame information.

  In addition, when there is arbitrary data that needs to be concealed in the communication frame data at the time of transmission / reception, if only arbitrary data is included in the encryption target, “partial encryption” that encrypts only a part of the data is included in this embodiment. Such a method can be applied. At this time, the electronic signature generation unit 6 of the transmission unit 4 includes a part of the control communication data f4 in the electronic signature f5 so that a part of the control communication data f4 is also an encryption target. Then, the determination unit 8 of the reception unit 5 does not use a part of the control communication data f4 obtained by decrypting the electronic signature f5 for determination of communication frame data. This makes it possible to encrypt and decrypt only the data that needs to be concealed.

[2. Second embodiment]
Next, an operation example of the receiving unit 5 according to the second embodiment of the present invention will be described.
FIG. 8 is an explanatory diagram illustrating an example of state transition of the authentication determination circuit 46 according to the second embodiment. Here, a method that does not consider synchronization of time counter information will be described.

  In this case, the transmission unit 4 does not include the time counter circuit 13. The block generation unit 17 generates blocks d8 to d10 by rearranging the unit fixed length bits separated from the check code f12, the sequence number f13, and the random number f14 in units of single bits or in units of multiple bits. Then, the encoding unit 21 generates an electronic signature f5 based on the blocks d8 to d10.

  The receiver 5 does not include the time counter circuit 37 and the first determination circuit 38. Therefore, the information extraction unit 7 performs a predetermined determination by the second determination circuit 40, the third determination circuit 42, and the fourth determination circuit 45, and the authentication determination circuit 46 determines the state based on the determination results of these determination circuits. Transitions and performs processing on communication frame data.

  The state of the authentication determination circuit 46 transitions between authentication intermediate determination OK 71, authentication determination OK 72, authentication non-determination 73, and authentication determination NG. The conditions for transition from the authentication undetermined 73 that is the initial state to the authentication intermediate determination OK 71, the authentication determination OK 72, and the authentication determination NG 74 are from the authentication undetermined 53 to the authentication intermediate determination OK 51, the authentication determination OK 52, and the authentication determination NG 54 shown in FIG. Same as the transition condition.

  However, FIG. 8 is different in that there is no state corresponding to the synchronization state 60 of the time counter information, and a transition condition for transition from the authentication determination OK 72 to the authentication non-determination 73 is added instead. This transition condition is when the frame reception process and the process of shifting the time counter information f11 of the previous cycle of the first storage circuit 43 to the second storage circuit 44 are completed. Thereafter, if the communication interval time for receiving communication frame data from another communication device is within the allowable error range determined by the fourth determination circuit 45, the authentication determination circuit 46 determines whether the authentication is not determined 73 and the authentication determination OK 72. Repeat the transition.

  In this way, if the operator can determine that there is no problem even if the tolerance range of the time counter information is widened, the security required for transmission / reception of communication frame data without synchronization between the communication devices. Can be realized.

  According to the present embodiment, it is not necessary to mount the time counter circuit 37 and the first determination circuit 38. Therefore, mounting of the hardware configuring the receiving unit 5 is simplified, and the manufacturing cost can be reduced. .

  In the present embodiment, the fourth determination circuit 45 needs to consider the influence of the frame loss due to the transient noise described above in advance. Specifically, the tolerance must be increased. For example, assume that the communication frame data reception interval is T milliseconds. When there is no transient noise, the difference between the time counter information stored in the first memory circuit 43 and the second memory circuit 44 is always about T milliseconds. A value with a slight margin added to seconds is sufficient. However, when it is assumed that there is a possibility that the transient noise may continue N times, this tolerance must be set to a value obtained by adding a margin to N × T milliseconds, and the expiration date of the electronic signature f5 This leads to a weak temporal localization. If attention is paid to this point, it can be said that the present embodiment is sufficiently practical.

[3. Modified example]
The transmission unit 4 and the reception unit 5 according to the first and second exemplary embodiments described above may be used as a transmission device having only a transmission function and a reception device having only a reception function, respectively.
FIG. 9 shows a system configuration diagram of the communication system 1A.
The communication system 1A includes a transmission device 9 and a reception device 10, and transmits and receives communication frame data from the transmission device 9 to the reception device 10 in one direction.
The transmission device 9 includes a control device 3 and a transmission unit 4, and transmits communication frame data to the reception device 10 via the network N.
The receiving device 10 includes a control device 3 and a receiving unit 5, and receives communication frame data from the transmitting device 9 via the network N.
Even in the communication system 1A configured as described above, it is possible to safely transmit and receive communication frame data.

  The electronic signature generation unit 6 has a plurality of conversion tables 19, and adds information related to the conversion table 19 used to generate the electronic signature f5 to the electronic signature f5. The information extraction unit 7 includes a plurality of reverse conversion tables 34, and decrypts the electronic signature f5 using the reverse conversion table 34 selected based on the information about the conversion table 19 added to the electronic signature f5. By using a plurality of conversion tables 19 and a plurality of reverse conversion tables 34 in this way, even if information of one conversion table 19 and reverse conversion table 34 leaks to the outside, another conversion table 19 and reverse conversion are immediately Processing can be continued by switching to the table 34.

Further, the present invention is not limited to the above-described embodiments, and various other application examples and modifications can be taken without departing from the gist of the present invention described in the claims.
For example, the above-described embodiments are detailed and specific descriptions of the configuration of the apparatus and the system in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Absent. In addition, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Is also possible. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.
Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

DESCRIPTION OF SYMBOLS 1 ... Communication system, 2A-2M ... Communication apparatus, 3 ... Control apparatus, 4 ... Transmission part, 5 ... Reception part, 6 ... Digital signature production | generation part, 7 ... Information extraction part, 8 ... Determination part, 12 ... Transmission port, 21 ... Encoding unit, 30 ... Decoding unit, 31 ... Reception port

Claims (12)

A transmission unit for transmitting communication frame data to another communication device;
A receiving unit for receiving the communication frame data from the other communication device,
The transmitter is
The first check code generated based on the control communication data received from the control device, the first sequence number indicating the transmission order of the communication frame data, and the random number are separated in predetermined units, respectively. An electronic signature generation unit for generating an electronic signature obtained by converting a block consisting of a rearranged bit number sequence set by an encoder;
A transmission port for transmitting the communication frame data obtained by adding the electronic signature to the control communication data to another communication device;
The receiver is
A receiving port for extracting the electronic signature from the communication frame data received from the other communication device;
An information extraction unit that extracts the first check code, the first sequence number, and the random number from the block obtained by inversely transforming the electronic signature by a decoder in a reverse order to the predetermined order;
A result of comparing the extracted first check code with the second check code generated from the control communication data of the communication frame data, the extracted first sequence number, and the communication in the previous period A determination unit that allows the control device to capture the control communication data when the communication frame data is determined to be normal based on a result of comparison with the second sequence number added to the frame data; A communication device. The electronic signature generation unit
A first check code generation unit that generates the first check code from the control communication data;
A sequence number generator that generates the first sequence number that is incremented each time the communication frame data is transmitted;
A random number generator for generating the random number;
A block generation unit that generates the block by rearranging the unit fixed length bits separated from each of the first check code, the first sequence number, and the random number in units of single bits or in units of multiple bits;
The communication device according to claim 1, further comprising: an encoding unit that converts the block by the encoder to generate the electronic signature. The electronic signature generation unit includes a first time counter information generation unit that generates first time counter information,
The block generation unit includes unit fixed length bits separated from the first time counter information, the first check code, the first sequence number, and the random number in units of single bits or in units of multiple bits, respectively. The communication apparatus according to claim 2, wherein the blocks are generated by rearranging. The communication apparatus according to claim 3, wherein the electronic signature generation unit includes a plurality of encoders and adds information related to the encoder used to generate the electronic signature to the electronic signature. The information extraction unit includes:
A decrypting unit that reversely transforms the electronic signature by the decoder and decrypts the electronic signature;
A bit extraction unit for rearranging the unit fixed-length bits extracted from the block in the predetermined order to extract the first check code, the first sequence number, and the random number;
A second check code generation unit that generates the second check code based on the control communication data of the communication frame data;
A sequence number storage unit for storing the first sequence number extracted from the communication frame data of the previous period;
A first time counter information storage unit for storing the first time counter information extracted from the communication frame data of the current period;
A second time counter information storage unit that stores the first time counter information extracted from the communication frame data of the previous period,
The determination unit
A check code determination unit that determines a difference between a first check code extracted from the communication frame data and a second check code generated from the control communication data of the communication frame data;
A first sequence number indicating the transmission order of the communication frame data extracted from the communication frame data of the current cycle, and the first sequence number extracted from the communication frame data of the previous cycle stored in the sequence number storage unit A sequence number determination unit for determining a difference from the sequence number of 2;
The first clock counter information of the current cycle stored in the first clock counter information storage unit and the first clock counter information of the previous cycle shifted to the second clock counter information storage unit An inter-period difference determining unit that determines whether the difference is within the first error range;
If the determination results of the check code determination unit, the sequence number determination unit, and the inter-period difference determination unit are normal, the control device allows the control communication data to be taken in. If the determination result is abnormal, The communication apparatus according to claim 1, further comprising: an authentication determination unit that discards the communication frame data. The information extraction unit includes a second time counter information generation unit that generates second time counter information.
The determination unit determines whether or not a difference between the first time counter information extracted from the communication frame data and the second time counter information is within a second error range. It has a judgment part,
The communication apparatus according to claim 5, wherein the authentication determination unit performs processing on the communication frame data based on determination results of the current cycle difference determination unit, the check code determination unit, and the sequence number determination unit. When the first check code and the second check code match and the first sequence number and the second sequence number are different, the information extraction unit includes the first time counter. The clock counter information of the previous cycle stored in the information storage unit is shifted to the second clock counter information storage unit, and the clock counter information of the current cycle is stored in the first clock counter information storage unit. 6. The communication device according to 6. The first time counter information generated by the other communication device as a master and the second time counter information are not synchronized, and are in an incomplete synchronization state;
The first clock counter information of the current cycle stored in the first clock counter information storage unit and the first clock counter information of the previous cycle shifted to the second clock counter information storage unit If the difference is within the first error range,
The second clock counter information generation unit copies the first clock counter information of the current period stored in the first clock counter information storage unit to the first clock counter information. The communication apparatus according to claim 7, wherein the second time counter information is synchronized. The communication apparatus according to claim 8, wherein the information extraction unit includes a plurality of the decoders, and decodes the electronic signature using the decoder selected based on information on the encoder added to the electronic signature. The electronic signature generation unit encodes the electronic signature generated including a part of the control communication data,
The communication apparatus according to claim 1, wherein the determination unit does not use a part of the control communication data obtained by decrypting the electronic signature for determining the communication frame data. The first check code generated based on the control communication data received from the control device, the first sequence number indicating the transmission order of the communication frame data, and the random number are each separated in a predetermined unit and rearranged in a predetermined order. An electronic signature generating unit that generates an electronic signature obtained by converting a block consisting of a set of bit sequences by an encoder;
A transmission port configured to transmit the communication frame data obtained by adding the electronic signature to the control communication data to another communication device. A reception port that receives communication frame data transmitted by another communication device and extracts an electronic signature from the communication frame data;
What is the predetermined order in which the first check code, the first sequence number, and the random number generated by the other communication device based on the communication frame data are rearranged from the block obtained by inversely converting the electronic signature by the decoder? An information extractor for extracting the first check code, the first sequence number, and the random number in reverse order;
The result of comparing the extracted first check code with the second check code generated from the control communication data of the communication frame data, the extracted first sequence number, and the communication frame of the previous period A determination unit that permits the control device to capture the control communication data when the communication frame data is determined to be normal based on a result of comparison with the second sequence number added to the data. Receiver device.

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