Communication systems and communication methods

Abstract

The communication system (1) includes: servo amplifiers (12a to 14a) connected in series; a control device (21) that controls the servo amplifier by transmitting and receiving communication data with it; and a protocol conversion device (22a) connected between the servo amplifier and the control device, which converts the communication protocol of the servo amplifier and the communication protocol of the control device to each other. Each of the control device, the protocol conversion device, and the servo amplifier is connected in series. Each device in the device group including the protocol conversion device and the servo amplifier has: a key storage unit that stores a first common key used with adjacent devices; an encryption unit that encrypts communication data using the first common key; a decryption unit that decrypts communication data using the first common key; and a transceiver unit that transmits and receives encrypted communication data with adjacent devices.

Description

Technical Field

[0001] This invention relates to a communication system and method that uses cryptographic techniques to perform communication between devices. Background Technology

[0002] The working machine is one type of communication system consisting of a control unit and multiple servo amplifiers connected in series (daisy-chain). In such a working machine, the control unit and the servo amplifiers, as well as the servo amplifiers themselves, are connected via a network using a communication protocol specific to the control unit manufacturer or a network using an open protocol.

[0003] In a working machine, for example, where a control device owned by the machine manufacturer and a servo amplifier owned by the control device manufacturer are connected, a protocol conversion device is provided between the control device and the servo amplifier to convert the communication protocol of the control device and the communication protocol of the servo amplifier to each other.

[0004] When using such a protocol conversion device, the concealment of the communication protocol between the device and the servo amplifier becomes a problem. The device converts the communication protocol of the control unit and the servo amplifier, resulting in a one-to-one correspondence between the communication data before and after the conversion. Therefore, it is conceivable that analyzing the communication data before and after the conversion could reveal the servo amplifier's communication protocol. Since the servo amplifier's communication protocol is concealed, its leakage poses a risk of enabling control outside the scope specified by the control unit manufacturer, damaging the equipment, or causing unintended actions. Furthermore, there is a risk of creating counterfeit control units or servo amplifiers by mimicking the communication protocol.

[0005] To prevent the communication protocol from being deciphered, the information transmitting device described in Patent Document 1 stores a common key distinguishing the target devices and data area information distinguishing each device within the communication data. It then encrypts each data area of ​​each information receiving device using the common key of that information receiving device. The information receiving device that receives the communication data stores the common key and uses it to decrypt its own data area.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2002-259634 Summary of the Invention

[0007] However, in the technology of the aforementioned Patent Document 1, the information sending device of the information sender stores the common key of all information receiving devices and the data area information of each information receiving device. Therefore, there is a risk that if the common key and data area information have been leaked to a third party, the data of all information receiving devices can be read by the third party.

[0008] The present invention was made in view of the above-mentioned problems, and its object is to provide a communication system that can suppress the extent of leakage in the data of the information receiving device even if the common key stored in the information transmitting device has been leaked.

[0009] To address the aforementioned issues and achieve the objective, the communication system of the present invention comprises: a controlled device connected in series; a control device that controls the controlled device by transmitting and receiving communication data with the controlled device; and a protocol conversion device connected between the controlled device and the control device, which converts the communication protocol of the controlled device and the communication protocol of the control device to each other. Each of the control device, the protocol conversion device, and the controlled device is connected in series. Each device in the device group, including the protocol conversion device and the controlled device, has a key storage unit that stores a first common key used with adjacent devices. Furthermore, the communication system of the present invention includes: an encryption unit that encrypts communication data using the first common key; a decryption unit that decrypts communication data using the first common key; and a transceiver unit that transmits and receives encrypted communication data with adjacent devices.

[0010] The effects of the invention

[0011] The communication system of the present invention achieves the effect of suppressing the scope of leakage in the data of the information receiving device even if the common key stored in the information transmitting device has been leaked. Attached Figure Description

[0012] Figure 1 This is a diagram showing the structure of the communication system involved in Implementation Method 1.

[0013] Figure 2 This is a diagram used to illustrate the data transmission direction in the communication system according to Embodiment 1.

[0014] Figure 3 This is a diagram showing the structure of the protocol conversion device involved in Embodiment 1.

[0015] Figure 4 This is a diagram showing the structure of the servo amplifier according to Embodiment 1.

[0016] Figure 5This is a diagram showing the structure of communication data transmitted and received in the communication system according to Embodiment 1.

[0017] Figure 6 This is a diagram illustrating the keys stored by each device in the communication system according to Embodiment 1.

[0018] Figure 7 This is a flowchart illustrating the downlink data communication processing flow of the communication system involved in Implementation 1.

[0019] Figure 8 This is a flowchart illustrating the uplink data communication processing flow of the communication system according to Implementation Method 1.

[0020] Figure 9 This is a diagram showing the structure of the protocol conversion device involved in Embodiment 2.

[0021] Figure 10 This is a diagram showing the structure of the servo amplifier according to Embodiment 2.

[0022] Figure 11 This is a diagram showing the structure of communication data transmitted and received in the communication system according to Embodiment 2.

[0023] Figure 12 This is a diagram illustrating the keys exchanged within the communication system described in Embodiment 2.

[0024] Figure 13 This is a diagram illustrating the keys stored by each device in the communication system according to Embodiment 2.

[0025] Figure 14 This is a flowchart illustrating the downlink public key transmission and reception process of the communication system involved in Implementation Method 2.

[0026] Figure 15 This is a flowchart illustrating the uplink common key transmission and reception process of the communication system involved in Implementation Method 2.

[0027] Figure 16 This is a diagram showing the structure of the protocol conversion device involved in Embodiment 3.

[0028] Figure 17 This is a diagram showing the structure of communication data transmitted and received in the communication system according to Embodiment 3.

[0029] Figure 18 This is a flowchart illustrating the downlink data communication processing flow of the communication system involved in Implementation Method 3.

[0030] Figure 19 This is a diagram illustrating an example of the hardware structure of the protocol conversion device involved in Implementation Method 1. Detailed Implementation

[0031] The communication system and communication method according to the embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0032] Implementation Method 1

[0033] Figure 1 This is a diagram illustrating the structure of the communication system according to Embodiment 1. Communication system 1 includes a control device 21, a protocol conversion device 22a, and servo amplifiers 12a to 12a connected in series.

[0034] 14a. In communication system 1, control device 21 is an information transmission device (transmission source device) for communication data, and servo amplifiers 12a to 14a are target devices for transmitting communication data. Servo amplifiers 12a to 14a are controlled devices controlled by control device 21.

[0035] In the following description, "front-end" refers to the control device 21 side, and "back-end" refers to the servo amplifier 14a side. Furthermore, in communication system 1, the control device 21 side is the upstream side, and the servo amplifier 14a side is the downstream side. Therefore, when the servo amplifier 14a, connected to the end in the device group consisting of the protocol conversion device 22a and servo amplifiers 12a to 14a, is designated as the most downstream device, the protocol conversion device 22a is the most upstream device. Moreover, the intermediate devices, other than those connected to the most downstream and most upstream devices, are the servo amplifiers 12a and 13a.

[0036] Communication system 1 is, for example, a working machine that controls a servo motor (not shown) via servo amplifiers 12a to 14a. In communication between the protocol conversion device 22a and the servo amplifiers 12a to 14a, communication system 1 pre-stores common keys between adjacent devices but does not store common keys used by non-adjacent devices. That is, communication system 1 stores the common key (first common key) used by each device in the device group consisting of protocol conversion device 22a and servo amplifiers 12a to 14a with adjacent devices, but does not store the common key (second common key) used by non-adjacent devices.

[0037] The control device 21, the protocol conversion device 22a, and the servo amplifiers 12a-14a are each connected via their respective networks. That is, the control device 21, the protocol conversion device 22a, and the servo amplifiers 12a-14a are connected in series in a linear daisy-chain configuration. Specifically, the control device 21 is connected to the protocol conversion device 22a via network 2, and the protocol conversion device 22a is connected to the servo amplifier 12a via network 3X. In other words, the protocol conversion device 22a is connected between the servo amplifier 12a and the control device 21. Furthermore, the servo amplifier 12a is connected to the servo amplifier 13a via network 3Y, and the servo amplifier 13a is connected to the servo amplifier 14a via network 3Z.

[0038] The control device 21 and the servo amplifiers 12a-14a are manufactured by different manufacturers, for example. The control device 21 is manufactured by a machine tool manufacturer, for example, and has its own control method, operating interface, communication protocol, etc. Similarly, the servo amplifiers 12a-14a are manufactured by a control device manufacturer, for example, and have their own communication protocol, etc. Therefore, the control device 21 and the servo amplifiers 12a-14a use different communication protocols.

[0039] Protocol conversion device 22a is a computer that converts the communication protocol of control device 21 and the communication protocols of servo amplifiers 12a-14a. Specifically, protocol conversion device 22a converts the communication protocol between control device 21 and protocol conversion device 22a, and the communication protocol between protocol conversion device 22a and servo amplifier 12a. The communication data before and after conversion by protocol conversion device 22a correspond one-to-one.

[0040] Furthermore, there are no particular limitations on the communication protocol in Implementation 1; it can also be an open protocol such as EtherCAT (Ethernet for Control Automation Technology).

[0041] Furthermore, if the communication protocols between the control device 21 and the protocol conversion device 22a, and between the protocol conversion device 22a and the servo amplifier 12a, are compatible, protocol conversion may not be required. In this case, the communication system 1 may not need to have the protocol conversion device 22a.

[0042] The control device 21 is a computer that generates control information, i.e., control information, for controlling each servo motor of the working machine. The control device 21 has a transceiver unit for communicating with a protocol conversion device 22a connected via network 2. The control information generated by the control device 21 is transmitted as communication data to the servo amplifiers 12a to 14a via the protocol conversion device 22a. Furthermore, the control device 21 receives control results generated by the servo amplifiers 12a to 14a, the status of the servo amplifiers 12a to 14a, and sensing information detected by sensors located on the working machine, all sent from the servo amplifiers 12a to 14a, for subsequent generation of control information.

[0043] Figure 2 This diagram illustrates the data transmission direction in the communication system according to Embodiment 1. Communication data sent from the control device 21 is transmitted in the order of protocol conversion device 22a, servo amplifier 12a, servo amplifier 13a, and servo amplifier 14a. The transmission direction of this communication data is downlink.

[0044] If the communication data reaches the end of the daisy chain, namely servo amplifier 14a, the communication data is transmitted back and forth from servo amplifier 14a in the order of servo amplifier 13a, servo amplifier 12a, protocol conversion device 22a, and control device 21. The transmission direction of this communication data is uplink.

[0045] Figure 3 This is a diagram showing the structure of the protocol conversion device according to Embodiment 1. The protocol conversion device 22a includes a control unit 41, transceiver units 42 and 43, a decryption unit 44, an encryption unit 45, a key storage unit 46, and a protocol conversion unit 47.

[0046] The transceiver unit 42 communicates with the control device 21, and the transceiver unit 43 communicates with the servo amplifier 12a. Alternatively, transceiver units 42 and 43 can be a single unit. The decryption unit 44 decrypts the communication data, and the encryption unit 45 encrypts the communication data. The key storage unit 46 stores the key used for encrypting and decrypting the communication data (the common key A1 described later).

[0047] The protocol conversion unit 47 converts the communication protocol between the control device 21 and the protocol conversion device 22a, and the communication protocol between the protocol conversion device 22a and the servo amplifier 12a.

[0048] The control unit 41 controls the transceiver units 42 and 43, the decryption unit 44, the encryption unit 45, the key storage unit 46, and the protocol conversion unit 47 by executing programs and performing numerical calculations.

[0049] Servo amplifiers 12a to 14a are computers that control servo motors based on control commands stored in received communication data. The structure of servo amplifiers 12a to 14a will be described here. Servo amplifiers 12a to 14a have the same structure.

[0050] Figure 4 This diagram illustrates the structure of the servo amplifier according to Embodiment 1. Each of the servo amplifiers 12a to 14a includes a control unit 51, a transceiver unit 52 and 53, a decryption unit 54, an encryption unit 55, and a key storage unit 56.

[0051] The transceiver unit 52 communicates with the transceiver unit of the preceding device, and the transceiver unit 53 communicates with the transceiver unit of the following device. Alternatively, transceiver units 52 and 53 may be a single unit. The transceiver unit 52 of the servo amplifier 12a communicates with the transceiver unit 43 of the preceding device, i.e., the protocol conversion device 22a, and the transceiver unit 53 of the servo amplifier 12a communicates with the transceiver unit 52 of the following device, i.e., the servo amplifier 13a.

[0052] Similarly, the transceiver unit 52 of servo amplifier 13a communicates with the transceiver unit 53 of servo amplifier 12a, and the transceiver unit 53 of servo amplifier 13a communicates with the transceiver unit 52 of servo amplifier 14a. The transceiver unit 52 of servo amplifier 14a communicates with the transceiver unit 53 of servo amplifier 13a. Furthermore, since servo amplifier 14a is a terminal device in communication system 1 and is not connected to downstream devices, it may not have a transceiver unit 53.

[0053] The decryption unit 54 decrypts the communication data. The encryption unit 55 encrypts the communication data. The key storage unit 56 of the servo amplifier 12a stores the keys used for encryption and decryption of the communication data (common keys A1 and B1 described later). Additionally, the key storage unit 56 of the servo amplifier 13a stores the keys used for encryption and decryption of the communication data (common keys B1 and C1 described later). Furthermore, the key storage unit 56 of the servo amplifier 14a stores the key used for encryption and decryption of the communication data (common key C1 described later).

[0054] That is, the common key A1 is a key pre-stored by the protocol conversion device 22a and the servo amplifier 12a, and is not stored by the servo amplifiers 13a and 14a. Similarly, the common key B1 is a key pre-stored by the servo amplifiers 12a and 13a, and is not stored by the protocol conversion device 22a and the servo amplifier 14a. Furthermore, the common key C1 is a key pre-stored by the servo amplifiers 13a and 14a, and is not stored by the protocol conversion device 22a and the servo amplifier 12a.

[0055] The control unit 51 controls the transceiver units 52 and 53, the decryption unit 54, the encryption unit 55, and the key storage unit 56 by executing programs and performing numerical calculations.

[0056] Furthermore, the servo amplifier 12a has a waveform output section for outputting control waveforms to the servo motor and an input section for receiving sensor signals, but these are omitted in Embodiment 1. Also, in Embodiment 1, the case where the communication system 1 has three servo amplifiers is described, but the number of servo amplifiers in the communication system 1 is not limited to three; it can be less than or equal to two, or greater than or equal to four.

[0057] Figure 5 This diagram illustrates the structure of communication data transmitted and received within the communication system according to Embodiment 1. The communication data 5a transmitted and received within the communication system 1 of Embodiment 1 includes a frame header 61 and payloads 62 to 64. The frame header 61 stores control information corresponding to the communication protocol. The frame header 61 includes, for example, information about the transmitting device and the length of the communication data. The payload 62 stores control information targeting the servo amplifier 12a and feedback information from the servo amplifier 12a. The payload 63 stores control information targeting the servo amplifier 13a and feedback information from the servo amplifier 13a. The payload 64 stores control information targeting the servo amplifier 14a and feedback information from the servo amplifier 14a.

[0058] Here, a comparative example, namely an existing communication system, is described. The existing communication system has a protocol converter 22X (not shown) corresponding to protocol converter 22a, and servo amplifiers 12X, 13X, and 14X (not shown) corresponding to servo amplifiers 12a, 13a, and 14a. In the existing communication system, the information transmitting device corresponding to protocol converter 22X stores the common keys A1, B1, and C1 for all servo amplifiers 12X, 13X, and 14X corresponding to the information receiving device. The information transmitting device encrypts the data corresponding to servo amplifier 12X using common key A1, encrypts the data corresponding to servo amplifier 13X using common key B1, and encrypts the data corresponding to servo amplifier 14X using common key C1. The servo amplifier 12X corresponding to the information receiving device stores only common key A1, servo amplifier 13X stores only common key B1, and servo amplifier 14X stores only common key C1. Servo amplifier 12X decrypts its own data using common key A1, servo amplifier 13X decrypts its own data using common key B1, and servo amplifier 14X decrypts its own data using common key C1.

[0059] Figure 6This diagram illustrates the keys stored in each device within the communication system according to Embodiment 1. The protocol conversion device 22a in communication system 1 stores a common key A1 via a key storage unit 46. The servo amplifier 12a in communication system 1 stores common keys A1 and B1 via a key storage unit 56. The servo amplifier 13a in communication system 1 stores common keys B1 and C1 via a key storage unit 56. The servo amplifier 14a in communication system 1 stores common key C1 via a key storage unit 56. Thus, common key A1 is stored by both the protocol conversion device 22a and the servo amplifier 12a, which are adjacent to each other. Similarly, common key B1 is stored by both the servo amplifiers 12a and 13a, which are adjacent to each other. Finally, common key C1 is stored by both the servo amplifiers 13a and 14a, which are adjacent to each other.

[0060] Common key A1 is used for encryption and decryption of communication data sent and received between protocol conversion device 22a and servo amplifier 12a. Common key B1 is used for encryption and decryption of communication data sent and received between servo amplifiers 12a and 13a. Common key C1 is used for encryption and decryption of communication data sent and received between servo amplifiers 13a and 14a. In communication system 1, protocol conversion device 22a and servo amplifiers 12a-14a each store the common key before starting data communication.

[0061] Next, the data communication processing flow during stable communication in communication system 1 will be explained. First, the downlink data communication will be explained. Figure 7 This is a flowchart illustrating the downlink data communication processing flow of the communication system according to Embodiment 1. Figure 7 The diagram shows the activity of the downward movement.

[0062] The control device 21 sends communication data containing information on control instructions for each servo amplifier 12a to 14a to the transceiver unit 42 of the protocol conversion device 22a (step S110).

[0063] In the protocol conversion device 22a, if the transceiver unit 42 receives communication data (step S120), the control unit 41 obtains the communication data from the transceiver unit 42 (step S130). Then, the control unit 41 uses the protocol conversion unit 47 to convert the communication data into a communication protocol for communicating with the servo amplifiers 12a to 14a. That is, the protocol conversion unit 47 converts the communication data protocol into a communication protocol for communicating with the servo amplifiers 12a to 14a (step S140).

[0064] The control unit 41 of the protocol conversion device 22a encrypts the protocol-converted communication data using the encryption unit 45. That is, the encryption unit 45 encrypts the protocol-converted communication data (step S150). At this time, the encryption unit 45 refers to the key storage unit 46 and uses the common key A1 between itself and the downstream device to encrypt the communication data. That is, the encryption unit 45 reads the common key A1 between itself and the downstream device, i.e., the servo amplifier 12a, from the key storage unit 46 and uses the common key A1 to encrypt the communication data. The encryption unit 45 transmits the encrypted communication data to the transceiver unit 43 (step S160). The transceiver unit 43 sends the communication data to the transceiver unit 52 of the servo amplifier 12a (step S170).

[0065] In the servo amplifier 12a, if the transceiver unit 52 receives communication data (step S180), the control unit 51 obtains the communication data from the transceiver unit 52 (step S190).

[0066] The control unit 51 of the servo amplifier 12a uses the decryption unit 54 to decrypt the acquired communication data. That is, the decryption unit 54 of the servo amplifier 12a decrypts the communication data sent from the protocol conversion device 22a (step S200). At this time, the decryption unit 54 of the servo amplifier 12a refers to the key storage unit 56 and uses the common key A1 between itself and the upstream device to decrypt the communication data. That is, the decryption unit 54 of the servo amplifier 12a reads the common key A1 between itself and the upstream device, namely the protocol conversion device 22a, from the key storage unit 56 and uses the common key A1 to decrypt the communication data.

[0067] Subsequently, the control unit 51 of the servo amplifier 12a refers to or modifies the data stored in the payload 62 of the decrypted communication data. If the control unit 51 of the servo amplifier 12a finishes referring to or modifying the data in the payload 62, it uses the encryption unit 55 to encrypt the communication data (step S210). At this time, the encryption unit 55 of the servo amplifier 12a refers to the key storage unit 56 and uses the common key B1 between the servo amplifier 12a and the downstream device to encrypt the communication data. That is, the encryption unit 55 of the servo amplifier 12a reads the common key B1 between the servo amplifier 12a and the downstream device, i.e., the servo amplifier 13a, from the key storage unit 56 and uses the common key B1 to encrypt the communication data.

[0068] The encryption unit 55 of the servo amplifier 12a transmits the encrypted communication data to the transceiver unit 53 (step S220). The transceiver unit 53 of the servo amplifier 12a sends the communication data to the transceiver unit 52 of the servo amplifier 13a (step S230).

[0069] In servo amplifier 13a, the same processing as in servo amplifier 12a is performed. That is, in servo amplifier 13a, transceiver 52 receives communication data (step S240), and control unit 51 obtains communication data from transceiver 52 (step S250). Then, decryption unit 54 of servo amplifier 13a decrypts the communication data (step S260). At this time, decryption unit 54 of servo amplifier 13a reads the common key B1 between itself and the upstream device, i.e., servo amplifier 12a, from key storage unit 56, and uses the common key B1 to decrypt the communication data.

[0070] Subsequently, the control unit 51 of the servo amplifier 13a refers to or modifies the data stored in the payload 63 of the decrypted communication data. The encryption unit 55 of the servo amplifier 13a reads the common key C1 between itself and the downstream device, namely the servo amplifier 14a, from the key storage unit 56, and encrypts the communication data using the common key C1 (step S270). The encryption unit 55 of the servo amplifier 13a transmits the encrypted communication data to the transceiver unit 53 (step S280), and the transceiver unit 53 transmits the communication data to the transceiver unit 52 of the servo amplifier 14a (step S290).

[0071] In servo amplifier 14a, the same processing as that in servo amplifiers 12a and 13a is performed. That is, in servo amplifier 14a, transceiver unit 52 receives communication data (step S300), and control unit 51 obtains communication data from transceiver unit 52 (step S310). Then, decryption unit 54 of servo amplifier 14a decrypts the communication data (step S320). At this time, decryption unit 54 of servo amplifier 14a reads the common key C1 between itself and the upstream device, i.e., servo amplifier 13a, from key storage unit 56, and uses the common key C1 to decrypt the communication data.

[0072] Subsequently, the control unit 51 of the servo amplifier 14a refers to or modifies the data stored in the payload 64 of the decrypted communication data. The encryption unit 55 of the servo amplifier 14a reads the common key C1 between itself and the upstream device, namely the servo amplifier 13a, from the key storage unit 56, and encrypts the communication data using the common key C1 (step S330). The encryption unit 55 of the servo amplifier 14a transmits the encrypted communication data to the transceiver unit 52 (step S340).

[0073] Next, we will explain the uplink data communication. Figure 8 This is a flowchart illustrating the uplink data communication processing flow of the communication system according to Embodiment 1. Figure 8 The diagram shows the upward movement.

[0074] Servo amplifier 14a is the end device in communication system 1, and therefore transmits communication data back to the preceding servo amplifier 13a. That is, the transceiver unit 52 of servo amplifier 14a transmits communication data to the transceiver unit 53 of servo amplifier 13a (step S410).

[0075] In the servo amplifier 13a, if the transceiver unit 53 receives communication data (step S420), the control unit 51 obtains the communication data from the transceiver unit 53 (step S430).

[0076] The control unit 51 of the servo amplifier 13a uses the decryption unit 54 to decrypt the acquired communication data. That is, the decryption unit 54 of the servo amplifier 13a decrypts the communication data sent from the servo amplifier 14a (step S440). At this time, the decryption unit 54 of the servo amplifier 13a refers to the key storage unit 56 and uses the common key C1 between the servo amplifier 13a and the downstream device to decrypt the communication data. That is, the decryption unit 54 of the servo amplifier 13a reads the common key C1 between the servo amplifier 13a and the downstream device, i.e., the servo amplifier 14a, from the key storage unit 56 and uses the common key C1 to decrypt the communication data.

[0077] Subsequently, the control unit 51 of the servo amplifier 13a refers to or modifies the data stored in the payload 63 of the decrypted communication data. If the control unit 51 of the servo amplifier 13a finishes referring to or modifying the data in the payload 63, it uses the encryption unit 55 to encrypt the communication data (step S450). At this time, the encryption unit 55 of the servo amplifier 13a refers to the key storage unit 56 and uses the common key B1 between the servo amplifier 13a and the upstream device to encrypt the communication data. That is, the encryption unit 55 of the servo amplifier 13a reads the common key B1 between the servo amplifier 13a and the upstream device, namely the servo amplifier 12a, from the key storage unit 56 and uses the common key B1 to encrypt the communication data. The encryption unit 55 of the servo amplifier 13a transmits the encrypted communication data to the transceiver unit 52 (step S460). The transceiver unit 52 of the servo amplifier 13a sends the communication data to the transceiver unit 53 of the servo amplifier 12a (step S470).

[0078] The same processing as that of servo amplifier 13a is performed in servo amplifier 12a. That is, in servo amplifier 12a, transceiver 53 receives communication data (step S480), and control unit 51 obtains communication data from transceiver 53 (step S490). Then, decryption unit 54 of servo amplifier 12a decrypts the communication data (step S500). At this time, decryption unit 54 of servo amplifier 12a reads the common key B1 between itself and the downstream device, i.e., servo amplifier 13a, from key storage unit 56, and uses the common key B1 to decrypt the communication data.

[0079] Subsequently, the control unit 51 of the servo amplifier 12a refers to or modifies the data stored in the payload 62 of the decrypted communication data. The encryption unit 55 of the servo amplifier 12a reads the common key A1 between itself and the upstream device, namely the protocol conversion device 22a, from the key storage unit 56, and encrypts the communication data using the common key A1 (step S510). The encryption unit 55 of the servo amplifier 12a transmits the encrypted communication data to the transceiver unit 52 (step S520). The transceiver unit 52 of the servo amplifier 12a sends the communication data to the transceiver unit 43 of the protocol conversion device 22a (step S530).

[0080] In the protocol conversion device 22a, if the transceiver unit 43 receives communication data sent from the servo amplifier 12a (step S540), the control unit 41 obtains the communication data from the transceiver unit 43 (step S550).

[0081] The control unit 41 of the protocol conversion device 22a uses the decryption unit 44 to decrypt the acquired communication data. That is, the decryption unit 44 of the protocol conversion device 22a decrypts the communication data sent from the servo amplifier 12a (step S560). At this time, the decryption unit 44 refers to the key storage unit 46 and uses the common key A1 between itself and the downstream device to decrypt the communication data. That is, the decryption unit 44 reads the common key A1 between itself and the downstream device, i.e., the servo amplifier 12a, from the key storage unit 46 and uses the common key A1 to decrypt the communication data.

[0082] Subsequently, in the protocol conversion device 22a, the protocol conversion unit 47 converts the decrypted communication data protocol into a communication protocol for communicating with the control device 21 (step S570). The protocol conversion unit 47 transmits the protocol-converted communication data to the transceiver unit 42 (step S580). The transceiver unit 42 sends the communication data to the control device 21 (step S590). The control device 21 then receives the communication data (step S600).

[0083] In this way, the protocol conversion device 22a and the servo amplifiers 12a-14a transmit and receive the communication data after encrypting the payloads 62-64. That is, the protocol conversion device 22a and the servo amplifiers 12a-14a encrypt the information representing the data area of ​​the sending target device and transmit and receive the communication data. As a result, the protocol conversion device 22a and the servo amplifiers 12a-14a can conceal the communication protocol. Therefore, the communication system 1 can suppress the imitation of the communication protocol, thus suppressing the execution of unwanted control and the manufacture of counterfeits. In this way, the communication system 1 can prevent the impact of the key leakage from the information transmission device from affecting the entire sending target device.

[0084] Furthermore, the protocol conversion device 22a and the servo amplifiers 12a to 14a use a common key between adjacent devices to perform data communication, so it is not necessary to store either the common key or the public key outside of this device. That is, the protocol conversion device 22a only needs to store the common key A1 with the servo amplifier 12a, and does not need to store the common keys B1 and C1 stored by the servo amplifiers 13a and 14a.

[0085] In addition, servo amplifier 12a only needs to store the common keys A1 and B1 between the protocol conversion device 22a and servo amplifier 13a, and does not need to store the common key C1 stored by servo amplifier 14a.

[0086] In addition, servo amplifier 13a only needs to store the common keys B1 and C1 between servo amplifiers 12a and 14a, and does not need to store the common key A1 stored by protocol conversion device 22a.

[0087] In addition, servo amplifier 14a only needs to store the common key C1 between servo amplifier 13a and servo amplifier 13a, and does not need to store the common keys A1 and B1 stored by protocol conversion device 22a or servo amplifier 12a.

[0088] Therefore, communication system 1 can reduce the number of keys of the target devices stored in the information transmitting device, thereby suppressing the leakage and imitation of the communication protocol. That is, in communication system 1, the information transmitting device of the information sender does not store the common key of all information receiving devices; therefore, even if the common key stored in the information transmitting device is leaked to a third party, there is no concern that the data of all information receiving devices will be read by a third party. Thus, even if the common key stored in the information transmitting device is leaked, communication system 1 can suppress the scope of leakage of data from the information receiving devices.

[0089] Furthermore, the protocol conversion device 22a and the information transmission device, i.e., the control device 21, do not need to pre-store the common key or public key of all the target devices (servo amplifiers 12a to 14a). Therefore, even if the number of target devices increases, it is not necessary to increase the area for storing the common key or public key. Additionally, the control device 21 and the protocol conversion device 22a do not need to store multiple keys; therefore, a small key storage area is sufficient. Moreover, for the communication system 1, the time spent on key exchange is reduced, and control related to encryption and decryption targeting each device becomes easier.

[0090] As described above, according to Embodiment 1, each device in the device group consisting of the protocol conversion device 22a and the servo amplifiers 12a to 14a in the communication system 1 stores a common key used with adjacent devices, but does not store a common key used by non-adjacent devices. Therefore, the communication system 1 can conceal the communication protocol by encrypting the communication data and reduce the number of keys for the target devices (servo amplifiers 12a to 14a) stored in the protocol conversion device 22a and the information transmitting device, i.e., the control device 21. Therefore, even if the common keys stored in the control device 21 and the protocol conversion device 22a are leaked, the communication system 1 can suppress the extent of leakage in the data of the information receiving devices, i.e., the servo amplifiers 12a to 14a.

[0091] Implementation Method 2

[0092] Next, use Figures 9 to 15 Implementation method 2 will be described. In implementation method 1, each device pre-stores the key, but in implementation method 2, each device does not have a fixed key. Before stable communication begins, each device generates a key and exchanges the keys.

[0093] The communication system 1 of Embodiment 2 includes a control device 21, a protocol conversion device 22b (described later), and servo amplifiers 12b to 14b (described later). That is, the communication system 1 of Embodiment 2 has a protocol conversion device 22b instead of a protocol conversion device 22a. Furthermore, the communication system 1 of Embodiment 2 has a servo amplifier 12b instead of a servo amplifier 12a. Additionally, the communication system 1 of Embodiment 2 has a servo amplifier 13b instead of a servo amplifier 13a, and a servo amplifier 14b instead of a servo amplifier 14a.

[0094] Similar to protocol conversion device 22a, protocol conversion device 22b is a computer that converts communication protocols. That is, protocol conversion device 22b converts the communication protocols of control device 21 and servo amplifiers 12b to 14b.

[0095] Servo amplifiers 12b to 14b, like servo amplifiers 12a to 14a, are computers that control servo motors based on control commands stored in received communication data. In embodiment 2, the downstream device is servo amplifier 14b, and the intermediate devices other than the downstream and upstream devices are servo amplifiers 12b and 13b.

[0096] Figure 9 This is a diagram showing the structure of the protocol conversion device according to Embodiment 2. Figure 9 Achievement and Figure 3Structural elements with the same function as those in the protocol conversion device 22a of Embodiment 1 shown are labeled with the same reference numerals, and repeated descriptions are omitted.

[0097] In addition to the structural elements of the protocol conversion device 22a, the protocol conversion device 22b also has a key generation unit 48. The key generation unit 48 generates a public key and a secret key. The protocol conversion device 22b exchanges the common key and the public key with the servo amplifier 12b. Specifically, the protocol conversion device 22b sends the public key generated by the key generation unit 48 to the servo amplifier 12b and receives the common key generated by the servo amplifier 12b.

[0098] Here, the structure of servo amplifiers 12b to 14b will be described. Servo amplifiers 12b to 14b have the same structure.

[0099] Figure 10 This is a diagram showing the structure of the servo amplifier according to Embodiment 2. Figure 10 Achievement and Figure 4 The structural elements with the same function as the servo amplifiers 12a to 14a of Embodiment 1 shown are labeled with the same reference numerals, and repeated descriptions are omitted.

[0100] In addition to the structural elements present in servo amplifiers 12a to 14a, servo amplifiers 12b to 14b also have a key generation unit 58. The key generation unit 58 generates a common key, a public key, or a secret key.

[0101] In Embodiment 2, the servo amplifier 12b exchanges a common key and a public key with the protocol conversion device 22b, and also exchanges a common key and a public key with the servo amplifier 13b. Specifically, the servo amplifier 12b receives the public key generated by the protocol conversion device 22b and sends the common key generated by the key generation unit 58 to the protocol conversion device 22b. Furthermore, the servo amplifier 12b sends the public key generated by the key generation unit 58 to the servo amplifier 13b and receives the common key generated by the servo amplifier 13b.

[0102] Similarly, servo amplifier 13b receives the public key generated by servo amplifier 12b and sends the common key generated by key generation unit 58 to servo amplifier 12b. Furthermore, servo amplifier 13b sends the public key generated by key generation unit 58 to servo amplifier 14b and receives the common key generated by servo amplifier 14b. Additionally, servo amplifier 14b receives the public key generated by servo amplifier 13b and sends the common key generated by key generation unit 58 to servo amplifier 13b. In embodiment 2, transceiver 53 is a first transceiver unit that transmits and receives communication data with a downstream device, and transceiver 52 is a second transceiver unit that transmits and receives communication data with an upstream device. Furthermore, transceiver units 52 and 53 may also be configured as a single transceiver unit.

[0103] Figure 11 This is a diagram illustrating the structure of communication data transmitted and received within the communication system according to Embodiment 2. The communication data 5b transmitted and received within the communication system 1 of Embodiment 2 includes a frame header 61, payloads 62-64, and a payload 70. The frame header 61 and payloads 62-64 of communication data 5b are the same as those of communication data 5a.

[0104] Payload 70 is the area used for storing the key. Furthermore, in Figure 11 The example shown is that the payload 70 is configured at the end of the communication data 5b, but the position of the payload 70 is arbitrary.

[0105] Alternatively, the payload 70 may not be configured in the communication data 5b, and any of the payloads 62 to 64, or a portion of the frame header 61, may be used as the area for storing the key. The case where the key is stored in the payload 70 in Embodiment 2 will be described.

[0106] Figure 12 This diagram illustrates the keys exchanged within the communication system according to Embodiment 2. In the communication system 1 of Embodiment 2, the key generation unit 48 of the protocol conversion device 22b generates a public key P. The protocol conversion device 22b sends its public key P to the servo amplifier 12b. As a result, the servo amplifier 12b obtains the public key P of the protocol conversion device 22b.

[0107] Additionally, the key generation unit 58 of servo amplifier 12b generates a public key Q. Servo amplifier 12b then sends its public key Q to servo amplifier 13b. Thus, servo amplifier 13b obtains the public key Q of servo amplifier 12b.

[0108] Additionally, the key generation unit 58 of servo amplifier 13b generates a public key R. Servo amplifier 13b then sends its public key R to servo amplifier 14b. Thus, servo amplifier 14b obtains the public key R of servo amplifier 13b.

[0109] Additionally, the key generation unit 58 of servo amplifier 14b generates a common key C1. The encryption unit 55 of servo amplifier 14b encrypts the common key C1 using the public key R of servo amplifier 13b. Servo amplifier 14b then sends the common key C1, encrypted using the public key R of servo amplifier 13b, to servo amplifier 13b. Thus, servo amplifier 13b obtains the common key C1 encrypted using the public key R.

[0110] Additionally, the key generation unit 58 of servo amplifier 13b generates a common key B1. The encryption unit 55 of servo amplifier 13b encrypts the common key B1 using the public key Q of servo amplifier 12b. Servo amplifier 13b then sends the common key B1, encrypted using the public key Q of servo amplifier 12b, to servo amplifier 12b. Thus, servo amplifier 12b obtains the common key B1 encrypted using the public key Q.

[0111] Furthermore, the key generation unit 58 of the servo amplifier 12b generates a common key A1. The encryption unit 55 of the servo amplifier 12b encrypts the common key A1 using the public key P of the protocol conversion device 22b. The servo amplifier 12b then sends the common key A1, encrypted using the public key P of the protocol conversion device 22b, to the protocol conversion device 22b. Thus, the protocol conversion device 22b obtains the common key A1 encrypted using the public key P.

[0112] Thus, the communication system 1 of embodiment 2 exchanges public and common keys through one round-trip communication between the protocol conversion device 22b and the servo amplifier 14b.

[0113] Furthermore, when generating the public key P, the key generation unit 48 of the protocol conversion device 22b pre-generates a secret key (hereinafter referred to as secret key X) corresponding to the public key P. The secret key X is the decryption key corresponding to the public key P, which serves as the cryptographic key.

[0114] Similarly, when generating the public key Q, the key generation unit 58 of the servo amplifier 12b pre-generates a secret key (hereinafter referred to as secret key Y) corresponding to the public key Q. The secret key Y is the decryption key corresponding to the public key Q, which serves as the cryptographic key.

[0115] Furthermore, when generating the public key R, the key generation unit 58 of the servo amplifier 13b pre-generates a secret key (hereinafter referred to as secret key Z) corresponding to the public key R. The secret key Z is the decryption key corresponding to the public key R, which serves as the cryptographic key.

[0116] From the perspective of servo amplifier 12b, the public key Q used with the downstream device, servo amplifier 13b, is the first public key, and the public key P used with the upstream device, protocol conversion device 22b, is the second public key. Similarly, from the perspective of servo amplifier 13b, the public key R used with the downstream device, servo amplifier 14b, is the first public key, and the public key Q used with the upstream device, servo amplifier 12b, is the second public key. Furthermore, from the perspective of protocol conversion device 22b, the public key P used with the downstream device, servo amplifier 12b, is the first public key. Furthermore, from the perspective of servo amplifier 14b, the public key R used with the upstream device, servo amplifier 13b, is the second public key.

[0117] Furthermore, from the perspective of servo amplifier 12b, the common key B1 used with the downstream device, servo amplifier 13b, is the downstream common key, and the common key A1 used with the upstream device, protocol conversion device 22b, is the upstream common key. Similarly, from the perspective of servo amplifier 13b, the common key C1 used with the downstream device, servo amplifier 14b, is the downstream common key, and the common key B1 used with the upstream device, servo amplifier 12b, is the upstream common key. Furthermore, from the perspective of protocol conversion device 22b, the common key A1 used with the downstream device, servo amplifier 12b, is the downstream common key. Furthermore, from the perspective of servo amplifier 14b, the common key C1 used with the upstream device, servo amplifier 13b, is the upstream common key.

[0118] Figure 13 This diagram illustrates the keys stored by each device in the communication system according to Embodiment 2. The protocol conversion device 22b in the communication system 1 stores the common key A1, the public key P of the protocol conversion device 22b, and the secret key X of the protocol conversion device 22b via the key storage unit 46.

[0119] The servo amplifier 12b in the communication system 1 stores the common keys A1 and B1, the public key P of the protocol conversion device 22b, the public key Q of the servo amplifier 12b, and the secret key Y of the servo amplifier 12b through the key storage unit 56.

[0120] The servo amplifier 13b in the communication system 1 stores the common key B1, C1, the public key Q of the servo amplifier 12b, the public key R of the servo amplifier 13b, and the secret key Z of the servo amplifier 13b through the key storage unit 56.

[0121] The servo amplifier 14b in the communication system 1 stores the common key C1 and the public key R of the servo amplifier 13b through the key storage unit 56.

[0122] Thus, the common key A1 and the public key P of the protocol conversion device 22b are stored by the adjacent protocol conversion device 22b and servo amplifier 12b. Furthermore, the common key B1 and the public key Q of the servo amplifier 12b are stored by the adjacent servo amplifiers 12b and 13b. Additionally, the common key C1 and the public key R of the servo amplifier 13b are stored by the adjacent servo amplifiers 13b and 14b.

[0123] In communication system 1, a common key is generated before stable communication begins, and the public key and common key are exchanged with adjacent devices.

[0124] Next, the key exchange process in communication system 1 will be explained. First, the downlink public key transmission and reception process will be explained. Figure 14 This is a flowchart illustrating the downlink public key transmission and reception processing flow of the communication system involved in Implementation Method 2. Figure 14 The diagram shows the activity of the downward movement.

[0125] In the protocol conversion device 22b, after power is turned on, the key generation unit 48 generates a public key P and a secret key X (step S610). The key generation unit 48 of the protocol conversion device 22b stores the generated public key P and secret key X in the key storage unit 46 (step S620). In addition, the key generation unit 48 stores the generated public key P in the payload 70 (step S630).

[0126] The key generation unit 48 transmits communication data containing the public key P to the transceiver unit 43 (step S640). The transceiver unit 43 then sends the communication data to the transceiver unit 52 of the subsequent device, namely the servo amplifier 12b (step S650). Furthermore, the processing in step S620 can also be performed after any of the processing in steps S630 to S650.

[0127] In the servo amplifier 12b, if the transceiver unit 52 receives communication data (step S660), the control unit 41 obtains the communication data from the transceiver unit 52 (step S670).

[0128] The control unit 51 of the servo amplifier 12b obtains the public key P of the preceding device, the protocol conversion device 22b, from the payload 70 and stores it in the key storage unit 56 (step S680). Additionally, the control unit 51 of the servo amplifier 12b uses the key generation unit 58 to generate a public key Q and a secret key Y. That is, the key generation unit 58 of the servo amplifier 12b generates the public key Q and the secret key Y (step S690). The key generation unit 58 of the servo amplifier 12b stores the generated public key Q and secret key Y in the key storage unit 56 (step S700). Furthermore, the key generation unit 58 of the servo amplifier 12b stores the generated public key Q in the payload 70 (step S710).

[0129] The key generation unit 58 of the servo amplifier 12b transmits communication data containing the public key Q to the transceiver unit 53 (step S720). The transceiver unit 53 of the servo amplifier 12b then transmits the communication data to the transceiver unit 52 of the servo amplifier 13b (step S730). Furthermore, the processing in step S680 can also be performed after any of the processing in steps S690 to S730. Additionally, the processing in step S700 can also be performed after any of the processing in steps S710 to S730.

[0130] The same processing as that of servo amplifier 12b is performed in servo amplifier 13b. That is, in servo amplifier 13b, transceiver 52 receives communication data (step S740), and control unit 51 obtains communication data from transceiver 52 (step S750).

[0131] Then, the control unit 51 of the servo amplifier 13b obtains the public key Q of the preceding device, namely the servo amplifier 12b, from the payload 70 and stores it in the key storage unit 56 (step S760). Additionally, the key generation unit 58 of the servo amplifier 13b generates a public key R and a secret key Z (step S770). The key generation unit 58 stores the generated public key R and secret key Z in the key storage unit 56 (step S780). Furthermore, the key generation unit 58 stores the generated public key R in the payload 70 (step S790).

[0132] The key generation unit 58 of the servo amplifier 13b transmits communication data containing the public key R to the transceiver unit 53 (step S800). The transceiver unit 53 of the servo amplifier 13b then transmits the communication data to the transceiver unit 52 of the servo amplifier 14b (step S810). Furthermore, the processing in step S760 can also be performed after any of the processing in steps S770 to S810. Additionally, the processing in step S780 can also be performed after any of the processing in steps S790 to S810.

[0133] In servo amplifier 14b, if transceiver 52 receives communication data (step S820), control unit 51 obtains the communication data from transceiver 52 (step S830). Control unit 51 of servo amplifier 14b obtains the public key R of the preceding device, servo amplifier 13b, from payload 70 and stores it in key storage unit 56 (step S840).

[0134] In this way, during the downlink, the generation of the public key and the secret key, and the transmission of the public key are repeated until the communication data reaches the device at the end of the daisy chain, namely the servo amplifier 14b.

[0135] Next, the process of sending and receiving the common key in the uplink will be explained. Figure 15 This is a flowchart illustrating the uplink common key transmission and reception processing flow of the communication system involved in Implementation Method 2. Figure 15 The diagram shows the upward movement.

[0136] Servo amplifier 14b generates a common key C1 using key generation unit 58. That is, key generation unit 58 of servo amplifier 14b generates common key C1 (step S900). Key generation unit 58 of servo amplifier 14b stores the generated common key C1 in key storage unit 56 (step S910). Additionally, key generation unit 58 of servo amplifier 14b stores the generated common key C1 in payload 70 (step S920).

[0137] The encryption unit 55 of the servo amplifier 14b reads the public key R obtained from the upstream device, namely the servo amplifier 13b, from the key storage unit 56, and uses the public key R to encrypt the communication data (step S930). Thus, the common key C1 contained in the communication data is encrypted by the public key R.

[0138] The encryption unit 55 of the servo amplifier 14b transmits the encrypted communication data to the transceiver unit 52 (step S940). The transceiver unit 52 of the servo amplifier 14b sends the communication data to the transceiver unit 53 of the servo amplifier 13b (step S950). Furthermore, the processing in step S910 can also be performed after the processing in any of steps S920 to S950.

[0139] In the servo amplifier 13b, if the transceiver unit 53 receives communication data (step S960), the control unit 51 obtains the communication data from the transceiver unit 53 (step S970).

[0140] The control unit 51 of the servo amplifier 13b uses the decryption unit 54 to decrypt the acquired communication data. That is, the decryption unit 54 of the servo amplifier 13b decrypts the communication data sent from the servo amplifier 14b (step S980). At this time, the decryption unit 54 of the servo amplifier 13b refers to the key storage unit 56 and uses the secret key Z to decrypt the communication data. That is, the decryption unit 54 of the servo amplifier 13b reads the secret key Z corresponding to the public key R from the key storage unit 56 and uses the secret key Z to decrypt the communication data. As a result, the common key C1 contained in the communication data is also decrypted.

[0141] The control unit 51 of the servo amplifier 13b obtains the common key C1 of the payload 70 of the decrypted communication data and stores it in the key storage unit 56 (step S990). The servo amplifier 13b uses the key generation unit 58 to generate the common key B1. That is, the key generation unit 58 of the servo amplifier 13b generates the common key B1 (step S1000).

[0142] The key generation unit 58 of the servo amplifier 13b stores the generated common key B1 in the key storage unit 56 (step S1010). In addition, the key generation unit 58 of the servo amplifier 13b stores the generated common key B1 in the payload 70 (step S1020).

[0143] The encryption unit 55 of the servo amplifier 13b reads the public key Q obtained from the upstream device, namely the servo amplifier 12b, from the key storage unit 56, and uses the public key Q to encrypt the communication data (step S1030). Thus, the common key B1 contained in the communication data is encrypted by the public key Q.

[0144] The encryption unit 55 of the servo amplifier 13b transmits the encrypted communication data to the transceiver unit 52 (step S1040). The transceiver unit 52 of the servo amplifier 13b sends the communication data to the transceiver unit 53 of the servo amplifier 12b (step S1050). Furthermore, the processing in step S990 can also be performed after any of the processing in steps S1000 to S1050. Additionally, the processing in step S1010 can also be performed after any of the processing in steps S1020 to S1050.

[0145] In the servo amplifier 12b, if the transceiver unit 53 receives communication data (step S1060), the control unit 51 obtains the communication data from the transceiver unit 53 (step S1070).

[0146] The control unit 51 of the servo amplifier 12b uses the decryption unit 54 to decrypt the acquired communication data. That is, the decryption unit 54 of the servo amplifier 12b decrypts the communication data sent from the servo amplifier 13b (step S1080). At this time, the decryption unit 54 of the servo amplifier 12b refers to the key storage unit 56 and uses the secret key Y to decrypt the communication data. That is, the decryption unit 54 of the servo amplifier 12b reads the secret key Y corresponding to the public key Q from the key storage unit 56 and uses the secret key Y to decrypt the communication data. As a result, the common key B1 contained in the communication data is also decrypted.

[0147] The control unit 51 of the servo amplifier 12b obtains the common key B1 of the payload 70 of the decrypted communication data and stores it in the key storage unit 56 (step S1090). The servo amplifier 12b uses the key generation unit 58 to generate the common key A1. That is, the key generation unit 58 of the servo amplifier 12b generates the common key A1 (step S1100).

[0148] The key generation unit 58 of the servo amplifier 12b stores the generated common key A1 in the key storage unit 56 (step S1110). In addition, the key generation unit 58 of the servo amplifier 12b stores the generated common key A1 in the payload 70 (step S1120).

[0149] The encryption unit 55 of the servo amplifier 12b reads the public key P obtained from the upstream device, namely the protocol conversion device 22b, from the key storage unit 56, and uses the public key P to encrypt the communication data (step S1130). Thus, the common key A1 contained in the communication data is encrypted by the public key P.

[0150] The encryption unit 55 of the servo amplifier 12b transmits the encrypted communication data to the transceiver unit 52 (step S1140). The transceiver unit 52 of the servo amplifier 12b sends the communication data to the transceiver unit 43 of the protocol conversion device 22b (step S1150). Furthermore, the processing in step S1090 can also be performed after any of the processing in steps S1000 to S1150. Additionally, the processing in step S1110 can also be performed after any of the processing in steps S1120 to S1150.

[0151] In the protocol conversion device 22b, if the transceiver unit 43 receives communication data sent from the servo amplifier 12b (step S1160), the control unit 41 obtains the communication data from the transceiver unit 43 (step S1170).

[0152] The control unit 41 of the protocol conversion device 22b uses the decryption unit 44 to decrypt the acquired communication data. That is, the decryption unit 44 of the protocol conversion device 22b decrypts the communication data sent from the servo amplifier 12b (step S1180). At this time, the decryption unit 44 of the protocol conversion device 22b refers to the key storage unit 46 and uses the secret key X to decrypt the communication data. That is, the encryption unit 45 of the protocol conversion device 22b reads the secret key X corresponding to the public key P from the key storage unit 56 and uses the secret key X to decrypt the communication data. As a result, the common key A1 contained in the communication data is also decrypted.

[0153] The control unit 41 of the protocol conversion device 22b obtains the common key A1 of the payload 70 of the decrypted communication data and stores it in the key storage unit 46 (step S1190).

[0154] Through Figure 14 and Figure 15 As described in the previous section, the protocol conversion device 22b and servo amplifiers 12b to 14b within communication system 1 can each obtain the processing described in the previous section. Figure 13 The key described earlier. Then, stable communication begins in communication system 1. In communication system 1 of embodiment 2, the same processing as in communication system 1 of embodiment 1 is performed (in... Figure 7 and Figure 8 (As explained in the previous section), stable communication is performed using the common keys A1 to C1.

[0155] Thus, in communication system 1, a common key can be shared between adjacent devices during the period when communication data is exchanged once between the protocol conversion device 22b and the servo amplifier 14b. After sharing the common key, communication system 1 can conceal the communication data and communication protocol by performing the data communication described in embodiment 1.

[0156] As described above, in Embodiment 2, the protocol conversion device 22b and servo amplifiers 12b and 13b generate a public key and a secret key, and send the public key to the downstream device. Additionally, servo amplifiers 12b to 14b generate a common key, and encrypt the common key using the public key obtained from the adjacent upstream device, and send the encrypted common key to the adjacent upstream device. The adjacent upstream device decrypts the common key using the secret key corresponding to the public key, and obtains the common key. Therefore, the protocol conversion device 22b and servo amplifiers 12b to 14b can pre-store the same common key between adjacent devices.

[0157] Implementation Method 3

[0158] Next, use Figures 16 to 18Implementation method 3 will be described. In implementation method 1, each device pre-stores the keys used for encryption and decryption. Furthermore, in implementation method 2, each device generates a key before starting stable communication and exchanges it with the other device, using the key in subsequent stable communication. As described above, in implementation methods 1 and 2, the same key is continuously used throughout stable communication. If the key information is leaked to the outside during stable communication, it could potentially lead to subsequent communication data being decrypted by an external attacker. Therefore, in implementation method 3, the key is regenerated at an arbitrary timing during stable communication and exchanged between the devices.

[0159] The communication system 1 of Embodiment 3 includes a control device 21, a protocol conversion device 22c (described later), and servo amplifiers 12b to 14b. That is, the communication system 1 of Embodiment 3 has a protocol conversion device 22c instead of a protocol conversion device 22b.

[0160] Similar to protocol conversion device 22b, protocol conversion device 22c is a computer that converts communication protocols. That is, protocol conversion device 22c converts the communication protocols of control device 21 and servo amplifiers 12b to 14b.

[0161] In Embodiment 3, the protocol conversion device 22c and servo amplifiers 12b and 13b perform stable communication while generating a common key at a specific period and sending the common key to the downstream device. Thus, the communication system 1 of Embodiment 3 performs stable communication while updating the common key at a specific period.

[0162] Figure 16 This is a diagram showing the structure of the protocol conversion device according to Embodiment 3. Figure 16 Achievement and Figure 9 Structural elements with the same function as those in the protocol conversion device 22b of Embodiment 2 shown are labeled with the same reference numerals, and repeated descriptions are omitted.

[0163] In addition to the structural elements of the protocol conversion device 22b, the protocol conversion device 22c also has a counter 49. The counter 49 periodically performs incrementing or decrementing counting.

[0164] The control unit 41 of the protocol conversion device 22c monitors whether the count value obtained by the counter 49 has reached a specific value through polling or notification from the counter 49. When the counter 49 reaches its count limit, the protocol conversion device 22c generates a new common key. That is, if the count value obtained by the counter 49 reaches a specific value, the protocol conversion device 22c generates a new common key. The protocol conversion device 22c sends the generated new common key to the servo amplifier 12b.

[0165] In Embodiment 3, when the servo amplifier 14b, which is connected to the end of the device group consisting of protocol conversion device 22c and servo amplifiers 12b to 14b, is set as the most downstream device, protocol conversion device 22c is the most upstream device. Furthermore, the upstream devices other than the downstream device (servo amplifier 14b) are protocol conversion device 22c and servo amplifiers 12b and 13b. If the count value obtained by counter 49 reaches a specific value, each of these upstream devices generates a new common key that is different from the stored common key.

[0166] Figure 17 This is a diagram illustrating the structure of communication data transmitted and received within the communication system according to Embodiment 3. The communication data 5c transmitted and received within the communication system 1 of Embodiment 3 includes a frame header 61X, payloads 62-64, and payload 70. The payloads 62-64 and 70 of the communication data 5c are the same as the payloads 62-64 and 70 of the communication data 5b.

[0167] Compared to frame header 61, frame header 61X has an area for storing flag 75. Flag 75 is a variable that the control unit 41 of the protocol conversion device 22c can set at any time. In embodiment 3, for example, when the control unit 41 receives a notification from the counter 49 indicating that the counter 49 has reached the end of its count, it sets data (e.g., 1) indicating the end of the count on the flag 75. Furthermore, the payload 70 of the communication data 5c is used for key exchange in the same way as in embodiment 2. That is, the newly generated common key is stored in the payload 70 of the communication data 5c.

[0168] Before stabilizing communication, the protocol conversion device 22c of embodiment 3 sets flag 75 to 1, indicating the timing for generating a common key. Furthermore, the protocol conversion device 22c generates an initial common key for stabilizing communication. The protocol conversion device 22c then sends communication data 5c, including the generated common key and flag 75 set to 1, to the servo amplifier 12b.

[0169] If the servo amplifier 12b receives the flag 75 set to 1, it generates the initial common key and sends the communication data 5c, which includes the generated common key and the flag 75 set to 1, to the servo amplifier 13b.

[0170] If the servo amplifier 13b receives the flag 75 set to 1, it generates the initial common key and sends the communication data 5c, which includes the generated common key and the flag 75 set to 1, to the servo amplifier 14b.

[0171] In communication system 1, after the initial common key is stored in servo amplifiers 12b-14b, stable communication begins. If stable communication begins, the protocol conversion device 22c starts counting using counter 49. If the count value obtained by counter 49 becomes a specific value, the protocol conversion device 22c sets flag 75 to 1, indicating the timing for generating the common key. Additionally, the protocol conversion device 22c generates a new common key for stable communication. The protocol conversion device 22c sends communication data 5c, including the generated common key and flag 75 set to 1, to servo amplifier 12b.

[0172] If servo amplifiers 12b and 13b each receive a flag 75 set to 1, they generate a new common key and send communication data 5c, including the generated common key and the flag 75 set to 1, to the downstream servo amplifier.

[0173] Furthermore, the communication system 1 in Embodiment 3 can also be similar to the communication system 1 in Embodiment 1, where each device stores a common key before stable communication begins. That is, the protocol conversion device 22c stores the common key A1, the servo amplifier 12b stores common keys A1 and B1, the servo amplifier 13b stores common keys B1 and C1, and the servo amplifier 14b stores the common key C1. In this case, if stable communication begins and the count value obtained by the counter 49 changes to a specific value, the protocol conversion device 22c also sets the flag 75 to 1, indicating the timing for generating the common key.

[0174] Next, the data communication processing flow during stable communication in communication system 1 will be explained. First, the downlink data communication will be explained. Figure 18 This is a flowchart illustrating the downlink data communication processing flow of the communication system according to Embodiment 3. Figure 18 The diagram shows the activity of the downward movement.

[0175] In addition, regarding Figure 18 The processing of the description and in Figure 7 The same processing described above, in Figure 18 The same step numbers are marked in the text, and their descriptions are omitted. Figure 18 In this document, the following situation will be explained: In the same manner as in Implementation 1, each device stores the common key A1 to C1 in advance before stable communication begins.

[0176] In addition, Figure 7 In the process, the control device 21 sends communication data to the protocol conversion device 22a, and the protocol conversion device 22a sends the communication data to the servo amplifier 12a, but... Figure 18In the process, control device 21 sends communication data to protocol conversion device 22c, and protocol conversion device 22c sends communication data to servo amplifier 12b. Additionally, in Figure 7 In the process, servo amplifier 12a sends communication data to servo amplifier 13a, and servo amplifier 13a sends communication data to servo amplifier 14a, but... Figure 18 In the process, servo amplifier 12b sends communication data to servo amplifier 13b, and servo amplifier 13b sends communication data to servo amplifier 14b.

[0177] In the communication system 1 of Embodiment 3, if stable communication begins, counter 49 starts counting. Then, control device 21 executes the processing of step S110, and protocol conversion device 22c executes the processing of steps S120 to S140. Alternatively, counter 49 may start counting after protocol conversion device 22c receives the initial communication data from control device 21.

[0178] In the protocol conversion device 22c, after the protocol conversion unit 47 performs the protocol conversion of the communication data, the control unit 41 determines whether the counter 49 has expired (step S141).

[0179] When the counter 49 reaches the end of its count period (step S141, Yes), the control unit 41 of the protocol conversion device 22c sets the flag 75 to 1 (step S142). Additionally, the control unit 41 resets the counter 49 (step S143).

[0180] Then, in the protocol conversion device 22c, the key generation unit 48 generates a new common key A2 for use with the servo amplifier 12b (step S144). That is, the key generation unit 48 of the protocol conversion device 22c generates a new common key A2 that is different from the common key A1. The key generation unit 48 of the protocol conversion device 22c stores the generated common key A2 in the key storage unit 46 (step S145). In addition, the key generation unit 48 of the protocol conversion device 22c stores the generated common key A2 in the payload 70 (step S146).

[0181] If the counter 49 has not reached the end of its count (step S141, No), the control unit 41 sets the flag 75 to a number indicating that the count has not reached the end of its count (e.g., 0) (step S147).

[0182] After the processing in step S146 or step S147, the protocol conversion device 22c executes the processing in steps S150 to S170. That is, the encryption unit 45 encrypts the protocol-converted communication data (step S150). The communication data encrypted by the encryption unit 45 contains a common key A1. At this time, the encryption unit 45 refers to the key storage unit 46 and uses the common key A1 between itself and the downstream device to encrypt the communication data. That is, the encryption unit 45 uses the common key A1 stored in the servo amplifier 12b to encrypt the communication data, and has not yet used the common key A2.

[0183] The encryption unit 45 transmits the encrypted communication data to the transceiver unit 43 (step S160). The transceiver unit 43 then sends the communication data to the transceiver unit 52 of the servo amplifier 12b (step S170). Furthermore, after sending the common key A2 to the servo amplifier 12b, the encryption unit 45 of the protocol conversion device 22c encrypts the communication data using the common key A2 in step S150. The process in step S145 can also be performed after any of the processes in steps S146, S150 to S170.

[0184] Then, the servo amplifier 12b performs the processing steps S180 and S190. Further, the control unit 51 of the servo amplifier 12b decrypts the communication data using the common key A1 between it and the upstream device (step S200).

[0185] The control unit 51 of the servo amplifier 12b confirms the value of the flag 75 (step S201) and determines whether the flag 75 is set to 1 (step S202).

[0186] When flag 75 is set to 1 (step S202, Yes), the control unit 51 of the servo amplifier 12b reads the common key A2 of the protocol conversion device 22c from the communication data and stores it in the key storage unit 56 (step S203).

[0187] Additionally, the key generation unit 58 of the servo amplifier 12b generates a new common key B2 for use with the servo amplifier 13b (step S204). That is, the key generation unit 58 of the servo amplifier 12b generates a new common key B2 that is different from the common key B1. The key generation unit 58 of the servo amplifier 12b stores the generated common key B2 in the key storage unit 56 (step S205). In addition, the key generation unit 58 of the servo amplifier 12b stores the generated common key B2 in the payload 70 (step S206).

[0188] Subsequently, the control unit 51 of the servo amplifier 12b refers to or modifies the data stored in the payload 62 of the decrypted communication data. Furthermore, if the flag 75 is not set to 1 (step S202, No), the servo amplifier 12b does not execute steps S203 to S206, but refers to or modifies the data stored in the payload 62 of the decrypted communication data. If the reference or modification of the data in the payload 62 is complete, the servo amplifier 12b executes steps S210 to S230.

[0189] In the servo amplifier 12b, the encryption unit 55, referring to the key storage unit 56, encrypts the communication data using the common key B1 between the encryption unit and the downstream device (step S210). The communication data encrypted by the encryption unit 55 includes the common key B2. The encryption unit 55 encrypts the communication data using the common key B1 stored in the servo amplifier 13b, but has not yet used the common key B2.

[0190] The encryption unit 55 transmits the encrypted communication data to the transceiver unit 53 (step S220). The transceiver unit 53 then sends the communication data to the transceiver unit 52 of the servo amplifier 13b (step S230). Furthermore, in step S210, the encryption unit 55 of the servo amplifier 12b encrypts the communication data using the common key B2 after sending the common key B2 to the servo amplifier 13b. The process in step S203 can also be performed after any of the processes in steps S204-S206 and S210-S230. Additionally, the process in step S205 can also be performed after any of the processes in steps S206 and S210-S230.

[0191] Subsequently, the servo amplifier 13b performs the processing steps S240 and S250. Further, the control unit 51 of the servo amplifier 13b decrypts the communication data using the common key B1 between it and the upstream device (step S260).

[0192] Then, the servo amplifier 13b further performs the same process as steps S201 to S206 performed by the servo amplifier 12b. That is, the control unit 51 of the servo amplifier 13b confirms the value of the flag 75 (step S261) and determines whether the flag 75 is set to 1 (step S262).

[0193] When flag 75 is set to 1 (step S262, Yes), the control unit 51 of servo amplifier 13b reads the common key B2 of servo amplifier 12b from the communication data and stores it in the key storage unit 56 (step S263).

[0194] Additionally, the key generation unit 58 of the servo amplifier 13b generates a new common key C2 for use with the servo amplifier 14b (step S264). That is, the key generation unit 58 of the servo amplifier 13b generates a new common key C2 that is different from the common key C1. The key generation unit 58 of the servo amplifier 13b stores the generated common key C2 in the key storage unit 56 (step S265). In addition, the key generation unit 58 of the servo amplifier 13b stores the generated common key C2 in the payload 70 (step S266).

[0195] Subsequently, the control unit 51 of the servo amplifier 13b refers to or modifies the data stored in the payload 63 of the decrypted communication data. Furthermore, if the flag 75 is not set to 1 (step S262, No), the servo amplifier 13b does not execute steps S263 to S266, but refers to or modifies the data stored in the payload 63 of the decrypted communication data. If the reference or modification of the data within the payload 63 is complete, the servo amplifier 13b executes steps S270 to S290.

[0196] In servo amplifier 13b, encryption unit 55, referring to key storage unit 56, encrypts communication data using a common key C1 shared with downstream devices (step S270). The communication data encrypted by encryption unit 55 includes common key C2. Encryption unit 55 encrypts communication data using common key C1 stored in servo amplifier 14b, but has not yet used common key C2.

[0197] The encryption unit 55 transmits the encrypted communication data to the transceiver unit 53 (step S280). The transceiver unit 53 then sends the communication data to the transceiver unit 52 of the servo amplifier 14b (step S290). Furthermore, after sending the common key C2 to the servo amplifier 14b, the encryption unit 55 of the servo amplifier 13b encrypts the communication data using the common key C2 in the processing of step S270. The processing of step S263 can also be performed after any of the processing of steps S264-S266 and S270-S290. Additionally, the processing of step S265 can also be performed after any of the processing of steps S266 and S270-S290.

[0198] Subsequently, the servo amplifier 14b performs the processing steps S300 and S310. Further, the control unit 51 of the servo amplifier 14b decrypts the communication data using the common key C1 between it and the upstream device (step S320).

[0199] Then, the servo amplifier 14b further performs the same processing as steps S201 and S202 performed by the servo amplifier 12b. That is, the control unit 51 of the servo amplifier 14b confirms the value of the flag 75 (step S321) and determines whether the flag 75 is set to 1 (step S322).

[0200] When flag 75 is set to 1 (step S322, Yes), the control unit 51 of servo amplifier 14b reads the common key C2 of servo amplifier 13b from the communication data and stores it in the key storage unit 56 (step S323).

[0201] Subsequently, the control unit 51 of the servo amplifier 14b refers to or modifies the data stored in the payload 64 of the decrypted communication data. Additionally, if the flag 75 is not set to 1 (step S322, No), the servo amplifier 14b does not perform the processing of step S323, but refers to or modifies the data stored in the payload 62 of the decrypted communication data.

[0202] If the reference or change of data within payload 64 ends, the servo amplifier 14b performs the same processing as steps S210 and S220 described above.

[0203] In the servo amplifier 14b, as a process corresponding to step S210 above, the encryption unit 55, referring to the key storage unit 56, encrypts the communication data using the latest common key between itself and the upstream device. That is, the encryption unit 55 encrypts the communication data using the common key C2 if it has it stored, and encrypts the communication data using the common key C1 if it does not have the common key C2 stored. Then, as a process corresponding to step S220 above, the encryption unit 55 transmits the encrypted communication data to the transceiver unit 52.

[0204] As described above, in this embodiment, at the point when the counter 49 expires and the downlink ends, each device enters a state where it has stored a new common key. Subsequently, during uplink data communication, the transceiver 52 of the servo amplifier 14b sends communication data to the transceiver 53 of the servo amplifier 13b. Then, the same processing as described in Embodiment 1 is performed. That is, in subsequent uplink communications, each device uses the latest common key to perform stable communication as in Embodiment 1.

[0205] As described above, according to Embodiment 3, if the counter 49 expires, the communication system 1 generates a new common key. Therefore, the same common key is not continuously used in stable communication. Thus, even if the common key information in stable communication is leaked to the outside, the use of the new common key for data communication can temporarily suppress the possibility of external attackers decrypting the communication data.

[0206] Next, the hardware structure of the protocol conversion devices 22a-22c and the servo amplifiers 12a-14a, 12b-14b will be described. Furthermore, since the hardware structure of the protocol conversion devices 22a-22c and the servo amplifiers 12a-14a, 12b-14b is the same, the hardware structure of the protocol conversion device 22a will be described here.

[0207] Figure 19 This diagram illustrates an example of the hardware structure of the protocol conversion device according to Embodiment 1. The protocol conversion device 22a can be implemented by a processor 100, a memory 200, and a transceiver 300. Examples of the processor 100 include a CPU (Central Processing Unit, also known as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, DSP (Digital Signal Processor)) or a system LSI (Large Scale Integration). Examples of the memory 200 include RAM (Random Access Memory) and ROM (Read Only Memory).

[0208] The protocol conversion device 22a is implemented by the processor 100 reading and executing a computer-executable communication program stored in the memory 200 for performing the actions of the protocol conversion device 22a. Alternatively, the communication program for performing the actions of the protocol conversion device 22a can be described as enabling the computer to execute the process or method of the protocol conversion device 22a.

[0209] The communication program executed by the protocol conversion device 22a is a modular structure including a control unit 41, a decryption unit 44, an encryption unit 45, a key storage unit 46, and a protocol conversion unit 47. These modules are loaded onto the main storage device and generated on the main storage device.

[0210] The transceiver 300 performs data communication between the upstream and downstream devices. In the case of the protocol conversion device 22a, data communication is performed between the control device 21 and the servo amplifier 12a. The transceiver 300 corresponds to the transceiver units 42 and 43.

[0211] The memory 200 stores common keys such as A1. Additionally, the memory 200 also serves as temporary storage when the processor 100 performs various processes.

[0212] The communication program executed by the protocol conversion device 22a can also be provided as a computer program product by storing it in a computer-readable storage medium in an installable or executable format. Alternatively, the communication program can also be provided to the protocol conversion device 22a via a network such as the Internet. Furthermore, the functions of the protocol conversion device 22a can be partially implemented by dedicated hardware such as dedicated circuitry, and partially by software or firmware.

[0213] The structure shown in the above embodiments is an example and can be combined with other known technologies. The embodiments can also be combined with each other. Without departing from the main idea, some parts of the structure can be omitted or changed.

[0214] Explanation of the label

[0215] 1. Communication system; 2. 3X-3Z network; 5a-5c communication data; 12a-14a, 12b-14b servo amplifiers; 21. Control device; 22a-22c protocol conversion device; 41, 51 control unit; 42, 43, 52, 53 transceiver unit; 44, 54 decryption unit; 45, 55 encryption unit; 46, 56 key storage unit; 47 protocol conversion unit; 48, 58 key generation unit; 49 counter; 61, 61X frame header; 62-64, 70 payload; 75 flag; 100 processor; 200 memory; 300 transceiver device.

Claims

1. A communication system comprising: a controlled device connected in series; and a control device that controls the controlled device by transmitting and receiving communication data with the controlled device; A protocol conversion device is connected between the controlled device and the control device to convert the communication protocol of the controlled device and the communication protocol of the control device to each other. Each of the control device, the protocol conversion device, and the controlled device is connected in series. The communication system is characterized by, Each device in the device group, including the protocol conversion device and the controlled device, has: The key storage unit stores the first common key used between adjacent devices, but does not store the common key used by non-adjacent devices. An encryption unit that encrypts the communication data using the first common key; The decryption unit uses the first common key to decrypt the communication data; as well as The transceiver unit transmits and receives encrypted communication data with the adjacent device. Even if the communication data contains data targeting the non-adjacent device, the encryption unit encrypts the communication data using the first common key.

2. The communication system according to claim 1, characterized in that, Before the transmission and reception of the communication data begins, the key storage unit stores the first common key in advance.

3. The communication system according to claim 1, characterized in that, When the controlled device connected to the end in the device group is set as the most downstream device, the intermediate devices in the device group other than the devices connected to the most downstream and the most upstream also have a key generation unit. Before the transmission and reception of the communication data begins, the key generation unit generates a first public key and a secret key corresponding to the first public key for use with the downstream device. The transceiver unit of the intermediate device has a first transceiver unit for transmitting and receiving communication data with a downstream device, and a second transceiver unit for transmitting and receiving communication data with an upstream device. In the intermediate device, before the transmission and reception of the communication data begin, The first transceiver unit sends the first public key to the downstream device, and the second transceiver unit receives the second public key sent from the upstream device. The encryption unit encrypts the upstream common key, which is the key used between the first common key and the upstream device, using the second public key. The second transceiver unit transmits the upstream common key, encrypted with the second public key, to the upstream device, and the first transceiver unit receives the downstream common key, which is the key used between the first common key and the downstream device, from the downstream device. The decryption unit decrypts the downstream common key using the secret key. In the intermediate device, if the transmission and reception of communication data begins, The encryption unit then uses the upstream common key to encrypt the communication data sent to the upstream device, and uses the downstream common key to encrypt the communication data sent to the downstream device. The decryption unit then uses the upstream common key to decrypt the communication data received from the upstream device, and uses the downstream common key to decrypt the communication data received from the downstream device.

4. The communication system according to claim 1, characterized in that, The protocol conversion device also includes a counter that performs incrementing or decrementing counting at a specific period. When the controlled device connected to the end in the device group is set as the downstream device, each of the upstream devices in the device group, excluding the downstream device, also has a key generation unit. If the count value obtained by the counter reaches a specific value, the key generation unit generates a new first common key that is different from the first common key stored in the key storage unit. The transceiver unit sends the new first common key to the downstream device in a manner included in the communication data.

5. A communication method used by a communication system comprising: a controlled device connected in series; and a control device that controls the controlled device by transmitting and receiving communication data with the controlled device. A protocol conversion device is connected between the controlled device and the control device to convert the communication protocol of the controlled device and the communication protocol of the control device to each other. Each of the control device, the protocol conversion device, and the controlled device is connected in series. The communication method is characterized by including: The key storage step includes each device in the device group, including the protocol conversion device and the controlled device, storing the first common key used with adjacent devices, and not storing the common key used by non-adjacent devices. In the encryption step, each device in the device group uses the first common key to encrypt the communication data; In the decryption step, each device in the device group uses the first common key to decrypt the communication data; as well as In the transmission and reception step, each device in the device group transmits and receives encrypted communication data with the adjacent devices. In the encryption step, even if the communication data contains data targeting the non-adjacent device, the communication data is encrypted using the first common key.

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