JP2011091471A - Communication terminal device, communication processing method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent leakage of an encryption key during data communication performed in an ad hoc network. <P>SOLUTION: A first node generates a first encryption key for data addressed to the node itself, at a prescribed interval and encrypts the first encryption key by a common key and notifies the other nodes of the encrypted first encryption key. The first node uses a second encryption key notified by a second node to encrypt data addressed to the second node and transmits a first data frame including encryption text data, to the second node. At this time, the first node transmits a dummy frame including dummy data to the second node as the first data frame at prescribed timing. On reception of a second data frame from the second node, the first node decrypts encryption text data included in the second data frame by the first encryption key. Then, the first node determines whether decrypted plain text data is proper or not, and discards the second data frame when it is not proper. Dummy frame transmission at prescribed timing prevents leakage of the encryption key during data communication. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present technology relates to a security maintenance technology in an ad hoc network.

  Conventionally, techniques such as WEP (Wired Equivalent Privacy) and WPA (Wi-Fi Protected Access) exist as encryption techniques in a wireless local area network (LAN). However, in an ad hoc network that does not have an access point, encryption techniques such as WEP and WPA cannot be employed. In addition, resources such as CPU (Central Processing Unit) and memory of communication terminal devices and communication bandwidth are often limited, and encryption algorithms that require a large amount of calculation and encryption keys with a large number of bits are used. It is difficult to do. Therefore, in an ad hoc network, encryption communication is often performed by a common key encryption method (sometimes called a symmetric key encryption method) using RC4 (Ron's Code 4) or the like.

  On the other hand, for example, an attack in which a malicious third party collects a large number of encrypted packets and performs statistical analysis on the collected packets to determine an encryption key (sometimes called a statistic attack) ) Is known in recent years. Therefore, if the same encryption key is used for a long time, the encryption key may be leaked to a third party.

Japanese Patent No. 3182617 JP 2006-54568 A WO96 / 02992 publication JP 2006-13781 A JP 2009-10596 A

  For example, there is a technique for changing an encryption key at regular intervals. However, threats to the network are becoming more sophisticated year by year, and it is difficult to estimate how often the encryption key is updated if it is safe. Further, for example, if the encryption key update interval is too short, there is a risk that the original communication may be hindered, such as an increase in load due to the encryption key update process. In other words, the conventional technology is not a sufficient security measure.

  Therefore, an object of the present technology is to provide a technology for preventing an encryption key from leaking during data communication performed in an ad hoc network.

  The communication terminal device includes a key storage unit that stores a common key, which is a common encryption key with other communication terminal devices, and a data for the first communication terminal device that is the own communication terminal device at a predetermined interval. An access key generation unit that generates a first access key that is an encryption key and stores the first access key in the key storage unit, and a common key that is stored in the key storage unit with the first access key generated by the access key generation unit And an access key notification unit that transmits the first access key notification frame including the encrypted first access key to another communication terminal device by broadcast, and a second of the other communication terminal devices. A second including an access key notification data, which is data obtained by encrypting a second access key generated as an encryption key for data addressed to the second communication terminal device from the communication terminal device with a common key; An access key receiving unit that receives the access key notification frame, and the access key notification data included in the second access key notification frame is decrypted using the common key stored in the key storage unit. The first plaintext data including the access key decryption unit that acquires the access key of 2 and stores the access key in association with the identification information of the second communication terminal device in the key storage unit; Is encrypted with a second access key stored in the key storage unit and corresponding to the second communication terminal device, thereby generating first ciphertext data, including the generated first ciphertext data A data transmission unit that transmits the first data frame to the second communication terminal device and a dummy frame including dummy data are generated at a predetermined timing, and the dummy data is generated in the data transmission unit. A dummy frame generation unit that transmits a frame as a first data frame to the second communication terminal device, and a data reception unit that receives a second data frame including the second ciphertext data from the second communication terminal device And a data decryption unit that obtains the second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit. And determining whether or not the second plaintext data is appropriate as the plaintext data in the second data frame, and if it is determined that the second plaintext data is not appropriate, a dummy frame determination unit that discards the second data frame. .

  It is possible to prevent the encryption key from leaking during data communication performed in the ad hoc network.

FIG. 1 is a diagram illustrating an example of an ad hoc network. FIG. 2 is a functional block diagram of the communication terminal apparatus according to the present embodiment. FIG. 3 is a diagram illustrating an example of data stored in the key storage unit. FIG. 4 is a diagram for explaining an outline of data communication between communication terminal apparatuses according to the present embodiment. FIG. 5 is a diagram showing a processing flow when an access key is generated and notified. FIG. 6 is a diagram illustrating an example of the format of the access key notification frame. FIG. 7 is a diagram illustrating a setting example of an access key notification frame transmitted from the node B to the node A. FIG. 8 is a diagram illustrating an example of an encrypted access key notification frame (no signature). FIG. 9 is a diagram illustrating an example of an access key notification frame (with signature) after encryption. FIG. 10 is a diagram showing a processing flow (first portion) at the time of data frame transmission and reception. FIG. 11 is a diagram illustrating an example of a data frame format. FIG. 12 is a diagram illustrating a setting example of a data frame transmitted from the node A to the node B. FIG. 13 is a diagram illustrating an example of an encrypted data frame (no signature). FIG. 14 is a diagram illustrating an example of an encrypted data frame (with a signature). FIG. 15 is a diagram illustrating an example of the format of a dummy frame. FIG. 16 is a diagram illustrating a setting example of a dummy frame (no signature) transmitted from the node A to the node B. FIG. 17 is a diagram illustrating an example of data stored in the key storage unit when dummy keys are stored. FIG. 18 is a diagram illustrating a setting example of a dummy frame (signed) transmitted from the node A to the node B. FIG. 19 is a diagram illustrating an example of an encrypted dummy frame (no signature). FIG. 20 is a diagram illustrating an example of an encrypted dummy frame (with a signature). FIG. 21 is a diagram showing a processing flow (second part) at the time of data frame transmission and reception. FIG. 22 is a functional block diagram of a computer. FIG. 23 is a functional block diagram of a communication terminal apparatus according to the first aspect of the present technology. FIG. 24 is a diagram illustrating a processing flow of the communication processing method according to the second aspect of the present technology.

  FIG. 1 shows an example of an ad hoc network according to an embodiment of the present technology. In FIG. 1, an ad hoc network is constructed by terminals A to I that can directly wirelessly communicate with adjacent terminals. Since it is an ad hoc network, FIG. 1 only shows a temporary state, and each terminal freely moves and transitions to a different network state. In the present embodiment, the terminals constituting the ad hoc network may be referred to as nodes or communication terminal devices.

  FIG. 2 shows a functional block diagram of the communication terminal apparatus. As shown in FIG. 2, the communication terminal device includes a key storage unit 1 that stores various access keys (encryption keys and the like), and a transmission unit that transmits a frame using data stored in the key storage unit 1. 3 and a receiving unit 5 that performs processing on a frame received using the data stored in the key storage unit 1.

  For example, as shown in FIG. 3, the key storage unit 1 stores a common key and various access keys. In the example of FIG. 3, the key storage unit 1 includes a key type column and a key (hexadecimal) column. The common key is an encryption key shared by all the nodes constituting the ad hoc network, and is stored in the key storage unit 1 in advance. The common key is used when encrypting and decrypting a payload portion of an access key notification frame described later. The access key is an encryption key generated at each node, and is notified to other nodes by broadcasting. The access key is used when encrypting transmission data to the generation source node. For example, the access key A shown in FIG. 3 is generated by the node A and notified to nodes other than the node A. Then, for example, the node B encrypts the data addressed to the node A using the access key A and transmits it to the node A. The node A uses the access key A to decrypt the data sent from the node B. Various access keys are periodically updated.

  The transmission unit 3 includes an access key generation unit 31 stored in the key storage unit 1, an access key notification frame generation unit 32, an access key notification frame encryption unit 33, a data frame generation unit 34, and a data frame encryption unit. 35, a dummy frame generation unit 36, and a frame transmission unit 37. The access key generation unit 31 periodically generates an access key for encrypting data addressed to the own node, and stores the access key in the key storage unit 1. The access key notification frame generation unit 32 generates an access key notification frame using the data stored in the key storage unit 1. The access key notification frame encryption unit 33 uses the data stored in the key storage unit 1 to perform encryption processing on the access key notification frame generated by the access key notification frame generation unit 32. The data frame generation unit 34 generates a data frame described later from data addressed to other nodes. The data frame encryption unit 35 performs an encryption process on the data frame generated by the data frame generation unit 34 using the data stored in the key storage unit 1. The dummy frame generation unit 36 generates a dummy frame, which will be described later, using data stored in the key storage unit 1 periodically or at a predetermined timing. The frame transmission unit 37 transmits the frame encrypted by the access key notification frame encryption unit 33 or the data frame encryption unit 35 and the frame generated by the dummy frame generation unit 36 to another node.

  The receiving unit 5 includes a frame receiving unit 51, a frame type determination unit 52, an access key notification frame decoding unit 53, an access key extraction unit 54, a data frame decoding unit 55, a dummy frame determination unit 56, and a data extraction. Part 57. The frame receiving unit 51 receives frames from other nodes and outputs them to the frame type determination unit 52. The frame type determination unit 52 determines the type of the frame received by the frame reception unit 51, and outputs it to the access key notification frame decoding unit 53 if it is an access key notification frame, and to the data frame decoding unit 55 if it is a data frame. Output. The access key notification frame decryption unit 53 uses the data stored in the key storage unit 1 to perform a decryption process on the access key notification frame. The access key extraction unit 54 extracts an access key from the frame decrypted by the access key notification frame decryption unit 53 and stores it in the key storage unit 1. The data frame decryption unit 55 performs a decryption process on the data frame using the data stored in the key storage unit 1. The dummy frame determination unit 56 determines whether or not the frame decoded by the data frame decoding unit 55 is a dummy frame. If the frame is a normal data frame, the dummy frame determination unit 56 outputs the frame to the data extraction unit 57. To do. The data extraction unit 57 extracts data addressed to the own node from the data frame.

  Next, an outline of data communication between communication terminal apparatuses (nodes) according to the present embodiment will be described with reference to FIG. Here, data communication between node A and node B will be described as an example, but the same applies to other nodes. First, each of the node A and the node B generates an access key and notifies other nodes by broadcasting. Specifically, node A generates access key A, encrypts it with a common key held in advance, and transmits it to another node. On the other hand, the node B generates an access key B, encrypts it with a common key held in advance, and transmits it to the node A. After this, the node A and the node B periodically perform such processing and periodically change the access key.

  Then, when there is data addressed to the node B, the node A encrypts the data using the access key B sent from the node B, and creates a data frame including the encrypted data (referred to as ciphertext data). Transmit to node B. At this time, for example, when an agreement is reached between the nodes regarding the inclusion of an electronic signature (for example, a MAC (Message Authentication Code)) in the data frame, the node A generates an electronic signature and converts the electronic signature into the data Include in the frame. In the following, data before encryption may be referred to as plain text data. In the present embodiment, node A transmits a data frame including dummy data (for example, a random number value) to node B at a predetermined timing. In this embodiment, a data frame including dummy data is called a dummy frame in order to distinguish it from a normal data frame. However, as will be described later, in practice, data is decrypted with a correct access key. Cannot determine whether the frame is a dummy frame. When the node B receives the data frame, the node B decrypts the data with the access key B, and determines whether the data included in the data frame is dummy data. If the received data frame is a dummy frame, Node B discards it.

  On the other hand, when there is data addressed to the node A, the node B also encrypts the data using the access key A sent from the node A, and transmits a data frame including the encrypted data (ciphertext data) to the node A. Send to. At this time, as described above, if there is an agreement between the nodes regarding the inclusion of the electronic signature in the data frame, the node B generates the electronic signature and includes the electronic signature in the data frame. Node B transmits a dummy frame to node A at a predetermined timing. When the node A receives the data frame, the node A decrypts the data with the access key A and determines whether the data included in the data frame is dummy data. If the received data frame is a dummy frame, node A discards it.

  As described above, in the present embodiment, dummy frames are transmitted at regular intervals in data communication between nodes. As a result, even if a data frame is intercepted by a third party, the third party cannot distinguish whether the data frame is a normal frame or a dummy frame. In the present embodiment, it is difficult to steal a correct access key by mixing a dummy frame.

  Since the ad hoc network is easily affected by the environment and unstable, each node notifies the other node of the access key generated by itself as an encryption key. For example, in a configuration in which an access key generated by itself is notified to another node as a decryption key, the other node may not be able to receive the access key due to a communication failure or the like. In this case, there arises a problem that other nodes cannot decrypt the data sent thereafter. On the other hand, as described above, if the other node is notified as the encryption key, the data transmitted from the other node should be encrypted with the notified access key, There is no problem that it cannot be decrypted.

  Next, a specific processing flow of the communication terminal apparatus shown in FIG. 2 will be described with reference to FIGS. First, the processing flow of access key generation and notification processing will be described with reference to FIGS. Here, a case where the node B generates the access key B and notifies the node A between the node A and the node B will be described as an example. In the following, for convenience of explanation, the processing unit and the storage unit of the node A are denoted by “a” after the code (for example, the key storage unit 1a), and the processing unit and the storage unit of the node B are denoted by the code. It is assumed that “b” is added after (for example, the key storage unit 1b).

  First, the access key generation unit 31b of the node B generates an access key B and stores it in the key storage unit 1b (FIG. 5: step S1). It is assumed that only the common key is stored in the key storage unit 1b until the access key B is first generated. Then, the access key notification frame generation unit 32b of the node B generates an access key notification frame including the access key B stored in the key storage unit 1b (Step S3), and outputs the access key notification frame to the access key notification frame encryption unit 33b. .

  FIG. 6 shows an example of the format of the access key notification frame. In the example of FIG. 6, the access key notification frame includes a header portion and a payload portion. The header part includes a destination address, a source address, a frame type (0x00: data frame / 0x01: access key notification frame), and a frame size (bytes). In the destination address, an address of a transmission destination node of the access key notification frame (for example, an IP (Internet Protocol) address or a MAC (Media Access Control) address) is set. The source address of the access key notification frame is set as the source address. In the case of an access key notification frame, a value (0x01) indicating that this frame is an access key notification frame is set as the frame type. In this embodiment, a fixed value and an access key are set in the payload portion of the access key notification frame. Here, the fixed value is a fixed character string such as “DATA”, for example. As will be described later, whether or not the frame is a dummy frame is determined based on whether or not the fixed value is included.

  For example, FIG. 7 shows a setting example of an access key notification frame transmitted from the node B to the node A. In the example of FIG. 7, in the header part, the MAC address “00: 00: 00: AA: BB: 01” of the node A is set as the destination address, and the MAC address “00: “00: 00: AA: BB: 02” is set, and the value “0x01” representing the access key notification frame is set as the frame type. In the example of FIG. 7, a fixed value “DATA” and an access key B “0x5242342342242...” Are set in the payload portion.

  Then, the access key notification frame encryption unit 33b of the Node B receives the access key notification frame from the access key notification frame generation unit 32b. Then, the access key notification frame encryption unit 33b generates an electronic signature for the payload portion of the access key notification frame using the common key stored in the key storage unit 1b, and attaches it to the access key notification frame (step) S5). For example, an algorithm such as HMAC-SHA1 (Keyed-Hashing for Message Authentication code-Secure Hash Algorithm-1) is used to generate the electronic signature. In some cases, an electronic signature may not be attached to the access key notification frame. In this case, the processing in this step is skipped, and therefore, the access key notification frame is indicated by a dotted line block in FIG. It is assumed that agreement between nodes is obtained in advance as to whether or not to attach an electronic signature to the access key notification frame.

  Then, the access key notification frame encryption unit 33b encrypts the payload part of the access key notification frame using the common key stored in the key storage unit 1b (step S7), and the encrypted access key notification frame Is output to the frame transmission unit 37b. For encryption, for example, an algorithm such as RC4 is used.

  8 and 9 show an example of the access key notification frame after encryption. 8 shows an example of an access key notification frame without an electronic signature, and FIG. 9 shows an example of an access key notification frame with an electronic signature. As shown in FIGS. 8 and 9, “0xab87c8f0d8760 ...” as ciphertext data (that is, encrypted “fixed value + access key B”) is stored in the payload portion of the encrypted access key notification frame. Is set. In FIG. 9, the signature “0xe231cb...” Is added at the end, and the data size is increased accordingly.

  The frame transmission unit 37b of the node B receives the access key notification frame from the access key notification frame encryption unit 33b and transmits the received access key notification frame to the node A (step S9). Actually, the transmission destination is not only the node A but also a plurality of nodes by broadcast.

  Then, the frame receiving unit 51a of the node A receives the frame from the node B (step S11), and outputs the received frame to the frame type determining unit 52a. Then, the frame type determination unit 52a of the node A determines the frame type of the frame received by the frame reception unit 51a (step S13). Specifically, it is determined whether the frame is an access key notification frame or a data frame by referring to the value of the frame type in the header part. For example, when a frame other than the access key notification frame is received in a state where the access key corresponding to the node B is not held, the frame other than the access key notification frame is regarded as invalid, and predetermined error processing is performed. May be implemented. Here, it is determined that the frame is an access key notification frame. When the received frame is an access key notification frame, the frame type determination unit 52a outputs the access key notification frame to the access key notification frame decoding unit 53a.

  Then, the access key notification frame decoding unit 53a of the node A receives the access key notification frame from the frame type determination unit 52a, and uses the common key stored in the key storage unit 1a to convert the payload part of the access key notification frame. Decryption is performed (step S15).

  When the access key notification frame has an electronic signature, the access key notification frame decryption unit 53a generates an electronic signature for the payload portion using the common key stored in the key storage unit 1a. Then, the attached electronic signature is verified by comparing with the electronic signature attached to the access key notification frame (step S17). If the electronic signature matches, it is proved that there is no tampering. Although not shown in the figure, if the electronic signatures do not match, it is assumed that there is a possibility that the electronic signature has been tampered with, and the process is terminated. Further, predetermined error processing may be performed. Note that when an electronic signature is not attached to the access key notification frame, the processing of this step is skipped, and therefore, it is indicated by a dotted line block in FIG.

  Thereafter, the access key notification frame decryption unit 53a outputs the decrypted access key notification frame to the access key extraction unit 54a. Then, the access key extraction unit 54a of the node A receives the access key notification frame from the access key notification frame decoding unit 53a, and determines whether the payload part of the access key notification frame has a predetermined format (step S19). Specifically, the determination is made based on whether or not a fixed value (for example, a character string “DATA”) is set at the head of the payload portion. If the payload part of the access key notification frame has a predetermined format (step S19: Yes route), the access key extraction part 54a removes the fixed value from the payload part of the access key notification frame and extracts the access key B. And stored in the key storage unit 1a (step S21). At this time, it is made clear that the access key B corresponds to the node B by associating it with the identification information of the node B. Thereafter, the process ends.

  On the other hand, if the payload part of the access key notification frame is not in a predetermined format (step S19: No route), the access key extraction part 54a determines that the data is invalid and performs predetermined error processing (step S19). S23). Thereafter, the process ends.

  Note that the node B determines whether a predetermined time has elapsed since the end of the previous process, and when it determines that the predetermined time has elapsed, the node B performs the process described above again. As a result, the access key can be changed periodically and notified to other nodes.

  Next, a processing flow of data frame transmission processing and reception processing will be described with reference to FIGS. Here, a case where node A transmits data to node B between node A and node B will be described as an example. It is assumed that the processing as described above is performed in advance, and the access key B generated by the node B is stored in the key storage unit 1a of the node A.

  First, the data frame generation unit 34a of the node A receives transmission data A (that is, data addressed to the node B) input by the user (FIG. 10: step S31). Then, the data frame generation unit 34a generates a data frame including the transmission data A (step S33) and outputs the data frame to the data frame encryption unit 35a.

  FIG. 11 shows an example of a data frame format. The format of the data frame is basically the same as the format of the access key notification frame shown in FIG. In the case of a data frame, a value (0x00) indicating that this frame is a data frame is set in the frame type of the header portion. In the payload portion, transmission data is set instead of the access key.

  For example, FIG. 12 shows a setting example of a data frame transmitted from the node A to the node B. In the example of FIG. 12, the MAC address “00: 00: 00: AA: BB: 02” of the node B is set as the destination address in the header portion, and the MAC address “00: “00: 00: AA: BB: 01” is set, and the value “0x00” indicating the data frame is set as the frame type. In the example of FIG. 12, a fixed value “DATA” and transmission data A “0x522ebc8a98aaa ...” are set in the payload portion.

  Then, the data frame encryption unit 35a of the node A receives the data frame from the data frame generation unit 34a. Then, the data frame encryption unit 35a generates an electronic signature for the payload portion of the data frame using the access key B stored in the key storage unit 1a, and attaches it to the data frame (step S35). In some cases, an electronic signature may not be attached to the data frame. In this case, the processing in this step is skipped, and therefore, the data frame is indicated by a dotted line block in FIG. As described above, it is assumed that there is an agreement between nodes in advance regarding whether or not to attach an electronic signature to a data frame.

  Then, the data frame encryption unit 35a encrypts the payload portion of the data frame using the access key (here, access key B) stored in the key storage unit 1a and corresponding to the destination node (step S37). The encrypted data frame is output to the frame transmission unit 37a.

  FIGS. 13 and 14 show examples of data frames after encryption. FIG. 13 shows an example of a data frame without an electronic signature, and FIG. 14 shows an example of a data frame with an electronic signature. As shown in FIGS. 13 and 14, “0x9876bcd54effff ...” is set as ciphertext data (that is, encrypted “fixed value + transmission data A”) in the payload portion of the encrypted data frame. Has been. In FIG. 14, the signature “0x2ed433 ...” is added at the end, and the data size is increased accordingly.

  Then, when receiving the data frame from the data frame encryption unit 35a, the frame transmission unit 37a of the node A determines whether it is necessary to transmit a dummy frame before transmitting the data frame (step S39). For example, a dummy frame transmission interval such as (1) transmitting a dummy frame every predetermined time, (2) transmitting a dummy frame once every time a predetermined number of data frames are transmitted, It is determined whether it is time to transmit. When it is not the timing to transmit the dummy frame (step S39: No route), the processing of steps S41 to S47 described below is skipped, and the process proceeds to step S49.

  On the other hand, when it is determined that it is time to transmit the dummy frame (step S39: Yes route), the dummy frame generation unit 36a of the node A generates a random number by a predetermined method and generates a dummy frame including the random value. (Step S41).

  FIG. 15 shows an example of a dummy frame format. The format of the dummy frame is basically the same as the format of the data frame shown in FIG. In the case of a dummy frame, a random value is set in the payload portion, but the header portion is set in the same manner as the data frame. That is, a value (for example, 0x00) indicating that it is a data frame is set in the frame type, as in the case of a data frame.

  For example, FIG. 16 shows a setting example of a dummy frame transmitted from the node A to the node B. Except for the data set in the payload portion, it is the same as the dummy frame shown in FIG. In FIG. 16, a random value “0x43ed24afffffff ...” is set in the payload portion. Actually, it is impossible to determine whether the data set in the payload portion is ciphertext data or a random value unless the payload portion is decrypted.

  Then, the dummy frame generation unit 36a generates an electronic signature for the payload portion of the dummy frame using the dummy key and attaches it to the dummy frame (step S43). Here, meaningless data may be used as a dummy key. As shown in FIG. 17, a dummy key may be stored in the key storage unit 1 in advance, or a random number is generated each time this step is performed. The random number value may be used as a dummy key. Instead of generating an electronic signature for the payload portion, another random number may be generated, and the random value may be attached to the dummy frame as a signature. For example, when a random value is attached as a signature to the dummy frame shown in FIG. 16, the dummy frame is as shown in FIG. In some cases, an electronic signature may not be attached to the dummy frame. In this case, the processing of this step is skipped, and therefore, the dummy frame is indicated by a dotted line block in FIG.

  Then, the dummy frame generation unit 36a encrypts the payload portion of the dummy frame using the dummy key (Step S45). In some cases, a dummy frame is transmitted without encrypting the payload portion, and in this case, the processing of this step is skipped, and therefore, it is indicated by a dotted line block in FIG. Thereafter, the dummy frame generation unit 36a outputs the dummy frame to the frame transmission unit 37a.

  For example, FIGS. 19 and 20 show examples of dummy frames after encryption. FIG. 19 shows an example of a dummy frame without an electronic signature, and FIG. 20 shows an example of a dummy frame with an electronic signature. As shown in FIGS. 19 and 20, “0xedfffaaa4234343...” Is set as ciphertext data (that is, an encrypted random value) in the payload portion of the encrypted dummy frame. In FIG. 20, the signature “0xaaab4...” Is added at the end, and the data size is increased accordingly.

  Then, the frame transmission unit 37a of the node A receives the dummy frame from the dummy frame generation unit 36a and transmits the received dummy frame to the node B (step S47). And a process transfers to the process of step S49.

  Thereafter, the process proceeds to step S49, and the frame transmission unit 37a transmits the data frame received from the data frame encryption unit 35a to the node B (step S49).

  Then, when the frame receiving unit 51b of the node B receives the frame from the node A (step S51), the frame receiving unit 51b outputs the received frame to the frame type determining unit 52b. Thereafter, the processing shifts to the processing in step S53 (FIG. 21) via the terminal A. In Node B, every time a frame is received, processing from Step S53 to Step S63 described below is performed.

  Moving to the description of FIG. 21, after terminal A, the frame type determination unit 52b of the node B determines the frame type of the frame received by the frame reception unit 51b (FIG. 21: step S53). Specifically, it is determined whether the frame is an access key notification frame or a data frame by referring to the value of the frame type in the header part. Here, it is assumed that the data frame is determined. However, at this time, it is not possible to determine whether the frame is a normal data frame or a dummy frame. When the received frame is a data frame, the frame type determination unit 52b outputs the data frame to the data frame decoding unit 55b.

  Then, the data frame decoding unit 55b of the node B receives the data frame from the frame type determination unit 52b, and uses the access key B stored in the key storage unit 1b (that is, the access key generated by the own node), The payload part of the data frame is decoded (step S55). If the received frame is a normal data frame, the plaintext data in the payload portion should be encrypted by the access key B in the node A that is the transmission source. The ciphertext data is decrypted into plaintext data. On the other hand, if the received frame is a dummy frame, since the random number value or data obtained by encrypting the random number value is set in the payload part, meaningless data is obtained when the processing of this step is performed. Derived.

  When an electronic signature is attached to the data frame, the data frame decryption unit 55b generates an electronic signature for the payload portion using the access key B stored in the key storage unit 1b, and the data frame By comparing with the electronic signature attached to, the attached electronic signature is verified (step S57). When the received frame is a normal data frame, if the digital signature matches, it is proved that there is no tampering. On the other hand, if the received frame is a dummy frame, the data generated with the random number value or the dummy key is attached as a signature, so the comparison result should be inconsistent. Therefore, if the comparison result does not match, it may be determined that the received frame is a dummy frame. In this case, the determination process in step S59 described below may be skipped and the process may proceed to step S61. Note that, when an electronic signature is not attached to the data frame, the processing of this step is skipped, and therefore, it is indicated by a dotted line block in FIG.

  Thereafter, the data frame decoding unit 55b outputs the decoded data frame to the dummy frame determination unit 56b. Then, the dummy frame determination unit 56b of the node B receives the data frame from the data frame decoding unit 55b, and determines whether or not the data frame is a dummy frame (step S59). Specifically, it is determined whether or not the payload portion of the received data frame has a predetermined format. As described above, if it is a normal data frame, it is decoded into plain text data (ie, “fixed value + transmission data”) by the process of step S55, and the fixed value is included at the head of the payload portion. Should be. On the other hand, if it is a dummy frame, meaningless data is derived by the process of step S55, and therefore no fixed value is included. Therefore, if a fixed value is set at the beginning of the payload portion, it is determined that the frame is a normal data frame, and if a fixed value is not set at the beginning of the payload portion, it is determined that the frame is a dummy frame.

  If it is determined that the data frame is a dummy frame (step S59: Yes route), the dummy frame determination unit 56b discards the data frame (dummy frame) (step S61). For example, when a dummy frame is transmitted in step S47 and received by the node B, the process of this step is performed and the dummy frame is discarded.

  On the other hand, when it is determined that the data frame is not a dummy frame (step S59: No route), that is, when it is a normal data frame, the dummy frame determination unit 56b converts the data frame into the data extraction unit 57b. Output to.

  Then, the data extraction unit 57b of the node B receives the data frame from the dummy frame determination unit 56b, removes the fixed value from the payload portion of the data frame, and extracts the transmission data A (step S63). For example, when a normal data frame is transmitted in step S49 and received by the node B, the process of this step is performed and transmission data A is extracted. Note that the extracted transmission data A may be displayed as necessary. Thereafter, the process ends.

  In this way, if you have the correct access key, you can easily determine whether the data frame is a dummy frame, but even if a third party who does not have the correct access key intercepts the data frame, It cannot be determined whether or not the data frame is a dummy frame. That is, since it becomes difficult for the encryption key to be stolen, the update interval of the encryption key can be set long, and as a result, communication efficiency is improved.

  Although one embodiment of the present technology has been described above, the present technology is not limited to this. For example, the functional blocks of the communication terminal apparatus shown in FIG. 2 do not necessarily match the actual program module configuration. Similarly, the configuration of the data storage unit is merely an example.

  Furthermore, the format of each frame described above is an example, and other configurations can be adopted. Even when other configurations are adopted, it is necessary to set the header portion in the same way so that a third party cannot distinguish a normal data frame and a dummy frame.

  Also in the processing flow, if the processing result does not change, the processing order can be changed. Further, it may be executed in parallel.

  Note that the communication terminal device described above is a computer device, and as shown in FIG. 22, a memory 2501, a CPU 2503, a hard disk drive (HDD) 2505, a display control unit 2507 connected to the display device 2509, and a removable device. A drive device 2513 for the disk 2511, an input device 2515, and a communication control unit 2517 for connecting to a network are connected by a bus 2519. An operating system (OS) and an application program for executing the processing in this embodiment are stored in the HDD 2505, and are read from the HDD 2505 to the memory 2501 when executed by the CPU 2503. If necessary, the CPU 2503 controls the display control unit 2507, the communication control unit 2517, and the drive device 2513 to perform necessary operations. Further, data in the middle of processing is stored in the memory 2501 and stored in the HDD 2505 if necessary. In an embodiment of the present technology, an application program for performing the above-described processing is stored in a computer-readable removable disk 2511 and distributed, and installed from the drive device 2513 to the HDD 2505. In some cases, the HDD 2505 may be installed via a network such as the Internet and the communication control unit 2517. Such a computer device realizes various functions as described above by organically cooperating the hardware such as the CPU 2503 and the memory 2501 described above with the OS and necessary application programs.

  Note that the HDD 2505, the display control unit 2507, the display device 2509, the drive device 2513, and the like are not necessarily provided. Some communication terminal devices are provided, and some communication terminal devices are not provided at all. In addition, there is a communication terminal device provided only as desired.

  The above-described embodiment can be summarized as follows.

  The communication terminal device according to the first aspect is a self-communication terminal device at a predetermined interval with a key storage unit (FIG. 23: 1501) that stores a common key that is a common encryption key with other communication terminal devices. A first access key, which is an encryption key for data addressed to the first communication terminal device, is generated and stored in the key storage unit (FIG. 23: 1503), and generated by the access key generation unit The first access key is encrypted with the common key stored in the key storage unit, and the first access key notification frame including the encrypted first access key is transmitted to another communication terminal apparatus by broadcasting. A second access key generated as an encryption key for data addressed to the second communication terminal device from the access key notification unit (FIG. 23: 1505) and the second communication terminal device among the other communication terminal devices. An access key receiving unit (FIG. 23: 1507) that receives a second access key notification frame including access key notification data that is data after the key is encrypted with the common key, and included in the second access key notification frame The second access key is obtained by decrypting the access key notification data using the common key stored in the key storage unit, and stored in correspondence with the identification information of the second communication terminal device The access key decryption unit (1509 in FIG. 23) stored in the unit and the first plaintext data including the data addressed to the second communication terminal device are stored in the key storage unit and correspond to the second communication terminal device The first ciphertext data is generated by encrypting with the second access key, and the first data frame including the generated first ciphertext data is transmitted to the second communication terminal device. A data transmission unit (FIG. 23: 1511) to transmit, and at a predetermined timing, a dummy frame including dummy data is generated, and the second communication terminal apparatus uses the dummy frame as a first data frame in the data transmission unit. A dummy frame generating unit (FIG. 23: 1513) to be transmitted to a data receiving unit (FIG. 23: 1515) for receiving a second data frame including the second ciphertext data from the second communication terminal device; A data decryption unit (FIG. 5) that obtains the second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit. 23: 1517), it is determined whether or not the second plaintext data is appropriate as the plaintext data in the second data frame. A dummy frame determination unit (FIG. 23: 1519) that discards the frame.

  According to this configuration, the dummy frame is transmitted as the first data frame from the own communication terminal device to another communication terminal device at a predetermined timing. As a result, even if a third party intercepts the first data frame, it is difficult for the third party to identify the dummy frame, so the dummy frame is mixed in the first data frame. A statistic attack will be performed without knowing that it is. Therefore, since the encryption key is less likely to be stolen, the update interval of the encryption key can be lengthened, resulting in an improvement in communication efficiency. The own communication terminal device decrypts the second ciphertext data included in the received second data frame, determines whether the decrypted second plaintext data is appropriate, and determines that it is not appropriate. In this case, since the received second data frame is discarded, no problem occurs even if a dummy frame is transmitted as the second data frame.

  Further, the data transmitting unit described above generates a first electronic signature for the first plaintext data using the second access key, and transmits a first data frame further including the first electronic signature. You may do it. Further, the data receiving unit described above receives a second data frame further including data presumed to be the second electronic signature generated from the second plaintext data using the first access key. It may be. Then, the dummy frame determination unit described above generates a third electronic signature for the second plaintext data by using the first access key stored in the key storage unit, and generates the second electronic signature. It is determined whether the data estimated as the signature matches the third electronic signature. If the data estimated as the second electronic signature does not match the third electronic signature, the second plaintext data is the second It may be determined that the plaintext data in the data frame is not appropriate. For example, when the received data frame is a dummy frame, the electronic signatures do not match. Therefore, it is possible to easily determine whether or not the received data frame is a dummy frame using the electronic signature.

  Furthermore, the dummy frame generation unit described above may generate a dummy signature and generate a dummy frame that further includes the dummy signature.

  Further, the data transmission unit described above may generate the first plaintext data by adding predetermined data to the data addressed to the second communication terminal device. The dummy frame determination unit described above determines whether the second plaintext data includes predetermined data. If the predetermined data is not included, the second plaintext data is stored in the second data frame. It may be determined that the plaintext data is not appropriate. In this way, it is possible to easily determine whether or not the received data frame is a dummy frame even when the data frame does not include an electronic signature. That is, even if the amount of calculation is reduced, it can be easily determined whether or not the data frame is a dummy frame.

  Furthermore, the predetermined data described above may be a predetermined character string. In addition, the dummy data described above may be a random number value or data after the random number value is encrypted with a dummy key. Further, the dummy signature described above may be a random number value or data after the random number value is encrypted with a dummy key.

  The communication processing method according to the second aspect is a communication processing method executed by a communication terminal device. And this method produces | generates the 1st access key which is an encryption key for data destined for the 1st communication terminal device which is a self-communication terminal device at a predetermined interval, and the encryption common to other communication terminal devices An access key generation step (FIG. 24: S1001) for storing the generated first access key in a key storage unit that stores a common key as a key in advance, and a first access generated by the access key generation step An access key notification step of encrypting a key with a common key stored in the key storage unit and transmitting a first access key notification frame including the encrypted first access key to another communication terminal device by broadcasting (FIG. 24: S1003) and generated from the second communication terminal device among the other communication terminal devices as an encryption key for data addressed to the second communication terminal device An access key receiving step (FIG. 24: S1005) for receiving a second access key notification frame including access key notification data, which is data obtained by encrypting the access key of No. 2 with a common key, and a second access key notification The access key notification data included in the frame is decrypted using the common key stored in the key storage unit, thereby obtaining the second access key and associating it with the identification information of the second communication terminal device The access key decrypting step (FIG. 24: S1007) stored in the key storage unit and the first plaintext data including the data addressed to the second communication terminal device are stored in the key storage unit and the second communication terminal The first ciphertext data is generated by encrypting with the second access key corresponding to the device, and the first data stream including the generated first ciphertext data is generated. A data transmission step (FIG. 24: S1009) for transmitting a message to the second communication terminal device, and a dummy frame including dummy data is generated at a predetermined timing, and the dummy frame is used as the first data frame. A dummy frame generation step (FIG. 24: S1011) to be transmitted to the communication terminal device and a data reception step (FIG. 24: receiving a second data frame including the second ciphertext data) from the second communication terminal device. S1013) and data decryption for obtaining the second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit Step (FIG. 24: S1015) and determining whether the second plaintext data is appropriate as the plaintext data in the second data frame (FIG. 24: S1017) includes a dummy frame determination step (FIG. 24: S1019) for discarding the second data frame when it is determined that the data frame is not appropriate (S1017: No route).

  It is possible to create a program for causing a computer to carry out the processes described above, and the program can be read by a computer such as a flexible disk, a CD-ROM, a magneto-optical disk, a semiconductor memory, and a hard disk. Stored in a storage medium or storage device. Note that data being processed is temporarily stored in a storage device such as a computer memory.

  The following supplementary notes are further disclosed with respect to the embodiments including the above examples.

(Appendix 1)
A communication terminal device,
A key storage unit that stores a common key that is a common encryption key with other communication terminal devices;
An access key generation unit that generates a first access key that is an encryption key for data addressed to the first communication terminal device that is the own communication terminal device at a predetermined interval, and stores the first access key in the key storage unit;
A first access key including the first access key encrypted by encrypting the first access key generated by the access key generation unit with the common key stored in the key storage unit An access key notification unit for transmitting a notification frame to the other communication terminal device by broadcasting;
After encrypting the second access key generated as the encryption key for data addressed to the second communication terminal device from the second communication terminal device among the other communication terminal devices with the common key An access key receiving unit that receives a second access key notification frame including access key notification data that is data;
Obtaining the second access key by decrypting the access key notification data included in the second access key notification frame using the common key stored in the key storage unit; An access key decryption unit stored in the key storage unit in association with the identification information of the second communication terminal device;
By encrypting the first plaintext data including data addressed to the second communication terminal device with the second access key stored in the key storage unit and corresponding to the second communication terminal device, A data transmission unit for generating first ciphertext data and transmitting a first data frame including the generated first ciphertext data to the second communication terminal device;
Generating a dummy frame including dummy data at a predetermined timing, and causing the data transmission unit to transmit the dummy frame as the first data frame to the second communication terminal device; and
A data receiving unit for receiving a second data frame including second ciphertext data from the second communication terminal device;
Data decryption for obtaining second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit And
Determining whether or not the second plaintext data is appropriate as plaintext data in the second data frame, and if it is determined that the second plaintext data is not appropriate, a dummy frame determination unit that discards the second data frame;
A communication terminal device.

(Appendix 2)
The data transmission unit is
Generating a first electronic signature for the first plaintext data using the second access key, and transmitting the first data frame further including the first electronic signature;
The data receiving unit is
Receiving the second data frame further including data presumed to be a second electronic signature generated from the second plaintext data using the first access key;
The dummy frame determination unit
Generating a third electronic signature for the second plaintext data using the first access key stored in the key storage unit;
It is determined whether the data estimated as the second electronic signature matches the third electronic signature. If the data estimated as the second electronic signature does not match the third electronic signature, The communication terminal apparatus according to claim 1, wherein the second plaintext data is determined not to be appropriate as plaintext data in the second data frame.

(Appendix 3)
The dummy frame generator is
The communication terminal device according to attachment 2, wherein a dummy signature is generated and the dummy frame further including the dummy signature is generated.

(Appendix 4)
The data transmission unit is
Generating the first plaintext data by adding predetermined data to the data addressed to the second communication terminal device;
The dummy frame determination unit
It is determined whether the predetermined data is included in the second plaintext data. If the predetermined data is not included, the second plaintext data is not appropriate as plaintext data in the second data frame. The communication terminal device according to any one of supplementary notes 1 to 3.

(Appendix 5)
The communication terminal device according to attachment 4, wherein the predetermined data is a predetermined character string.

(Appendix 6)
The communication terminal device according to any one of appendices 1 to 5, wherein the dummy data is a random number value or data after the random number value is encrypted with a dummy key.

(Appendix 7)
The communication terminal device according to attachment 3, wherein the dummy signature is a random number value or data after the random number value is encrypted with a dummy key.

(Appendix 8)
In the communication terminal device
At a predetermined interval, a first access key that is an encryption key for data addressed to the first communication terminal device that is the own communication terminal device is generated, and a common key that is an encryption key common to other communication terminal devices is generated. An access key generation step of storing the generated first access key in a pre-stored key storage unit;
A first access key including the first access key encrypted by encrypting the first access key generated in the access key generation step with the common key stored in the key storage unit An access key notification step of transmitting a notification frame to the other communication terminal device by broadcasting;
After encrypting the second access key generated as the encryption key for data addressed to the second communication terminal device from the second communication terminal device among the other communication terminal devices with the common key An access key receiving step of receiving a second access key notification frame including access key notification data that is data;
Obtaining the second access key by decrypting the access key notification data included in the second access key notification frame using the common key stored in the key storage unit; An access key decryption step of storing in the key storage unit in association with the identification information of the second communication terminal device;
By encrypting the first plaintext data including data addressed to the second communication terminal device with the second access key stored in the key storage unit and corresponding to the second communication terminal device, A data transmission step of generating first ciphertext data and transmitting a first data frame including the generated first ciphertext data to the second communication terminal device;
Generating a dummy frame including dummy data at a predetermined timing, and transmitting the dummy frame as the first data frame to the second communication terminal device; and
A data receiving step for receiving a second data frame including second ciphertext data from the second communication terminal device;
Data decryption for obtaining second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit Step,
Determining whether or not the second plaintext data is appropriate as plaintext data in the second data frame, and determining that the second plaintext data is not appropriate, discarding the second data frame;
A program for running

(Appendix 9)
A communication processing method executed by a communication terminal device,
At a predetermined interval, a first access key that is an encryption key for data addressed to the first communication terminal device that is the own communication terminal device is generated, and a common key that is an encryption key common to other communication terminal devices is generated. An access key generation step of storing the generated first access key in a pre-stored key storage unit;
A first access key including the first access key encrypted by encrypting the first access key generated in the access key generation step with the common key stored in the key storage unit An access key notification step of transmitting a notification frame to the other communication terminal device by broadcasting;
After encrypting the second access key generated as the encryption key for data addressed to the second communication terminal device from the second communication terminal device among the other communication terminal devices with the common key An access key receiving step of receiving a second access key notification frame including access key notification data that is data;
Obtaining the second access key by decrypting the access key notification data included in the second access key notification frame using the common key stored in the key storage unit; An access key decryption step of storing in the key storage unit in association with the identification information of the second communication terminal device;
By encrypting the first plaintext data including data addressed to the second communication terminal device with the second access key stored in the key storage unit and corresponding to the second communication terminal device, A data transmission step of generating first ciphertext data and transmitting a first data frame including the generated first ciphertext data to the second communication terminal device;
Generating a dummy frame including dummy data at a predetermined timing, and transmitting the dummy frame as the first data frame to the second communication terminal device; and
A data receiving step for receiving a second data frame including second ciphertext data from the second communication terminal device;
Data decryption for obtaining second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit Step,
Determining whether or not the second plaintext data is appropriate as plaintext data in the second data frame, and determining that the second plaintext data is not appropriate, discarding the second data frame;
A communication processing method including:

DESCRIPTION OF SYMBOLS 1 Key storage part 3 Transmission part 5 Reception part 31 Access key generation part 32 Access key notification frame generation part 33 Access key notification frame encryption part 34 Data frame generation part 35 Data frame encryption part 36 Dummy frame generation part 37 Frame transmission part 51 Frame Receiving Unit 52 Frame Type Determination Unit 53 Access Key Notification Frame Decoding Unit 54 Access Key Extraction Unit 55 Data Frame Decoding Unit 56 Dummy Frame Determination Unit 57 Data Extraction Unit

Claims (5)

A communication terminal device,
A key storage unit that stores a common key that is a common encryption key with other communication terminal devices;
An access key generation unit that generates a first access key that is an encryption key for data addressed to the first communication terminal device that is the own communication terminal device at a predetermined interval, and stores the first access key in the key storage unit;
A first access key including the first access key encrypted by encrypting the first access key generated by the access key generation unit with the common key stored in the key storage unit An access key notification unit for transmitting a notification frame to the other communication terminal device by broadcasting;
After encrypting the second access key generated as the encryption key for data addressed to the second communication terminal device from the second communication terminal device among the other communication terminal devices with the common key An access key receiving unit that receives a second access key notification frame including access key notification data that is data;
Obtaining the second access key by decrypting the access key notification data included in the second access key notification frame using the common key stored in the key storage unit; An access key decryption unit stored in the key storage unit in association with the identification information of the second communication terminal device;
By encrypting the first plaintext data including data addressed to the second communication terminal device with the second access key stored in the key storage unit and corresponding to the second communication terminal device, A data transmission unit for generating first ciphertext data and transmitting a first data frame including the generated first ciphertext data to the second communication terminal device;
Generating a dummy frame including dummy data at a predetermined timing, and causing the data transmission unit to transmit the dummy frame as the first data frame to the second communication terminal device; and
A data receiving unit for receiving a second data frame including second ciphertext data from the second communication terminal device;
Data decryption for obtaining second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit And
Determining whether or not the second plaintext data is appropriate as plaintext data in the second data frame, and if it is determined that the second plaintext data is not appropriate, a dummy frame determination unit that discards the second data frame;
A communication terminal device. The data transmission unit is
Generating a first electronic signature for the first plaintext data using the second access key, and transmitting the first data frame further including the first electronic signature;
The data receiving unit is
Receiving the second data frame further including data presumed to be a second electronic signature generated from the second plaintext data using the first access key;
The dummy frame determination unit
Generating a third electronic signature for the second plaintext data using the first access key stored in the key storage unit;
It is determined whether the data estimated as the second electronic signature matches the third electronic signature. If the data estimated as the second electronic signature does not match the third electronic signature, The communication terminal apparatus according to claim 1, wherein the second plaintext data is determined not to be appropriate as plaintext data in the second data frame. The data transmission unit is
Generating the first plaintext data by adding predetermined data to the data addressed to the second communication terminal device;
The dummy frame determination unit
It is determined whether the predetermined data is included in the second plaintext data. If the predetermined data is not included, the second plaintext data is not appropriate as plaintext data in the second data frame. The communication terminal device according to claim 1 or 2. In the communication terminal device
At a predetermined interval, a first access key that is an encryption key for data addressed to the first communication terminal device that is the own communication terminal device is generated, and a common key that is an encryption key common to other communication terminal devices is generated. An access key generation step of storing the generated first access key in a pre-stored key storage unit;
A first access key including the first access key encrypted by encrypting the first access key generated in the access key generation step with the common key stored in the key storage unit An access key notification step of transmitting a notification frame to the other communication terminal device by broadcasting;
After encrypting the second access key generated as the encryption key for data addressed to the second communication terminal device from the second communication terminal device among the other communication terminal devices with the common key An access key receiving step of receiving a second access key notification frame including access key notification data that is data;
Obtaining the second access key by decrypting the access key notification data included in the second access key notification frame using the common key stored in the key storage unit; An access key decryption step of storing in the key storage unit in association with the identification information of the second communication terminal device;
By encrypting the first plaintext data including data addressed to the second communication terminal device with the second access key stored in the key storage unit and corresponding to the second communication terminal device, A data transmission step of generating first ciphertext data and transmitting a first data frame including the generated first ciphertext data to the second communication terminal device;
Generating a dummy frame including dummy data at a predetermined timing, and transmitting the dummy frame as the first data frame to the second communication terminal device; and
A data receiving step for receiving a second data frame including second ciphertext data from the second communication terminal device;
Data decryption for obtaining second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit Step,
Determining whether or not the second plaintext data is appropriate as plaintext data in the second data frame, and determining that the second plaintext data is not appropriate, discarding the second data frame;
A program for running A communication processing method executed by a communication terminal device,
At a predetermined interval, a first access key that is an encryption key for data addressed to the first communication terminal device that is the own communication terminal device is generated, and a common key that is an encryption key common to other communication terminal devices is generated. An access key generation step of storing the generated first access key in a pre-stored key storage unit;
A first access key including the first access key encrypted by encrypting the first access key generated in the access key generation step with the common key stored in the key storage unit An access key notification step of transmitting a notification frame to the other communication terminal device by broadcasting;
After encrypting the second access key generated as the encryption key for data addressed to the second communication terminal device from the second communication terminal device among the other communication terminal devices with the common key An access key receiving step of receiving a second access key notification frame including access key notification data that is data;
Obtaining the second access key by decrypting the access key notification data included in the second access key notification frame using the common key stored in the key storage unit; An access key decryption step of storing in the key storage unit in association with the identification information of the second communication terminal device;
By encrypting the first plaintext data including data addressed to the second communication terminal device with the second access key stored in the key storage unit and corresponding to the second communication terminal device, A data transmission step of generating first ciphertext data and transmitting a first data frame including the generated first ciphertext data to the second communication terminal device;
Generating a dummy frame including dummy data at a predetermined timing, and transmitting the dummy frame as the first data frame to the second communication terminal device; and
A data receiving step for receiving a second data frame including second ciphertext data from the second communication terminal device;
Data decryption for obtaining second plaintext data by decrypting the second ciphertext data included in the second data frame with the first access key stored in the key storage unit Step,
Determining whether or not the second plaintext data is appropriate as plaintext data in the second data frame, and determining that the second plaintext data is not appropriate, discarding the second data frame;
A communication processing method including:

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