JP2015084603A - Node and group key updating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a group key updating technique that achieves reduction in the number of group key updating messages to be sent and received when a group key is updated in a network in which a directed acyclic graph topology is formed by a plurality of nodes including a node serving as the root node and having a parent-child relation between nodes of adjacent hierarchy levels.SOLUTION: In a network in which a directed acyclic graph topology is formed by a plurality of nodes including a node serving as a root node and having a parent-child relation between nodes of adjacent hierarchy levels, the root node creates a group key and a list indicating a first node as an object to which group key delivery is prohibited, and encrypts a group key decodable by a first child node other than the first node among child nodes of the root node, and transmits a first message containing an encrypted group key that is the group key encrypted and the list to the first child node.

Description

  Embodiments described herein relate generally to a node and group key update method.

  Conventionally, a group key is distributed to each node in a network in which an acyclic directed graph topology is formed by a plurality of nodes including a node that becomes one root node (called a root node) and having a parent-child relationship between nodes in adjacent hierarchies. There is technology to do. The group key is used, for example, for authentication for confirming whether communication with each node connected to the network is possible. In this technique, the group key is encrypted and delivered from the root node (edge router) to each node. At this time, the group key delivery message including the encrypted group key is transferred from the upper node to the lower node. The encryption key used for encryption when the group key is delivered is generated when the network access authentication executed with the root node when each node joins the group is successful. Such a group key is updated every time a node connected to the network is changed, for example, and the group key encrypted for each node that can communicate in the network in the same manner as the group key distribution message. Each of the group key update messages including is delivered.

JP 2010-108520 A

  However, in the conventional technique for delivering a group key, the number of group key update messages to be transferred increases as the node becomes higher. A method of delivering a group key by broadcast or multicast is also conceivable, but its application is difficult in a wireless mesh network where reliability of broadcast and multicast is low and there are also dormant nodes.

  One aspect of the present invention is to update a group key in a network that includes a node that is a root node and that forms an acyclic directed graph topology with a plurality of nodes that have a parent-child relationship between nodes in adjacent hierarchies. An object of the present invention is to provide a node and a group key update method capable of reducing the number of group key update messages transmitted and received.

  A node according to an embodiment includes a node that is a root node, and a first node other than the root node of a network that forms an acyclic directed graph topology by a plurality of nodes having a parent-child relationship between nodes in adjacent hierarchies A first group including an encrypted group key, which is a group key encrypted so that the first node can be decrypted, and a list indicating a second node to which delivery of the group key is prohibited A receiving unit that receives a message from a parent node of the first node; a decrypting unit that decrypts the encrypted group key to obtain the group key; and the list of child nodes of the first node. An encryption unit that encrypts the group key so that a first child node other than the second node can decrypt, and a group encrypted with respect to the first child node Comprising the encrypted group key is, and a transmission unit for transmitting a second message including said list.

The figure which illustrates the network of one embodiment. The figure which illustrates the functional structure of the first rank node apparatus 50. The figure which illustrates the data structure of a group key update message. The figure which illustrates the functional structure of a non-first stage node apparatus. The sequence chart which shows the outline | summary of a group key update process. The flowchart which shows the procedure of the process which the first rank node apparatus 50 performs. The flowchart which shows the procedure of the process which a non-first stage node apparatus performs. The figure which illustrates the structure of MKB of one modification, and allocation of a device key.

  Hereinafter, a node and group key updating method according to the present embodiment will be described in detail with reference to the accompanying drawings.

[First embodiment]
A network that forms a non-acyclic directed graph topology with a plurality of nodes that have a parent-child relationship between nodes of adjacent hierarchies and that includes a node that is one root node according to the present embodiment forms a tree-structure topology To do. FIG. 1 is a diagram illustrating a network forming a tree-structure topology according to the present embodiment. The network shown in the figure has three hierarchies each having a parent-child relationship between nodes in adjacent hierarchies. A first-stage node device 50 corresponding to the root node exists in the highest hierarchy, second-stage node devices 60a and 60b exist in the second highest hierarchy, and leaf nodes exist in the lowest hierarchy. There are third-stage node devices 70a, 70b, 70c corresponding to. The child nodes of the first stage node device 50 are the second stage node devices 60a and 60b, the child nodes of the second stage node device 60a are the third stage node devices 70a and 70b, and the children of the second stage node device 60b. The node is the third stage node device 70c. In addition, when it is not necessary to distinguish any of the first-stage node device 50, the second-stage node devices 60a and 60b, and the third-stage node devices 70a, 70b, and 70c, they are simply referred to as node devices. When it is necessary to distinguish the first-stage node device 50 from node devices other than the first-stage node device 50, the latter may be referred to as a non-first-stage node device. Each node device is assigned node identification information for identifying each node device.

  Next, a hardware configuration of the node device according to the present embodiment will be described. The node device includes a control unit such as a CPU (Central Processing Unit) that controls the entire device, a main storage unit such as a ROM (Read Only Memory) and a RAM (Random Access Memory) that stores various data and various programs, and various types of devices. Auxiliary storage units such as HDD (Hard Disk Drive) and CD (Compact Disk) drive devices that store data and various programs, a communication I / F (interface) that controls communication with external devices, and a bus that connects them And has a hardware configuration using a normal computer. In addition, a display unit that displays information and an operation input unit such as a keyboard or a mouse that receives a user's instruction input may be connected to the node device by wire or wirelessly. The non-first stage node device is assigned with an encryption key used for encryption at the time of group key distribution, and the auxiliary storage unit of each first stage node device is assigned with the encryption key assigned to itself. And an encryption key assigned to its own child node. On the other hand, the auxiliary storage unit of the first-stage node device 50 stores encryption keys assigned to the second-stage node devices 60a and 60b that are child nodes of the first-stage node device 50, respectively. Also, encryption key identification information for identifying each of these encryption keys is assigned.

  Next, various functions realized by the node device in such a hardware configuration will be described. Since the functional configuration of the first-stage node device 50 is different from the functional configuration of the non-first-stage node device, these will be described separately. First, the functional configuration of the first-stage node device 50 will be described with reference to FIG. The first-stage node device 50 includes a communication control unit 51 and a key update control unit 52. The function of the communication control unit 51 is realized by the communication I / F of the first stage node device 50 and the CPU of the first stage node device 50 executing various programs stored in the main storage unit and the auxiliary storage unit. The function of the key update control unit 52 is realized by the CPU of the first-stage node device 50 executing various programs stored in the main storage unit and the auxiliary storage unit.

  The communication control unit 51 controls communication with the non-first-stage node device, and corresponds to a transmission unit and a reception unit. Specifically, the communication control unit 51 transmits a group key update message generated by the key update control unit 52, which will be described later, to the second stage node devices 60a and 60b that are child nodes of the first stage node device 50, respectively. , Receiving a delivery confirmation message indicating that the group key update message has been received from the second-stage node devices 60a and 60b, or transmitting a group key update completion message described later to all the node devices connected to the network. .

  The key update control unit 52 controls group key update, and corresponds to a generation unit and an encryption unit. Specifically, the key update control unit 52 indicates a new group key and node identification information of a non-first-stage node device (referred to as a delivery-prohibited node) to which group key delivery is prohibited in accordance with a predetermined update condition. A group key distribution prohibition list is generated. It is assumed that group key identification information for identifying the group key is assigned to the group key. The predetermined update condition is, for example, that a node device configuring the network has changed. The delivery-prohibited node is, for example, a non-first-stage node device that has left the network, or a non-first-stage node device that is temporarily or permanently prohibited from using the network due to a contract regarding the use of the network. For the former delivery-prohibited node, the key update control unit 52 detects the non-first-stage node device connected to the network via the communication control unit 51 at regular or arbitrary timings, and thereby the The first node device is detected as a delivery prohibition node, and node identification information of the non-first node device is acquired. For the latter delivery-prohibited node, the node identification information of the delivery-prohibited node is stored in advance in, for example, the auxiliary storage unit of the first-stage node device 50, and the key update control unit 52 reads the node identification information from the auxiliary storage unit. To get by.

  Then, the key update control unit 52 includes a group key including a group key (referred to as an encrypted group key) encrypted so that the child node that is not a delivery-prohibited node among the child nodes of the first-stage node device 50 can be decrypted. An update message is generated, and this group key update message is transmitted via the communication control unit 51. Here, it is assumed that the second-stage node devices 60a and 60b that are child nodes of the first-stage node device 50 are not delivery-prohibited nodes. In this case, specifically, the key update control unit 52 encrypts a new group key with respect to the second-stage node device 60a using the encryption key assigned to the second-stage node device 60a, A group key update message including an encrypted group key (encrypted group key) and a delivery-prohibited node list is generated and transmitted via the communication control unit 51. Similarly, for the second stage node device 60b, the key update control unit 52 encrypts a new group key using the encryption key assigned to the second stage node device 60b, and the encrypted group key and A group key update message including a delivery prohibition node list is generated, and this group key update message is transmitted via the communication control unit 51.

  FIG. 3 is a diagram illustrating a data configuration of the group key update message. The group key update message includes group key information and a delivery prohibition node list. The group key information includes an encrypted group key, which is a group key encrypted using an encryption key, group key identification information for identifying the group key, and encryption used for encrypting the group key. And encryption key identification information for identifying the key. In the example shown in the figure, the delivery-prohibited node list indicates N pieces of node identification information of the delivery-prohibited nodes as list elements, and indicates the number of list elements (number of list elements) itself. The data structure of the group key update message is not limited to this as long as it includes at least the encrypted group key and the delivery-prohibited node.

  Further, the key update control unit 52, when the communication control unit 51 receives the delivery confirmation message from all the child nodes (here, the second stage node devices 60a and 60b) that transmitted the group key update message, A group key update completion message indicating that can be used is simultaneously transmitted to all the nodes connected to the network via the communication control unit 51 to validate the group key. Making the group key valid means that the group key is used for authentication for confirming whether communication with each node device connected to the network is possible.

  Next, the functional configuration of the non-first-stage node device will be described with reference to FIG. The non-first stage node device includes a communication control unit 81 and a key update control unit 82. The function of the communication control unit 81 is realized by the communication I / F of the non-first stage node device and the CPU of the non-first stage node device executing various programs stored in the main storage unit and the auxiliary storage unit. The function of the key update control unit 82 is realized by the CPU of the non-first stage node device executing various programs stored in the main storage unit and the auxiliary storage unit.

  The communication control unit 81 controls communication with a child node and a parent node of the non-first stage node device, and corresponds to a transmission unit and a reception unit. Specifically, the communication control unit 81 receives a group key update message from the parent node of the non-first stage node device, or the key update control unit 82 described later generates a child key of the non-first stage node device. Send a group key update message, receive a delivery confirmation message indicating that a group key update message has been received from the child node, or receive a delivery confirmation message from the child node. A delivery confirmation message is transmitted to the parent node, or a group key update completion message simultaneously transmitted from the first node device 50 is received. The communication control unit 81 transmits a group key update message when a key update control unit 82 (to be described later) does not generate a group key update message after receiving the group key update message from the parent node of the non-first stage node device. Instead, a delivery confirmation message is transmitted to the parent node of the non-first stage node device.

  The key update control unit 82 controls group key update, and corresponds to a decryption unit and an encryption unit. Specifically, when the key update control unit 82 receives the group key update message from its parent node via the communication control unit 81, the key update control unit 82 displays the encrypted group key and the group key distribution prohibition list included in the group key update message. Obtain the group key by decrypting the encrypted group key using the encryption key assigned to itself. Then, when there is a child node in itself, the key update control unit 82 can decrypt the child node for a child node whose node identification information is not indicated by the group key distribution prohibition list among the child nodes. Then, a group key update message including the encrypted group key (referred to as an encrypted group key) is generated and transmitted via the communication control unit 81. Specifically, the key update control unit 82 encrypts the group key using the encryption key assigned to the child node, the encrypted group key that is the encrypted group key, and the received group key A group key update message including a delivery prohibition node list included in the update message is generated and transmitted via the communication control unit 81. It should be noted that the key update control unit 82 has a case where no child node exists in itself, or a case where all the child nodes are delivery-prohibited nodes even when there are child nodes in itself, that is, all of the child nodes. When the node identification information is indicated by the group key distribution prohibition list, the node group key update message is not generated.

  When the key update control unit 82 receives the group key update completion message from the first-stage node device 50 via the communication control unit 81, the key update control unit 82 validates the group key obtained by decryption.

  Next, a group key update process for updating a group key in the network according to the present embodiment will be described. FIG. 5 is a sequence chart showing an outline of the group key update process. The first-stage node device 50 generates a new group key and a group key distribution prohibition list indicating node identification information of the distribution prohibition node according to a predetermined update condition. Here, the third-stage node device 70b is a delivery-prohibited node. For this reason, the first stage node device 50 generates a group key distribution prohibition list indicating the node identification information of the third stage node device 70b.

  Since the second-stage node devices 60a and 60b that are child nodes of the first-stage node device 50 are not delivery-prohibited nodes, the first-stage node device 50 generates a group key update message for each of the second-stage node devices 60a and 60b. To do. Specifically, the first-stage node device 50 encrypts each group key using the encryption key assigned to each of the second-stage node devices 60a and 60b, and the encrypted group is an encrypted group key. Each of the group key update messages including the key and the group key distribution prohibition list is generated. Then, the first stage node device 50 transmits the group key update message generated for the second stage node device 60a to the second stage node device 60a (step S1), and the group generated for the second stage node device 60b. The key update message is transmitted to the second stage node device 60b by unicast with delivery confirmation (step S2).

  When the second stage node device 60a receives the group key update message transmitted from the first stage node device 50, the second stage node device 60a acquires the encrypted group key and the group key distribution prohibition list included in the group key update message, and is assigned to itself. The group key is obtained by decrypting the encrypted group key using the encrypted key. The second-stage node device 60a refers to the node identification information indicated by the group key distribution prohibition list, and the third-stage node device 70b among the third-stage node devices 70a and 70b that are its own child nodes delivers It is determined that the node is a prohibited node, and it is determined not to generate and transmit a group key update message to the third-stage node device 70b. Then, the second-stage node device 60a encrypts the group key using the encryption key assigned to the third-stage node device 70a that is a child node other than the delivery-prohibited node among its child nodes. A group key update message including an encrypted group key that is a group key and a group key distribution prohibition list is generated. Then, the second stage node device 60a transmits the generated group key update message to the third stage node device 70a by unicast with delivery confirmation (step S3). When receiving the group key update message transmitted from the first stage node device 50, the second stage node device 60b refers to the node identification information indicated by the group key distribution prohibition list in the same manner as the second stage node device 60a. At this time, the second-stage node device 60b determines that the third-stage node device 70c that is its own child node is not a delivery-prohibited node, and uses the encryption key assigned to the third-stage node device 70c. The group key is encrypted, and an encrypted group key that is the encrypted group key and a group key update message including a group key distribution prohibition list are generated. Then, the second stage node device 60b transmits the generated group key update message to the third stage node device 70c by unicast with delivery confirmation (step S4).

  When the third stage node device 70a receives the group key update message transmitted from the second stage node device 60a, which is the parent node, the child node does not exist, so that the group key is sent to the second stage node device 60a. A delivery confirmation message indicating that the update message has been received is transmitted (step S5). Similarly to the third-stage node device 70a, the third-stage node device 70c receives the group key update message transmitted from the second-stage node device 60b that is the parent node. A delivery confirmation message is transmitted to the two-stage node device 60b (step S6).

  When receiving the delivery confirmation message transmitted from the third stage node device 70a, the second stage node device 60a transmits the delivery confirmation message to the first stage node device 50 that is the parent node (step S7). Similarly to the second stage node device 60a, the second stage node device 60b also transmits a delivery confirmation message to the first stage node device 50 that is the parent node when it receives the delivery confirmation message transmitted from the third stage node device 70c. (Step S8).

  When the first node device 50 receives the delivery confirmation message transmitted from the second node device 60a and the delivery confirmation message transmitted from the second node device 60b, the group key update indicating that the group key can be used. A completion message is simultaneously transmitted to all the node devices connected to the network (step S9), and the group key is validated. As a method of simultaneous transmission, either broadcast or multicast may be used.

  Upon receiving the group key update completion message, the second stage node devices 60a and 60b and the third stage node devices 70a and 70c validate the group key obtained from the group key update message received from its parent node. The group key is updated as described above.

  Details of processing performed by the first-stage node device 50 in the above-described group key update processing will be described with reference to FIG. As described above, the first-stage node device 50 generates a new group key and the group key distribution prohibition list P indicating the node identification information of the distribution prohibition node according to a predetermined update condition (step S20). Here, L is a list indicating node identification information of child nodes of the first-stage node device 50, and T is a list indicating node identification information of target child nodes waiting to receive a delivery confirmation message for the group key update message. The initial value of T is “null”, the group key update completion message transmission flag indicating whether or not the group key update completion message can be transmitted is set to S, and the value of S is set to “false”.

  Next, the first node device 50 determines whether the condition “L is empty?” Is true or false. If the condition is true, the process proceeds to step S25. If the condition is false, the process proceeds to step S22. In step S22, the first-stage node device 50 extracts one node identification information that has not been extracted from the node identification information indicated by L. Let this be X. The first-stage node device 50 determines whether the condition “X is indicated by P?” Is true or false (step S23). If the condition is true, the process returns to step S21, and if the condition is false. The process proceeds to step S24. In step S24, the first-stage node device 50 encrypts the group key using the encryption key assigned to the node device corresponding to X (in this case, either the second-stage node device 60a or 60b). A group key update message M including encrypted group keys KEYMAT and P, which are group keys, is generated, transmitted to a node device corresponding to X, and X is added to T.

  In step S25, the first node apparatus 50 determines whether the condition “T is empty?” Is true or false. If the condition is true, the process proceeds to step S29. If the condition is false, the process proceeds to step S26. move on. In step S26, the first-stage node device 50 waits for reception of the delivery confirmation message for the group key update message transmitted in step S24, sets the node identification information of the child node that is the standby target to X, and deletes X from T. . Then, the first-stage node device 50 determines whether the condition “has the delivery confirmation message been received”, that is, whether the delivery confirmation result is successful (step S27), and if the condition is true. The process proceeds to step S28, and if the condition is false, the process returns to step S25. In step S28, the first-stage node device 50 sets S to true and returns to step S25.

  In step S29, the first node device 50 determines whether the condition “S is true?” Is true or false. If the condition is true, the process proceeds to step S30. If the condition is false, the process is terminated. To do. In step S30, the first-stage node device 50 transmits a key update completion message to all the node devices connected to the network, validates the group key, and ends the process.

  Details of processing performed by the non-first-stage node device in the above-described group key update processing will be described with reference to FIG. As described above, when receiving the group key update message M from the parent node, the non-first stage node device acquires the encrypted group key and the group key distribution prohibition list P included in the group key update message, and is assigned to itself. The encrypted group key KEYMAT is decrypted using the encrypted key to obtain the group key K (step S40). Here, the list indicating the node identification information of the child node of the non-first stage node device is L, and the node identification information of the target child node waiting to receive the delivery confirmation message for the group key update completion message is T, The initial value of T is “null”.

  Next, the non-first stage node apparatus determines whether the condition “L is empty?” Is true or false (step S41). If the condition is true, the process proceeds to step S45. Proceed to S42. In step S42, the non-first-stage node device extracts one node identification information that has not been extracted from the node identification information indicated by L. Let this be X. The first-stage node device 50 determines whether the condition “X is indicated by P?” Is true or false (step S43). If the condition is true, the process returns to step S41, and if the condition is false. The process proceeds to step S44. In step S44, the first-stage node device 50 encrypts the group key using the encryption key assigned to the node device corresponding to X, and includes a group including encrypted group keys KEYMAT 'and P that are encrypted group keys. A key update message M is generated, transmitted to the node device corresponding to X, and X is added to T.

  In step S45, the non-first stage node apparatus determines whether the condition “T is empty?” Is true or false. If the condition is true, the process proceeds to step S47. If the condition is false, the process proceeds to step S46. move on. In step S46, the non-first stage node device waits for reception of the delivery confirmation message for the group key update message transmitted in step S44, sets the node identification information of the child node that is the standby target to X, and deletes X from T. . In step S47, the non-first-stage node device transmits a delivery confirmation message to the parent node. Thereafter, the non-first stage node device determines whether or not the key update completion message transmitted from the first stage node device 50 has been successfully received (step S48). If the determination result is affirmative, the process proceeds to step S49. If the determination result is negative, the process is terminated. In step S49, the non-first-stage node device validates the group key and ends the process.

  As described above, encryption is performed when a group key is updated in a network in which an acyclic directed graph topology is formed by a plurality of nodes having a parent-child relationship between nodes in an adjacent hierarchy including a node that is one root node. The group key update message including the new group key and the key update prohibition node list is propagated to the lower layer between the node devices having the parent-child relationship in order from the root node of the network by unicast with delivery confirmation. As a result, the number of group key update messages transmitted by each node device does not depend on the hierarchy in which the node device exists, and the total number of group key update messages transmitted and received in the network can be reduced. In addition, the group key can be updated even in a network with low broadcast or multicast reliability.

[Modification]
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined. Further, various modifications as exemplified below are possible.

  In the embodiment described above, various programs executed by the node device may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. The various programs are recorded in a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, and a DVD (Digital Versatile Disk) in a file in an installable or executable format. The computer program product may be provided.

  In the above-described embodiment, the node device is a power meter, an electric vehicle, a sensor, a home appliance, a storage battery, a solar power generation device, a HEMS (Home Energy Management System), a BEMS (Building EMS), a CEMS (Community EMS), or the like. It may be incorporated in energy equipment.

  In the above-described embodiment, when the child node is in the sleep state, the node device may pending transmission of the group key update message until the child node is in the normal state. When a packet (for example, an IEEE 802.15.4 Data Request MAC frame) is received, the child node may be considered to be in a normal state and a group key update message may be transmitted to the child node.

  In the embodiment described above, the first-stage node device 50 may retransmit at a predetermined time interval after transmitting the group key update message to child nodes other than the delivery-prohibited node among its own child nodes. The first-stage node device 50 completes the group key update even when reception of the delivery confirmation message from the child node is successful or unsuccessful, that is, according to the result of reception of the delivery confirmation message from the child node. A group key may be activated by broadcasting a message.

  Further, the non-first-stage node device may retransmit at a predetermined time interval after transmitting the group key update message to child nodes other than the delivery-prohibited node among its child nodes. And even if the non-first stage node device succeeds or fails in receiving the delivery confirmation message from the child node, that is, depending on the result of receipt of the delivery confirmation message from the child node, Alternatively, a delivery confirmation message may be transmitted.

  The non-first stage node device, when receiving the group key update message or receiving the group key update message succeeds but fails to receive the group key update completion message, You may acquire the group key updated using the method.

In the embodiment described above, the acyclic directed graph topology includes a node which is a root node and has a parent-child relationship between nodes in adjacent hierarchies, and the topology information generated by the routing protocol is configured below. You may make it. For example, an acyclic directed graph topology may be configured based on DODAG (Destination Oriented Directed Acyclic Graph) information generated by RPL (IPv6 Routing Protocol for Low power and Lossy Networks) defined in Reference Document 1. .
(Reference 1) http://tools.ietf.org/html/draft-ietf-roll-rpl-15

  In the embodiment described above, when a child node has a plurality of parent nodes, one parent node (referred to as a representative parent node) is selected from the plurality of parent nodes, and a group key update message is received from the representative parent node. In this case, as in the above-described embodiment, when a group key update message is generated and transmitted to child nodes other than the delivery-prohibited node among its child nodes, and a delivery confirmation message is received from the child node Then, a delivery confirmation message is transmitted to the representative parent node. On the other hand, when a child node having a plurality of parent nodes receives a group key update message from a parent node other than the representative parent node, it operates as if its own child node does not exist, that is, a parent node other than the representative parent node Without decrypting the encrypted group key included in the group key update message received from, the group key update message is not generated and transmitted to its child node.

  In the embodiment described above, the encryption key used for encrypting the group key is not limited to the above example. For example, a public key assigned to a child node may be used as an encryption key. A shared key shared only between the child node and the parent node may be used as the encryption key.

  Further, an MKB (media key block) may be used as the encryption key. The MKB is generated, for example, by the first-stage node device 50, and a device key included in the MKB is assigned to each non-first-stage node device. FIG. 8 is a diagram exemplifying the structure of the MKB and assignment of a device key as an encryption key to a non-first-stage node device according to this modification. In the MKB shown in the figure, a plurality of device keys K1, K21, K22, K31 to K34, and K41 to K48 have a one-dimensional tree structure. In this tree structure, the root node existing in the highest hierarchy is the device key K1, and the leaf nodes existing in the lowest hierarchy are the device keys K41 to K48. Each non-first node device is associated with each leaf node in this tree structure, and a device key pair on the path from the root node to the leaf node in this tree structure is assigned to each non-first node device as an encryption key . For example, the device key “DK2 = (K1, K21, K31, K42)” is assigned to the second stage node device 60a, and the device key “DK3 = (K1, K21, K32) is assigned to the second stage node device 60b. , K43) ”, the device key“ DK4 = (K1, K21, K32, K44) ”is assigned to the third stage node device 70a, and the device key“ DK5 = ”is assigned to the third stage node device 70b. (K1, K22, K33, K45) ”is assigned, and the device key“ DK6 = (K1, K22, K33, K46) ”is assigned to the third stage node device 70c. In such a configuration, the first-stage node device 50 encrypts the encrypted group key included in the group key update message with each of the valid device keys assigned to each non-first-stage node device. A set of encryption group keys, that is, {E (GK, DK2), E (GK, DK3), E (GK, DK4), E (GK, DK5), E (GK, DK6)} may be used. Here, E (m, y) is a value obtained by encrypting m with y. However, as in the above-described embodiment, when the third-stage node device 70b is a delivery-prohibited node, the device key DK5 of the third-stage node device 70b may be invalidated. In this case, the first-stage node device 50 may exclude E (GK, DK5) from the encrypted group key included in the group key update message. On the other hand, when each non-first stage node device receives the group key update message from its parent node, it decrypts the encrypted group key using the device key assigned to itself. Each non-first-stage node device transmits a group key update message to its child node without encrypting the group key using the device key that is the encryption key assigned to the child node. The group key update message received from its parent node may be transmitted.

  Specifically, in the group key update process of FIG. 5, the first-stage node device 50 sends a group key update message including a set of encrypted group keys and a group key distribution prohibition list to the second-stage node device in steps S1 and S2. It transmits to each of 60a and 60b. In step S3, when the second stage node device 60a receives the group key update message transmitted from the first stage node device 50, the second stage node device 60a obtains a set of encrypted group keys and a group key distribution prohibition list included in the group key update message. Then, using the device key assigned to itself, the encryption group key (here, E (GK, DK2)) included in the set of encryption group keys is decrypted to obtain the group key. Then, the second stage node device 60a transmits the group key update message received from the first stage node device 50 to the third stage node device 70a. Step S4 is the same as step S3.

  Even with the above configuration, when updating a group key in a network that includes a node that is a root node and that forms an acyclic directed graph topology with a plurality of nodes that have a parent-child relationship between nodes in adjacent hierarchies. The number of group key update messages transmitted and received can be reduced. Furthermore, the non-first-stage node device does not need to encrypt the group key, and can eliminate the need to store the encryption key assigned to its child node.

50 First-stage node device 51 Communication control unit 52 Key update control unit 60a, 60b Second-stage node device 70a, 70b, 70c Third-stage node device 81 Communication control unit 82 Key update control unit

Claims (7)

A first node other than the root node of a network that includes a node that is a root node and forms an acyclic directed graph topology by a plurality of nodes having a parent-child relationship between nodes in adjacent hierarchies;
A first message including an encrypted group key, which is a group key encrypted so that the first node can be decrypted, and a list indicating a second node to which delivery of the group key is prohibited is sent to the first message. A receiving unit that receives from a parent node of one node;
A decryption unit for decrypting the encrypted group key to obtain the group key;
An encryption unit that encrypts the group key so that a first child node other than the second node indicated by the list among the child nodes of the first node can be decrypted;
An encryption group key that is an encrypted group key for the first child node, and a transmission unit that transmits a second message including the list,
The first child node that has received the encryption group key further transmits the received encryption group key to a child node of the first child node.
node. The said transmission part transmits the 3rd message which shows that the said 1st message was received to the said parent node, when the child node of the said 1st node or the said 1st child node does not exist. Node described in. When the first child node exists, the receiving unit further receives a fourth message indicating that the second message has been received from the first child node;
When the first child node is present, the transmitter further retransmits the second message transmitted to the first child node at a predetermined time interval, from the first child node. The node according to claim 2, wherein the third message is transmitted to the parent node in accordance with a result of receiving the transmitted fourth message. The receiving unit further receives a fifth message transmitted from the root node indicating that the group key is usable,
The node according to any one of claims 1 to 3, further comprising: an enabling unit that validates the group key when the fifth message is received. When there are a plurality of the parent nodes, further comprising a selection unit for selecting a first parent node from the plurality of the parent nodes,
The decryption unit does not decrypt the encryption group key included in the first message received from a second parent node other than the first parent node among the plurality of parent nodes. 5. The node according to any one of 4. In a network including a node that is a root node and forming an acyclic directed graph topology by a plurality of nodes having a parent-child relationship between nodes in adjacent hierarchies,
The root node is
Generating a group key and a list indicating a first node for which delivery of the group key is prohibited;
The group key is encrypted so that a first child node other than the first node among the child nodes of the root node can be decrypted,
Sending a first message including an encrypted group key, which is an encrypted group key, to the first child node and the list;
A second node other than the root node is
A second message including an encrypted group key, which is a group key encrypted so that the second node can be decrypted, and a list indicating a third node to which delivery of the group key is prohibited; Received from the parent node of node 2
Decrypting the encrypted group key to obtain the group key;
The group key is encrypted so that a second child node other than the third node indicated by the list among the child nodes of the second node can be decrypted,
Transmitting a third message including an encrypted group key, which is an encrypted group key, to the second child node, and the list;
The second child node that has received the encryption group key further transmits the received encryption group key to a child node of the second child node.
Group key update method. The root node further retransmits the first message transmitted to the first child node at a predetermined time interval,
If the second node does not have a child node of the second node or the second child node, the second node sends a sixth message indicating that the second message has been received to the parent node; When the second child node exists, the third message transmitted to the second child node is further retransmitted at a predetermined time interval, and the third message from the second child node is transmitted. In response to the result of receiving the seventh message indicating that the message has been received, the sixth message is sent to the parent node;
A fifth key indicating that the group key is usable according to a result of receiving a fourth message indicating that the root node has received the first message from the first child node; Sending a message to the plurality of nodes to activate the group key;
The group key update method according to claim 6, wherein all or a part of the plurality of nodes receives the fifth message and validates the group key.

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