KR100729527B1 - A group key transmitting method in broadcasting environment - Google Patents

Abstract

A group key transmitting method in broadcasting environment is provided to divide subscribers by group, sort a subscriber whose terminal is to receive a service coding key among the groups, and transmit a single message per the group, thereby reducing waste of transmission band width for a broadcasting channel. A group key transmitting method in broadcasting environment includes the steps of randomly generating a group key for a terminal group including at least one or more terminals(S310), sorting terminals having the right to receive the group key in the terminal group(S320), generating a group key coding key for coding the group key transmitted to the terminals(S330), coding the group key by the group key coding key(S340), and transmitting data on the terminals to receive the group key and the coded group key to the terminals(S350).

Description

A group key transmitting method in broadcasting environment

1 is a system configuration diagram for group key transmission according to the present invention;

2 is a flowchart illustrating a management key set generation for group key management according to the present invention;

3 is a flow chart for group key transmission according to the present invention;

4 is a full binary tree diagram for a group configuration in an embodiment of the present invention;

5 is a key configuration diagram of nodes other than the root node according to the present invention,

6 is a flowchart for decrypting a group key according to the present invention.

<Explanation of symbols for the main parts of the drawings>

110: server 111: group management unit

112: group key encryption key generation unit 113: group key generation unit

114: group key encryption unit 115: transmission unit

120: terminal 121: key storage unit

122: group key decryption key generation unit 123: group key decryption unit

124: receiver

The present invention relates to a method for transmitting a group key in a broadcast environment, and more particularly, when paying for a service to receive a paid broadcast service, the decryption key enabling the payer to watch the encrypted pay broadcast service efficiently to only the paying buyer. The present invention relates to a method for grouping subscribers for delivery and for delivering a service encryption key for each group.

In general, in a pay broadcasting service, a subscriber must purchase a service (channel) for a fee to view the service. In order to prevent the subscribers who did not purchase the service from watching the service, the contents of the service are encrypted with a secure encryption algorithm, and a decryption key is delivered only to the subscriber who purchased the service so that only the purchased subscriber can watch it. do.

The key that encrypts a service is changed every tens of seconds, or every few hours, to prevent key exposure attacks such as real-time key distribution attacks. In order to deliver the service decryption key to each subscriber who pays every tens of seconds or several hours using the changed service encryption key as a broadcasting channel, a very large transmission bandwidth is required. This is because a broadcast channel cannot constitute an individual channel that can be connected to a specific subscriber, but is a channel that is unilaterally delivered to all subscribers. For example, if there are 100,000 paid subscribers, and the service encryption key is changed every 60 seconds, and the size of the service encryption key change message is 32 bytes, the transmission bandwidth of about 416.67 kbits / sec is required. This bandwidth requirement is very large, and in general, because the number of paid services is larger, the total bandwidth of the message to be delivered due to the change of the service encryption key becomes very large.

Therefore, in order to deliver the changed service encryption key to the subscriber with less transmission bandwidth, a method of grouping the subscribers in groups and delivering the service encryption key change information in groups may be considered. If you configure a group of 256 subscribers and assume that each group delivers a service encryption key change message (one message that is common to the subscribers in the group, not a message to each subscriber in the group), 100,000 Sending a 32 byte key change message every 60 seconds to a group of 391 users can reduce the transmission bandwidth to 1.63 kbits / sec. Even if the service encryption key is delivered in groups, there are subscribers who have purchased the service and subscribers who have not purchased the service. Therefore, there must be a way to encrypt the service encryption key into a group key and configure the group key so that only the subscriber who purchased the service can obtain it (not the subscriber who did not purchase the service).

In the present invention, in transmitting a service encryption key capable of receiving a service by decrypting a paid broadcast service through a broadcast channel to a terminal, the service encryption key must be received from among the subscribers belonging to the group by dividing the subscribers into groups. It is an object of the present invention to provide a grouping method for delivering a group key in a broadcast environment in which a terminal is selected but only one message is transmitted per group, thereby reducing waste of transmission bandwidth of a broadcast channel.

In addition, the present invention transmits a service encryption key that can receive and decrypt a pay broadcast service to each pay broadcast service receiving terminal through a broadcast channel, so that only the service subscriber terminal that should receive the service receives the service encryption key. The purpose is to provide a transmission method.

According to an aspect of the present invention, there is provided a method of generating a management key set for group key management, the method comprising: generating a full binary tree having leaf nodes as terminals in a group and for child nodes of the full binary tree; A second step of generating a left key and a right key, a third step of generating a root node key of the entire binary tree, a fourth step of generating a key of nodes other than the root node, and each terminal included in the group In a fifth step of transmitting a user management key set corresponding to the group or the method of transmitting a group key, the first step of generating the group key and the second step of identifying the terminal that should receive the group key in the group And a third step of generating a group key encryption key for encrypting the group key and encrypting the group key using the group key encryption key. In the fifth step of transmitting the terminal information identified in the fourth step and the third step and the encrypted group key of the fourth step, or in the group key decryption method, the user management key set and the terminal information transmitted from the server A first step of generating a candidate key set using a second step; a second step of generating a group key encryption key from the candidate key set; and a third step of decrypting a group key encrypted using the group key encryption key; It is achieved by group key transmission method in broadcast environment.

 Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principles that can be defined, it should be interpreted as meanings and concepts corresponding to the technical spirit of the present invention.

1 is a system configuration diagram for group key transmission according to the present invention. As shown in FIG. 1, the group key transmission server 110 generates a group key encryption key for generating a group encrypting the group key after generating the group key with the group manager 111 for managing the generated group. Section 112, a group key generation unit 113 for generating a group key, a group key encryption unit 114 for encrypting a group key with a group key encryption key, and a transmission unit 115 for transmitting an encrypted group key. It is.

The group manager 111 groups one or more terminals 120 and reconfigures the generated group into a completely binary tree, and generates arbitrary left_key and right_key for the reconstructed full binary tree. .

Left_Key is used to generate the key of the child node located on the left side from the parent node, and Right_Key is used to generate the key of the child node located on the right side from the parent node. In addition, the Left_Key and Right_Key should be safely delivered to the terminals 120 belonging to the group, and may generate and transmit the same Left_Key and Right_Key for all groups, and may generate and transmit different Left_Key and Right_Key for all groups. .

In addition, the group manager 111 generates a key of an arbitrary root node, and generates a key of a child node using a key of a parent node and Left_Key or Right_Key. The key of the child node located on the left side from the parent node can be generated using the following equation.

K (j) = H (K (i) XOR Left _ Key )

In Equation 1, K (j) is a key of a node to be obtained and is a key of a node existing to the left of the parent node. Further, K (i) is the key of the parent node, _ Left Key is any key for generating a key on the left of the node belonging to the group. At this time, K (i) and Left _ Key are hashed by using H (hash function) after XOR (Exclusive Or).

In addition, the key of the child node located to the right from the parent node can be generated using the following equation.

K (k) = H (K (i) XOR Right _ Key )

In Equation 2, K (k) is a key of a node to be obtained and is a key of a node existing to the right of the parent node. In addition, K (i) is the key of the parent node, _ Right Key is any key for generating a key of the node belonging to the right group. In this case, K (i) and _ Right Key is hashed by using the after (Exclusive Or) XOR, H (hash function).

The group key encryption key generator 112 generates a candidate key set by using terminal list information having a right to receive a group key, thereby generating a group key encryption key, and generating a group key encryption key ( 114). In this case, a candidate key set may be generated through the following process.

First, when both a leaf node corresponding to a predetermined terminal 120 and a sibling node of a leaf node do not have a right to receive a group key, the key of the leaf node and the parent node of the sibling node corresponding thereto is included in the candidate key set. Let's do it. If the child nodes corresponding to the parent node's sibling nodes also do not have the right to receive the group key, do not include the parent node's key in the candidate key set and use the parent node's and its sibling's parent node's key as the candidate key set. Include it in

That is, the following description will be given according to the full binary tree shown in FIG.

If both leafnode A and its siblings, leafnode B, do not have the right to receive group keys, include the keys of leafnode A and its siblings, node 3, the parent nodes of leafnode B, in the candidate key set, If all of Node 3's siblings, Node 4's child nodes (Leafnode C and Leafnode D), are also not entitled to receive a group key, do not include Node 3's and Node 4's keys in the candidate key set. In addition, the key of node 1, which is the parent node of node 3 and node 4, is included in the candidate key set. In this case, when both leaf nodes do not have a right to receive the group key, the key of the node 1 and the node 2 except for the root node are included in the candidate key set without including the key of the root node at the highest level in the candidate key set. .

Second, when a leaf node corresponding to a predetermined terminal 120 and a sibling node of a leaf node both have a right to receive a group key, the candidate hashes the key value of a key of the leaf node and a sibling node's parent node. Include in the key set. If the child nodes corresponding to the parent node's sibling nodes also have the right to receive the group key, do not include the hashed value of the parent node's key in the candidate key set, but the parent node's parent node's parent node's key. The hashed value is included in the candidate key set.

That is, the following description will be given according to the full binary tree shown in FIG.

If both leaf node E and its siblings, leaf node F, have the right to receive a group key, hashing the key of leaf node E and its siblings, node 5's parent node, node 5, to the candidate key set If all of the child nodes of node 6 (leaf node G and leaf node H), which are also nodes of node 5, are also entitled to receive the group key, the value of hashing node 5's key and node 6's key Instead of including the hashed value in the candidate key set, the hashed value of the key of node 2, which is the parent node of node 5 and node 6, is included in the candidate key set. At this time, if both leaf nodes have the right to receive the group key, the hashed key of node 1 except for the root node and the node 2 are not included in the candidate key set without hashing the root node's key. The hashed value of the key is included in the candidate key set.

Third, if a leaf node corresponding to a predetermined terminal 120 has a right to receive a group key, but its sibling node does not have a right to receive a group key, a key of a leaf node having a right to receive a group key is set as a candidate key set. Include it in

That is, the following description will be given according to the full binary tree shown in FIG.

Leaf node C has the right to receive a group key, but if its sibling node leaf node D does not have the right to receive a group key, it includes the leaf node C's key to the group key in the candidate key set.

At this time, the hash function for hashing the key of the node in the second process may use a recognized algorithm such as SHA-1 or MD5.

The group key generator 113 randomly generates a group key to be protected and periodically generates a group key at a predetermined time interval.

The group key encryption unit 114 encrypts the group key generated using the group key encryption key transmitted from the group key encryption key generation unit 112 and transmits the group key to the transmission unit 115.

The transmitting unit 115 transmits the terminal list information having the right to receive the encrypted group key and the group key and various key information generated for the terminal 120 by the group manager 111 to the terminal 120. Do it.

The terminal 120 receives the encrypted group key received from the server 110 and the terminal list information having the right to receive the group key and various key information generated for the terminal 120 by the group manager 111. A set of keys, ancestors, and ancestors of each node belonging to a leaf node corresponding to a member received from the receiver 124 and the receiver 124, a left key, a right key, and a sibling node set (SNS) (ANS: It includes a key storage unit 121 for storing a key hashed the key of each node belonging to an ancestor node set, and using the terminal list information having the right to receive the group key received from the receiving unit 124 candidate And a group key decryption key generation unit 122 for generating a group key decryption key after generating a key set.

In addition, the terminal 120 decrypts the encrypted group key transmitted from the receiver 124 using the group key decryption key transmitted from the group key decryption key generation unit 122 to generate a group key decryption unit ( 123).

2 is a flowchart illustrating a management key set generation for group key management according to the present invention. As shown in FIG. 2, when a group including one or more terminals is generated (S210), a fully binary balanced tree having a depth of Log ₂ N having a terminal of a corresponding group as a leaf node is logged. (S220). For example, if N (the number of terminals included in the group) is 256, the depth of the entire binary tree is eight. 4 shows a full binary tree where N is 8 and the depth of the full binary tree is 3

After creating the tree of the corresponding group, the left and right keys, which are the keys for generating keys of the left and right nodes, which are the child nodes of each node from the root node (16 bytes each), and the right key. Randomly generates (S230). The randomly generated left and right keys do not necessarily have to be confidential, and each group may constitute a left key and a right key, or each group may constitute the same left and right key.

After generating the left key and the right key, a key of the root node for generating a key of the child node is randomly generated using the left key or the right key (S240). The root node's key is also randomly generated, and the root node's key is not transmitted to the terminal and can be safely stored in the server or deleted after the child node's key is generated.

After generating the key of the root node, the keys of the lower nodes of the root node is generated (S250). The child nodes are child nodes connected from the root node. In the entire binary tree, any node except the leaf node has child nodes of the left node and the right node.

As shown in FIG. 5, a method of generating keys of subnodes is as follows.

In order through the key K (i) of the i of the first node, generating a key K (j) and K (k) of the sub-nodes that have already been created left key, Left _ Key and the right key, using the Right _ Key, and the node i The key K (j) of the left child node is generated by K (j) = H (K (i) XOR Left_Key) , which is the above Equation 1.

In this case, K (j) is a key of a node to be obtained and is a key of a node existing to the left of the parent node. Further, K (i) is the key of the parent node, _ Left Key is any key for generating a key on the left of the node belonging to the group. In this case, K (i) and Left_Key are hashed using H (hash function) after XOR (Exclusive Or).

Also, K (k), which is the key of the left child node of node i , is K (k) = H (K (i) XOR Right _ Key ) .

In this case, K (k) is a key of a node to be obtained and is a key of a node existing to the right of the parent node. In addition, K (i) is the key of the parent node, _ Right Key is any key for generating a key of the node belonging to the right group. In this case, K (i) and _ Right Key is hashed by using the after (Exclusive Or) XOR, H (hash function).

The keys of each node in a full binary tree using a group containing one or more terminals have the same lifecycle as the group.

Thereafter, the server transmits a user management key set, which is a set of keys required for a terminal included in the group (S260). The set of user management keys to be delivered to the terminal corresponding to the leaf node i is a hashed key of the leaf node i, the key of each node constituting the SNS (i), and the key of each node constituting the ANS (i). In this case, ANS (i) means a set of nodes in the path from leaf node i to the root node, except for the root node. SNS (i) means a set of sibling nodes for each node of the ancestor nodes of leaf node i. Since the root node has no sibling nodes, it is not included in SNS (i). For example, the entire binary tree illustrated in FIG. 4 will be described. A set of user management keys delivered to a terminal corresponding to leaf node 8 is K (8), which is a key corresponding to leaf node 8, and K constituting SNS (8). (4), H (K (3)) and H (K (1)) which hashed the key of each node which comprises K (2) and ANS (8).

3 is a flowchart of group key transmission according to the present invention. As shown in FIG. 3, a group key for a group including one or more terminals is randomly generated (S310). The group key is generated to encrypt the service decryption key.

After the group key is generated, the terminal having the right to receive the group key is identified from the terminals included in the group (S320). That is, in the case of paying broadcasting channels among the broadcasting services transmitted to the terminal, the broadcasting service is encrypted and transmitted with a service encryption key so that the paying broadcasting channel can be viewed only by the terminal possessed by the user who can watch the broadcasting. At this time, the service encryption key is encrypted using the group key for the security of the service encryption key, the group key is encrypted with the group key encryption key, and the terminal receives the encrypted group key and uses the already received management key set. To generate a group key decryption key. Therefore, it is necessary to identify the terminal that should receive the group key for the broadcast service. In this case, the method of identifying the terminal may be any one of a mobile directory number (MDN), a mobile identification number (MIN), an electronic serial number (ESN), an international mobile subscriber identity (IMSI), a mobile subscriber number (MSN), and a serial number of the terminal. Use one.

After the terminal to receive the group key is identified, a group key encryption key for encrypting the group key transmitted to the terminal is generated (S330). The group key encryption key uses a candidate key set, which is a set of keys of nodes or keys hashed of nodes included in a group so that only terminals that can receive the group key can obtain the group key encryption key. Create That is, the group key encryption key is a hashed value after XORing all the keys included in the candidate key set.

The key constituting the candidate key set is determined by the following method.

First, when both a leaf node corresponding to a predetermined terminal and a sibling node of a leaf node do not have a right to receive a group key, the key of the leaf node and the parent node of the sibling node corresponding thereto is included in the candidate key set. If the child nodes corresponding to the parent node's sibling nodes also do not have the right to receive the group key, do not include the parent node's key in the candidate key set, but instead insert the parent node's and its sibling's parent node's keys into the candidate key set. Include it.

That is, the following description will be given according to the full binary tree shown in FIG.

If both leaf node A and its siblings, leaf node B, are not entitled to receive the group key, include the key of node 3, the parent node of leaf node A and its siblings, leaf node B, in the candidate key set, If all of Node 3's siblings, Node 4's child nodes (leafnode C and leafnode D), are also not entitled to receive the group key, do not include Node 3's and Node 4's keys in the candidate key set, The key of node 1, which is the parent node of node 3 and node 4, is included in the candidate key set. In this case, when both leaf nodes do not have a right to receive the group key, the key of the node 1 and the node 2 except for the root node are included in the candidate key set without including the key of the root node at the highest level in the candidate key set. .

Second, if both a leaf node and a leaf node's sibling node have a right to receive a group key, the hashing key of the leaf node and the parent node of the corresponding sibling node is hashed to the candidate key set. Include it. If the child nodes corresponding to the parent node's sibling nodes also have the right to receive the group key, do not include the hashed value of the parent node's key in the candidate key set and use the parent node's and its sibling's parent node's keys. Include the hashed value in the candidate key set.

That is, the following description will be given according to the full binary tree shown in FIG.

If both leaf node E and its siblings, leaf node F, have the right to receive a group key, hashing the key of leaf node E and its siblings, node 5's parent node, node 5, to the candidate key set If all of the child nodes of node 6 (leaf node G and leaf node H), which are also nodes of node 5, are also entitled to receive the group key, the value of hashing node 5's key and node 6's key Instead of including the hashed value in the candidate key set, the hashed value of the key of node 2, which is the parent node of node 5 and node 6, is included in the candidate key set. At this time, if both leaf nodes have the right to receive the group key, the hashed key of node 1 except for the root node and the node 2 are not included in the candidate key set without hashing the root node's key. The hashed value of the key is included in the candidate key set.

Third, if a leaf node corresponding to a predetermined terminal has a right to receive a group key, but its sibling node does not have a right to receive a group key, the leaf node having the right to receive a group key is included in the candidate key set. .

That is, the following description will be given according to the full binary tree shown in FIG.

Leaf node C has the right to receive a group key, but if its sibling node leaf node D does not have the right to receive a group key, it includes the leaf node C's key to the group key in the candidate key set.

After the group key encryption key is generated, the group key is encrypted with the group key encryption key (S340), and the terminal information and the encrypted group key to receive the group key are transmitted to the terminal (S350).

In addition, as another embodiment of the present invention, the service decryption key may be encrypted using the group key encryption key without separately generating the group key.

6 is a flowchart for decrypting an encrypted group key according to the present invention. As shown in FIG. 6, the terminal generates a candidate key set using terminal information having a right to receive a group key received from the server (S410). Generation of the candidate key set is configured in the same manner as described in FIG. 3, and generates a group key encryption key using the generated candidate key set (S420), and generates a group key encrypted using the generated group key encryption key. Decode (S430).

Although the present invention has been shown and described with reference to the preferred embodiments as described above, it is not limited to the above embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

Accordingly, the present invention is to solve the problems of the prior art, real-time key distribution in transmitting a service encryption key that can receive the service by decrypting the pay-TV service through the broadcast channel (real-time key distribution) To prevent key exposure attacks such as attacks, the service encryption key should be changed periodically for a short time. The change of the service encryption key can reduce the waste of transmission bandwidth incurred when transmitting the service encryption key to each terminal. It has an effect.

In addition, in transmitting a service encryption key capable of receiving a service by decrypting a paying broadcast service through a broadcast channel, the terminal needs to divide the subscribers into groups and receive the service encryption key among terminals belonging to the group. Although the service encryption key can be transmitted through only one message per group, the service encryption key can be transmitted only to a terminal that needs to receive the service encryption key with less transmission bandwidth.

Claims (20)

In the method for generating a management key set for group key management, Generating a full binary tree including leaf nodes as terminals in a group; Generating a left key and a right key for child nodes of the full binary tree; Generating a root node key of the full binary tree; Generating a key of nodes excluding the root node; And A fifth step of transmitting a user management key set corresponding to each terminal included in the group; Group key transmission method in a broadcast environment comprising a. The method of claim 1, The group is composed of one or more, and if there are a plurality of groups, the left key and the right key is the same or not the same for each group group key transmission method in a broadcast environment. The method of claim 1, And the root node key and the keys of the nodes generated in the fourth step have the same life cycle as the group. The method of claim 3, wherein In the fourth step, the key of the node left of the parent node among the nodes other than the root node is generated by the following equation. Equation: K (j) = H (K (i) XOR Left_Key) Where K (j) is the key of the corresponding node (located to the left of the parent node), H is the hash function, and K (i) is the key of the parent node. The method of claim 3, wherein In the fourth step, the key of the node on the right side from the parent node among the nodes other than the root node is generated by the following equation. Equation: K (k) = H (K (i) XOR Right_Key) Where K (k) is the key of the node (to the right of the parent node), H is the hash function, and K (i) is the key of the parent node. The method of claim 1, wherein the user management key set of the fifth step is Left key of the binary tree; Right key of the binary tree; A key of a leaf node corresponding to the terminal; A set of sibling node keys of an ancestor node corresponding to the terminal; And A set of hashed ancestor node keys corresponding to the terminal Group key transmission method in a broadcast environment comprising a. The method of claim 6, Group key transmission method in a broadcast environment for transmitting a user management key set of each of the terminals in the group in one message. In the group key transmission method, A first step of generating the group key; A second step of identifying a terminal to receive the group key in the group; Generating a group key encryption key for encrypting the group key; Encrypting the group key using the group key encryption key; And A fifth step of transmitting the terminal information identified in the second step and the encrypted group key of the fourth step; Group key transmission method in a broadcast environment comprising a. The method of claim 8, And generating the group key randomly at predetermined intervals. The method of claim 8, The group key encryption key is a group key transmission method in a broadcast environment that uses a hashed value after performing an exclusive OR of keys included in a candidate key set which is a set of selected keys of leaf nodes corresponding to the terminals. . The method of claim 10, wherein the group key encryption key is A first step in which a predetermined leaf node corresponding to the terminal and a sibling node of the leaf node do not receive a group key; A second step of receiving a group key from a predetermined leaf node corresponding to the terminal and a sibling node of the leaf node; And A third process in which a predetermined leaf node corresponding to the terminal receives a group key and a sibling node of the leaf node does not receive a group key Group key transmission method in the broadcast environment generated by the. The method of claim 11, wherein the first process is And a key of a first parent node corresponding to the leaf node and a sibling node of the leaf node in the candidate key set. The method of claim 11, wherein the second process is And a value obtained by hashing a key of the leaf node and a first parent node corresponding to the leaf node's sibling node in the candidate key set. The method of claim 11, wherein the third process is And transmitting the key of the leaf node to the candidate key set. The method of claim 12, If neither of the child nodes included in the sibling node of the first parent node receives a group key, the key of the candidate key set is a key of the second parent node corresponding to the sibling node of the first parent node and the first parent node. Group key transmission method in a broadcast environment included in the. The method of claim 15, And a key of the first parent node and a key of a sibling node of the first parent node in the candidate key set when the second parent node is a root node. The method of claim 15, When all of the child nodes included in the sibling node of the first parent node receive a group key, a value obtained by hashing a key of a key of the second parent node corresponding to the sibling node of the first parent node and the first parent node is used. A method of transmitting a group key in a broadcast environment included in a candidate key set. The method of claim 17, If the second parent node is a root node, the candidate key set includes a hashed key of the first parent node and a hashed key of the sibling node of the first parent node in the candidate key set. How to send group key. In the group key transmission method of the broadcast environment for decrypting the group key received by the terminal, Generating a candidate key set using the user management key set and the terminal information transmitted from the server; Generating a group key encryption key from the candidate key set; And A third step of decrypting the group key encrypted using the group key encryption key And wherein the terminal information is information for identifying the terminal to receive the group key. 20. The method of claim 19, wherein the user management key set is Left key of the binary tree generated by the server; A right key of the binary tree created by the server; A key of a leaf node corresponding to the terminal; A set of sibling node keys of an ancestor node corresponding to the terminal; And A set of hashed ancestor node keys corresponding to the terminal Group key transmission method in a broadcast environment comprising a.

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