JP2004166153A - Key change system in multicast distribution system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid delay in a process involved when a client acquires a new decryption key in the key change (replacement). <P>SOLUTION: A contents server 11 distributes a decryption key to be used next within a valid time of a now-using key to a key control sever 31 and transmits a multicast packet including a key number. Each client 51-5n requests the key control server 31 to send the next usable decryption key corresponding thereto at a time within its valid time of the now using key after the contents server 11 distributes the next usable decryption keys to the key control server 31. Each client also decrypts encrypted data in the multicast packet, using the decryption key corresponding to the key number in the multicast packet. The key control server 31 receives the next usable decryption key from the contents server 11 and, in response to a send request from each client 51-5n, sends the next usable decryption key corresponding thereto to the requesting client. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multicast distribution system for preventing eavesdropping by encrypting with a different key at fixed time intervals during multicast distribution, and a key in the multicast distribution system for controlling and managing the exchange of keys (encryption key / decryption key). Regarding the exchange method.
[0002]
[Prior art]
In general, a multicast packet is received by an unspecified number of recipients. To permit viewing only by a specific client, the data distributed by the packet is encrypted with an encryption key, and viewed. It is necessary to distribute the decryption key only to the client that has permitted the decryption.
[0003]
At this time, by periodically changing the key, the client can be managed, and the confidentiality of the encryption can be further improved.
[0004]
2. Description of the Related Art Conventionally, in a multicast distribution system in which distribution data (data to be distributed) is encrypted, an encryption key and a decryption key are exchanged in order to prevent eavesdropping by performing encryption with a different key at predetermined time intervals. (For example, see Patent Document 1).
[0005]
Such a conventional multicast distribution system includes a content server (expressed as a “transmitting unit” in Patent Literature 1), a client (expressed as a “receiving unit” in Patent Literature 1), and a key management server. The content server sends a packet with key request information attached at regular time intervals, and the client that receives the request requests the key from the key management server, so that the key is acquired at regular time intervals. The update prevents the encrypted data from leaking when the key is passed to a third party.
[0006]
[Patent Document 1]
JP 2001-285273 A (pages 2-4, FIG. 1)
[0007]
[Problems to be solved by the invention]
The above-described key exchange method in the conventional multicast distribution system has the following problems.
[0008]
The first problem is that a time lag occurs when receiving the key request information. The reason that such a problem exists is that when the client receives the key request information, the client requests the key from the key management server and starts decryption after receiving a response (key) to the request. This is because the client cannot decrypt the encrypted information (encrypted data) until a response is returned from the key management server.
[0009]
The second problem is that if a user participates in a multicast broadcast during a broadcast, the user cannot view the broadcast immediately. The reason that such a problem exists is that a packet attached with key request information is generated at regular intervals, so that a client participating in the multicast broadcast decrypts the packet until the next key request information is sent. This is because the key cannot be obtained and cannot be decrypted.
[0010]
A third problem is that when key request information distributed by multicast is lost on a route, a period during which a key cannot be obtained may be long. The reason that such a problem exists is that the multicast distribution does not check the response, so it cannot be confirmed that the packet has been lost on the route. This is because a new key cannot be obtained until key request information is sent. Therefore, the encrypted information cannot be decrypted until a new key can be obtained.
[0011]
In view of the above, an object of the present invention is to solve the above-described problems, and to prevent eavesdropping by performing encryption with a different key at fixed time intervals during multicast distribution. It is an object of the present invention to provide a key exchange method in a multicast distribution system that enables real-time data processing without the confirmation delay (key exchange delay).
[0012]
That is, the feature of the present invention is that, when the distribution data is encrypted at the time of multicast distribution, the encryption key and the decryption key are periodically changed to improve the confidentiality of the encryption, and the new key information when the key is changed. It is possible to prevent a delay caused by obtaining (a key and information accompanying the key) (obtaining by a client).
[0013]
[Means for Solving the Problems]
The key exchange method in the multicast distribution system of the present invention is an encryption key / decryption key (an encryption key and a decryption key to be paired. The same key may be used in a network system where multicast distribution of encrypted data is performed). ), Its key number (information for identifying the key) and its remaining valid time (key information relating to the key), and the encryption / decryption key to be used next, its key number, its remaining valid time, And a key information management table in the content server holding the set of keys, and the remaining valid time of the key in use (encryption key / decryption key) is smaller than the first set value (the initial value of the remaining valid time of the key in use). When the value becomes a value larger than 0, the key information message concerning the decryption key to be used next (the decryption key to be used next, its key number, and the remaining valid time) is sent to the key management server. Is transmitted, and when the remaining valid time of the key being used becomes 0, it is stored in its own table (the key information management table in the content server) as the next key to be used. The key being used is switched to a new key in use, a new encryption key / decryption key to be used next is created, and its key information (the encryption key / decryption key, its key number, and its remaining valid time) Key) in the content server for storing the set in its own table, and encrypting the distribution data using the encryption key in use held in the own table (the key information management table in the content server) during multicast distribution. Means for transmitting a multicast packet having encrypted data and a key number of the encryption key in the content server, a decryption key being used, and the key number And a key information management table in the client capable of holding a set of a decryption key to be used next, its key number, and its remaining valid time, and a key information management table in the client A multicast packet is received, and a decryption key is searched from its own table (the key information management table in the client where it is present) using the key number in the received multicast packet. Packet reception / decryption means in the client for decrypting the encrypted data, and a remaining valid time of the key being used is set to a second set value (a value smaller than the first set value and larger than 0). A key information request is sent to the key management server, and the next decryption key and its key number in the response message And a set of the remaining valid time in a self-table (the key information management table in the client where the self exists), and based on the recognition of the change of the key number in the multicast packet transmitted from the content server, The key management means in the client that switches the key held in its own table as the next key to be used to the new key in use, and the set of the used decryption key, its key number, and its remaining valid time And a key information management table in the key management server capable of holding a set of a decryption key to be used next, its key number, and its remaining valid time, and a decryption to be used next in the key information message received from the content server. A set of a key, its key number, and its remaining valid time is stored in its own table (the key information management table in the key management server), and the remaining valid time of the key being used is stored in the second table. When a key information request is received from the client when the value becomes a fixed value, a response message including a set of a decryption key to be used next, its key number, and its remaining valid time is returned to the client, and the A key management means in the key management server for switching the key held in the own table as a key to be used next when the remaining valid time becomes 0 to a new key in use.
[0014]
Here, the key exchange method in the multicast distribution system according to the present invention is a content server key exchange control for causing the content server to function as the key information management table, the key management means, and the encryption / packet transmission means. A program, a client key management program for causing the client to function as the key information management table, the packet reception / decryption unit, and the key management unit; and a key management server for the key management server. The present invention can also be realized in a mode having a table and a key management server key exchange control program for functioning as a key management unit.
[0015]
The above-described key exchange method in the multicast distribution system of the present invention is more generally performed by creating an encryption key / decryption key in a network system where multicast distribution of encrypted data is performed, and And the key number and the remaining valid time are managed, and the next decryption key to be used is distributed to the key management server within the valid time of the key in use (before the remaining valid time becomes 0), and the encrypted data and A content server that transmits a multicast packet having a key number of an encryption key used in the encryption, and a decryption key that is used within the valid time of the key being used and that the content server next uses for the key management server. Requesting the key management server to send the decryption key to be used next at a point in time after the distribution of the multicast packet received from the content server. Manages the client that decrypts the encrypted data in the multicast packet with the decryption key corresponding to the key number in the client, the decryption key, its key number, and the remaining valid time, and uses the decryption key for the next time from the content server. It can be described as having the key management server that receives a decryption key and transmits the next decryption key to be used to the client in response to a request from the client.
[0016]
Further, the key exchange method in the multicast distribution system of the present invention holds a set of an encryption key in use, its key number, and its remaining valid time in a network system in which multicast distribution of encrypted data is performed. A key information management table in the content server which can hold a set of an encryption key to be used, its key number, and its remaining valid time; When the value becomes smaller than the initial value of the effective time and larger than 0), a key creation request is issued to the key management server to create a key to be used next, and the key received as a response The set of the encryption key to be used next in the information response message, its key number, and its remaining valid time is stored in its own table (the key information management table in the content server) and used. When the remaining valid time of the key becomes 0, the key management means in the content server for switching the key held in the own table as the next key to be used to the new key in use, and the own table ( In the content server for encrypting the distribution data using the encryption key in use held in the key information management table in the content server) and transmitting a multicast packet having the encrypted data and the key number of the encryption key Of the encryption / packet transmitting means, and the set of the decryption key in use, its key number, and its remaining valid time, and the set of the decryption key to be used next, its key number, and its remaining valid time The key information management table in the client, which can receive the multicast packet transmitted from the content server, and the received multicast packet A client that retrieves a decryption key from its own table (the key information management table in the client in which it resides) using the key number in the client, and decrypts the encrypted data in the multicast packet using the decryption key with that key number When the remaining valid time of the key in use becomes a second set value (a value smaller than the first set value and larger than 0), the key receiving server A key information request is transmitted to the client device, and a set of the decryption key to be used next in the response message that is the reply, the key number, and the remaining valid time is stored in its own table (the key information management table in the client where the client exists). ), And based on the recognition of the change in the key number in the multicast packet transmitted from the content server, stores it in its own table as the key to be used next until then. The key management means in the client that switches the key that it has to the new key in use, the set of the encryption / decryption key that is being used, its key number, and its remaining valid time, and the encryption to be used next A key information management table in a key management server capable of holding a set of a key / decryption key, its key number, and its remaining valid time, and an encryption key / key to be used next in response to a key creation request received from the content server. A decryption key is created, and a set of the encryption key / decryption key to be used next, its key number, and its remaining valid time is stored in its own table (the key information management table in the key management server). A key information response message relating to the encryption key to be used (a message having key information that is a set of the encryption key to be used next, its key number, and its remaining valid time) is returned to the content server, and the remaining key in use is returned. Valid time is When a key information request is received from the client when the set value is reached, a response message including the set of the decryption key to be used next, its key number, and its remaining valid time is returned to the client, and the key in use is returned. And the key management means in the key management server for switching the key held in its own table as the next key to be used when the remaining effective time of the key becomes 0 to a new key in use. It is possible.
[0017]
Here, the key exchange method in the multicast distribution system according to the present invention is a content server key exchange control for causing the content server to function as the key information management table, the key management means, and the encryption / packet transmission means. A program, a client key management program for causing the client to function as the key information management table, the packet reception / decryption unit, and the key management unit; and a key management server for the key management server. The present invention can also be realized in a mode having a table and a key management server key exchange control program for functioning as a key management unit.
[0018]
Incidentally, the key exchange method in the multicast distribution system of the present invention described above, more generally, in a network system in which multicast distribution of encrypted data is performed, manages the encryption key and its key number and the remaining valid time, Requesting the key management server to create an encryption key / decryption key to be used next within the valid time of the key in use; obtaining the encryption key created in response to the request from the key management server; And a content server for transmitting a multicast packet having a key number of an encryption key used in the encryption, and a cipher which is used within the validity time of the key being used and which the content server next uses for the key management server. At a point in time after requesting the creation of a key / decryption key, the key management server is requested to send the next decryption key to be used. A client for decrypting the encrypted data in the multicast packet by a decryption key corresponding to the key number in the received multicast packet, managing the encryption key / decryption key, the key number and the remaining valid time, Creates and stores an encryption key / decryption key to be used next in response to a request from the server, transmits the encryption key to be used next to the content server, and uses the encryption key / decryption key to be used next in response to a request from the client It can be expressed as having the key management server that transmits a decryption key to the client.
[0019]
Further, in the key exchange method in the multicast distribution system of the present invention enumerated above, the key information request on the client side is added by adding the address of the key management server to the information in the multicast packet transmitted from the content server to the client. It is also possible to eliminate the need for setting the transmission destination (inquiry / request destination of the decryption key).
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in detail with reference to the drawings.
[0021]
(1) First embodiment
[0022]
FIG. 1 is a block diagram showing a configuration of a key exchange method in the multicast distribution system according to the first embodiment of the present invention.
[0023]
Referring to FIG. 1, the key exchange method in the multicast distribution system according to the present embodiment includes a content server 11 that transmits a multicast packet, and clients 51, 52,... That receive the multicast packet transmitted from the content server 11. 5n (n is a positive integer) and the key information relating to the decryption key in the key information message 71 sent from the content server 11 are stored in response to a key information request 81 from the client 5i (i is a positive integer of 1 to n). A key management server 31 that transmits a response message 82 to the client, and a network 100 that connects the content server 11, the client 5i, and the key management server 31 to each other.
[0024]
The content server 11 includes a key (encryption key / decryption key) used for encryption / decryption of data (delivery data) distributed by the multicast packet, a key number for identifying the key, and a remaining valid time for the key. (Key information) that holds a set of key information (key information management table can hold a plurality of key information). Note that the encryption key and the decryption key used in the pair of encryption / decryption processes may be the same or different depending on the encryption method, but in any case, they are identified by the same key number.
[0025]
Here, the key information management table 21 holds key information on a key in use and key information on a key to be used next.
[0026]
The content server 11 includes a key management unit 111 and an encryption / packet transmission unit 112.
[0027]
The key management server 31 stores a key information management table 41 that holds a set (key information) of a key (a decryption key in the present embodiment), a key number for identifying the key, and a remaining valid time for the key. Have.
[0028]
Here, the key information management table 41 holds key information on a key in use, and can hold key information on a key to be used next. In the initial state, the key information management table 41 has no information.
[0029]
Further, the key management server 31 is configured to include a key management unit 311.
[0030]
The client 5i holds key information (key information) including a key (decryption key) used for decrypting data distributed by a multicast packet, a key number for identifying the key, and a remaining valid time for the key. It has a management table 6i.
[0031]
Here, the key information management table 6i holds key information on a key in use, and can hold key information on a key to be used next. In the initial state, the key information management table 6i has no information.
[0032]
The client 5i includes a key management unit 5i1 and a packet reception / decryption unit 5i2.
[0033]
The content server 11, the key management server 31, and each client 5i determine the remaining valid time in the key information management table 21, the key information management table 41, and the key information on each key information management table 6i, respectively. Update every time (e.g., update based on its own clock signal).
[0034]
FIG. 2 is a flowchart showing a multicast packet transmission / reception process of the key exchange system in the multicast distribution system according to the present embodiment. This processing includes a distribution data encryption step A1, a multicast packet transmission step A2, a multicast packet reception step A3, a used key number match determination step A4, a next use key number match determination step A5, and encrypted data decryption. And a key management server inquiry step A7.
[0035]
FIG. 3 is a flowchart showing processing related to key management of the key exchange method in the multicast distribution system according to the present embodiment (processing at the time when the value of the remaining valid time of the key in use becomes the first set value). . This process includes a first set value reaching recognition step B1, a key information message transmission step B2, a key information message reception step B3, and a next use key information storage step B4.
[0036]
FIG. 4 is a flowchart showing processing related to key management of the key exchange scheme in the multicast distribution system according to the present embodiment (processing at the time when the value of the remaining valid time of the key in use becomes the second set value). . This processing includes a second set value reaching recognition step C1, a key information request transmission step C2, a key information request reception step C3, a response message transmission step C4, a response message reception step C5, and a next use key information storage step. C6.
[0037]
FIG. 5 is a block diagram for explaining a specific operation of the key exchange method in the multicast distribution system according to the present embodiment.
[0038]
FIG. 6 is a sequence diagram for explaining a specific operation of the key exchange method in the multicast distribution system according to the present embodiment.
[0039]
Next, the overall operation of the key exchange scheme in the multicast distribution system according to the present embodiment configured as described above will be described in detail with reference to FIGS.
[0040]
First, an operation related to a multicast packet transmission / reception process performed from the content server 11 to each client 5i via the network 100 will be described (see FIG. 2).
[0041]
At the time of multicast distribution, the encryption / packet transmitting means 112 in the content server 11 holds the currently used encryption key (encryption key in the key information related to the used key in the key information management table 21) held by itself. Is used to encrypt distribution data (data to be distributed) (step A1).
[0042]
Then, a multicast packet having the encrypted data (encrypted distribution data) and the key number of the encryption key is transmitted on the network 100 (step A2).
[0043]
The packet receiving / decoding means 5i2 in the client 5i participating in the multicast address receives the multicast packet transmitted from the content server 11 (step A3), and transmits the encrypted data contained in the received multicast packet. Perform decryption processing.
[0044]
At the time of this decryption processing, first, the key number in the received multicast packet and the key number of the currently used decryption key stored therein (in the key information relating to the used key in the key information management table 6i). Key number) to determine whether the two key numbers match (step A4).
[0045]
If it is determined in step A4 that “the two key numbers match”, the encrypted data in the multicast packet is decrypted using the decryption key of the key number (step A6).
[0046]
On the other hand, if it is determined in step A4 that "the two key numbers do not match", the key number in the multicast packet and the key number of the next decryption key stored in the multicast packet itself (in the key information management table 6i). (Key number in the key information relating to the key to be used next) and determines whether or not both key numbers match (step A5).
[0047]
If it is determined in step A5 that "the two key numbers match", the encrypted data in the multicast packet is decrypted using the decryption key of the key number (step A6).
[0048]
On the other hand, if it is determined in step A5 that “the two key numbers do not match” (including the case where there is no key information related to the key to be used next in the key information management table 6i), If neither key number of the key to be used matches the key number in the multicast packet, it means that the acquisition process of the key information has not been performed correctly, and the key management server 31 An inquiry to the effect is made (step A7).
[0049]
Second, an operation related to key management in a period in which the value of the remaining valid time of the key being used is from the initial value (the initial value of the remaining valid time) to the first set value (a value smaller than the initial value) will be described.
[0050]
During this period, the key information management table 21 in the content server 11 stores key information (a set of a key, a key number, and a remaining valid time) relating to a key in use (an encryption key and a decryption key), and uses the key information next. It holds key information on keys (encryption key and decryption key). These keys and key numbers are created by the key management unit 111 in the content server 11.
[0051]
Also, during this period, the key information management table 41 in the key management server 31 holds key information on the key in use (decryption key).
[0052]
Further, during this period, the key information management table 6i in each client 5i stores the key information (the multicast packet including the data encrypted by the used key from the content server 11) regarding the used key (decryption key). Until it is received, it is managed as key information of a key to be used next). Until a multicast packet having data encrypted with a new key in use is received from the content server 11, the key information about the key that was used immediately before is also held.
[0053]
If there is a client 5i newly joining the multicast address during this period, and the key management means 5i1 in the client 5i transmits the key information request 81 to the key management server 31, the key management in the key management server 31 The means 311 sends a response message 82 having key information about the key in use to the client 5i.
[0054]
Third, an operation related to key management when the value of the remaining valid time of the key in use becomes the first set value will be described (see FIG. 3).
[0055]
The key management unit 111 in the content server 11 determines that the value of the remaining valid time of the key in use managed in the key information management table 21 has become the first set value (the value of the remaining valid time has decreased. Recognizing that the first set value has been reached (step B1), a message (key information message) having key information (a set of a key number, a key, and a remaining valid time) relating to a key (decryption key) to be used next time 71) is transmitted to the key management server 31 (step B2).
[0056]
Upon receiving the key information message 71 from the content server 11 (step B3), the key management means 311 in the key management server 31 stores the key information relating to the next key in the key information message 71 in the key information management table 41. Save (step B4). As a result, the key information management table 41 in the key management server 31 holds the key information regarding the key in use and the key information regarding the key to be used next.
[0057]
Note that if there is a client 5i that has newly joined the multicast address during a period from this time to the time when the value of the remaining valid time of the key in use becomes the second setting value described later, the key in the client 5i When the management unit 5i1 sends a key information request 81 to the key management server 31, the key management unit 311 in the key management server 31 sends a response message 82 having key information about the key being used and key information about the key to be used next. Is transmitted to the client 5i.
[0058]
Fourth, an operation related to key management when the value of the remaining valid time of the key in use becomes the second set value (a value smaller than the first set value and larger than 0) will be described (FIG. 4).
[0059]
When the value of the remaining valid time of the key in use in the key information management table 6i of the client 5i becomes the second set value, the key managing unit 5i1 (that is, the value of the remaining valid time decreases). (Step C1), and transmits a key information request 81 to the key management server 31 in order to obtain key information on a key (decryption key) to be used next. (Step C2). Note that the address of the key management server 31 that is the transmission destination of the key information request 81 is set in the client 5i in advance.
[0060]
Upon receiving the key information request 81 from the client 5i (step C3), the key management means 311 in the key management server 31 responds by receiving key information on the currently used key (decryption key) and the key to be used next. A response message 82 having key information regarding the (decryption key) is transmitted to the client 5i (step C4).
[0061]
Upon receiving the response message 82 (step C5), the client 5i stores the key information on the next key to be used in the response message 82 in its own key information management table 6i (step C6).
[0062]
Fifth, an operation related to key management when the value of the remaining valid time of the key in use becomes 0 will be described.
[0063]
When the remaining valid time of the used key held in the key information management table 21 becomes 0, the key management unit 111 in the content server 11 discards the key information on the used key. The key information held as the key information about the key to be used is stored in the key information management table 21 as the key information about the new key in use. As a result, the encryption / packet transmitting means 112 performs the subsequent encryption processing using the key.
[0064]
At this time, the key management unit 111 further creates a new key (encryption key and decryption key) to be used next, and stores key information relating to the key to be used next in the key information management table 21.
[0065]
Further, the encryption / packet transmitting means 112 changes the key number included in the encrypted packet (the multicast packet having the encrypted data) to the key number for the new key in use, thereby providing the client 5i with Indicates that the key in use has changed.
[0066]
The key management unit 5i1 in each client 5i confirms that the key number included in the encrypted packet sent from the content server 11 (the encrypted packet received by the packet reception / decryption unit 5i2) has been changed. Then, the key to be used next having the key number in its own key information management table 6i is stored as a new key in use. At this time, since each of the clients 5i has not yet obtained a new key to be used next, the client 5i does not have key information on the key to be used next in its own key information management table 6i.
[0067]
On the other hand, when the remaining valid time in the key information on the key in use held in the key information management table 41 becomes 0, the key management unit 311 in the key management server 31 The information is discarded, and the key information held as the key information about the key to be used next is stored in the key information management table 41 as the key information about the new key in use. At this time, since the key management server 31 has not yet obtained a new key to be used next, the key information management table 41 has no key information on the key to be used next.
[0068]
The initial value of the remaining valid time, the first setting value (X), and the second setting value (Y) can be set by, for example, the following method a or b.
[0069]
a. Manual setting is performed as a setting value common to the entire multicast distribution system.
[0070]
b. By transmitting the initial value together with the remaining valid time of the key to each device (key management server and client), a certain ratio of time from the initial value is determined as X and Y in each device. This “constant ratio” is set to be common to the entire multicast distribution system. As a specific example, if X is 50% of the initial value of the remaining key valid time and Y is 25% of the initial value of the remaining key valid time, the initial value of the remaining key valid time is 1 hour. , X becomes 30 minutes and Y becomes 15 minutes.
[0071]
Next, a specific operation (a series of operation sequences) of the key exchange method in the multicast distribution system according to the present embodiment will be described with reference to FIGS.
[0072]
FIG. 5 is a diagram specifically showing information in each key information management table and contents of each packet / request / message. In FIG. 5, a key in use is indicated by a key A, a key to be used next is indicated by a key B, and these key numbers are indicated as “key number A” and “key number B”. are doing. In this example, it is assumed that the encryption key and the decryption key are the same key (for example, the key A is both an encryption key and a decryption key). Further, the first set value is indicated by X, and the second set value is indicated by Y.
[0073]
FIG. 6 is a diagram showing an operation sequence over time when information having contents as shown in FIG. 5 is handled.
[0074]
In this operation sequence, in the initial state (the state where the value of the remaining valid time of the key A is the initial value), the content server 11 sets the key information on the key A of the key in use and the key B of the key to be used next. have. Further, the key management server 31 and the client 51 (here, pay attention to the client 51 from the plurality of clients 51 to 5n) have only the key information related to the key A in the key information shown in FIG. It is assumed that the initial value of the remaining valid time and the values of X and Y are set in advance in the content server 11, the key management server 31, and the clients 51 to 5n.
[0075]
When the value of the remaining valid time of the key A becomes X (first set value), the content server 11 sends a key information message 71 having key information on the key B (the key to be used next) to the key management server 31. Send to. As a result, the key management server 31 has key information on the keys A and B as shown in FIG.
[0076]
When the value of the remaining valid time of the key A becomes Y (the second setting value), the client 51 transmits a key information request 81 requesting key information relating to a key to be used next to the key management server 31. I do.
[0077]
Upon receiving the key information request 81, the key management server 31 transmits, as a response, a response message 82 having key information regarding the currently used key (key A) and the key to be used next (key B). As a result, the client 51 has key information regarding the keys A and B as shown in FIG.
[0078]
When the value of the remaining valid time of the key A becomes 0, the content server 11 discards the key information relating to the key A being used and newly replaces the stored key B which is the next key to be used. The key B is used as the key in use, and the key B is used to encrypt the distribution data. At this time, the content server 11 generates a key C as a new key to be used next, and stores key information relating to the key C in the key information management table 21. The key information on the key C is transmitted from the content server 11 to the key management server 31 by the key information message 71 when the remaining valid time of the key B reaches X.
[0079]
When the value of the remaining valid time of the key A becomes 0, the key management server 31 discards the key information related to the key A and holds the key B stored as the next key to be used as the currently used key. I do. Further, when the key information about the key C is received by the key information message 71 from the content server 11, the key information is stored in the key information management table 41 as the key information about the next key to be used. As a result, the key information stored in the key information management table 41 is such that the key information relating to the key A in FIG. 5 is replaced with the key information relating to the key B, and the key information relating to the key B in FIG. Will be replaced with
[0080]
Upon receiving the multicast packet having the key number of the key B from the content server 11, the client 51 discards the key information related to the key A and holds the key B stored as the next key to be used as the currently used key. I do. Further, when key information relating to the key C which is the key to be used next to the key B is received by the response message 82 from the key management server 31, the key information is stored in its own key information management table 6i. As a result, the key information stored in the key information management table 6i is such that the key information relating to the key A in FIG. 5 is replaced with the key information relating to the key B, and the key information relating to the key B in FIG. It will be replaced with information.
[0081]
By repeating the above operation, the client 51 (generally, each client 5i) can acquire the key information regarding the key to be used next before the key is changed. .
[0082]
In the present embodiment, a communication delay required for communication between the content server 11, the key management server 31, and the client 5i is not considered. Therefore, it is conceivable that the value of the remaining valid time in the key information of the same key number in each of the key information management tables 21, 41, and 6i is shifted by the communication delay. Although it is unlikely that such a deviation actually becomes a problem, when this is taken into account, appropriate measures can be taken as shown in a and b below.
[0083]
a. Before the validity time of the key being used expires (before the remaining validity time becomes 0), the encrypted data using the key to be used next (the encrypted data and the key number of the key to be used next) (Multicast packet having the following), the client 5i retains the key information on the key to be used next by the above-described configuration and operation, so that the key (decryption key) can be specified. Decryption (decryption) using the decryption key becomes possible.
[0084]
b. Even if the encrypted data using the old key is sent after the expiration of the validity period, the client 5i continues to transmit the multicast packet having the key number of the new key in use even after the remaining validity period becomes zero. Until the key is received, the key information about the old key is held, so that decryption using the key (decryption key) is possible.
[0085]
(2) Modification of the first embodiment
[0086]
With respect to the first embodiment as described above, with respect to the information included in the multicast packet distributed from the content server 11 to the client 5i, the following modifications a and b can be considered ( A form having both a and b is also possible).
[0087]
a. In the first embodiment, the multicast packet has the encrypted data and the key number. However, the multicast packet further includes the address of the key management server 31 (the information indicating the inquiry destination as in the case of the address). ) Can also be added. In this way, by sending the multicast packet with the key management server address added thereto, it is possible to eliminate the need for the client 5i to set the inquiry / request destination of the key information (the destination of the key information request 81).
[0088]
b. Further, the remaining valid time of the key identified by the key number of the multicast packet can be added to the multicast packet.
[0089]
(3) Second embodiment
[0090]
FIG. 7 is a block diagram showing a configuration of a key exchange method in the multicast distribution system according to the second embodiment of the present invention.
[0091]
Referring to FIG. 7, the key exchange method in the multicast distribution system according to the present embodiment includes a content server 12 that transmits a multicast packet, and clients 51, 52,... That receive the multicast packet transmitted from the content server 12. 5n (n is a positive integer) and a key (encryption key and decryption key) created and stored in response to the key creation request 91 sent from the content server 12, and a key number for identifying the encryption key and the key A key information response message 92 having a set (key information) of a key and a remaining valid time for the key is returned to the content server 12, and a key information request 81 from the client 5i (i is a positive integer of 1 to n) is received. A key management server 32 for transmitting a response message 82, a content server 12, a client 5i, and a key management server It is configured to include a network 100 that connects 32.
[0092]
The content server 12 stores a key (encryption key) used for encrypting data distributed by a multicast packet, a key number for identifying the key, and a set (key information) of a remaining valid time for the key. It has an information management table 22 (the key information management table can hold a plurality of key information).
[0093]
Here, the key information management table 22 holds key information on a key in use, and can hold key information on a key to be used next.
[0094]
Further, the content server 12 is configured to include a key management unit 121 and an encryption / packet transmission unit 122.
[0095]
The key management server 32 has a key information management table 42 that stores a set (key information) of a key (encryption key / decryption key), a key number for identifying the key, and a remaining valid time for the key. In the present embodiment, since the key is created by the key management server 32, the key information management table 42 of the key management server 32 holds key information on the encryption key and the decryption key.
[0096]
Here, the key information management table 42 holds key information regarding a key in use and key information regarding a key to be used next.
[0097]
Further, the key management server 32 includes a key management unit 321.
[0098]
The client 5i holds key information (key information) including a key (decryption key) used for decrypting data distributed by a multicast packet, a key number for identifying the key, and a remaining valid time for the key. It has a management table 6i.
[0099]
Here, the key information management table 6i holds key information on a key in use, and can hold key information on a key to be used next. In the initial state, the key information management table 6i has no information.
[0100]
The client 5i includes a key management unit 5i1 and a packet reception / decryption unit 5i2.
[0101]
Note that the content server 12, the key management server 32, and each client 5i manage the key information management table 22, the key information management table 42, and the remaining valid time in the key information on each key information management table 6i. Update every time (e.g., update based on its own clock signal).
[0102]
The key exchange method in the multicast distribution system according to the present embodiment is different from the first embodiment in that the content server 12 transmits a key creation request 91 to the key management server 32, The difference is that the management server 32 creates a key (encryption key / decryption key) and returns a key information response message 92 having key information about the created encryption key to the content server 12.
[0103]
FIG. 8 is a flowchart showing processing related to key management of the key exchange scheme in the multicast distribution system according to the present embodiment (processing at the time when the value of the remaining valid time of the key in use becomes the first set value). . This processing includes a first set value reaching recognition step D1, a key creation request transmission step D2, a key creation request reception step D3, a next use key creation step D4, a next use key information storage step D5, a key information response It comprises a message transmitting step D6, a key information response message receiving step D7, and a next use key information storing step D8.
[0104]
Next, with reference to FIG. 7 and FIG. 8 (refer to FIG. 1 to FIG. 4 as appropriate), the operation of the key exchange method in the multicast distribution system according to the present embodiment configured as described above will be described in the first place. The following description focuses on the differences from the above embodiment.
[0105]
First, an operation related to multicast packet transmission / reception processing performed from the content server 12 to each client 5i via the network 100 will be described.
[0106]
This operation is similar to the operation in the first embodiment (the operation relating to the multicast packet transmission / reception processing performed from the content server 11 to each client 5i via the network 100 in FIG. 1).
[0107]
Secondly, an operation related to key management in a period in which the value of the remaining valid time of the key being used is from the initial value to the first set value (a value smaller than the initial value) will be described.
[0108]
During this period, the key information management table 22 in the content server 12 holds key information (a set of a key, a key number, and a remaining valid time) regarding a key (encryption key) in use. These keys and key numbers are created by the key management means 321 in the key management server 32.
[0109]
Also, during this period, the key information management table 42 in the key management server 32 holds key information (a set of a key, a key number, and a remaining valid time) regarding a key in use (encryption key / decryption key). ing. These keys and key numbers are created by the key management means 321 in the key management server 32.
[0110]
The operation other than the above is the same as the operation in the first embodiment.
[0111]
Third, an operation related to key management when the value of the remaining valid time of the key in use reaches the first set value will be described (see FIG. 8).
[0112]
In the first embodiment, the content server 11 transmits the key information message 71 to the key management server 31 when recognizing that the value of the remaining valid time of the key being used has reached the first set value. .
[0113]
On the other hand, in the present embodiment, the key management unit 121 in the content server 12 sets the value of the remaining valid time of the key in use managed in the key information management table 22 to the first setting value. (Step D1), the key creation request 91 is transmitted to the key management server 32 to obtain the key information of the key (encryption key) to be used next (Step D1). D2).
[0114]
Upon receiving the key creation request 91 from the content server 12 (step D3), the key management means 321 in the key management server 32 sends the next key (encryption key / decryption key) in response to the key creation request 91. It is created (step D4), and key information (a set of a key, a key number, and a remaining valid time) relating to the key is stored in the key information management table 42 (step D5). As a result, the key information management table 42 in the key management server 32 holds the key information on the key in use and the key information on the key to be used next.
[0115]
Further, the key management unit 321 transmits (returns) a key information response message 92 having key information (a set of an encryption key, a key number, and a remaining valid time) relating to the encryption key created in step D4 to the content server 12 ( Step D6).
[0116]
Upon receiving the key information response message 92 from the key management server 32 (step D7), the key management means 121 in the content server 12 transmits key information on the next key (encryption key) in the key information response message 92. It is stored in the key information management table 22 (step D8). As a result, the key information management table 22 in the content server 12 holds the key information on the key in use and the key information on the key to be used next.
[0117]
The operation other than the above is the same as the operation in the first embodiment.
[0118]
Fourth, an operation related to key management when the value of the remaining valid time of the key in use becomes the second set value (a value smaller than the first set value and larger than 0) will be described.
[0119]
This operation is similar to the operation in the first embodiment.
[0120]
Fifth, an operation related to key management when the value of the remaining valid time of the key in use becomes 0 will be described.
[0121]
When the remaining valid time of the used key held in the key information management table 22 becomes 0, the key management unit 121 in the content server 12 discards the key information relating to the used key. The key information held as the key information regarding the key to be used is stored in the key information management table 22 as the key information regarding the new key in use. At this time, since the content server 12 has not yet obtained a new key to be used next, the key information management table 22 does not have key information regarding the key to be used next.
[0122]
As a result, the encryption / packet transmitting unit 122 performs the subsequent encryption processing using the key (encryption key).
[0123]
The operation other than the above is the same as the operation in the first embodiment.
[0124]
In the first embodiment, when a failure occurs in the communication between the content server 11 and the key management server 31, the key (decryption key) may not be distributed. On the other hand, in the present embodiment (second embodiment), even when a failure occurs in communication between the content server 12 and the key management server 32, the previous key is kept used, It becomes possible to continue communication of a multicast packet having encrypted data.
[0125]
As described above, in the present invention, as described in the first and second embodiments, both a configuration in which a key is created by a content server and a configuration in which a key is created by a key management server are realized. It is possible.
[0126]
(4) Modification of the second embodiment
[0127]
With respect to the above-described second embodiment, a modification similar to the modification of the first embodiment described in a and b of (2) can be considered.
[0128]
(5) Third embodiment
[0129]
FIG. 9 is a block diagram showing a configuration of a key exchange system in the multicast distribution system according to the third embodiment of the present invention.
[0130]
Referring to FIG. 9, the key exchange scheme in the multicast distribution system according to the third embodiment of the present invention is different from the key exchange scheme in the multicast distribution system according to the first embodiment shown in FIG. The difference is that a key exchange control program 901 for the content server, a key exchange control program 902 for the key management server, and a key exchange control program 903 for the client are provided.
[0131]
The content server key exchange control program 901 is read by the content server 11, and controls the operation of the content server 11 as the key information management table 21, the key management unit 111, and the encryption / packet transmission unit 112. The operation of the content server 11 under the control of the content server key exchange control program 901 (operation relating to the key information management table 21, the key management means 111, and the encryption / packet transmission means 112) is the same as the content server in the first embodiment. Since the operation is exactly the same as the operation of No. 11, detailed description thereof will be omitted.
[0132]
The key management server key exchange control program 902 is read by the key management server 31 and controls the operation of the key management server 31 as the key information management table 41 and the key management means 311. The operation of the key management server 31 under the control of the key management server key exchange control program 902 (operation relating to the key information management table 41 and the key management means 311) is exactly the same as the operation of the key management server 31 in the first embodiment. Therefore, the detailed explanation is omitted.
[0133]
Further, the client key exchange control program 903 is read by each client 5i, and controls the operation of each client 5i as a key information management table 6i, a key management unit 5i1, and a packet reception / decryption unit 5i2. The operation of each client 5i under the control of the client key exchange control program 903 (operation relating to the key information management table 6i, the key management means 5i1, and the packet reception / decryption means 5i2) is the same as that of the client 5i in the first embodiment. Since the operation is completely the same, a detailed description thereof will be omitted.
[0134]
(6) Fourth embodiment
[0135]
FIG. 10 is a block diagram showing a configuration of a key exchange method in the multicast distribution system according to the fourth embodiment of the present invention.
[0136]
Referring to FIG. 10, the key exchange scheme in the multicast distribution system according to the fourth embodiment of the present invention is different from the key exchange scheme in the multicast distribution system according to the second embodiment shown in FIG. The difference is that a key exchange control program for content server 1001, a key exchange control program for key management server 1002, and a key exchange control program for client 1003 are provided.
[0137]
The content server key exchange control program 1001 is read by the content server 12, and controls the operation of the content server 12 as the key information management table 22, the key management unit 121, and the encryption / packet transmission unit 122. The operation of the content server 12 under the control of the content server key exchange control program 1001 (operation relating to the key information management table 22, the key management means 121, and the encryption / packet transmission means 122) is the same as the content server in the second embodiment. Since the operation is exactly the same as the operation in FIG. 12, its detailed description is omitted.
[0138]
The key management server key exchange control program 1002 is read by the key management server 32 and controls the operation of the key management server 32 as the key information management table 42 and the key management means 321. The operation of the key management server 32 under the control of the key management server key exchange control program 1002 (operation relating to the key information management table 42 and the key management means 321) is exactly the same as the operation of the key management server 32 in the second embodiment. Therefore, the detailed explanation is omitted.
[0139]
Further, the client key exchange control program 1003 is read by each client 5i, and controls the operation of each client 5i as a key information management table 6i, a key management unit 5i1, and a packet reception / decryption unit 5i2. The operation of each client 5i (operation related to the key information management table 6i, the key management means 5i1, and the packet reception / decryption means 5i2) under the control of the client key exchange control program 1003 is the same as that of the client 5i in the second embodiment. Since the operation is completely the same, a detailed description thereof will be omitted.
[0140]
【The invention's effect】
As described above, according to the present invention, the following effects are produced.
[0141]
The first effect is that a delay for acquiring a new key does not occur when a key is changed. That is, the key can be changed at the time of multicast distribution without a key exchange delay. The reason for this effect is that the key itself and the key information having the remaining valid time of the key are managed, and the key to be used next by the client within the validity period of the key being used is obtained in advance. This is because, by making it possible, when a key is exchanged, decryption can be immediately performed using a new key.
[0142]
A second effect is that, even when a client joins any multicast address, it is not necessary to set an address of a key management server requesting a key to the client. The reason why such an effect occurs is that a multicast packet transmitted by the content server can include the key management server address, so that the client can make a request for a key to the key management server address. .
[0143]
A third effect is that the information of the viewer (client) can be obtained accurately and in real time. The reason that such an effect occurs is that the use of the present invention eliminates the delay at the time of key change, so that the key change cycle can be shortened without increasing the communication delay, and the client management information is transmitted to the key management server. The cycle of counting (the cycle of counting information of the client by the key management server when the client requests the key management server to perform the key acquisition every predetermined time for decryption) can be shortened, and a more accurate client can be obtained. Is obtained.
[0144]
A fourth effect is that the advantage of the encryption method of limiting the audience (client) by encryption and preventing an unauthorized party from acquiring information can be realized more reliably. The reason for such an effect is that, as described above, the present invention can efficiently realize changing the key at regular intervals, so that even if the key is leaked, unauthorized persons can continue to change by changing the key. This is because it is possible to prevent the user from watching the video. Another reason is that, by setting a party to whom viewing is permitted or a party to which viewing is not permitted in a key management server that manages keys required for decryption, the party to whom the decryption key is to be passed can be specified.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a key exchange system in a multicast distribution system according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing a multicast packet transmission / reception process of a key exchange method in the multicast distribution system shown in FIG. 1;
FIG. 3 is a flowchart showing processing related to key management of the key exchange method in the multicast distribution system shown in FIG. 1 (processing at the time when the value of the remaining valid time of the key in use becomes a first set value).
FIG. 4 is a flowchart showing processing related to key management of the key exchange method in the multicast distribution system shown in FIG. 1 (processing at the time when the value of the remaining valid time of the key in use becomes a second set value).
FIG. 5 is a block diagram for explaining a specific operation of a key exchange method in the multicast distribution system shown in FIG. 1;
FIG. 6 is a sequence diagram for explaining a specific operation of a key exchange method in the multicast distribution system shown in FIG. 1;
FIG. 7 is a block diagram illustrating a configuration of a key exchange method in a multicast distribution system according to a second embodiment of the present invention.
8 is a flowchart showing a process related to the key management of the key exchange method in the multicast distribution system shown in FIG. 7 (a process at the time when the value of the remaining valid time of the key being used becomes the first set value).
FIG. 9 is a block diagram showing a configuration of a key exchange system in a multicast distribution system according to a third embodiment of the present invention.
FIG. 10 is a block diagram showing a configuration of a key exchange system in a multicast distribution system according to a fourth embodiment of the present invention.
[Explanation of symbols]
11,12 Content server
21, 22, 41, 42, 61, 62,..., 6n Key information management table
31, 32 key management server
51, 52, ..., 5n client
71 Key information message
81 Key information request
82 Response message
91 Key creation request
92 Key information response message
100 networks
111, 121, 311, 321, 511, 521, ..., 5n1 key management means
112, 122 Encryption / packet transmission means
.., 5n2 packet receiving / decoding means
901, 1001 Content server key exchange control program
902, 1002 Key management server key exchange control program
903, 1003 Key exchange control program for client

Claims (8)

In a network system where multicast distribution of encrypted data is performed,
Creates an encryption key / decryption key, manages the encryption key / decryption key, its key number and remaining valid time, and distributes the next decryption key to be used within the valid time of the key being used to the key management server. A content server that transmits a multicast packet having encrypted data and a key number of an encryption key used in the encryption,
At the time within the valid time of the key in use and after the content server distributes the next decryption key to the key management server, the content server sends the next decryption key to the key management server. A client that requests and decrypts encrypted data in the multicast packet by a decryption key corresponding to a key number in the multicast packet received from the content server;
Managing the decryption key and its key number and remaining valid time, receiving the next decryption key from the content server, and transmitting the next decryption key to the client in response to a request from the client; A key exchange method in a multicast distribution system, comprising: a key management server. In a network system where multicast distribution of encrypted data is performed,
It manages the encryption key, its key number, and the remaining valid time, requests the key management server to create the next encryption key / decryption key within the valid time of the key being used, and creates the key in response to the request. A content server that obtains the encrypted key from the key management server, and transmits a multicast packet having encrypted data and a key number of the encryption key used in the encryption.
Within the validity period of the key in use and at the point in time after the content server has requested the key management server to create an encryption key / decryption key to be used next, the key server is used next. A client that requests transmission of a decryption key and decrypts encrypted data in the multicast packet by a decryption key corresponding to a key number in the multicast packet received from the content server;
It manages the encryption key / decryption key, its key number and the remaining valid time, creates and stores the encryption key / decryption key to be used next in response to the request from the content server, and stores the encryption key / decryption key to be used next. A key management server for transmitting to the content server and transmitting the next decryption key to be used to the client in response to a request from the client. The method according to claim 1 or 2, wherein by adding the address of the key management server to information in a multicast packet transmitted from the content server to the client, it is unnecessary to set a query / request destination of the decryption key on the client side. A key exchange method in the multicast distribution system according to claim 2. In a network system where multicast distribution of encrypted data is performed,
A key in a content server that holds a pair of an encryption key / decryption key in use, its key number, and its remaining valid time, and a pair of an encryption key / decryption key to be used next, its key number, and its remaining valid time An information management table,
When the remaining valid time of the key being used has reached the first set value, a key information message relating to the next decryption key to be used is transmitted to the key management server, and the remaining valid time of the key being used becomes zero. At the time of switching, the key held in the own table as the next key to be used is switched to the new key in use, a new encryption key / decryption key to be used next is created, and the key information is stored in the own table Key management means in the content server to perform
An encryption / packet in a content server for encrypting distribution data using an encryption key in use held in its own table at the time of multicast distribution, and transmitting a multicast packet having the encrypted data and the key number of the encryption key Transmission means;
A key information management table in a client that holds a pair of a decryption key in use, its key number, and its remaining valid time, and can hold a pair of a decryption key to be used next, its key number, and its remaining valid time When,
A multicast packet transmitted from the content server is received, a decryption key is searched from its own table by a key number in the received multicast packet, and decryption of encrypted data in the multicast packet is performed by a decryption key of the key number. Packet receiving / decoding means in the client for performing
When the remaining valid time of the key in use reaches the second set value, a key information request is transmitted to the key management server, and the next decryption key and its key number in the response message that is the reply are sent. The set with the remaining valid time is stored in its own table, and based on the recognition of the change in the key number in the multicast packet transmitted from the content server, the key held in its own table as the key to be used next until then. Key management means in the client to switch to a new active key;
Key information in a key management server that holds a pair of a decryption key in use, its key number, and its remaining valid time, and can hold a pair of a decryption key to be used next, its key number, and its remaining valid time A management table,
The set of the decryption key to be used next in the key information message received from the content server, its key number, and its remaining valid time is stored in its own table, and the remaining valid time of the key being used becomes the second set value. When a key information request is received from the client at the time of receipt, a response message including a set of a decryption key to be used next, its key number, and its remaining valid time is returned to the client, and the remaining valid time of the key being used is returned. A key management means in a key management server for switching a key held in its own table as a key to be used next to a new key in use when the value of the key becomes 0. Exchange method. In a network system where multicast distribution of encrypted data is performed,
Key information management in a content server that holds a pair of an encryption key in use, its key number, and its remaining valid time, and can hold a pair of an encryption key to be used, its key number, and its remaining valid time Table and
When the remaining valid time of the key in use reaches the first set value, the key management server issues a key creation request for creating a key to be used next, and receives a key information response message as a response to the key creation request. The set of the encryption key to be used next, its key number, and its remaining valid time is stored in its own table. When the remaining valid time of the key being used becomes 0, it is stored in its own table as the next key to be used. Key management means in the content server for switching the held key to a new key in use;
An encryption / packet in a content server for encrypting distribution data using an encryption key in use held in its own table at the time of multicast distribution, and transmitting a multicast packet having the encrypted data and the key number of the encryption key Transmission means;
A key information management table in a client that holds a pair of a decryption key in use, its key number, and its remaining valid time, and can hold a pair of a decryption key to be used next, its key number, and its remaining valid time When,
A multicast packet transmitted from the content server is received, a decryption key is searched from its own table by a key number in the received multicast packet, and decryption of encrypted data in the multicast packet is performed by a decryption key of the key number. Packet receiving / decoding means in the client for performing
When the remaining valid time of the key in use reaches the second set value, a key information request is transmitted to the key management server, and the next decryption key and its key number in the response message that is the reply are sent. The set with the remaining valid time is stored in its own table, and based on the recognition of the change in the key number in the multicast packet transmitted from the content server, the key held in its own table as the key to be used next until then. Key management means in the client to switch to a new active key;
A key that holds a pair of an encryption key / decryption key in use, its key number, and its remaining valid time, and that can hold a pair of an encryption key / decryption key to be used next, its key number, and its remaining valid time A key information management table in the management server,
In response to the key creation request received from the content server, an encryption key / decryption key to be used next is created, and a set of the encryption key / decryption key to be used next, its key number, and the remaining valid time is stored in its own table. And returns a key information response message relating to the next encryption key to be used to the content server. When a key information request is received from the client when the remaining valid time of the key in use reaches the second set value, A response message including a set of a decryption key to be used next, its key number, and its remaining valid time is returned to the client. When the remaining valid time of the key being used becomes 0, the key to be used next is returned. A key management means in a key management server for switching a key held in its own table to a new key in use. 5. The method according to claim 4, wherein the setting of the transmission destination of the key information request on the client side is unnecessary by adding the address of the key management server to the information in the multicast packet transmitted from the content server to the client. Item 6. A key exchange method in the multicast distribution system according to Item 5. In a network system where multicast distribution of encrypted data is performed,
A key for holding a set of an encryption key / decryption key in use, its key number and its remaining valid time, and a pair of an encryption key / decryption key to be used next, its key number and its remaining valid time In the information management table, when the remaining valid time of the key being used has reached the first set value, a key information message regarding the decryption key to be used next is transmitted to the key management server, and the remaining valid time of the key being used is transmitted. Becomes 0, the key held in the table as the key to be used next is switched to the new key in use, a new encryption / decryption key to be used next is created, and the key information is A key management means for storing the data in its own table; and a multicast packet having encrypted data and a key number of the encryption key, wherein the distribution data is encrypted by using an in-use encryption key held in the own table during multicast distribution. A key exchange control program content server to function as an encryption packet transmitting means for transmitting bets,
A key information management table which can hold a set of a decryption key in use, its key number, and its remaining valid time, and hold a pair of a decryption key to be used next, its key number, and its remaining valid time. , Receives a multicast packet transmitted from a content server, retrieves a decryption key from its own table using the key number in the received multicast packet, and decrypts the encrypted data in the multicast packet using the decryption key of the key number. A key information request is transmitted to the key management server when the remaining valid time of the key in use reaches the second set value, and the next message in the response message that is a reply The set of the decryption key, its key number and the remaining valid time to be used for is stored in its own table, and the multicast transmitted from the content server Key exchange control program for a client to function as a key management means for switching a key held in its own table as a next key to be used to a new key in use based on recognition of a change in a key number in the packet When,
The key management server holds a pair of a decryption key in use, its key number, and its remaining valid time, and key information that can hold a pair of a decryption key to be used next, its key number, and its remaining valid time. The management table and the set of the decryption key to be used next in the key information message received from the content server, its key number, and its remaining valid time are stored in its own table, and the remaining valid time of the key being used is stored in the second table. When a key information request is received from the client when the set value is reached, a response message including the set of the decryption key to be used next, its key number, and its remaining valid time is returned to the client, and the key in use is returned. When the remaining valid time of the key becomes zero, the key exchange control program for the key management server for functioning as a key management means for switching the key held in the own table as the next key to be used to a new key in use. Key exchange method in a multicast distribution system and having a gram. In a network system where multicast distribution of encrypted data is performed,
Key information management capable of storing a set of a cryptographic key in use, its key number, and its remaining valid time, and storing a pair of a cryptographic key to be used next, its key number, and its remaining valid time Table, when the remaining valid time of the key in use reaches the first set value, issues a key creation request to the key management server to create a key to be used next, and receives a key information response as a response to the key creation request The set of the encryption key to be used next in the message, its key number, and its remaining valid time is stored in its own table, and when the remaining valid time of the key being used becomes 0, it becomes the key to be used next. Key management means for switching the key held in the table to a new key in use; and encrypting the distribution data using the encryption key in use held in the table at the time of multicast distribution, and encrypting the encrypted data and the encryption. Key of the key A key exchange control program content server to function as an encryption packet transmitting means for transmitting a multicast packet having a No.,
A key information management table which can hold a set of a decryption key in use, its key number, and its remaining valid time, and hold a pair of a decryption key to be used next, its key number, and its remaining valid time. , Receives a multicast packet transmitted from a content server, retrieves a decryption key from its own table using the key number in the received multicast packet, and decrypts the encrypted data in the multicast packet using the decryption key of the key number. A key information request is transmitted to the key management server when the remaining valid time of the key in use reaches the second set value, and the next message in the response message that is a reply The set of the decryption key, its key number and the remaining valid time to be used for is stored in its own table, and the multicast transmitted from the content server Key exchange control program for a client to function as a key management means for switching a key held in its own table as a next key to be used to a new key in use based on recognition of a change in a key number in the packet When,
The key management server holds a pair of the encryption key / decryption key in use, its key number, and its remaining valid time, and sets the next pair of the encryption key / decryption key to be used, its key number, and its remaining valid time. A key information management table capable of holding the key, and a key generation request received from the content server, generate an encryption key / decryption key to be used next, and generate the encryption key / decryption key to be used next and its key number. The set with the remaining valid time is stored in its own table, and a key information response message relating to the encryption key to be used next is returned to the content server. When the remaining valid time of the key being used reaches the second set value, When a key information request is received from the client, a response message including a set of a decryption key to be used next, its key number, and its remaining valid time is returned to the client, and the remaining valid time of the key being used is set to 0. Became A key exchange control program for a key management server for functioning as key management means for switching a key held in its own table as a key to be used next to a new key in use. Key exchange method in the system.

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