Data protection system that protects data by encrypting the data
First Claim
1. A data protection system that comprises three or more terminals, an encryption device, and an encryption key designation device, and that protects distribution data that is to be distributed to said terminals, according to said encryption device encrypting the distribution data, wherein:
- each terminal is operable to(i) store a decryption key group assigned individually to the terminal, respectively, according to(a) a determination of two or more terminal groups, which are groups having two or more terminals as members, so that each of the terminals is a member of at least one of the terminal groups, and so that any one of the terminal groups that shares a same terminal as a member with another one of the terminal groups does not completely include the other one of the terminal groups sharing the same terminal as a member and is not completely included in the other one of the terminal groups sharing the same terminal as a member,(b) a decision of one or more decryption keys individually in correspondence with each terminal and each determined terminal group, and(c) an assignment, to each terminal, the decryption key group, where the decryption key group is based on the decryption key decided in correspondence with the terminal, and decryption keys decided in correspondence with all terminal groups that include the terminal, respectively;
(ii) obtain an encrypted distribution data group that has been output from said encryption device, and(iii) use a stored decryption key to decrypt encrypted distribution data;
said encryption key designation device is operable to designate encryption keys, and includes;
an invalid terminal designation unit for designating one or more terminals as invalid terminals; and
an encryption key designation unit for designating, when all the decryption keys assigned to the terminals, other than decryption keys assigned to the one or more invalid terminals, are prescribed as valid decryption keys, and when a procedure for selecting an assigned valid decryption key for the most terminals not designated as invalid terminals is repeated until all terminals not designated as invalid terminals have been assigned a selected valid decryption key, encryption keys that respectively correspond to each of the valid decryption keys that are selected as a result of the procedure; and
said encryption device includes an encryption unit for encrypting distribution data by successively using all the designated encryption keys to encrypt distribution data, generating the encrypted distribution data group, and outputting the generated encrypted distribution data group.
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Abstract
A data protection system is provided that reduces, to a degree, the amount of encrypted data that is distributed to a plurality of terminals. In the data protection system a terminal whose decryption keys are exposed by a dishonest party is made to be unable to decrypt the data correctly, while other terminals are able to decrypt the data correctly.
The data protection system includes a plurality of terminals, and an encryption device that encrypts distribution data distributed to each terminal. Each terminal is corresponded with one node on a lowest level of a 4-ary tree structure or the like having a plurality of hierarchies. The data protection system, for each node in the tree structure, excluding those on the lowest level, determines a plurality of combination patterns that include combinations of two or more of all four nodes that are reached one level below the node, decides an individual decryption key for each determined combination pattern, and decides an individual decryption key for each node on the lowest level. Further, the data protection system has each terminal store all decryption keys decided for the nodes on the path from the node on the lowest level that corresponds to the terminal through to the node on the highest level. The data protection system prescribes nodes that are reached from the node on the lowest level that corresponds to the terminal through to the node on the highest level that correspond to a terminal that has been dishonestly analyzed as invalid nodes. For invalid nodes, other than invalid nodes on the lowest level, the data protection system designates an encryption key that corresponds to the decryption key decided in correspondence with the combination pattern that combines all nodes, excluding invalid nodes, of the four nodes that are reached one level below the node, and has the encryption device encrypt distribution data that uses each of the designated encryption keys.
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Citations
14 Claims
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1. A data protection system that comprises three or more terminals, an encryption device, and an encryption key designation device, and that protects distribution data that is to be distributed to said terminals, according to said encryption device encrypting the distribution data, wherein:
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each terminal is operable to (i) store a decryption key group assigned individually to the terminal, respectively, according to (a) a determination of two or more terminal groups, which are groups having two or more terminals as members, so that each of the terminals is a member of at least one of the terminal groups, and so that any one of the terminal groups that shares a same terminal as a member with another one of the terminal groups does not completely include the other one of the terminal groups sharing the same terminal as a member and is not completely included in the other one of the terminal groups sharing the same terminal as a member, (b) a decision of one or more decryption keys individually in correspondence with each terminal and each determined terminal group, and (c) an assignment, to each terminal, the decryption key group, where the decryption key group is based on the decryption key decided in correspondence with the terminal, and decryption keys decided in correspondence with all terminal groups that include the terminal, respectively; (ii) obtain an encrypted distribution data group that has been output from said encryption device, and (iii) use a stored decryption key to decrypt encrypted distribution data; said encryption key designation device is operable to designate encryption keys, and includes; an invalid terminal designation unit for designating one or more terminals as invalid terminals; and an encryption key designation unit for designating, when all the decryption keys assigned to the terminals, other than decryption keys assigned to the one or more invalid terminals, are prescribed as valid decryption keys, and when a procedure for selecting an assigned valid decryption key for the most terminals not designated as invalid terminals is repeated until all terminals not designated as invalid terminals have been assigned a selected valid decryption key, encryption keys that respectively correspond to each of the valid decryption keys that are selected as a result of the procedure; and said encryption device includes an encryption unit for encrypting distribution data by successively using all the designated encryption keys to encrypt distribution data, generating the encrypted distribution data group, and outputting the generated encrypted distribution data group. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of using a data protection system that comprises three or more terminals, an encryption device, and an encryption key designation device, to protect distribution data that is to be distributed to said terminals, according to said encryption device encrypting the distribution data, said method comprising:
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using each terminal to (i) store a decryption key group assigned individually to the terminal, respectively, according to (a) a determination of two or more terminal groups, which are groups having two or more terminals as members, so that each of the terminals is a member of at least one of the terminal groups, and so that any one of the terminal groups that shares a same terminal as a member with another one of the terminal groups does not completely include the other one of the terminal groups sharing the same terminal as a member and is not completely included in the other one of the terminal groups sharing the same terminal as a member, (b) a decision of one or more decryption keys individually in correspondence with each terminal and each determined terminal group, and (c) an assignment, to each terminal, the decryption key group, where the decryption key group is based on the decryption key decided in correspondence with the terminal, and decryption keys decided in correspondence with all terminal groups that include the terminal, respectively; (ii) obtain an encrypted distribution data group that has been output from said encryption device, and (iii) use a stored decryption key to decrypt encrypted distribution data;
using said encryption key designation device to designate encryption keys by(i) using an invalid terminal designation unit of said encryption key designation device to designate one or more terminals as invalid terminals, and (ii) using an encryption key designation unit of said encryption key designation device to designate, when all the decryption keys assigned to the terminals, other than decryption keys assigned to the one or more invalid terminals, are prescribed as valid decryption keys, and when a procedure for selecting an assigned valid decryption key for the most terminals not designated as invalid terminals is repeated until all terminals not designated as invalid terminals have been assigned a selected valid decryption key, encryption keys that respectively correspond to each of the valid decryption keys that are selected as a result of the procedure; and using an encryption unit of said encryption device to encrypt distribution data by successively using all the designated encryption keys to encrypt distribution data, generating the encrypted distribution data group, and outputting the generated encrypted distribution data group.
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Specification