| 摘要 |
PROBLEM TO BE SOLVED: To reduce a communication amount and the number of labels that a user holds while maintaining resistance against coalition attacks of a conventional SD (Subset Difference) method. SOLUTION: The ternary SD method for configuring a ternary tree structure and distributing a content key only to a legitimate user terminal allocated to a leaf node of the ternary trees in a content distribution service for distributing contents from a content server to a user terminal includes: partial set extraction processing of obtaining a set C of a partial set of the legitimate user terminals; label allocation processing of allocating the labels to the respective user terminals allocated to the leaf node; encryption processing of causing the content server to encrypt a plain text message; and decryption processing of causing the user terminal to decrypt the received encrypted message. COPYRIGHT: (C)2010,JPO&INPIT
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