| 摘要 |
PROBLEM TO BE SOLVED: To provide a key management method and system adopting a tree structure whereby the increase in key information amount in a recording medium can be suppressed and a secret information amount which a reproducing apparatus is to store can be decreased. SOLUTION: An information provider uses a first encryption key to generate encrypted contents and encrypts a first decryption key corresponding to the first encryption key by using a second encryption key to produce encrypted key information. The information provider provides the encrypted contents and the encrypted key information in a form of a recording medium or the like to information recipients. The information recipients have information to generate a second decryption key corresponding to the second encryption key beforehand and acquire the first decryption key by using the information to decrypt the contents. The information provider distributes the first and second decryption keys on the basis of the key management system utilizing the tree structure, wherein the information recipients are assigned to leaves, to the information recipients. By subdividing the tree structure into a plurality of hierarchical layers to specify a plurality of subtrees and assigning the key information in units of the subtrees, the information amount of the key information which the information recipients should store can be reduced. COPYRIGHT: (C)2004,JPO
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