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METHOD FOR GENERATING DECRYPTION KEY, APPARATUS AND METHOD USING DECRYPTION KEY

  • US 20070180233A1
  • Filed: 09/13/2006
  • Published: 08/02/2007
  • Est. Priority Date: 01/27/2006
  • Status: Active Grant
First Claim
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1. A decryption key generation method including:

  • dividing a group of a plurality of user identification information items for individually identifying a plurality of user systems into a plurality of subgroups;

    assigning the subgroups to a plurality of different leaves on a tree structure respectively, the tree structure including a root node, one or a plurality of nodes and the leaves;

    assigning different individual key generation polynomials to all or some of the root, the nodes, and the leaves on the tree structure respectively;

    assigning each subgroup one of the individual key generation polynomials which corresponds to one of leaves assigned to the each subgroup or an ancestor node of the one of the leaves; and

    substituting each user identification information item in the each subgroup into the one of the individual key generation polynomial assigned to the each subgroup and a common key generation polynomial common to the root, the nodes, and the leaves, to obtain a decryption key unique to each user system which corresponds to the each user identification information item, wherein at least one of linear sums of coefficients with the same degree of the one of the individual key generation polynomial and the common key generation polynomial differs for each of the root, the nodes, and the leaves on the tree structure, and the linear sums of other coefficients with the same degrees are constant.

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