| 摘要 |
PROBLEM TO BE SOLVED: To efficiently deliver an encryption key while simultaneously excluding a plurality of terminal stations. SOLUTION: A database 201 constitutes 2<SP>m</SP>groups existing in an m-th hierarchy (m is an integer from 0 to M-1) or constitutes sub-groups in an m+1-th hierarchy by dividing a sub-group into two and stores each delivery key that is assigned to each group or each sub-group. When excluding a single or a plurality of specific terminals from the groups, a delivery-key selection part 203 searches the hierarchy and the sub-group to which the specific terminals belong by decrementing m from M in a prescribed terminal number i (i is an integer from 0 to I). If the searched m is not the M, the delivery-key selection part reads out a group key or an individual key assigned to the sub-group to which the specific terminals do not belong in the sub-groups in the m+1-th hierarchy formed by dividing the searched sub-group into two. COPYRIGHT: (C)2009,JPO&INPIT
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