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    "Reserch for Group Signature suitable for Application"

    The group signature schemes were proposed by Chaum and van Heyst for
    the first time.  A group signature scheme allows a group member to
    anonymously sign a message on behalf of the group and anyone can
    verify whether or not the signature was created by some 
    (unknown) member of the group.
    But in case of dispute or necessity, the
    group manager can reveal the signer's identity.  At present,
    Group signature scheme based on RSA signature is proposed.
    However this scheme is
    disadvantageous in that the signature length is long.
    On the other hand, as an alternative,
    Group signature scheme with bilinear maps is proposed.  The group
    signature scheme with bilinear maps is advantageous in that
    computational cost of verification is efficient and signature length
    is short.  However, the current bilinear-map-based group signature 
    are suffering from much computational cost of  verification
    dependent on the number revoked members.
    Here we propose the group signature scheme indepent
    of the number of revoked members.  Our scheme divides members into sub 
    groups to reduce
    the cost of signature verification which depends on the number of
    revoked member in one sub-group.
    By using the proposed
    scheme, cost of signature verification depends on the number of
    revoked members who belong to the sub-group.

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