| 摘要 |
PROBLEM TO BE SOLVED: To provide the key delivery method by which a length of data for having a key jointly is decreased even when many recipients (key users) are in existence and which can cope with conspiracy attacks. SOLUTION: A broadcast station 100 generates finite sets A(= s(ij)|1<=i<=m, 1<=j<=n}) consisting of its own secret information and sets Vj(= X1-Xm}|fj(X1- Xm, s(lj)-s(mj))=0), fj is mapping image from a set (z1-z2m)|zi is an integer} to a set Wj(0 belongs to Wi)). r(X, ij)(1<=i<=m) belongs to Vj is selected at random, and s(X, i)=r(X,γ(i)) (1<=i<=mn) (γis mapping image from a set 1-mn} to the set ij}, a secret of te broadcast station) is used for a secret key of a recipient X. u(ij) is generated as information corresponding to s(ij), and y(i)=u(γ(i)) (1<=i<=mn) is used. Identification information dx of the recipient X is calculated by using the s(x, i), and y(1)-y(mn) and the identification information dx are sent to the recipient X. A recipient X200 uses a proper function (h) to calculate a common key K with K=h(s(x, 1)-s(x, mn), y(1)-y(mn), dx).
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