| 摘要 |
The invention relates to a method for obtaining through a first entity U a derived value Kr on the basis of an input parameter r and of encrypted information ?. This method comprises the following steps: the selecting of a W- tuple of indices (i1,i2,....,iw), where W = 1, in a predetermined set of indices; and the obtaining of said derived value Kr by applying a predetermined pseudo-random function FU, termed the "derivation function", to said encrypted information ?, said derivation function FU depending at least on a personal identifier / on said first entity, and on blocks ( TUi1, TUi2,..., TU iw) read from a predetermined table TU of blocks TUi, said table being associated with the first entity. Each of said blocks TUi has been respectively engendered by a second entity by combining, as a function of said personal identifier I U, m respective blocks T(0)i, T(1)i,...,,..., T(m-1)i, where m = 2, each of said blocks T (k)i (where k = 0,1,..., m - 1 ) being constructed by means of a pseudo-random function G (k)(i), termed the "construction function", parameterized by a master value S(k) , said master values S(k) not being disclosed to said first entity. Application to the encryption of paying digital contents. |
