| 摘要 |
The invention proposes a method and a device for decrypting an encrypted message represented by a sequence C or applying an electronic signature to a sequence C, said sequence C consisting of data belonging to a finite field K=GF(q), where q>1, in which there are processed successive blocks each comprising (n·d) successive data items from the sequence C, where n and d are predetermined integers greater than 1, the processing of such a block including the following steps: applying a predetermined affine invertible transformation t−1 to said block; interpreting the resulting block as being formed of n successive elements (y1, y2, . . . , yn) of an extension E=GF(qd) of the field K; calculating an n-tuplet (x1, x2, . . . , xn) of elements of the field E by solving a system f of n predetermined polynomials of the form y k =∑1≤i≤j≤n a k ( ij ) x i qαi x j qβj +∑1≤i≤n b k i x i qγ i + c k ( 1≤k≤n ) in which the coefficients ak(ij), bk(i), and ck belong to E and the exponentsαi,βj, andγi are positive or zero integers; interpreting said n-tuplet (x1, x2, . . . , xn)as being a new block formed of (n·d) successive elements from the field K; and applying a predetermined affine invertible transformation s−1 to said new block. |
