| 摘要 |
<p>The invention relates to a method for protecting an assembly by carrying out a cryptographic calculation process using a f homographic function of the type: f(z)= (az+b) / (cz+d), when (cz+d) is not 0 and f(-d/c)=a/c, wherein the f function operating on masked variables is characterised in that for any k, if x is the input and y = f(x+k) is the output of the function f, in order to directly pass from a masked value x+m_I (XOR-type additional masking) to a masked value x+m_I, the method consists in carrying out said operation with the aid of a composition of several transformations operating on GF(2 &cir& k) with addition of an infinite which is defined in the form of (ax+b)/(cx+d) and the transformations which exchange two points.</p> |
