In this paper we focus on S-box constructions. We consider the uniformity property of an S-box which plays an important role in Threshold Implementations (TI). Most papers so far have studied TI sharings for given S-boxes. We proceed in the opposite way: starting from n-bit S-boxes with known sharings we construct new (n + 1)-bit S-boxes from them with the desired sharings. In addition, we investigate the self-equivalency of S-boxes and show some interesting properties.maximal algebraic degree of a balanced n-variable Boolean function is n − 1 [5,8]. De Cannière lists 302 equivalence classes for the 4 × 4 bijections: the class of affine functions, 6 classes containing quadratic functions and the remaining 295 classes containing cubic functions. There is a transformation [3] which expands the 3-bit classes Q 3 1 , Q 3 2 , and Q 3 3 into Q 4 4 , Q 4 12 and Q 4 300 correspondingly. That is, given a 3-bit permutation S(x 1 , x 2 , x 3 ) = (y 1 , y 2 , y 3 ), its 4-bit extension is generated by S(x 1 , x 2 , x 3 , x 4 ) = (y 1 , y 2 , y 3 , x 4 ).Recently a classification of all quadratic 5 × 5 bijective S-boxes was presented in [1]. The authors have also pointed out that the 5-bit classes Q 5 1 , Q 5 3 , Q 5 4 , Q 5 7 , Q 5 13 and Q 5 30 are extensions of the 4-bit quadratic classes Q 4 4 , Q 4 294 , Q 4 12 , Q 4 299 , Q 4 293and Q 4 300 from [3] respectively. That is, given a 4-bit permutation S(x 1 , x 2 , x 3 , x 4 ) = (y 1 , y 2 , y 3 , y 4 ), its 5-bit extension is generated by S(x 1 , x 2 , x 3 , x 4 , x 5 ) = (y 1 , y 2 , y 3 , y 4 , x 5 ). Letx = (x 1 , ..., x n ) then the method used in the above mentioned publications can be summarized as follows S(x, x n+1 ) = S 1 (x) for the first n bits (1) = x n+1 for the (n + 1)-st bitAnother well known construction is the so-called Shannon expansion.