The security of most symmetric ciphers depends critically on properties of Substitution boxes (S-boxes). Generally S-box is a permutation or set of permutations mapping m-bits input to n-bits output. Efficiency of S-box construction algorithms directly depends on permutation generation algorithms efficiency. In this paper we describe a novel permutation generation algorithm and for this purpose introduce the concept Loop as initial permutation and all permutations generated from it. In conclusion we illustrate how the method may be used for key-dependent and dynamically varying S-boxes constructing.