The Rijndael cryptosystem uses a particular polynomial to create its constants. All calculations within the encryption and decryption layers are based on this polynomial. This arouse the curiosity to see what happens if the polynomial is substituted by other polynomials. This paper’s main area of study is to investigate the consequences of using different polynomials to construct the Rijndael cryptosystem. To do so, as a phase of this study, a Mathematica package has been created to ease the investigations. As the second phase, using the aforementioned package, some kind of diffusion analysis has been done on the newly constructed Rijndael-like cryptosystems. The fundamental challenge was to figure out the reason of having the particular polynomial chosen. By the end of the experiment, we concluded that choosing other polynomials with the same characteristics as an ingredient of the Rijndael algorithm, does not have any perceptible effects on the diffusion level.