hill_cipher 工程數學 homework 4 https://en.wikipedia.org/wiki/Hill_cipher https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.259.1186&rep=rep1&type=pdf https://stackoverflow.com/questions/960190/how-to-calculate-the-inverse-key-matrix-in-hill-cipher-algorithm
