the first task of the ”main” program aes_demo is

a call to aes_init in Line 1. This initialization routine supplies 1 the actual en- and

decryption functions (cipher and inv_cipher) with the expanded key schedule w, the

substitution tables s_box and inv_s_box, and the polynomial matrices poly_mat and

inv_poly_mat. These quantities have to be generated only once and can be used by any

subsequent en- or decipher call.