AES MixColumn Polynomial Transformation
Each column of 4x4 byte array S is regarded as column vector over the Rijndael field F.
It is then updated by multiplying the column vector by a specified 4x4 matrix over F.
Thus muxColumns modifies the state array by hte matrix multiplication (0&lt;=j&lt;=3),
Hence, in your example you are encoding ${S_{(3,3)}}$ which is last row of Matrix and represented as polynomial ${3x^3+x^2+x+2}$