Multiply inverse Galois Fields

I need to multiplicate 2 Galois fields, one of them is inversed. It is right to add zeros in the end in order to make it like a square matrix and then to perform multiplication? Something like this:

>>b=[1 0 1 1 1 1 1 1]

>>b1=[1 0 1; 1 1 1; 1 1 1]

>>gfconv(a,b,n)