suppose we have 3 matrix named A,B,C (2x2, 3x3, 10x10 or whatever). As we know A^(-1) A C B B^(-1)=C
So i take a file and convert it to numbers e.g. ASCII code (lets say 65,72,71...) and i add a number sequence.
Then i multiply A*C and the result (D) is send.
The other guy multiplies D*B and sends the result (E) back.
Then i multiply A^(-1)*E and send the result (F).
At last the other guy multiplies F*B^(-1) , gets the original file C, subtracts the number sequence and gets the original file.
My question is: how will a cryptanalyst break it?