Hill Cipher

To work this cipher, enter the 4 values for a,b,c,d.
An example of invertible matrix is a=3, b=17, c=1, d=6. The inversion
of this matrix is left for you to compute. The algorithm completes the
inversion for decryption, but does not display the inverted matrix.
TO DECRYPT: Please copy and paste the info from the output field into
the input field before clicking the decrypt button.

HERE is a copy of the java applet code