Figuring out key in hill cipher (chosen-plaintext attack) I have been wondering what approach to take in order to figure out what key was used to encrypt a message using the hill cipher. 
I know it is possible to obtain it even if it were just a known-plaintext attack, so it should be fairly possible for a chosen-plaintext one. 
I'm trying to figure it out with just intuition, but since I know freq. analysis won't be of help, I don't know what else to try. I want to get my head around this, but could someone point me in the right direction?
Sure.  Assuming that you're using the encoding $A = 0$, $B = 1$, etc., just choose your plaintext messages to be the one-block strings:

$$
BA \dots A \\
AB \dots A \\
\vdots \\
AA \dots B
$$

The encryptions of these strings will then directly give you the columns of your key matrix.