Suppose I have an arbitrary 256 bit number $m$ another secret number $k$ of the same bit length, and then I multiply them both modulo a 256 bit prime number $p$ to get $c$ as follows:
$$
c = (m\cdot k) \mod p
$$
Is there any way to get $m$ back without knowing $k$?
Is this problem as hard as the discrete log problem?
How can this task be made more computationally difficult?