  Recently, Hwang et al. introduced a knapsack type public-key cryptosystem.
They proposed a new algorithm called permutation combination algorithm. By
exploiting this algorithm, they attempt to increase the density of knapsack to
avoid the low-density attack.
  We show that this cryptosystem is not secure, as it based on basic
Merkel-Hellman knapsack cryptosystem and because of the superincreasing
structure, we can use shamir's attack on the basic Merkel-Hellman knapsack to
break this cryptosystem.
