Deciding whether a quantum state has secret correlations is an   NP-complete problem
  From the NP-hardness of the quantum separability problem and the relation between bipartite entanglement and the secret key correlations, it is shown that the problem deciding whether a given quantum state has secret correlations in it or not is in NP-complete. 
Jae-Weon Lee, DoYong Kwon, Jaewan Kim