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.
@article{arxiv.quant-ph/0612052,
title = {Deciding whether a quantum state has secret correlations is an NP-complete problem},
author = {Jae-Weon Lee and DoYong Kwon and Jaewan Kim},
journal= {arXiv preprint arXiv:quant-ph/0612052},
year = {2015}
}