We show how two distrustful parties, "Bob" and "Charlie", can share a secret key with the help of a mutually trusted "Alice", counterfactually - that is with no information-carrying particles travelling between any of the three parties.
Cite
@article{arxiv.1404.5540,
title = {Tripartite Counterfactual Quantum Cryptography},
author = {Hatim Salih},
journal= {arXiv preprint arXiv:1404.5540},
year = {2014}
}