Quantum key distribution uses a quantum channel and an authenticated classical channel to distribute information theoretic secure key to two parties. The technical challenge is to build point-to-point connections that allow a high secure bit rate over lossy channels. I will briefly review the theoretical concepts of current schemes and their respective challenges. It is worth to note that some improvements can be done by improving the classical communication protocols that post-process the data. We show limitations for this situation. Finally, networks with some partial trust assumptions about repeaters can increase the usefulness of QKD applications.