  In theory, quantum key distribution (QKD) provides information-theoretic
security based on the laws of physics. Owing to the imperfections of real-life
implementations, however, there is a big gap between the theory and practice of
QKD, which has been recently exploited by several quantum hacking activities.
To fill this gap, a novel approach, called measurement-device-independent QKD
(mdiQKD), has been proposed. It can remove all side-channels from the
measurement unit, arguably the most vulnerable part in QKD systems, thus
offering a clear avenue towards secure QKD realisations. Here, we review the
latest developments in the framework of mdiQKD, together with its assumptions,
strengths and weaknesses.
