  Secure communication plays a crucial role in the Internet Age. Quantum
mechanics may revolutionise cryptography as we know it today. In this Review
Article, we introduce the motivation and the current state of the art of
research in quantum cryptography. In particular, we discuss the present
security model together with its assumptions, strengths and weaknesses. After a
brief introduction to recent experimental progress and challenges, we survey
the latest developments in quantum hacking and counter-measures against it.
