I. Introduction
Quantum cryptography is a combination between quantum physics and the art of encoding. For the first time, the idea of quantum cryptography was introduced in an unpublished manuscript by Stephen Wiesner in 1970, and was presented by Bennett and Brassard in 1984, becoming thus a subject of interest. The purpose of quantum cryptography is to solve problems that are impossible or hard to solve by classical cryptography. Quantum cryptography uses quantum physics properties like: the no-cloning theorem, the Heisenberg uncertainty principle, and irreversibility of quantum measurements. As compared to the classical cryptography, whose security is most often based on undemonstrated assumptions, quantum cryptography has the great advantage of its security, which is based on physical laws. In a bigger context, quantum cryptography is a field of quantum information processing, including quantum computation, quantum measurements, and quantum teleportation.