Quantum Cryptography: A Novel Approach to Communication Security

Quantum Cryptography aims at solving the everlasting problem of unconditional security in private communication. Every time we send personal information over a telecom channel, like when we buy something on the web, a sophisticated protocol protects our privacy making our data unintelligible to unauthorised receivers. These protocols resulted from the long history of cryptography. The security of modern cryptographic systems is guaranteed by complexity: the computational power that would be needed for gaining info on the code key largely exceeds the available one. Security of actual crypto systems is not "by principle" but "practical". On the contrary, quantum technology promises to make possible to realise provably secure protocols. Quantum cryptology exploits paradigmatic aspects of quantum mechanics, like superposition principle and uncertainty relations, for realising protocols whose security is intrinsic. In this contribution, after a brief historical introduction, we aim to provide a survey on the physical principles underlying the quantum approach to cryptography. Then, in the second part, we analyse in more detail two of the possible protocols and glance over the state of art of the research in the field.