Christian Schaffner
Quantum Cryptography

Discussion: Issue #49

I will entertain the audience with a science talk about quantum cryptography, covering both some classics (Quantum Key Distribution) and the latest developments (position-based quantum cryptography) in this fascinating research field.

(No previous knowledge of quantum mechanics is required to follow the talk.)

The most well-known application of quantum cryptography is Quantum Key Distribution (QKD) which was invented in 1984 by Bennett and Brassard. QKD allows two players Alice and Bob to securely communicate over an insecure line which is overheard by an eavesdropper Eve. Security can be proven in an information-theoretic sense against an unrestricted Eve. Such a high level of security is impossible to achieve with classical communication. In the first part of the talk, I will introduce some basic concepts of quantum information theory in order to understand and appreciate the security of QKD.

However, quantum cryptography offers a wide range of other applications that go beyond the task of key distribution. For instance, the goal of “position-based cryptography” is to use a player’s physical position as cryptographic credential. The combination of relativistic constraints (assuring that information cannot travel faster than the speed of light) and quantum mechanical effects (such as the impossibility to perfectly copy a quantum state) enables entirely new cryptographic applications like sending a message in such a way that it can only be read at a particular geographic position. In the second part, I will introduce you to this intriguing new branch of quantum cryptography.

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