Grant: Strategic Projects Supplemental Competition

Security is an endless game of cat and mouse. Throughout the history, people have built the castle walls higher and thicker, yet this has not prevented the marauders find a clever way inside. The history of cryptography narrates stories of many so-called unbreakable codes that have been cracked. This is due to the fact that conventional cryptosystems offer only computational security based on some mathematical complexity of the encryption. A breakthrough in quantum computing, for example, would leave today's cryptosystems totally vulnerable to threats. Based on the firm laws of physics rather than unproven foundations of mathematical complexity, quantum cryptography provides a radically different solution for encryption and promises unconditional security. Quantum cryptography systems are typically built between two nodes connected to each other through fibre optic. This proposal focuses on quantum cryptography systems operating over free-space optical channels as a cost-effective and license-free alternative to fibre optic counterparts. From a communication theory perspective, we address the performance analysis and optimization of free-space quantum cryptography systems investigating the achievable rates and devising methods to approach them under practical constraints.