Free-space quantum cryptography systems for next generation communication networks

安全是一场无休止的猫捉老鼠的游戏。纵观历史，人们把城堡的城墙修得越来越高、越来越厚，但这并没有阻止掠夺者找到一条聪明的进去的路。密码学的历史讲述了许多所谓的不可破解的代码被破解的故事。这是因为传统的密码系统只提供基于加密的一些数学复杂性的计算安全性。例如，量子计算的突破将使今天的密码系统完全容易受到威胁。基于坚实的物理定律，而不是未经证实的数学复杂性基础，量子密码学为加密提供了一种截然不同的解决方案，并保证了无条件的安全性。量子密码系统通常建立在通过光纤相互连接的两个节点之间。这项提议的重点是在自由空间光通道上运行的量子密码系统，作为光纤通道的一种具有成本效益和免许可证的替代方案。从通信理论的角度，我们研究了自由空间量子密码系统的性能分析和优化，研究了可达到的速率，并设计了在实际约束下逼近它们的方法。

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