Self-compensating GigaHertz-clocked Quantum Key Distribution

我们所有人的生活都曾在某种程度上被密码学所触动。从简单的童年秘密日记，到网上购物和银行，再到政府的国家安全，扰乱信息以隐藏其内容以防止潜在窃听者的行为，是现代生活的一部分。今天最常用的加密形式是所谓的公钥系统，就像电子商务和许多其他应用程序中使用的那样。这种加密方法依赖于将某些数学函数从初始起始值的答案还原回来所涉及的困难。这类似于烘焙蛋糕，在这个过程中，混合原料和制作蛋糕相对容易，但实际上不可能拿到完成的蛋糕并回到最初的配料。然而，没有长期保证这些数学函数将保持难以逆转的状态。量子计算机的发展将允许相对容易地解密公钥加密的消息。幸运的是，预示着公钥加密系统终结的同一物理也可能以量子密钥分发的形式提供解决方案。量子密钥分发(QKD)使用量子力学的科学来提供一种方法，以提供可验证的安全性的方式来分发加密或解密消息(密钥)所需的信息。它使我们认识到，光子(轻粒子)的某些性质不能绝对确定。如果使用这些特性将信息的单个二进制位(位)编码到单光子上，那么任何监听密钥交换的窃听者都将干扰对光子的分析，从而在传输上留下虚拟指纹，以便发送者和接收者能够检测到窃听者的存在。量子密钥分发系统可以使用光纤将单光子传输给Bob，也可以通过空中传输它们。已经在全球范围内大规模投资了用于传输电话的光纤基础设施，因此QKD系统与该网络兼容可能被证明是至关重要的。然而，为这个光纤网络设计的最佳传输波长的检测器还没有达到其他检测器的性能水平，导致密钥交换的最大速率大幅降低。我们已经能够使用更先进的检测器来开发一个现有的系统，用于校园规模的实施，与电信光纤完全兼容。该QKD系统能够传输产生高达每秒数百万比特的比特，据我们所知，这是目前存在的最快时钟速率的QKD系统。在这些比特传输速率下，在传输和纠错技术之后，实时加密视频会议成为可能。该系统还特别适用于多用户(一个Alice和多个BOB)使用。尽管该系统以世界级的密钥交换速率运行，但该系统确实存在长期稳定性的严重问题，并且基于一种安全性较低的QKD协议。我们建议利用在我们现有系统的开发中获得的专业知识来构建一系列三个新的、可能更稳定的QKD系统，所有这些系统都将使用可以证明是更安全的协议。前两个系统将基于现有的设计，已经在更长的波长上运行，但密钥交换率(即每秒几千比特)要低得多。第三个系统将基于一种新的设计，这种设计从未完全实现，但可能会有更高的安全性，免受窃听攻击。利用这三个系统，将研究多用户操作的潜力，并将进行多用户网络的演示。

All of our lives have been touched by cryptography at some point or another. From the simple secret diaries of childhood, through internet shopping and banking to the national security of governments, the scrambling of information to hide its contents from potential eavesdroppers is part of modern life.The most commonly used form of encryption today is the so-called public key system, as used in e-commerce and many other applications. This encryption method relies on the difficulty involved in reversing certain mathematical functions back from an answer to the initial starting values. This is analogous to baking a cake, where it is relatively easy to mix the ingredients and produce a cake but virtually impossible to take a finished cake and return to the initial ingredients. However, there is no long-term guarantee that these mathematical functions will remain as difficult to reverse. The development of quantum computers would allow relatively easy decryption of public key encrypted messages. It is fortunate that the same physics that may signal the end of public key encryption systems may also provide the solution in the form of quantum key distribution.Quantum key distribution (QKD) uses the science of quantum mechanics to provide a means of distributing the information needed to encrypt or decrypt a message (the key) in a way that provides verifiable security. It makes us of the fact that certain properties of a photon (a light particle ) cannot be determined with absolute certainty. If single binary digits (bits) of information are encoded onto single-photons using these properties, then any eavesdropper listening in on the key exchange will disturb the analysis of photons sufficiently to leave a virtual fingerprint on the transmission so that sender and receiver can detect the presence of the eavesdropper.QKD systems can either operate using optical fibres to transmit the single-photons to Bob or transmit them through the air. There has already been a large scale investment in a worldwide infrastructure of optical fibre to transmit telephone calls, so it could prove critical that a QKD system would have compatibility with this network. However, the detectors designed for use at the optimum transmission wavelengths for this fibre network have not yet attained the level of performance available from other detectors, leading to a massive reduction in the maximum rate of cryptographic key exchange.We have been able to use more advanced detectors designed for use at shorter wavelengths to develop an existing system for use in a campus sized implementation that is fully compatible with the telecommunications optical fibre. This QKD system is capable of transmission of bits generating up to several million bits per second, which is, to the best of our knowledge, the fastest clock rate QKD system currently in existence. At these bit transmission rates, after transmission and error correction techniques, real-time encrypted video conferencing becomes a possibility. This system has also been uniquely adapted for multi-user (one Alice and multiple Bobs) use.Although operating at world-class key exchange rates, this system does suffer from serious issues with long-term stability and is based on an arguably less secure QKD protocol. We propose to construct a series of three new, potentially much more stable, QKD systems using the expertise gained in the development of our existing system, all of which will use an arguably more secure protocol. The first two systems will be based on existing designs already operating at longer wavelengths but at much lower key exchange rates (ie a few thousands of bits per second). The third system will be based around a novel design that has never been fully implemented but has potentially greater security from eavesdropping attacks. With all three systems, the potential for multi-user operation will be investigated and demonstrations of multi-user networks will be made.