Quantum Digital Signatures

利用量子效应进行通信和计算在无条件安全密码学和量子计算等应用中显示出巨大的潜力。后者将允许更快的算法用于重要的计算任务，如分解和数据库搜索，这些可以用于日常应用，如互联网安全和快速医疗诊断或DNA搜索。然而，除了极少数例外，实验与理论结果相差甚远。一个值得注意的例外是量子密钥分发（QKD），它有许多令人印象深刻的演示，甚至有一些原始系统可以在商业上使用。然而，总的来说，量子信息协议的实验原理证明实现仍然是一个重要的，在许多情况下，是一个雄心勃勃的目标。数字签名是公钥密码学的一个重要且广泛应用的应用，它允许一方安全地签署文件，从而使另一方可以确定其来源和真实性。不幸的是，经典的公钥密码学依赖于未经证明的假设，即为了破解代码而反转所谓的“单向数学函数”的计算难度。另一方面，量子公钥加密基于信息理论的限制，可以实现无条件安全。我们的主要目标是实现量子数字签名的原理证明实验。该协议是对Gottesman和Chuang的方案的改编，修改后使用相干态和线性光学。从本质上讲，安全性是有保证的，因为如果一个量子系统的可能状态是非正交的，就不可能完美地确定它的状态。

Harnessing quantum effects for communication and computation shows great potential in applications such as unconditionally secure cryptography and quantum computation. The latter would allow for faster algorithms for important computational tasks such as factorisation and database search, which can be used in everyday applications, such as internet security and rapid medical diagnosis or DNA searching. With very few exceptions, however, experiments are far from implementing theoretical results. A notable exception is quantum key distribution (QKD), for which a number of impressive demonstrations exist, with even some primitive systems being commercially available. On the whole, however, experimental proof-of-principle realisations of quantum information protocols remain an important, and in many cases, an ambitious objective.Digital signatures is an important and widely used application of public key cryptography, and allows one party to securely sign documents so that other parties can be sure of their origin and authenticity. Classical public key cryptography unfortunately relies on unproven assumptions regarding the computational difficulty of reversing a so-called ``one-way mathematical function in order to break the code. Quantum public key cryptography, on the other hand, can be made unconditionally secure based on information-theoretical limits. Our main objective is to realise a proof-of-principle experiment for quantum digital signatures. The protocol is an adaption of the scheme by Gottesman and Chuang modified to use coherent states and linear optics. Essentially, the security is guaranteed because it is impossible to perfectly determine the state of a quantum system, if its possible states are non-orthogonal.