Two-party quantum cryptography

1984年，贝内特和布拉萨德提出了一个方案，允许双方在一个能够传输量子比特的信道上就一个密钥达成协议。这种方案被称为量子密钥分发，它非常了不起，因为它实现了仅通过经典手段无法实现的事情。直到90年代中期，量子信息似乎是密码学家最好的朋友。人们期望所有现代密码学应用都可以使用量子通信无条件地解决，而经典密码学只能依靠未经证明的计算假设来希望安全性，而大多数计算假设都不能对抗量子对手。加密应用程序的一个基本类别是涉及愿意合作但不相互信任的双方。许多日常的电子交易都是这种类型的，这使得两方密码学成为信息时代的关键工具。一个例子是，我们经常与自动取款机互动，要求我们在被允许访问我们的银行账户之前证明自己的身份。1995年，Mayers和Lo & Chau打破了这个梦想，他们证明了两方密码学中最重要的密码原语不能使用量子通信安全地实现。另一方面，量子协议已被发现用于弱两方原语，否则仅使用经典通信是不可能的。与密钥分发不同，量子密码学在两方设置中的功能还没有得到很好的理解。该项目的主要目标是为双方应用中量子密码学的真正力量提供更深入的理解。提高我们对它在这种情况下所能达到的效果的认识，可能会对在电子交易中提供安全性的系统的设计产生重要影响。受这项研究启发的新系统可以在更弱的假设下更有效地提供隐私。即使是完全经典的协议也可以从这项工作中受益，将其安全领域扩展到拥有量子计算机的对手。对我们主要目标的任何令人满意的进展都将提高我们对经典信息和量子信息之间差异的理解。

In 1984, Bennett and Brassard proposed a scheme allowing two parties to agree on a secret key provided they have access to a channel capable of transmitting quantum bits. This scheme, called quantum key distribution, is remarkable since it achieves something impossible through classical means alone. Until the mid 90's quantum information appeared to be cryptographers' best friend. Expectations were that all modern cryptographic applications could be resolved unconditionally using quantum communication whereas classical cryptography could only hope for security relying upon unproven computational assumptions out of which the majority do not hold against quantum adversaries. One essential class of cryptographic applications are the ones involving two parties willing to collaborate but otherwise not trusting each other. Many daily electronic transactions are of that kind, making two-party cryptography a critical tool for the information age. An example is our frequent interactions with ATMs asking us to identify ourselves before being granted access to our bank account. In 1995, Mayers and Lo & Chau shattered this dream when they prove that the most important cryptographic primitives for two-party cryptography cannot be implemented securely using quantum communication. On the other hand, quantum protocols have been found for weak two-party primitives otherwise impossible using classical communication alone. Unlike for key distribution, the capabilities of quantum cryptography in the two-party setting are not well understood. The project's main goal is to provide a deeper understanding for the true power of quantum cryptography in two-party applications. Improving our insight on what it can achieve in this setting could have important consequences for the design of systems providing security in electronic transactions. New systems inspired by this research could offer privacy more efficiently and under weaker assumptions. Even entirely classical protocols could benefit from this work by extending the realm of their security to adversaries in possession of quantum computers. Any satisfactory advance toward our main objective would improve our comprehension of the differences between classical and quantum information.