Anonymity in networked communication is vital for many privacy-preserving tasks. Secure key distribution alone is insufficient for high-security communications, often knowing who transmits a message to whom and when must also be kept hidden from an adversary. Here we experimentally demonstrate 5 information-theoretically secure anonymity protocols on an 8 user city-wide quantum network using polarisation-entangled photon pairs. At the heart of these protocols is anonymous broadcasting, which is a cryptographic primitive that allows one user to reveal one bit of information while keeping her identity anonymous. For a network of $n$ users, the protocols retain anonymity for the sender, given less than $n-2$ users are dishonest. This is one of the earliest implementations of genuine multi-user cryptographic protocols beyond standard QKD. Our anonymous protocols enhance the functionality of any fully-connected Quantum Key Distribution network without trusted nodes.

中文翻译：

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八用户量子网络上安全匿名协议的实验实现

网络通信中的匿名性对于许多隐私保护任务至关重要。对于高安全性通信而言，仅靠安全密钥分发是不够的，因为通常知道谁向谁发送消息以及何时还必须对对手隐藏。在这里，我们使用极化纠缠光子对在 8 个用户的城市范围量子网络上实验性地演示了 5 个信息理论上安全的匿名协议。这些协议的核心是匿名广播，这是一种加密原语，允许一个用户透露一点信息，同时保持其身份匿名。对于 $n$ 用户的网络，如果少于 $n-2$ 用户是不诚实的，则协议为发送者保留匿名性。这是超越标准 QKD 的真正多用户加密协议的最早实现之一。