Apps such as Firechat and Bridgefy have been used during recent protests in Hong Kong and Iran, as they allow communication over ad-hoc wireless networks even when internet access is restricted. However, these apps do not provide sufficient protection as they do not achieve forward secrecy in unreliable networks. Without forward secrecy, caught protesters' devices will disclose all previous messages to the authorities, putting them and others at great risk. In this paper, we introduce FoSAM, the first protocol to provide proven anonymous and forward secret messaging in unreliable ad-hoc networks. Communication in FoSAM requires only the receiver's public key, rather than an interactive handshake. We evaluate the performance of FoSAM using a large-scale simulation with different user movement patterns, showing that it achieves between 92% and 99% successful message delivery. We additionally implement a FoSAM prototype for Android.

翻译：近期香港和伊朗的抗议活动中，Firechat和Bridgefy等应用程序被广泛使用，因为它们允许在互联网访问受限时通过自组织无线网络进行通信。然而，这些应用未能提供充分保护，因为它们无法在不可靠网络中实现前向保密。缺乏前向保密性意味着被捕抗议者的设备将向当局披露所有历史消息，使其自身及他人面临巨大风险。本文提出FoSAM协议，这是首个在不可靠自组织网络中提供可证明匿名性与前向保密性的消息传递方案。FoSAM的通信过程仅需接收方公钥，无需交互式握手协议。通过采用不同用户移动模式的大规模仿真实验，我们评估了FoSAM的性能表现，结果表明其消息成功投递率达到92%至99%。此外，我们还实现了面向Android平台的FoSAM原型系统。