在朋友们的帮助下：即时消息的传输拒绝性
With a Little Help from My Friends: Transport Deniability for Instant Messaging
摘要：
即时消息（IM）应用程序的流量分析继续构成重要的隐私挑战。特别是，传输级数据可能会无意中泄露有关IM的信息，比如谁与谁通信。现有的元数据隐私工具存在采用障碍，包括安装特定应用程序时被审查的风险，以及与移动设备不兼容的性能开销。我们认为，流量分析的弹性必须由主要的IM服务本身直接支持，并且必须在不破坏现有功能的情况下以低成本的方式完成。作为这个方向的第一步，我们提出了一个混合消息传递模型，结合了常规和可否认的消息。我们提出了一个新的协议，可否认的即时消息，我们称之为DenIM。DenIM是建立在这样一个原则上的，即在用户朋友的帮助下，可以使可拒绝的消息与常规消息难以区分。可否认消息的网络流量可以通过一个看似合理的封面故事来解释。DenIM实现的开销与发送的消息成比例，而不是随时间或用户数量而扩展。为了显示DenIM的有效性，我们实现了一个跟踪模拟器，并显示DenIM的可否认性保证对强大的对手，如互联网服务提供商。
英文摘要：
Traffic analysis for instant messaging (IM) applications continues to pose an important privacy challenge. In particular, transport-level data can leak unintentional information about IM -- such as who communicates with whom. Existing tools for metadata privacy have adoption obstacles, including the risks of being scrutinized for having a particular app installed, and performance overheads incompatible with mobile devices. We posit that resilience to traffic analysis must be directly supported by major IM services themselves, and must be done in a low-cost manner without breaking existing features. As a first step in this direction, we propose a hybrid messaging model that combines regular and deniable messages. We present a novel protocol for deniable instant messaging, which we call DenIM. DenIM is built on the principle that deniable messages can be made indistinguishable from regular messages with a little help from a user's friends. Deniable messages' network traffic can then be explained by a plausible cover story. DenIM achieves overhead proportional to the messages sent, as opposed to scaling with time or number of users. To show the effectiveness of DenIM, we implement a trace simulator, and show that DenIM's deniability guarantees hold against strong adversaries such as internet service providers.
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