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Publication Detail
LiLAC: Lightweight Low-Latency Anonymous Chat
Low latency anonymity systems, like Tor and I2P, support private online communications, but offer limited protection against powerful adversaries with widespread eavesdropping capabilities. It is known that general-purpose communications, such as web and file transfer, are difficult to protect in that setting. However, online instant messaging only requires a low bandwidth and we show it to be amenable to strong anonymity protections. In this paper, we describe the design and engineering of LiLAC, a Lightweight Low-latency Anonymous Chat service, that offers both strong anonymity and a lightweight client-side presence. LiLAC implements a set of anonymizing relays, and offers stronger anonymity protections by applying dependent link padding on top of constant-rate traffic flows. This leads to a key trade-off between the system's bandwidth overhead and end-to-end delay along the circuit, which we study. Additionally, we examine the impact of allowing zero-installation overhead on the client side, by instead running LiLAC on web browsers. This introduces potential security risks, by relying on third-party software and requiring user awareness; yet it also reduces the footprint left on the client, enhancing deniability and countering forensics. Those design decisions and trade-offs make LiLAC an interesting case to study for privacy and security engineers.
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