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Abstract
In the rapidly expanding landscape of Large Language Model (LLM)
applications, real-time output streaming has become the dominant interaction
paradigm. While this enhances user experience, recent research reveals that it
exposes a non-trivial attack surface through network side-channels. Adversaries
can exploit patterns in encrypted traffic to infer sensitive information and
reconstruct private conversations. In response, LLM providers and third-party
services are deploying defenses such as traffic padding and obfuscation to
mitigate these vulnerabilities.
This paper starts by presenting a systematic analysis of contemporary
side-channel defenses in mainstream LLM applications, with a focus on services
from vendors like OpenAI and DeepSeek. We identify and examine seven
representative deployment scenarios, each incorporating active/passive
mitigation techniques. Despite these enhanced security measures, our
investigation uncovers significant residual information that remains vulnerable
to leakage within the network traffic.
Building on this discovery, we introduce NetEcho, a novel, LLM-based
framework that comprehensively unleashes the network side-channel risks of
today's LLM applications. NetEcho is designed to recover entire conversations
-- including both user prompts and LLM responses -- directly from encrypted
network traffic. It features a deliberate design that ensures high-fidelity
text recovery, transferability across different deployment scenarios, and
moderate operational cost. In our evaluations on medical and legal applications
built upon leading models like DeepSeek-v3 and GPT-4o, NetEcho can recover avg
$\sim$70\% information of each conversation, demonstrating a critical
limitation in current defense mechanisms. We conclude by discussing the
implications of our findings and proposing future directions for augmenting
network traffic security.