Structural Decomposability of Encrypted Traffic Side-Channel Leakage
Abstract
Existing side-channel theories treat leakage as a holistic quantity I(X;Y), without characterizing its internal structure. This paper studies the \emph{structural decomposability} of encrypted-traffic side-channel leakage. Via the structural causal model X → Ysize → Ydir → Ytime and the mutual-information chain rule, total leakage is decomposed into three sequential increments for packet size, direction, and timing. Defenses are formalized as mechanism replacement by a strategy variable~D; coupling information Csize,dir=I(Ysize;Ydir | X) measures inter-dimensional dependence, and the Markov residual gives a testable condition for a single-dimension defense to sever downstream leakage. Causal efficacy~ηd quantifies per-unit-cost suppression, and a Fisher-geometric approximation I(X;Y)≈1/(2ln 2)Tr(GΣθ) holds under small perturbations. On the Wang dataset (95 websites), Ydir dominates undefended leakage (0.637\,bits), while Tor's fixed 512-byte cells make Ysize degenerate; FRONT suppresses the direction term by 63\%, yet its Markov residual of 0.021\,bits (95\% CI $[0.016,0.027]$) shows it cannot sever timing leakage; ηdir=0.97 vs. ηtime≈ 0 confirms FRONT's design intent. This yields a computable, structured leakage-accounting method for multi-dimensional joint defense design.
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BibTeX
@misc{liu2026structural,
title = {{Structural Decomposability of Encrypted Traffic Side-Channel Leakage}},
author = {Guangjie Liu and Guang Cheng and Weiwei Liu},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.19036},
eprint = {2609.19036},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.19036},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Structural Decomposability of Encrypted Traffic Side-Channel Leakage
AU - Guangjie Liu
AU - Guang Cheng
AU - Weiwei Liu
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.19036
UR - https://arxiv.org/abs/2609.19036
AB - Existing side-channel theories treat leakage as a holistic quantity I(X;Y), without characterizing its internal structure. This paper studies the \emph{structural decomposability} of encrypted-traffic side-channel leakage. Via the structural causal model X → Y_size → Y_dir → Y_time and the mutual-information chain rule, total leakage is decomposed into three sequential increments for packet size, direction, and timing. Defenses are formalized as mechanism replacement by a strategy variable~D; coupling information C_size,dir=I(Y_size;Y_dir | X) measures inter-dimensional dependence, and the Markov residual gives a testable condition for a single-dimension defense to sever downstream leakage. Causal efficacy~η_d quantifies per-unit-cost suppression, and a Fisher-geometric approximation I(X;Y)≈1/(2ln 2)Tr(GΣ_θ) holds under small perturbations. On the Wang dataset (95 websites), Y_dir dominates undefended leakage (0.637\,bits), while Tor's fixed 512-byte cells make Y_size degenerate; FRONT suppresses the direction term by 63\%, yet its Markov residual of 0.021\,bits (95\% CI $[0.016,0.027]$) shows it cannot sever timing leakage; η_dir=0.97 vs. η_time≈ 0 confirms FRONT's design intent. This yields a computable, structured leakage-accounting method for multi-dimensional joint defense design.
ER -