From Packets to Patterns: Interpreting Encrypted Network Traffic as Longitudinal Behavioral Signals

TL;DR

This paper demonstrates that encrypted smartphone network traffic can be passively analyzed to reveal longitudinal behavioral patterns related to sleep, stress, and loneliness using a transformer-based model and interpretable features.

Contribution

It introduces a novel approach combining transformer models and autoencoders to interpret encrypted traffic as behavioral signals, capturing individual deviations over time.

Findings

Stress correlates with stable between-person differences.

Loneliness is associated with within-person variation.

Sleep disturbance involves both between- and within-person dynamics.

Abstract

Human behavior is difficult to observe continuously at scale, yet it leaves measurable traces in everyday device use. We test whether encrypted smartphone network traffic -- a ubiquitous, always-on, passive sensing modality -- can passively capture behavioral patterns related to sleep, stress, and loneliness. We model shared behavioral structure using a transformer backbone with per-user adapters, allowing the model to represent both typical individual behavior and deviations from it. To make these representations interpretable, we apply a sparse autoencoder to extract behavioral features corresponding to distinct patterns of activity. We relate these features to sleep disturbance, stress, and loneliness using generalized estimating equations with Mundlak decomposition, separating between-person differences from within-person changes over time. We find that the three outcomes reflect distinct temporal structures: stress is primarily associated with stable between-person differences, loneliness with within-person variation, and sleep disturbance with a combination of both. Notably, these within-person dynamics are not captured by predefined network-traffic features, demonstrating the value of learned representations for longitudinal behavioral sensing. These results establish encrypted network traffic as a viable passive sensing modality, revealing interpretable behavioral dynamics -- particularly deviations from an individual's baseline -- that are not visible in raw traffic features.