Debreach: Mitigating Compression Side Channels via Static Analysis and Transformation

TL;DR

Debreach is a static analysis and transformation method that mitigates compression side-channel leaks in web applications without degrading compression efficiency or requiring significant developer effort.

Contribution

It introduces a sound static analysis and program transformation approach that automatically instruments code and enhances compressors to prevent sensitive data leakage.

Findings

Ensures leakage-free compression in web applications.

Achieves higher compression performance than existing methods.

Compatible with existing systems without protocol changes.

Abstract

Compression is an emerging source of exploitable side-channel leakage that threatens data security, particularly in web applications where compression is indispensable for performance reasons. Current approaches to mitigating compression side channels have drawbacks in that they either degrade compression ratio drastically or require too much effort from developers to be widely adopted. To bridge the gap, we develop Debreach, a static analysis and program transformation based approach to mitigating compression side channels. Debreach consists of two steps. First, it uses taint analysis to soundly identify flows of sensitive data in the program and uses code instrumentation to annotate data before feeding them to the compressor. Second, it enhances the compressor to exploit the freedom to not compress of standard compression protocols, thus removing the dependency between sensitive data and the size of the compressor's output. Since Debreach automatically instruments applications and does not change the compression protocols, it has the advantage of being non-disruptive and compatible with existing systems. We have evaluated Debreach on a set of web server applications written in PHP. Our experiments show that, while ensuring leakage-freedom, Debreach can achieve significantly higher compression performance than state-of-the-art approaches.