Contour: A Practical System for Binary Transparency

TL;DR

Contour is a practical system designed to ensure transparency, privacy, and availability in the distribution of software binaries, effectively preventing man-in-the-middle attacks and enabling real-world deployment.

Contribution

It introduces Contour, the first efficient binary transparency system tailored for software distribution, with proactive security measures and real-world deployment validation.

Findings

Contour achieves efficiency suitable for deployment

It maintains transparency despite man-in-the-middle attacks

Demonstrated successful deployment in Debian repository

Abstract

Transparency is crucial in security-critical applications that rely on authoritative information, as it provides a robust mechanism for holding these authorities accountable for their actions. A number of solutions have emerged in recent years that provide transparency in the setting of certificate issuance, and Bitcoin provides an example of how to enforce transparency in a financial setting. In this work we shift to a new setting, the distribution of software package binaries, and present a system for so-called "binary transparency." Our solution, Contour, uses proactive methods for providing transparency, privacy, and availability, even in the face of persistent man-in-the-middle attacks. We also demonstrate, via benchmarks and a test deployment for the Debian software repository, that Contour is the only system for binary transparency that satisfies the efficiency and coordination requirements that would make it possible to deploy today.