CHAINIAC: Proactive Software-Update Transparency via Collectively Signed Skipchains and Verified Builds

Authors: 

Kirill Nikitin, Eleftherios Kokoris-Kogias, Philipp Jovanovic, Nicolas Gailly, and Linus Gasser, École polytechnique fédérale de Lausanne (EPFL); Ismail Khoffi, University of Bonn; Justin Cappos, New York University; Bryan Ford, École polytechnique fédérale de Lausanne (EPFL)

Abstract: 

Software-update mechanisms are critical to the security of modern systems, but their typically centralized design presents a lucrative and frequently attacked target. In this work, we propose CHAINIAC, a decentralized software-update framework that eliminates single points of failure, enforces transparency, and provides efficient verifiability of integrity and authenticity for software-release processes. Independent witness servers collectively verify conformance of software updates to release policies, build verifiers validate the source-to-binary correspondence, and a tamper-proof release log stores collectively signed updates, thus ensuring that no release is accepted by clients before being widely disclosed and validated. The release log embodies a skipchain, a novel data structure, enabling arbitrarily out-of-date clients to efficiently validate updates and signing keys. Evaluation of our CHAINIAC prototype on reproducible Debian packages shows that the automated update process takes the average of 5 minutes per release for individual packages, and only 20 seconds for the aggregate timeline. We further evaluate the framework using real-world data from the PyPI package repository and show that it offers clients security comparable to verifying every single update themselves while consuming only one-fifth of the bandwidth and having a minimal computational overhead.

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BibTeX
@inproceedings {203724,
author = {Kirill Nikitin and Eleftherios Kokoris-Kogias and Philipp Jovanovic and Nicolas Gailly and Linus Gasser and Ismail Khoffi and Justin Cappos and Bryan Ford},
title = {{CHAINIAC}: Proactive Software-Update Transparency via Collectively Signed Skipchains and Verified Builds},
booktitle = {26th {USENIX} Security Symposium ({USENIX} Security 17)},
year = {2017},
isbn = {978-1-931971-40-9},
address = {Vancouver, BC},
pages = {1271--1287},
url = {https://www.usenix.org/conference/usenixsecurity17/technical-sessions/presentation/nikitin},
publisher = {{USENIX} Association},
}