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


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)


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 The release log embodies a skipchain, a novel data structure, enabling arbitrarily out-of-date clients to efficiently validate updates and signing keys.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.

Open Access Media

USENIX is committed to Open Access to the research presented at our events. Papers and proceedings are freely available to everyone once the event begins. Any video, audio, and/or slides that are posted after the event are also free and open to everyone. Support USENIX and our commitment to Open Access.

@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 = {},
publisher = {USENIX Association},
month = aug,

Presentation Video