Abstract
Trust in publicly verifiable Certificate Transparency (CT) logs is reduced through cryptography, gossip, auditing, and monitoring. The role of a monitor is to observe each and every log entry, looking for suspicious certificates that interest the entity running the monitor. While anyone can run a monitor, it requires continuous operation and copies of the logs to be inspected. This has lead to the emergence of monitoring as-a-service: a trusted third-party runs the monitor and provides registered subjects with selective certificate notifications. We present a CT/bis extension for verifiable light-weight monitoring that enables subjects to verify the correctness of such certificate notifications, making it easier to distribute and reduce the trust which is otherwise placed in these monitors. Our extension supports verifiable monitoring of wild-card domains and piggybacks on CT’s existing gossip-audit security model.
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Notes
- 1.
https://sslmate.com/certspotter/, accessed 2018-09-15.
- 2.
https://developers.facebook.com/tools/ct/, accessed 2018-09-15.
- 3.
https://ct.grahamedgecombe.com/, accessed 2018-09-15.
- 4.
Efficient iff less than a linear number of log entries are received per log update.
- 5.
Two audit paths may contain redundancy, but we ignored this favouring simplicity.
- 6.
It would be better if logs supported verifiable and historical get-STH queries.
- 7.
Instead of an index to detect missing notifications (STHs), a log could announce STHs as part of a verifiable get-STH endpoint. See the sketch of Nordberg: https://web.archive.org/web/20170806160119/https://mailarchive.ietf.org/arch/msg/trans/JbFiwO90PjcYzXrEgh-Y7bFG5Fw, accessed 2018-09-16.
- 8.
- 9.
Open source implementation available at https://github.com/rgdd/lwm.
- 10.
http://s3.amazonaws.com/alexa-static/top-1m.csv.zip, accessed 2018-08-05.
- 11.
https://www.grahamedgecombe.com/blog/2016/12/22/compressing-x509-certificates, accessed 2018-08-15.
- 12.
https://sslmate.com/labs/ct_growth/, accessed 2018-08-15.
- 13.
https://github.com/ethereum/wiki/wiki/Patricia-Tree, accessed 2018-08-15.
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Acknowledgments
We would like to thank Linus Nordberg for value feedback. This research was funded by the Swedish Knowledge Foundation as part of the HITS research profile.
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Dahlberg, R., Pulls, T. (2018). Verifiable Light-Weight Monitoring for Certificate Transparency Logs. In: Gruschka, N. (eds) Secure IT Systems. NordSec 2018. Lecture Notes in Computer Science(), vol 11252. Springer, Cham. https://doi.org/10.1007/978-3-030-03638-6_11
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DOI: https://doi.org/10.1007/978-3-030-03638-6_11
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