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Aggregation-Based Certificate Transparency Gossip
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).ORCID iD: 0000-0003-0840-5072
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).ORCID iD: 0000-0001-6459-8409
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).ORCID iD: 0000-0001-7358-8675
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).ORCID iD: 0000-0001-5241-6815
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2019 (English)In: Proceedings of the The Thirteenth International Conference on Emerging Security Information, Systems and Technologies - SECURWARE 2019, October 27, 2019 to October 31, 2019 - Nice, France / [ed] Stefan Rass; George Yee, International Academy, Research and Industry Association (IARIA), 2019Conference paper, Published paper (Refereed)
Abstract [en]

Certificate Transparency (CT) requires that every certificate which is issued by a certificate authority must be publicly logged. While a CT log can be untrusted in theory, it relies on the assumption that every client observes and cryptographically verifies the same log. As such, some form of gossip mechanism is needed in practice. Despite CT being adopted by several major browser vendors, no gossip mechanism is widely deployed. We suggest an aggregation-based gossip mechanism that passively observes cryptographic material that CT logs emit in plain text, aggregating at packet processors (such as routers and switches) to periodically verify log consistency off-path. In other words, gossip is provided as-a-service by the network. Our proposal can be implemented for a variety of programmable packet processors at line-speed without aggregation distinguishers (throughput), and, based on 20 days of RIPE Atlas measurements that represent clients from 3500 autonomous systems, we show that significant protection against split-viewing CT logs can be achieved with a realistic threat model and an incremental deployment scenario.

Place, publisher, year, edition, pages
International Academy, Research and Industry Association (IARIA), 2019.
Keywords [en]
Certificate Transparency, Gossip, P4, XDP
National Category
Computer Sciences
Research subject
Computer Science
Identifiers
URN: urn:nbn:se:kau:diva-77388ISBN: 9781713800521 (print)OAI: oai:DiVA.org:kau-77388DiVA, id: diva2:1420772
Conference
The Thirteenth International Conference on Emerging Security Information, Systems and Technologies - SECURWARE 2019, October 27, 2019 to October 31, 2019 - Nice, France
Projects
HITS
Funder
Knowledge Foundation, 4707Available from: 2020-03-31 Created: 2020-03-31 Last updated: 2023-05-02Bibliographically approved
In thesis
1. On Certificate Transparency Verification and Unlinkability of Websites Visited by Tor Users
Open this publication in new window or tab >>On Certificate Transparency Verification and Unlinkability of Websites Visited by Tor Users
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Certificate Transparency is an ecosystem of logs, monitors, and auditors that hold certificate authorities accountable while issuing certificates. We show how the amount of trust that TLS clients and domain owners need to place in Certificate Transparency can be reduced, both in the context of existing gradual deployments and the largely unexplored area of Tor. Our contributions include improved third-party monitoring, a gossip protocol plugging into Certificate Transparency over DNS, an incrementally deployable gossip-audit model tailored for Tor Browser, and using certificates with onion addresses. The methods used range from proof sketches to Internet measurements and prototype evaluations. An essential part of our evaluation in Tor is to assess how the protocols used during website visits—such as requesting an inclusion proof from a Certificate Transparency log—affect unlinkability between senders and receivers. We find that most false positives in website fingerprinting attacks can be eliminated for all but the most frequently visited sites. This is because the destination anonymity set can be reduced due to how Internet protocols work: communication is observable and often involves third-party interactions. Some of the used protocols can further be subject to side-channel analysis. For example, we show that remote (timeless) timing attacks against Tor’s DNS cache reliably reveal the timing of past exit traffic. The severity and practicality of our extension to website fingerprinting pose threats to the anonymity provided by Tor. We conclude that access to a so-called website oracle should be an assumed attacker capability when evaluating website fingerprinting defenses.

Abstract [sv]

Projektet Certificate Transparency är ett ekosystem av loggar, övervakare och granskare som håller certifikatutfärdare till svars för utfärdade webbcertifikat. Vi visar hur säkerheten kan höjas i ekosystemet för både domäninnehavare och TLS-klienter i nuvarande system samt som del av anonymitetsnätverket Tor. Bland våra större bidrag är förbättrad övervakning av loggarna, ett skvallerprotokollsom integrerats med DNS, ett skvaller- och granskningsprotokoll som utformats specifikt för Tors webbläsare och ett förslag på hur domännamn med adresser i Tor kan bli mer tillgängliga. De metoder som använts varierar från säkerhetsbevis till internetmätningar och utvärderingar av forskningsprototyper. En viktig del av vår utvärdering i Tor är att avgöra hur protokoll som används av webbläsare påverkar möjligheten att koppla ihop användare med besökta webbplatser. Detta inkluderar existerande protokoll samt nya tillägg för att verifiera om webbplatsers certifikat är transparensloggade. Våra resultat visar att i många fall kan falska positiva utslag filtreras bort vid mönsterigenkänning av Tor-användares krypterade trafik (eng: website fingerprinting). Orsaken är att besök till de flesta webbplatser kan uteslutas till följd av hur internetprotokoll fungerar: kommunikation är observerbar och involverar ofta interaktioner med tredjeparter. Vissa protokoll har dessutom sidokanaler som kan analyseras. Vi visar exempelvis att Tors DNS-cache kan undersökas med olika varianter av tidtagningsattacker. Dessa attacker är enkla att utföra över internet och avslöjar vilka domännamn som slagits upp vid angivna tidpunkter. De förbättrade mönsterigenkänningsattackerna mot webbplatser är realistiska och hotar därför Tors anonymitet. Vår slutsats är att framtida försvar bör utvärderas utifrån att angripare har tillgång till ett så kallat webbplatsorakel.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2023. p. 29
Series
Karlstad University Studies, ISSN 1403-8099 ; 2023:15
Keywords
Auditing, Certificate Transparency, DNS, Gossip, Side-Channels, Timing Attacks, Tor, Tor Browser, Website Fingerprinting, Website Oracles, Granskning, Certificate Transparency, DNS, Skvaller, Sidokanaler, Tidtagningsattacker, Tor, Torswebbläsare, Mönsterigenkänning, Webbplatsorakel
National Category
Computer Sciences
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-94343 (URN)978-91-7867-372-8 (ISBN)978-91-7867-373-5 (ISBN)
Public defence
2023-06-12, Eva Eriksson, 21A 342, Karlstad University, Karlstad, 10:15 (English)
Opponent
Supervisors
Projects
HITS (4707), SURPRISE (SSF, RIT17-0005)
Available from: 2023-05-22 Created: 2023-04-18 Last updated: 2023-05-22Bibliographically approved

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Dahlberg, RasmusPulls, TobiasVestin, JonathanHøiland-Jørgensen, TokeKassler, Andreas

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