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\begin{frame}
\mktitle{Tor crash course}
\centering\includegraphics[width=.8\textwidth]{img/tor/overview}
\footnotetext[1]{\tiny{Credit: figure created by Tobias Pulls}}
\footnotetext[2]{\tiny{Design: \burl{https://murdoch.is/papers/tor14design.pdf}}}
\end{frame}
\begin{frame}
\mktitle{Tor Browser}
\begin{columns}
\begin{column}{0.6\textwidth}
\begin{itemize}
\item Firefox derivative
\item Route all traffic through Tor
\item Prevent user activity on one site from
being linked to activity on another
\item \alert<2->{Do not write any state to disk}
\item ...
\end{itemize}
\end{column}
\begin{column}{0.4\textwidth}
\includegraphics[width=.67\columnwidth]{img/tor/tb}
\end{column}
\end{columns}
\footnotetext[1]{\tiny{Credit: Tom Ritter, see \burl{https://ritter.vg/p/tor-v1.6.pdf}}}
\footnotetext[2]{\tiny{Design: \burl{https://2019.www.torproject.org/projects/torbrowser/design/}}}
\end{frame}
\begin{frame}
\centering
\includegraphics[width=.75\textwidth]{img/ctor/paper}
\vfill
\includegraphics[width=.75\textwidth]{img/ctor/blog}
\end{frame}
\begin{frame}
\mktitle{Problem statement}
\begin{columns}
\begin{column}{0.6\textwidth}
\begin{itemize}
\item Tor Browser does not enforce CT
\item Guard against prominent threats
\begin{itemize}
\item DigiNotar style attacks
\item Interception to deanonymize
\end{itemize}
\item Go beyond ``just CT compliance''
\end{itemize}
\end{column}
\begin{column}{0.4\textwidth}
\centering
\includegraphics[width=.67\columnwidth]{img/tor/tb}
\end{column}
\end{columns}
\vfill\pause
\alert{Attacker in Tor's threat model + controls a CA and two CT logs}
\end{frame}
\begin{frame}
\mktitle{Incremental deployment}
\begin{enumerate}
\item Catch up with CT compliant browsers
\floatright{\emph{pairs of logs} are trusted blindly}
\item Steps towards decentralized verification
\floatright{\emph{some log} is trusted blindly}
\item Fully decentralized verification
\floatright{\emph{no log} is trusted blindly}
\end{enumerate}
\end{frame}
\begin{frame}
\mktitle{Full design}
\centering\includegraphics[height=.5\textheight]{img/ctor/full}
\vfill
\pause
\alert{Security? Difficult to interfere without detection in any phase}
\end{frame}
\begin{frame}
\mktitle{Why not just...?}
\begin{columns}
\begin{column}{.5\textwidth}\centering
\includegraphics[width=.9\columnwidth]{img/ctor/tb-to-log}\\\vspace{.25cm}
Fetch an inclusion proof
\end{column}
\begin{column}{.5\textwidth}\centering
\includegraphics[width=.77\columnwidth]{img/ctor/tb-to-auditor}\\\vspace{.25cm}
Rely on a centralized party
\end{column}
\end{columns}
\end{frame}
\begin{frame}
\mktitle{Phase 1: Submission}
\centering\includegraphics[width=.75\textwidth]{img/ctor/phase-1}
\vfill
\begin{columns}
\begin{column}{.2\textwidth}\centering
\end{column}
\begin{column}{.3\textwidth}\centering
\alert{1.} Probabilistic submit
\end{column}
\begin{column}{.3\textwidth}\centering
\alert{2.} Random CTR
\end{column}
\begin{column}{.2\textwidth}\centering
\end{column}
\end{columns}
\pause
\vfill
\alert{Best attack: quickly take control over Tor Browser}
\end{frame}
\begin{frame}
\mktitle{Phase 2: Buffering}
\begin{columns}
\begin{column}{.5\textwidth}
\begin{enumerate}
\item Buffer until logging is required
\item Add a random delay to leak less
\item Cache audited SFOs to leak less
\end{enumerate}
\end{column}
\begin{column}{.5\textwidth}
\centering
\includegraphics[width=.45\columnwidth]{img/ctor/phase-2}
\end{column}
\end{columns}
\pause
\vfill\centering
\alert{Best attack: network-wide flush}
\end{frame}
\begin{frame}
\mktitle{Phase 3: Auditing}
\begin{columns}
\begin{column}{.4\textwidth}
\begin{enumerate}
\item Fetch inclusion proof
\item STH from Tor's consensus
\item Collaborate with a watchdog
\begin{itemize}
\item CTR identification
\item ``Tagging''
\end{itemize}
\end{enumerate}
\end{column}
\begin{column}{.6\textwidth}
\centering
\includegraphics[width=\columnwidth]{img/ctor/phase-3}
\end{column}
\end{columns}
\pause
\vfill\centering
\alert{Best attack: quickly take control over CTR}
\end{frame}
\begin{frame}
\mktitle{Phase 4: Reporting}
\centering\includegraphics[width=.4\textwidth]{img/ctor/phase-4}
\vfill
\alert{1.} Report SFO on timeout
\pause
\vfill
\alert{Best attack: n/a}
\end{frame}
\begin{frame}
\vfill
\mktitle{This is quite the leap from ``just CT compliance''}
\end{frame}
\begin{frame}
\mktitle{Incremental design}
\centering\includegraphics[height=.33\textheight]{img/ctor/incremental}
\vfill
\pause
\alert{Use the log ecosystem against the attacker}\\
\end{frame}
\begin{frame}
\vfill
\begin{columns}
\begin{column}{.41\textwidth}
\mktitle{Conclusion}
\begin{itemize}
\item Tor's setting is quite different
\item Delegated audiding is key here
\item Roadmap from start to finnish
\end{itemize}
\end{column}
\begin{column}{.25\textwidth}
\mktitle{Resources}
\begin{itemize}
\item PETS paper\footnotemark[1]
\item PETS talk\footnotemark[2]
\item Tor blog post\footnotemark[3]
\end{itemize}
\end{column}
\begin{column}{.35\textwidth}
\mktitle{Next steps}
\begin{itemize}
\item Torspec proposal(s)
\item Browser implementation
\item Relay implementation
\end{itemize}
\end{column}
\end{columns}
\footnotetext[1]{\burl{https://petsymposium.org/2021/files/papers/issue2/popets-2021-0024.pdf}}
\footnotetext[2]{\burl{https://www.youtube.com/watch?v=f7yDJOd6g3U}}
\footnotetext[3]{\burl{https://blog.torproject.org/tor-certificate-transparency/}}
\end{frame}
\begin{frame}
\vfill
\mktitle{Halftime}
\end{frame}
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