\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}
