Add figure for TLS-handshake and reference in text

methods.tex

@@ -859,23 +859,47 @@ for example.
 \label{subsec:tls session resumption}
 
 \gls{TLS} \cite{rescorlaTransportLayerSecurity2018} is widely used today to
-securely encapsulate communication across the web. For bandwidth savings and
-better performance, it is possible to cache a \gls{TLS} session to allow reusing
-an already established secure connection at a later point in time. Versions
-prior to \gls{TLS} 1.3 used two mechanisms to accomplish this: \gls{TLS} session
-identifiers and session tickets. Session identifiers are sent by the server
-along with the initial handshake with the user agent. The identifier is randomly
-generated and saved by the server so that the current session can be found
-later. To resume a session, the user agent sends the identifier with the
-ClientHello message to the server. The server can then match the identifier to
-the previously initiated session and responds with the same session identifier
-to signal to the user agent that the session can be resumed. Session tickets are
-only issued by the server when the client has expressed support for them. They
-are encrypted and provided by the server after a successful handshake via an
-out-of-band message. The ticket contains all the necessary information to
-reestablish a secure connection. When the user agent wishes to resume a
-connection, the session ticket is sent along with the first ClientHello message
-and the server can decrypt the ticket and resume the session.
+securely encapsulate communication across the web. For the secured communication
+to work, client and server first have to authenticate themselves and then agree
+on protocol version, cipher suite and compression method. The exchange of this
+information at the beginning of a connection is called a \emph{handshake}.
+Figure~\ref{fig:tls-handshake} shows how the initial handshake is performed
+after which both the client and the server are ready for sending and receiving
+application data. For bandwidth savings and better performance, it is possible
+to cache a \gls{TLS} session to allow reusing an already established secure
+connection at a later point in time. Versions prior to \gls{TLS} 1.3 used two
+mechanisms to accomplish this: \gls{TLS} session identifiers and session
+tickets. Session identifiers are sent by the server along with the initial
+handshake with the user agent. The identifier is randomly generated and saved by
+the server so that the current session can be found later. To resume a session,
+the user agent sends the identifier with the \emph{ClientHello} message to the
+server. The server can then match the identifier to the previously initiated
+session and responds with the same session identifier to signal to the user
+agent that the session can be resumed. Session tickets are only issued by the
+server when the client has expressed support for them. They are encrypted and
+provided by the server after a successful handshake via an out-of-band message.
+The ticket contains all the necessary information to reestablish a secure
+connection. When the user agent wishes to resume a connection, the session
+ticket is sent along with the first \emph{ClientHello} message and the server
+can decrypt the ticket and resume the session.
+
+\begin{figure}
+    \begin{center}
+        \includegraphics[width=0.75\textwidth]{figures/tls-handshake.png}
+        \caption{A \gls{TLS}-handshake between a client and a server. First, the
+            client sends a \emph{ClientHello} message to the server which the
+            server has to answer with a \emph{ServerHello} message or else the
+            connection fails. These two initial messages establish protocol
+            version, session ID, cipher suite and compression method
+            \cite[p.~44]{rescorlaTransportLayerSecurity2008}. The server also
+            checks for a session resumption. If the client sends a session ID
+            with the \emph{ClientHello} message, the server knows that it should
+            resume a previously established connection. The next three messages
+            are used for the key exchange which allows client and server to
+        authenticate themselves.}
+        \label{fig:tls-handshake}
+    \end{center}
+\end{figure}
 
 In \gls{TLS} version 1.3 \cite{rescorlaTransportLayerSecurity2018} the session
 identifiers and tickets have been replaced with a \gls{PSK}. Instead of sending

references.bib

@@ -1180,9 +1180,19 @@ Impact of CSS-based history detection},
   note = {Accessed 2020-02-08}
 }
 
+@misc{rescorlaTransportLayerSecurity2008,
+  title = {The {{Transport Layer Security}} ({{TLS}}) {{Protocol Version}} 1.2},
+  author = {Rescorla, Eric},
+  year = {2008},
+  month = aug,
+  url = {https://tools.ietf.org/html/rfc5246},
+  urldate = {2020-08-26},
+  note = {Accessed 2020-08-26}
+}
+
 @misc{rescorlaTransportLayerSecurity2018,
   title = {The {{Transport Layer Security}} ({{TLS}}) {{Protocol Version}} 1.3},
-  author = {Rescorla {$<$}ekr@rtfm.com{$>$}, Eric},
+  author = {Rescorla, Eric},
   year = {2018},
   month = aug,
   url = {https://tools.ietf.org/html/rfc8446},