\section{System Architecture}\label{system_architecture}
As the charity backend and donor wallet implementation are not yet developed
the following architecture is reduced to the Donau backend.

\begin{figure}[ht]
  \includegraphics[width=1\textwidth]{donau_system_arch}
  \caption{Donau system architecture} \label{fig:donau_system_arch}
\end{figure}

The Donau backend implements the REST API and HTTP handler which communicates
with the database plugin. The postgresql database is further described in
section \ref{donau_database} of the thesis.
The HTTP handler includes a key handler that interacts with the three secmod
processes. The secmod processes generate the keys. Only they have access to the
private keys.
