\subsection{Money laundering}\label{sec:threats}

\ifodd0

The presented protocol is using similar cryptographic constructions as
the GNU Taler payment system itself, primarily blind signatures and
regular signatures. However, it does not use the ``refresh'' protocol
of GNU Taler, as there is no need to render change.  As a result, the
Donau protocol suffers from a subset of the threats from quantum
computing.~\cite{lange2024}
\fi

A new Donau-specific threat is that donations could be used for
laundering criminal assets. This does not mean that we expect
charities themselves to play foul, but tax benefits that could be
transferred to someone else would indirectly represent actual value
(even commercially tradeable): donations from someone paying lower tax
rates could be used to artificially lower the income of a person
paying a higher rate. The money going to the charity would essentially
be used to trigger a laundered partial payout in the legitimate world.
The Donau protocol does not prove that the donor identification $\DI$
used in the $\UDI$s inside the BKPs is that of the actual donor, as
that is incompatible with the anonymity and confidentiality guarantees
of the system.  In practice, we expect this threat to be largely
theoretical: the hypothetical money launderer would need complex arrangements
as well as be willing to take a significant loss (depending on the tax rate,
but generally probably more than half, given that common effective tax rates
are rarely above 50\%).  Thus, the overhead of laundering money with this
method would most likely substantially exceed the cost of other methods to
launder criminal assets.
