marketing

2026-UHA-ENSISA.tex (33337B)

---

 \documentclass[aspectratio=169,t]{beamer}
 
 \input texinputs/taler-macros
 
 \usepackage{tikz}
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 \usetikzlibrary{positioning,fit,patterns}
 
 %
 %  Presentation at "P15 Biel/Bienne le 30 avril 2026"
 %   Copyright (C) 2026 Emmanuel Benoist,
 
 %    This program is free software: you can redistribute it and/or modify
 %    it under the terms of the GNU General Public License as published by
 %    the Free Software Foundation, either version 3 of the License, or
 %    (at your option) any later version.
 %
 %    This program is distributed in the hope that it will be useful,
 %    but WITHOUT ANY WARRANTY; without even the implied warranty of
 %    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 %    GNU General Public License for more details.
 %
 %    You should have received a copy of the GNU General Public License
 %    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 %
 
 % *Especially* edit these...
 % \setbeameroption{show notes on second screen=right} % Both
 
 \newcommand{\SPEAKER}{Emmanuel Benoist}
 \newcommand{\DATE}{} {}
 
 \newcommand{\TITLE}{Presentation of GNU Taler}
 \newcommand{\SUB}{26.05.26, ENSISA, Mulhouse}
 \newcommand{\AUTHOR}{Emmanuel Benoist / Ch. Grothoff}
 \newcommand{\INST}{https://www.taler.net}
 
 % Do not edit this part
 \title{\TITLE}
 \subtitle{\SUB}
 \date{\DATE}
 \author[\SPEAKER]{\AUTHOR}
 \institute{\INST}
 
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 \usepackage[utf8]{inputenc}
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 \usepackage{graphicx}
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 \usepackage{booktabs}
 \usepackage{makecell}
 \usepackage{arydshln}
 \usepackage{ulem}
 \begin{document}
 
 \begin{frame}[plain]
 \maketitle
 \end{frame}
 
 \begin{frame}{Agenda}
   \tableofcontents
 \end{frame}
 
 \section{GNU Taler: Introduction}
 
 
 \begin{frame}{GNU Taler~\cite{taler2016space,DBLP:phd/hal/Dold19,cbdc2021chaum}}
   \vfill
   \begin{center}
     {\huge {\bf Digital} cash, made \textbf{socially responsible}.}
   \end{center}
   \vfill
   \begin{center}
   \includegraphics[scale=0.3]{taler-logo-2021-inkscape.pdf}
   \end{center}
   \vfill
   \begin{center}
     Privacy-Preserving, Practical, Taxable, Free Software, Efficient
   \end{center}
  \vfill
  \vfill
 \ %
 \end{frame}
 
 
 \begin{frame}{What is Taler?}
   \framesubtitle{\url{https://taler.net/en/features.html}}  \noindent
 Taler is
   \vfill
   \begin{itemize}
     \item a Free/Libre software \emph{payment system} infrastructure project
     \item ... with a surrounding software ecosystem
     \item ... and a company (Taler Systems S.A.) and community that wants to deploy it
       as widely as possible.
   \end{itemize}
   \vfill
 \noindent
  However, Taler is
   \begin{itemize}
     \item \emph{not} a currency or speculative asset
     \item \emph{not} a long-term store of value
     \item \emph{not} a network or instance of a system
     \item \emph{not} based on proof-of-work or proof-of-stake
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Design principles}
   \framesubtitle{https://taler.net/en/principles.html}
 GNU Taler must ...
 \begin{enumerate}
   \item {... be implemented as {\bf free software}.}
   \item {... protect the {\bf privacy of buyers}.}
   \item {... enable the state to {\bf tax income} and crack down on
     illegal business activities.}
   \item {... prevent payment fraud.}
   \item {... only {\bf disclose the minimal amount of information
     necessary}.}
   \item {... be usable.}
   \item {... be efficient.}
   \item {... avoid single points of failure.}
   \item {... foster {\bf competition}.}
 \end{enumerate}
 \end{frame}
 
 
 \begin{frame}
 \frametitle{Taler Overview}
 \begin{center}
 \begin{tikzpicture}
  \tikzstyle{def} = [node distance= 5em and 6.5em, inner sep=1em, outer sep=.3em];
  \node (origin) at (0,0) {};
  \node (exchange) [def,above=of origin,draw]{Exchange};
  \node (customer) [def, draw, below left=of origin] {Customer};
  \node (merchant) [def, draw, below right=of origin] {Merchant};
  \node (auditor) [def, draw, above right=of origin]{Auditor};
 % \node (regulator) [def, draw, above=of auditor]{CSSF};
 
  \tikzstyle{C} = [color=black, line width=1pt]
 
  \draw [<-, C] (customer) -- (exchange) node [midway, above, sloped] (TextNode) {withdraw coins};
  \draw [<-, C] (exchange) -- (merchant) node [midway, above, sloped] (TextNode) {deposit coins};
  \draw [<-, C] (merchant) -- (customer) node [midway, above, sloped] (TextNode) {spend coins};
  \draw [<-, C] (exchange) -- (auditor) node [midway, above, sloped] (TextNode) {verify};
 % \draw [<-, C] (regulator) -- (auditor) node [midway, above, sloped] (TextNode) {report};
 
 \end{tikzpicture}
 \end{center}
 \end{frame}
 
 
 
 \begin{frame}
 \frametitle{Architecture of Taler}
 \begin{center}
   \includegraphics[width=0.8\textwidth]{operations.png}
 \end{center}
 \end{frame}
 
 
 \begin{frame}{Consumer Impact of Taler}
 \begin{itemize}
 \item {\bf Convenient:} pay with one click instantly --– in Euro,
 Dollar, Yen or Bitcoin
 \item {\bf Friction-free security:} Payments do not require sign-up,
 login or multi-factor authentication
 \item {\bf Privacy-preserving:} payment requires/shares no personal information
 \item {\bf Bank account:} not required
 \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Merchant Impact of Taler}
 \begin{itemize}
 \item {\bf Instant clearance:} one-click transactions and instant clearance at par
 \item {\bf Easy \& compliant:} GDPR \& PCI-DSS compliance-free and without any effort
 \item {\bf Major profit increase:} efficient protocol $+$ no fraud $=$ extremely low costs
 \item {\bf 1-click checkout:} without Amazon and without false positives in fraud detection
 \end{itemize}
 \end{frame}
 
 
 
 \section{Protocol Basics}
 
 
 %\begin{frame}[plain]
 %   \begin{tikzpicture}[remember picture,overlay]
 %     \node[anchor=south west, inner sep=0pt] at (current page.south west) {%
 %       \movie[height = \paperheight, width = \paperwidth, poster, showcontrols] {BFH Bachelor's thesis video}{cs-movie.mp4}%
 %     };
 %   \end{tikzpicture}
 %\end{frame}
 
 
 \begin{frame}{How does it work?}
 We use a few ancient constructions:
   \begin{itemize}
   \item Cryptographic hash function (1989)
   \item Blind signature (1983)
   \item Schnorr signature (1989)
   \item \sout{Diffie-Hellman key exchange (1976)} Deterministic signatures (1977) % 1977: RSA, 2008: EdDSA
   \item Cut-and-choose zero-knowledge proof (1985)
   \end{itemize}
 But of course we use modern instantiations.
 \end{frame}
 
 
 \begin{frame}{Definition: Taxability}
   We say Taler is taxable because:
   \begin{itemize}
   \item Merchant's income is visible from deposits.
   \item Hash of contract is part of deposit data.
   \item State can trace income and enforce taxation.
   \end{itemize}%\pause
   Limitations:
   \begin{itemize}
   \item withdraw loophole
   \item {\em sharing} coins among family and friends
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Exchange setup: Create a denomination key (RSA)}
    \begin{minipage}{6cm}
     \begin{enumerate}
     \item Generate random primes $p,q$.
     \item Compute $n := pq$, $\phi(n) = (p-1)(q-1)$
     \item Pick small $e < \phi(n)$ such that
           $d := e^{-1} \mod \phi(n)$ exists.
     \item Publish public key $(e,n)$.
     \end{enumerate}
   \end{minipage}
   \begin{minipage}{6cm}
   \begin{tikzpicture}
  \tikzstyle{def} = [node distance=1em and 1em, inner sep=0em, outer sep=.3em];
     \node (origin) at (0,0) {\includegraphics[width=0.2\textwidth]{dice.pdf}};
     \node (primes) [draw=none, below = of origin] at (0,0) {$(p, q)$};
     \node (seal) [def, draw=none, below left=of primes]{\includegraphics[width=0.15\textwidth]{seal.pdf}};
     \node (hammer) [def, draw=none, below right=of primes]{\includegraphics[width=0.15\textwidth]{hammer.pdf}};
 
     \tikzstyle{C} = [color=black, line width=1pt]
 
     \draw [<-, C] (primes) -- (origin) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (seal) -- (primes) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (hammer) -- (primes) node [midway, above, sloped] (TextNode) {};
   \end{tikzpicture}
 %  \includegraphics[width=0.4\textwidth]{seal.pdf}
   \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Merchant: Create a signing key (EdDSA)}
   \begin{minipage}{6cm}
     \begin{itemize}
   \item Generate random number $m \mod o$ as private key
   \item Compute public key $M := mG$
   \end{itemize}
   \end{minipage}
   \begin{minipage}{6cm}
   \begin{tikzpicture}
    \tikzstyle{def} = [node distance= 1em and 1em, inner sep=0em, outer sep=.3em];
     \node (origin) at (0,0) {\includegraphics[width=0.2\textwidth]{dice.pdf}};
     \node (m) [draw=none, below = of origin] at (0,0) {$m$};
     \node (seal) [draw=none, below=of m]{M};
    \tikzstyle{C} = [color=black, line width=1pt]
 
     \draw [<-, C] (m) -- (origin) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (seal) -- (primes) node [midway, above, sloped] (TextNode) {};
   \end{tikzpicture}
   \end{minipage}
   \parbox[t]{3cm}{{\bf Capability:} $m \Rightarrow$ }
   \raisebox{\dimexpr-\height+\baselineskip}{\includegraphics[width=0.1\textwidth]{merchant-sign.pdf}}
 \end{frame}
 
 
 \begin{frame}{Customer: Create a planchet (EdDSA)}
   \begin{minipage}{8cm}
   \begin{itemize}
   \item Generate random number $c \mod o$ as private key
   \item Compute public key $C := cG$
   \end{itemize}
   \end{minipage}
   \begin{minipage}{4cm}
   \begin{tikzpicture}
    \tikzstyle{def} = [node distance= 1em and 1em, inner sep=0em, outer sep=.3em];
     \node (origin) at (0,0) {\includegraphics[width=0.2\textwidth]{dice.pdf}};
     \node (c) [draw=none, below = of origin] at (0,0) {$c$};
     \node (planchet) [draw=none, below=of c]{\includegraphics[width=0.4\textwidth]{planchet.pdf}};
     \tikzstyle{C} = [color=black, line width=1pt]
 
     \draw [<-, C] (c) -- (origin) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (planchet) -- (c) node [midway, above, sloped] (TextNode) {};
   \end{tikzpicture}
   \end{minipage}
   \parbox[t]{3cm}{{\bf Capability:} $c \Rightarrow$ }
   \raisebox{\dimexpr-\height+\baselineskip}{\includegraphics[width=0.1\textwidth]{planchet-sign.pdf}}
 \end{frame}
 
 
 \begin{frame}{Customer: Blind planchet (RSA)}
   \begin{minipage}{6cm}
     \begin{enumerate}
     \item Obtain public key $(e,n)$
     \item Compute $f := FDH(C)$, $f < n$.
     \item Generate random blinding factor $b \in \mathbb Z_n$
     \item Transmit $f' := f b^e \mod n$
     \end{enumerate}
   \end{minipage}
   \begin{minipage}{6cm}
   \begin{tikzpicture}
    \tikzstyle{def} = [node distance= 2em and 0.5em, inner sep=0em, outer sep=.3em];
     \node (origin) at (0,0) {\includegraphics[width=0.2\textwidth]{dice.pdf}};
     \node (b) [def, draw=none, below = of origin] at (0,-0.2) {$b$};
     \node (blinded) [def, draw=none, below right=of b]{\includegraphics[width=0.2\textwidth]{blinded.pdf}};
     \node (planchet) [def, draw=none, above right=of blinded]{\includegraphics[width=0.15\textwidth]{planchet.pdf}};
     \node (exchange) [node distance=4em and 0.5em, draw, below =of blinded]{Exchange};
     \tikzstyle{C} = [color=black, line width=1pt]
 
     \draw [<-, C] (b) -- (origin) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (blinded) -- (planchet) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (blinded) -- (b) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (exchange) -- (blinded) node [midway, above, sloped] (TextNode) {{\small transmit}};
   \end{tikzpicture}
   \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Exchange: Blind sign (RSA)}
    \begin{minipage}{6cm}
     \begin{enumerate}
     \item Receive $f'$.
     \item Compute $s' := f'^d \mod n$.
     \item Send signature $s'$.
     \end{enumerate}
    \end{minipage}
   \begin{minipage}{6cm}
   \begin{tikzpicture}
    \tikzstyle{def} = [node distance= 2em and 0.5em, inner sep=0em, outer sep=.3em];
     \node (hammer) [def, draw=none] at (0,0) {\includegraphics[width=0.15\textwidth]{hammer.pdf}};
     \node (signed) [def, draw=none, below left=of hammer]{\includegraphics[width=0.2\textwidth]{sign.pdf}};
     \node (blinded) [def, draw=none, above left=of signed]{\includegraphics[width=0.15\textwidth]{blinded.pdf}};
     \node (customer) [node distance=4em and 0.5em, draw, below =of signed]{Customer};
     \tikzstyle{C} = [color=black, line width=1pt]
 
     \draw [<-, C] (signed) -- (hammer) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (signed) -- (blinded) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (customer) -- (signed) node [midway, above, sloped] (TextNode) {{\small transmit}};
   \end{tikzpicture}
   \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Customer: Unblind coin (RSA)}
   \begin{minipage}{6cm}
    \begin{enumerate}
     \item Receive $s'$.
     \item Compute $s := s' b^{-1} \mod n$ % \\
     % ($(f')^d = (f b^e)^d = f^d b$).
     \end{enumerate}
    \end{minipage}
   \begin{minipage}{6cm}
   \begin{tikzpicture}
    \tikzstyle{def} = [node distance= 2em and 0.5em, inner sep=0em, outer sep=.3em];
     \node (b) [def, draw=none] at (0,0) {$b$};
     \node (coin) [def, draw=none, below left=of b]{\includegraphics[width=0.2\textwidth]{coin.pdf}};
     \node (signed) [def, draw=none, above left=of coin]{\includegraphics[width=0.15\textwidth]{sign.pdf}};
     \tikzstyle{C} = [color=black, line width=1pt]
 
     \draw [<-, C] (coin) -- (b) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (coin) -- (signed) node [midway, above, sloped] (TextNode) {};
   \end{tikzpicture}
   \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Customer: Build shopping cart}
   \begin{center}
   \begin{tikzpicture}
    \tikzstyle{def} = [node distance= 1em and 1em, inner sep=0em, outer sep=.3em];
     \node (origin) [draw=none] at (0,0) {\includegraphics[width=0.15\textwidth]{cart.pdf}};
     \node (merchant) [node distance=4em and 0.5em, draw, below =of origin]{\includegraphics[width=0.15\textwidth]{shop.pdf}};
     \tikzstyle{C} = [color=black, line width=1pt];
     \draw [<-, C] (merchant) -- (origin) node [midway, right] (TextNode) {{\small transmit}};
   \end{tikzpicture}
   \end{center}
 \end{frame}
 
 
 \begin{frame}{Merchant: Propose contract (EdDSA)}
    \begin{minipage}{6cm}
    \begin{enumerate}
     \item Complete proposal $D$.
     \item Send $D$, $EdDSA_m(D)$
     \end{enumerate}
    \end{minipage}
   \begin{minipage}{6cm}
   \begin{tikzpicture}
    \tikzstyle{def} = [node distance=2em and 0.5em, inner sep=0em, outer sep=.3em];
     \node (cart) [def, draw=none] at (0,0) {\includegraphics[width=0.15\textwidth]{cart.pdf}};
     \node (proposal) [def, draw=none, below right=of cart]{\includegraphics[width=0.3\textwidth]{merchant_propose.pdf}};
     \node (customer) [node distance=4em and 0.5em, draw, below =of proposal]{Customer};
     \tikzstyle{C} = [color=black, line width=1pt];
     \node (sign) [def, draw=none, above right=of proposal] {$m$};
     \tikzstyle{C} = [color=black, line width=1pt]
 
     \draw [<-, C] (proposal) -- (sign) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (proposal) -- (cart) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (customer) -- (proposal) node [midway, right] (TextNode) {{\small transmit}};
   \end{tikzpicture}
   \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Customer: Spend coin (EdDSA)}
   \begin{minipage}{6cm}
    \begin{enumerate}
     \item Receive proposal $D$, $EdDSA_m(D)$.
     \item Send $s$, $C$, $EdDSA_c(D)$
     \end{enumerate}
    \end{minipage}
   \begin{minipage}{6cm}
   \begin{tikzpicture}
    \tikzstyle{def} = [node distance=1.5em and 0.4em, inner sep=0em, outer sep=.3em];
     \node (proposal) [def, draw=none] at (0,0) {\includegraphics[width=0.15\textwidth]{merchant_propose.pdf}};
     \node (contract) [def, draw=none, below right=of cart]{\includegraphics[width=0.3\textwidth]{contract.pdf}};
     \node (c) [def, draw=none, above=of contract] {$c$};
     \node (merchant) [node distance=4em and 0.5em, draw, below=of contract]{Merchant};
     \node (coin) [def, draw=none, right=of contract]{\includegraphics[width=0.2\textwidth]{coin.pdf}};
     \tikzstyle{C} = [color=black, line width=1pt]
 
     \draw [<-, C] (contract) -- (c) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (contract) -- (proposal) node [midway, above, sloped] (TextNode) {};
     \draw [<-, C] (merchant) -- (contract) node [midway, above, sloped] (TextNode) {{\small transmit}};
     \draw [<-, C] (merchant) -- (coin) node [midway, right] (TextNode) {{\small transmit}};
   \end{tikzpicture}
   \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Merchant and Exchange: Verify coin (RSA)}
    \begin{minipage}{6cm}
  \begin{equation*}
    s^e \stackrel{?}{\equiv} FDH(C) \mod n
    \end{equation*}
    \end{minipage}
   \begin{minipage}{6cm}
   \begin{minipage}{0.2\textwidth}
     \includegraphics[width=\textwidth]{coin.pdf}
   \end{minipage}
   $\stackrel{?}{\Leftrightarrow}$
   \begin{minipage}{0.2\textwidth}
     \includegraphics[width=\textwidth]{seal.pdf}
   \end{minipage}
   \end{minipage}
   \vfill
   The exchange does not only verify the signature, but also
   checks that the coin was not double-spent.
   \vfill
   %\pause
   \begin{center}
   {\bf Taler is an online payment system.}
   \end{center}
   \vfill
 \end{frame}
 
 
 \begin{frame}
   \frametitle{Blind Signature implementations}
   \begin{block}{RSA}
     \begin{itemize}
     \item Chaum e-cash
     \end{itemize}
   \end{block}
   \begin{block}{Eliptic curves}
     \begin{itemize}
     \item Clause Schnorr
     \item Shorter
     \end{itemize}
   \end{block}
     \begin{block}{Post quantic cryptography}
     \begin{itemize}
     \item New protocol designed in NGI-Taler
     \item Implementation : work in progress 
     \end{itemize}
   \end{block}
 
 \end{frame}
 
 
 %\input refresh.tex
 
 
 \section{Component Zoo}
 
 
 \begin{frame}{The Taler Software Ecosystem: Overview}
   \framesubtitle{\url{https://taler.net/en/docs.html}}
   Taler is based on modular components that work together to provide a
   complete payment system:
   \vfill
   \begin{itemize}
     \item {\bf Exchange:} Service provider for digital cash
       \begin{itemize}
         \item Core exchange software (cryptography, database)
         \item Air-gapped key management, real-time {\bf auditing}
         \item {\bf libeufin}: Modular integration with banking systems
         \item {\bf challenger}: KYC service with OAuth 2.0 API
       \end{itemize}
     \item {\bf Merchant:} Integration service for existing businesses
       \begin{itemize}
         \item Core merchant backend software (cryptography, database)
         \item {\bf Back-office interface} for staff
         \item {\bf Frontend integration} (E-commerce, Point-of-sale)
       \end{itemize}
     \item {\bf Wallet:} Consumer-controlled applications for e-cash
       \begin{itemize}
         \item Multi-platform wallet software (for browsers \& mobile phones)
         \item Wallet backup storage providers ({\bf sync} \& {\bf Anastasis})
       \end{itemize}
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Taler Exchange}
   The {\bf Exchange} is the core logic of the payment system.
 
   \begin{itemize}
     \item One exchange at minimum must be operated per currency
     \item Offers a REST API for merchants and customers
     \item Uses several helper processes for configuration and to
           interact with RTGS and cryptography
     \item KYC support via OAuth 2.0, KycAID or Persona APIs
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Taler Merchant}
   The {\bf Merchant} is the software run by merchants to accept\\
   GNU Taler payments.
 
   \begin{minipage}{6cm}
   \begin{itemize}
     \item REST API for integration with e-commerce
     \item SPA provides Web interface for administration
     \item Features include:
       \begin{itemize}
       \item Multi-tenant support
       \item Refunds
       \item Templates
       \item Webhooks
       \item Inventory management (optional)
       \end{itemize}
   \end{itemize}
   \end{minipage}
   \begin{minipage}{5cm}
   \includegraphics[width=5cm]{screenshots/merchant-spa-settings}
   \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Taler Wallet}
   The {\bf Wallet} is the software run by consumers to store
   their digital cash and authorize transactions.
 
   \begin{minipage}{8cm}
   \begin{itemize}
     \item {\bf wallet-core} is the logic shared by all interfaces
     \item Works on Android, F-Droid, iOS, Ubuntu Touch,
           WebExtension (Chrome, Chromium, Firefox, etc.)
     \item Features include:
       \begin{itemize}
       \item Multi-currency support
       \item Wallet-to-wallet payments (NFC or QR code)
       \item CRDT-like data model
       \end{itemize}
   \end{itemize}
   \end{minipage}
   \begin{minipage}{3cm}
   \includegraphics[width=3cm]{screenshots/Screenshot_20230225-103520.png}
   \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Taler Auditor}
   The {\bf Auditor} is the software run by an independent auditor
   to validate the operation of an Exchange.
 
   \begin{itemize}
     \item REST API for additional report inputs by merchants (optional)
     \item Secure database replication logic
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{libeufin-nexus}
   libeufin-nexus allows Taler components to interact with a core banking system. It:
 
   \begin{itemize}
     \item provides an implementation of the Wire Gateway for the exchange
     \item supports EBICS 2.5 and 3.0
     \item other APIs such as FinTS or PSD2-style XS2A APIs can be added
       without requiring changes to the Exchange
     \item was tested with GLS Bank (DE) and Postfinance (CH) accounts and real EUR/CHF
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{libeufin-bank}
   libeufin-bank implements a standalone bank with a Web interface. It:
 
   \begin{itemize}
     \item provides the Taler Core Bank API for RESTful online banking
        using a Web interface (with multi-factor authentication)
     \item includes a Taler Wire Gateway for the exchange
     \item offers the Taler Bank Integration API to allow wallets
        to easily withdraw digital cash
     \item optionally provides the Taler Conversion Info API for currency
        conversion between fiat and regional currencies
     \item optionally integrates with libeufin-nexus to interact with
        a core banking system
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Challenger}
   Challenger allows clients to obtain validated address (KYC) data about
   users:
 
   \begin{itemize}
     \item Customizable Web-based process for address validation
     \item Can validate phone numbers, e-mail addresses or physical mailing addresses
     \item Provides an exchange-compatible OAuth 2.0 API
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Depolymerization}
   Depolymerization is a bridge between GNU Taler and blockchains,
   making Taler a layer 2 system for crypto-currencies (like Lightning).
 
   \begin{itemize}
     \item provides an implementation of the Wire Gateway for the exchange
     \item Works on top of Bitcoin and Ethereum
           crypto-currencies, with the DLTs as the ``RTGS''
     \item Provides same API to Exchange as libeufin-nexus
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Point-of-Sale App for Android}
 \begin{minipage}{7cm}
   \begin{itemize}
     \item Allows merchant to generate orders against Taler backend
           and display QR code to enable customer to pay in person
     \item Patterned after ViewTouch restaurant UI
   \end{itemize}
 \end{minipage}
 \begin{minipage}{4cm}
   \includegraphics[width=4cm]{screenshots/Screenshot_20230224-194112.jpg}
   \includegraphics[width=4cm]{screenshots/Screenshot_20230224-194119.jpg}
   \includegraphics[width=4cm]{screenshots/Screenshot_20230224-195348.jpg}
 \end{minipage}
 \end{frame}
 
 
 \begin{frame}{Payment plugins}
 \begin{minipage}{5cm}
   \includegraphics[width=4cm]{screenshots/woocommerce-cart.png}
   \includegraphics[width=4cm]{screenshots/pretix.png}
   \end{minipage}
 \begin{minipage}{5cm}
   \begin{itemize}
     \item Pretix, ticket sales system
     \item Joomla!, an e-commerce platform
     \item WooCommerce, an e-commerce solution on top of WordPress
     \item DrupalCommerce, an e-commerce solution on top of Drupal
   \end{itemize}
 \end{minipage}
 \end{frame}
 
 
 
 
 
 
 
 \section{Future Work \& Conclusion}
 
 
 \begin{frame}{Use Case: Journalism}
   Today:
   \begin{itemize}
     \item Corporate structure % ($\Rightarrow$ filter)
     \item Advertising primary revenue % ($\Rightarrow$ dependence)
     \item Tracking readers critical for business success
     \item Journalism and marketing hard to distinguish
   \end{itemize}\vfill%\pause
   With GNU Taler:
   \begin{itemize}
     \item One-click micropayments per article
     \item Hosting requires no expertise % (no PCI DSS)
     \item Reader-funded reporting separated from marketing
     \item Readers can remain anonymous
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Taler: Project Status}
 \framesubtitle{\url{https://docs.taler.net/}}
 \begin{itemize}
     \item Cryptographic protocols and core exchange component are stable
     \item Pilot project at Bern University of Applied Sciences cafeteria
     \item Netzbon (regional currency) in Basel launched
     \item Taler Operations AG live Swiss-wide
     \item Internal alpha deployment with Magnet Bank (Hungary)
     \item Deployment in Germany / Eurozone 2027
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Competitor comparison}
   \begin{center} \small
     \begin{tabular}{l||c|c|c|c|c}
                 & Cash     & Bitcoin    & Zerocoin  & Creditcard & GNU Taler  \\ \hline \hline
     Online      &$-$$-$$-$ &   ++       &    ++     &     +      &   +++      \\ \hline
     Offline     & +++      &   $-$$-$   &    $-$$-$ &     +      &   $+$$+$   \\ \hline
     Trans. cost & +        & $-$$-$$-$  & $-$$-$$-$ &     $-$    &   ++       \\ \hline
     Speed       & +        & $-$$-$$-$  & $-$$-$$-$ &     o      &   ++       \\ \hline
     Taxation    & $-$      &   $-$$-$   & $-$$-$$-$ &    +++     &  +++       \\ \hline
     Payer-anon  &  ++      &   o        &    ++     &  $-$$-$$-$ &  +++       \\ \hline
     Payee-anon  & ++       &   o        &    ++     &  $-$$-$$-$ &  $-$$-$$-$ \\ \hline
     Security    &  $-$     &   o        &    o      &    $-$$-$  &  ++        \\ \hline
     Conversion  & +++      &  $-$$-$$-$ & $-$$-$$-$ &    +++     &  +++       \\ \hline
     Libre       &  $-$     &  +++       &    +++    & $-$ $-$ $-$&  +++       \\
   \end{tabular}
   \end{center}
 \end{frame}
 
 
 \begin{frame}{Other ongoing developments}
   \begin{itemize}
     \item Privacy-preserving auctions (trading, currency exchange) ({\tt oezguer@taler.net})
     \item Hardware and software support for embedded systems ({\tt mikolai@taler.net})
     \item Tax-deductable receipts for donations to charities (donau.git)
     \item Unlinkable anonymous subscriptions and discount tokens ({\tt ivan@taler.net})
     \item Support for illiterate and innumerate users\footnote{Background: \url{https://myoralvillage.org/}}
          ({\tt marc@taler.net})
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{Open Challenges}
   \begin{itemize}
     \item Try to explain this to lawyers and AML staff of banks
     \item What are convincing arguments for citizens to switch?
     \item How to address anti-competitive cash-back from card payments?
     \item $\ldots$
   \end{itemize}
 \end{frame}
 
 
 \begin{frame}{How to support?}
   \begin{description}
     \item[Join:] {\small \url{https://lists.gnu.org/mailman/listinfo/taler}}
     \item[Discuss:] {\small \url{https://ich.taler.net/}}
     \item[Develop:] \url{https://bugs.taler.net/}, \url{https://git.taler.net/}
     \item[Apply:] \url{https://nlnet.nl/propose}, \url{https://nlnet.nl/taler}
     \item[Translate:] \url{https://weblate.taler.net/}, \url{translation-volunteer@taler.net}
     \item[Integrate:] \url{https://docs.taler.net/}
     \item[Donate:] \url{https://gnunet.org/ev}
     \item[Partner:] \url{https://taler-systems.com/}
   \end{description}
 \end{frame}
 
 \begin{frame}
   \frametitle{Install the Wallet}
   \begin{columns}
     \begin{column}{0.35\textwidth}
       \begin{block}{Google Play Store}
       \end{block}
       \begin{center}
 \includegraphics[width=0.5\textwidth]{./images/google_play_GNU_Taler.jpg}
 \end{center}
 \end{column}
 \begin{column}{0.35\textwidth}
   \begin{block}{Apple Store}    
   \end{block}
       \begin{center}
         \includegraphics[width=0.5\textwidth]{./images/Apple-Store-taler-app.png}
       \end{center}
     \end{column}
 \begin{column}{0.35\textwidth}
   \begin{block}{F-Droid}    
   \end{block}
       \begin{center}
         \includegraphics[width=0.5\textwidth]{./images/QR-Code-f-droid.png}
       \end{center}
 
 \end{column}
 
   \end{columns}
 \end{frame}
 
 
 
 \begin{frame}{Demonstration}
   \vfill
   \begin{center}
     \url{https://demo.taler.net/}
   \end{center}
   \begin{enumerate}
   \item Install browser extension.
   \item Visit the {\tt bank.demo.taler.net} to withdraw coins.
   \item Visit the {\tt shop.demo.taler.net} to spend coins.
   \end{enumerate}
   \vfill
 \end{frame}
 
 \subsection{Pay with Taler}
 \begin{frame}
   \frametitle{Pay with Taler I}
   \begin{columns}
     \begin{column}{0.4\textwidth}
  \begin{block}{Withdraw e-cash}
     \begin{itemize}
     \item Withdraw in the app
     \item Transfer money to the Exchange
     \item Wait until the transfer is finalized
     \end{itemize}
   \end{block}
 
     \end{column}
     \begin{column}{0.5\textwidth}
 \begin{center}
   \includegraphics[width=0.4\textwidth]{./images/screenShot-withdraw.jpeg}
 \end{center}
 \end{column}
 
   \end{columns}
 
 \end{frame}
 
 \begin{frame}
   \frametitle{Pay with Taler II}
   \begin{columns}
     \begin{column}{0.4\textwidth}
   \begin{block}{Scan the QR code presented by the merchand}
     \begin{itemize}
     \item Validate the payment in the app
     \item DONE
     \end{itemize}
   \end{block}
 
     \end{column}
     \begin{column}{0.5\textwidth}
 \begin{center}
   \includegraphics[width=0.4\textwidth]{./images/taler-snack-automat.jpg}
 \end{center}
     \end{column}
 
   \end{columns}
 
 \end{frame}
 
 
 \begin{frame}{Conclusion}
   \begin{center}
     {\bf  What can we do?}
    \end{center}
   \vfill
 \begin{itemize}
  \item{Suffer mass-surveillance enabled by credit card oligopolies with high fees, and}
  \item{Engage in arms race with deliberately unregulatable blockchains}
 % \item{Enjoy the ``benefits'' of cash \\
 %  \hfill  \includegraphics[height=0.3\textheight]{atm-rupee.jpg} \hfill}
 \end{itemize}
 \vfill
 \begin{center}
   {\bf OR}
 \end{center}
 \vfill
 \begin{itemize}
  \item{Establish free software alternative balancing social goals!}
 \end{itemize}
 \vfill
 \end{frame}
 
 
 
 \section*{References}
 \begin{frame}[allowframebreaks]{References}
 \bibliographystyle{plain}
 \bibliography{ref,extra,rfc,biblio-defqa}
 \end{frame}
 
 
 % This should be last...
 \begin{frame}{Acknowledgments}
 
   \begin{minipage}{0.45\textwidth} \ \\
     {\tiny Funded by the European Union (Project 101135475).}
 
     \begin{center}
       \includegraphics[width=0.5\textwidth]{./images/bandera.jpg}
     \end{center}
   \end{minipage}
   \hfill
   \begin{minipage}{0.45\textwidth}
     {\tiny Funded by SERI (HEU-Projekt 101135475-TALER).}
 
     \begin{center}
       \includegraphics[width=0.65\textwidth]{./images/sbfi.jpg}
     \end{center}
   \end{minipage}
 
   \vfill
 
   {\tiny
 
     Views and opinions expressed are however those of the author(s) only
     and do not necessarily reflect those of the European Union. Neither the
     European Union nor the granting authority can be held responsible for
     them.
 
   }
 \end{frame}
 
 
 \end{document}
 
 
 
 \begin{frame}{Future work}
   \begin{itemize}
     \item Performance improvements for RSA in FLOSS crypto libraries
     \item Integrate with e-ID for easier \& cheaper KYC
     \item Buy anonymous pre-paid debit cards on-demand with Taler wallet
     \item Implement PQC across the stack (with cipher agility, where possible with additive security)
   \end{itemize}
 \end{frame}