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6
articles/ui/ui.bib
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@ -11,6 +11,12 @@
@Unpublished{talercrypto,
author = {Florian Dold and Sree Harsha Totakura and Benedikt M\"uller and Jeff Burdges and Christian Grothoff},
title = {Taler: Taxable Anonymous Libre Electronic Reserves}},
note = {\url{http://grothoff.org/christian/taler-draft.pdf}},
}
@techreport{dominguez1993,
title = "Does Central Bank Intervention Increase the Volatility of Foreign Exchange Rates?",
author = "Kathryn M. Dominguez",

110
articles/ui/ui.tex
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@ -20,7 +20,7 @@
\date{}
\begin{document}
\title{Taler: Usable, privacy-preserving payments for the Web}
\title{GNU Taler: Usable, privacy-preserving payments for the Web}
% Not sure how to do authors with the
@ -36,17 +36,18 @@ Marcello Stanisci}
\maketitle
\begin{abstract}
Taler is a new electronic online payment system which provides
anonymity for customers and, due to this design choice, also offers
significantly better usability. This paper first describes the interaction
processes of online payment systems, and analytically compares their
usability for both customers and merchants. We then focus on the
resulting assurances that Taler provides, as---particularly for payment
systems---usability and security are intertwined. Web payment systems
must also face the reality of constraints imposed by modern Web
browser security architecture, so the analysis includes considerations of
how Web payment systems exploit the security infrastructure provided
by the modern Web.
GNU Taler is a new electronic online payment system which provides
anonymity for customers and accountability for merchants. This paper
first describes the interaction processes of online payment systems,
and analytically compares their usability for both customers and
merchants. We then focus on the resulting assurances that Taler
provides, as---particularly for payment systems---usability and
security are intertwined. Web payment systems must also face the
reality of constraints imposed by modern Web browser security
architecture, so the analysis includes considerations of how Web
payment systems exploit the security infrastructure provided by the
modern Web. We argue that the resulting system offers a good
combination of accountability, privacy, security and usability.
\end{abstract}
\section{Introduction}
@ -59,7 +60,7 @@ has been critical as state institutions can dampen fluctuations in the
value of the currency.~\cite{dominguez1993} Controlling money supply
is critical to ensure stable prices that facilitate
trade~\cite{quantitytheory1997volckart} instead of speculation~\cite{lewis_btc_is_junk}.
As Internet transactions, such as sending an e-mail or reading
As Internet transactions, such as sending an e-mail or reading
a Web site, tend to be of smaller value than traditional transactions
involving the exchange of physical goods, we are faced with the
challenge of reducing the mental and technical overheads of existing
@ -72,27 +73,28 @@ state hastens our society's regression towards
post-democracy~\cite{rms2013democracy}.
The focus of this paper is Taler, a new free software payment
system designed to meet certain key ethical considerations. In Taler,
the customer remains anonymous while the merchant is taxable. Here,
anonymous simply means that the payment system does not require
The focus of this paper is GNU Taler, a new free software payment
system designed to meet certain key ethical considerations from a
social liberalism perspective. In Taler, the paying customer remains
anonymous while the merchant is easily identified and thus taxable.
Here, anonymous simply means that the payment system does not require
any personal information from the customer, and that different
transactions by the same customer are unlinkable. Naturally, the
specifics of the transaction---such as delivery of goods to a shipping
address, or the use of non-anonymous IP-based communication---may
still leak information about the customer's identity. {\em Taxable}
means that the state can obtain the necessary information about the
contract to levy income, sales, or value-added taxes. Taler uses blind
signatures~\cite{chaum1983blind} to create digital coins, and a new
{\em refresh} protocol to allow giving change and refunds while
maintaining unlinkability.
contract to levy income, sales, or value-added taxes. Taler uses
blind signatures~\cite{chaum1983blind} to create digital coins, and a
new {\em refresh} protocol~\cite{talercrypto} to allow giving change
and refunds while maintaining unlinkability.
This paper will not consider the details of Taler's cryptographic
protocols\footnote{Details of the protocol are documented
at \url{https://api.taler.net/}} and instead focuses on how a modern
payment system using blind signatures could practically be integrated
with the modern Web. This includes the challenge of hiding the
cryptography from the users. Our goal is to show that existing {\em
cryptography from the users. We also illustrate how existing {\em
mental models} users have from existing widespread payment systems
apply naturally to Taler.
@ -117,11 +119,9 @@ Key contributions of this paper are:
Before we look at the payment workflow for Taler, we sketch the
workflow of existing payment systems. This establishes a common
terminology which we will use to compare different payment processes,
and crucially also provide an indication as to how we can relate
Taler's workflow to existing {\em mental models} that users already
have. Detailed interaction diagrams for some of the payment systems
discussed here can be found in the Appendix.
terminology which we will use to compare different payment processes.
We include interaction diagrams for some of the payment systems
based on resources from the W3c Web Payments Interest Group.
\subsection{Cash}
@ -170,6 +170,14 @@ bank.
% \smallskip
\subsection{Credit and debit cards}
\begin{figure*}[h!]
\begin{center}
\includegraphics[width=0.95\textwidth]{figs/cc3ds.pdf}
\end{center}
\caption{Card payment processing with 3DS. (From: W3c Web Payments IG.)}
\label{fig:cc3ds}
\end{figure*}
Credit and debit card payments operate by the customer providing their
credentials to the merchant. Many different
authentication and authorization schemes are in use in various
@ -188,9 +196,9 @@ provided by TLS is at best questionable.}
{(4.)} (optionally) authorizing the transaction via mobile TAN, or
by authenticating against the customer's bank,
often on a Web site that is operated by the payment
processor and {\em not} the customer's bank. Figure~\ref{fig:cc3ds} in the
processor and {\em not} the customer's bank. Figure~\ref{fig:cc3ds}
% FIXME why "..on the Web today using.." and not just "..on the Web using.."
Appendix shows a typical card-based payment process on the Web today using the
shows a typical card-based payment process on the Web today using the
UML style of the W3c payment interest group~\cite{pigs}. Most of the details
are not relevant to this paper, but the diagram nicely illustrates the
complexity of the common 3-D secure (3DS) process.
@ -248,6 +256,13 @@ their online shopping~\cite[p. 50]{ibi2014}.
% \smallskip
\subsection{Bitcoin}
\begin{figure*}[b!]
\includegraphics[width=\textwidth]{figs/bitcoin.pdf}
\caption{Bitcoin payment processing. (From: W3c Web Payments IG.)}
\label{fig:bitcoin}
\end{figure*}
Bitcoin operates by recording all transactions in a pseu\-do\-ny\-mous
public {\em ledger}. A Bitcoin account is identified by its public
key, and the owner must know the corresponding private key to authorize
@ -284,7 +299,7 @@ The wallet application would
then transmit the request to the Bitcoin peer-to-peer overlay network.
The use of an external payment application makes wallet-based payments
significantly less browser-friendly than ordinary card payments, as
illustrated in Figure~\ref{fig:bitcoin} in the Appendix.
illustrated in Figure~\ref{fig:bitcoin}.
Bitcoin payments are only confirmed when they appear in the public
ledger, which is updated at an average frequency of once every 10
@ -312,12 +327,21 @@ There are several examples of Bitcoin's pseudononymity being broken
by investigators~\cite{BTC:Anonymity}. This has resulted in the
development of new protocols with better privacy protections.
\begin{figure*}[b!]
\includegraphics[width=\textwidth]{figs/paypal.pdf}
\caption{Payment processing with Paypal. (From: W3c Web Payments IG.)}
\label{fig:paypal}
\end{figure*}
Zerocoin \cite{miers2013zerocoin} is such an extension of Bitcoin:
It affords protection against linkability of transactions,
but at non-trivial additional computational costs even for
spending coins. This currently makes using Zerocoin unattractive for payments
with mobile devices.
%
Bitcoin's pseudononymity applies equally to both customers and
merchants, which makes Bitcoin amen\-able to tax evasion, money
laundering, and sales of contraband. As a result, anonymity tools
@ -1228,36 +1252,12 @@ e-commerce industry still relies mostly on TLS for security given
that usability, security and privacy can clearly {\em all} be improved
simultaneously using a modern payment protocol.
The following pages include figures with more detailed illustrations
of various payment protocols. They are based on resources from the
W3c Web Payments Interest Group.
Figures~\ref{listing:presence} and~\ref{listing:contract} provide more
detailed sample source code for how merchants might integrate their
systems with Taler.
\begin{figure*}
\begin{center}
\includegraphics[width=0.95\textwidth]{figs/cc3ds.pdf}
\end{center}
\caption{Card payment processing with 3DS. (From: W3c Web Payments IG.)}
\label{fig:cc3ds}
\end{figure*}
\begin{figure*}
\includegraphics[width=\textwidth]{figs/bitcoin.pdf}
\caption{Bitcoin payment processing. (From: W3c Web Payments IG.)}
\label{fig:bitcoin}
\end{figure*}
\begin{figure*}
\includegraphics[width=\textwidth]{figs/paypal.pdf}
\caption{Payment processing with Paypal. (From: W3c Web Payments IG.)}
\label{fig:paypal}
\end{figure*}
% \tinyskip