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@Unpublished{talercrypto,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