53 lines
3.1 KiB
TeX
53 lines
3.1 KiB
TeX
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\chapter{Abstract}
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%As our society becomes more and more digitalized, an electronic version of cash
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%becomes inevitable. The design of payment systems is not just a technological
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%matter, but has far-reaching sociopolitical consequences.
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\begin{samepage}
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We describe the design and implementation of GNU Taler, an electronic payment
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system based on an extension of Chaumian online e-cash with efficient change.
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In addition to anonymity for customers, it provides the novel notion of
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\emph{income transparency}, which guarantees that merchants can reliably
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receive a payment from an untrusted payer only when their income from the
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payment is visible to tax authorities.
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Income transparency is achieved by the introduction of a \emph{refresh
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protocol}, which gives anonymous change for a partially spent coin without
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introducing a tax evasion loophole. In addition to income transparency, the
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refresh protocol can be used to implement Camenisch-style \emph{atomic swaps}, and to
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preserve anonymity in the presence of protocol \emph{aborts} and crash faults with
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data loss by participants.
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Furthermore, we show the provable security of our income-transparent anonymous
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e-cash, which, in addition to the usual \emph{anonymity} and
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\emph{unforgeability} properties of e-cash, also formally models
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\emph{conservation} of funds and income transparency.
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Our implementation of GNU Taler is usable by non-expert users and integrates
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with the modern Web architecture. Our payment platform addresses a range of
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practical issues, such as tipping customers, providing refunds, integrating
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with banks and know-your-customer (KYC) checks, as well as Web platform
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security and reliability requirements. On a single machine, we achieve
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transaction rates that rival those of global, commercial credit card
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processors. We increase the robustness of the exchange---the component that
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keeps bank money in escrow in exchange for e-cash---by adding an auditor
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component, which verifies the correct operation of the system and allows to
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detect a compromise or misbehavior of the exchange early.
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Just like bank accounts have reason to exist besides bank notes, e-cash only
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serves as part of a whole payment system stack. Distributed ledgers have
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recently gained immense popularity as potential replacement for parts of the
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traditional financial industry. While cryptocurrencies based on proof-of-work
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such as Bitcoin have yet to scale to be useful as a replacement for established
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payment systems, other more efficient systems based on blockchains with more
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classical consensus algorithms might still have promising applications in the
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financial industry.
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We design, implement and analyze the performance of \emph{Byzantine Set Union
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Consensus} (BSC), a Byzantine consensus protocol that agrees on a (super-)set
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of elements at once, instead of sequentially agreeing on the individual
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elements of a set. While BSC is interesting in itself, it can also be used as
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a building block for permissioned blockchains, where---just like in
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Nakamoto-style consensus---whole blocks of transactions are agreed upon at once,
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increasing the transaction rate.
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\end{samepage}
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