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misc edits based on Neal's comments

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Christian Grothoff 2016-05-15 18:19:02 +02:00
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@ -1106,10 +1106,10 @@ usually only happen if the wallet is unaware of a backup operation
voiding its internal invariants. If a payment fails in-flight due to voiding its internal invariants. If a payment fails in-flight due to
insufficient funds, the wallet can use Taler's refresh protocol to insufficient funds, the wallet can use Taler's refresh protocol to
obtain a refund for those coins that were not actually double-spent, obtain a refund for those coins that were not actually double-spent,
and then explain the user that the balance was inaccurate due to and then explain to the user that the balance was inaccurate due to
inconsistencies from recovery, and overall insufficient for payment. inconsistencies, and insufficient for payment.
For the user, this failure mode appears equivalent to an insufficient For the user, this failure mode appears equivalent to an insufficient
balance or credit line when paying with cards. balance or credit line when paying with debit or credit cards.
\end{itemize} \end{itemize}
\subsection{Comparison} \subsection{Comparison}
@ -1129,7 +1129,7 @@ With Taler, the authentication itself is straightforward, as the customer is
at the time visiting the Web portal of the bank, and the authentication is at the time visiting the Web portal of the bank, and the authentication is
with the bank (Figure~\ref{fig:taler-withdraw}). With PayPal, the with the bank (Figure~\ref{fig:taler-withdraw}). With PayPal, the
shop redirects the customer to the PayPal portal (step 5 in shop redirects the customer to the PayPal portal (step 5 in
Figure~\ref{fig:paypal}) after the user selected PayPal as the payment Figure~\ref{fig:paypal}) after the user selects PayPal as the payment
method. The customer then provides the proof of payment to the method. The customer then provides the proof of payment to the
merchant. Again, this is reasonably natural. The 3DS workflow merchant. Again, this is reasonably natural. The 3DS workflow
(Figure~\ref{fig:cc3ds}) has to deal with a multitude of banks and (Figure~\ref{fig:cc3ds}) has to deal with a multitude of banks and
@ -1155,11 +1155,11 @@ especially given that the digital wallet is likely to only contain a
% he has. % he has.
small fraction of the customer's available funds. As a result, Taler small fraction of the customer's available funds. As a result, Taler
improves usability if the customer is able to withdraw funds once to improves usability if the customer is able to withdraw funds once to
then facilitate many micropayments, while Taler is likely less usable then facilitate many micropayments while Taler is likely less usable
if for each transaction the customer first visits the bank to withdraw if for each transaction the customer first visits the bank to withdraw
funds. This is deliberate, as Taler can only achieve reasonable funds. This is deliberate, as Taler can only achieve reasonable
privacy for customers if they do keep a balance in their wallet, privacy for customers if they keep a balance in their wallet,
thereby breaking the association between withdrawal and deposit. which breaks the association between withdrawal and deposit.
% FIXME the sentence above can be in contrast with how the exchange % FIXME the sentence above can be in contrast with how the exchange
% actually deposits funds to merchants, that is through 'aggregate % actually deposits funds to merchants, that is through 'aggregate
% deposits' that may add unpredictable delays (but that doesn't affect % deposits' that may add unpredictable delays (but that doesn't affect
@ -1168,9 +1168,9 @@ thereby breaking the association between withdrawal and deposit.
Bitcoin's payment process (Figure~\ref{fig:bitcoin}) resembles that of Bitcoin's payment process (Figure~\ref{fig:bitcoin}) resembles that of
Taler in one interesting point, namely that the wallet is given Taler in one interesting point, namely that the wallet is given
details about the contract the user is to enter (steps 7 to 11). details about the contract the user enters (steps 7 to 11).
However, in contrast to Taler, here the Bitcoin wallet(s) are expected However, in contrast to Taler, Bitcoin wallets are expected
to fetch the ``invoice'' from the merchant, while in Taler the browser to fetch the ``invoice'' from the merchant. In Taler, the browser
provides the Taler wallet with the proposed contract directly. In provides the Taler wallet with the proposed contract directly. In
PayPal and 3DS, the user is left without a cryptographically secured PayPal and 3DS, the user is left without a cryptographically secured
receipt. receipt.
@ -1186,14 +1186,14 @@ credentials to the legitimate
auto-completion.} However, relying on users understanding their auto-completion.} However, relying on users understanding their
browser's indications of the security context is inherently browser's indications of the security context is inherently
problematic. Taler addresses this challenge by ensuring that digital problematic. Taler addresses this challenge by ensuring that digital
coins are only accessible from fully wallet-generated pages, hence coins are only accessible from wallet-generated pages. As such
there is no risk of Web pages mimicking the look of the respective there is no risk of Web pages mimicking the look of the respective
page, as they would still not obtain access to the digital coins. page, as they would still not obtain access to the digital coins.
Once the payment process nears its completion, merchants need to have Once the payment process nears its completion, merchants need to have
some assurance that the contract is now valid. In Taler, merchants some assurance that the contract is valid. In Taler, merchants
obtain a non-repudiable confirmation of the payment. With 3DS and obtain a non-repudiable confirmation of the payment. With 3DS and
PayPal, the confirmation may be disputed later (i.e. in case of PayPal, the confirmation may be disputed later (e.g. in case of
fraud), or accounts may be frozen arbitrarily~\cite{diaspora2011}. fraud), or accounts may be frozen arbitrarily~\cite{diaspora2011}.
Payments in cash require the merchant to assume the risk of receiving Payments in cash require the merchant to assume the risk of receiving
counterfeit money. counterfeit money.
@ -1201,7 +1201,7 @@ counterfeit money.
% about maintaining change and depositing the money earned % about maintaining change and depositing the money earned
% CG: No, it's not optional, ``should'' doesn't come into the equation % CG: No, it's not optional, ``should'' doesn't come into the equation
% here. It's a mandatory business expense. % here. It's a mandatory business expense.
Furthermore, merchants have the cost maintaining change and depositing Furthermore, merchants have the cost of maintaining change and depositing
the money earned. With Bitcoin, there is no definitive time until a the money earned. With Bitcoin, there is no definitive time until a
payment can be said to be confirmed (step 19, Figure~\ref{fig:bitcoin}), payment can be said to be confirmed (step 19, Figure~\ref{fig:bitcoin}),
leaving merchants in a bit of a tricky situation. leaving merchants in a bit of a tricky situation.
@ -1210,7 +1210,7 @@ leaving merchants in a bit of a tricky situation.
Customers and merchants should be able to easily adapt their existing Customers and merchants should be able to easily adapt their existing
mental models and technical infrastructure to Taler. In contrast, mental models and technical infrastructure to Taler. In contrast,
Bitcoin's payment models fail to match common expectations, be it in Bitcoin's payment models fail to match common expectations be it in
terms of performance, durability, security, or privacy. Minimizing terms of performance, durability, security, or privacy. Minimizing
the need to authenticate to pay fundamentally improves usability. the need to authenticate to pay fundamentally improves usability.
@ -1227,7 +1227,7 @@ of the Reich of big data corporations.
We encourage readers to try our prototype for Taler We encourage readers to try our prototype for Taler
at \url{https://demo.taler.net/}, and to ponder why the billion dollar at \url{https://demo.taler.net/}, and to ponder why the billion dollar
e-commerce industry still relies mostly on TLS for security, given e-commerce industry still relies mostly on TLS for security given
that usability, security and privacy can clearly {\em all} be improved that usability, security and privacy can clearly {\em all} be improved
simultaneously using a modern payment protocol. simultaneously using a modern payment protocol.