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Diffstat (limited to 'doc/paper')
-rw-r--r-- | doc/paper/taler.tex | 38 |
1 files changed, 25 insertions, 13 deletions
diff --git a/doc/paper/taler.tex b/doc/paper/taler.tex index eb06da588..ea096ba6f 100644 --- a/doc/paper/taler.tex +++ b/doc/paper/taler.tex @@ -1361,16 +1361,16 @@ protocol is never used. \subsection{Exculpability arguments} -\begin{lemma} +\begin{lemma}\label{lemma:double-spending} The exchange can detect and prove double-spending. \end{lemma} \begin{proof} -A coin can only be spent by either running the deposit protocol or the refresh +A coin can only be spent by running the deposit protocol or the refresh protocol with the exchange. Thus every time a coin is spent, the exchange obtains either a deposit-permission or a refresh-record, both of which contain a signature made with the public key of coin to authorizing the -respective operation. If the exchange as a set of refresh-records and +respective operation. If the exchange has a set of refresh-records and deposit-permissions whose total value exceed the value of the coin, the exchange can show this set to prove that a coin was double-spend. \end{proof} @@ -1383,33 +1383,45 @@ that the total value exceeds the coin's value. \begin{lemma} % only holds given sufficient time -Customers can either obtain proof-of-payment or their money back. +Customers can either obtain proof-of-payment or their money back, even +when the merchant is faulty. \end{lemma} \begin{proof} - - +When the customer sends the deposit-permission for a coin +to a correct merchant, the merchant will pass it on to the +exchange, and pass the exchange's response, a deposit-confirmation, on +to the customer. If a faulty merchant deposits the coin +but does not pass the deposit-confirmation to the customer, +the customer will receive the deposit-confirmation as an error +response from the refreshing protocol. Otherwise if the merchant +doesn't deposit the coin, the customer can get a new, unlinkable +coin by running the refresh protocol. \end{proof} -\begin{lemma} -If a customer paid for a contract, they can prove it. -\end{lemma} - -\begin{proof} -\end{proof} +\begin{corollary} +If a customer paid for a contract, they can prove it by showing +the deposit permissions for all coins. +\end{corollary} \begin{lemma} The merchant can issue refunds, and only to the original customer. \end{lemma} \begin{proof} +Since the refund only increases the balance of a coin that the original +customer owns, only the original customer can spend the refunded coin again. \end{proof} - \begin{theorem} The protocol prevents double-spending and provides exculpability. \end{theorem} +\begin{proof} + Follows from Lemma \ref{lemma:double-spending} and the assumption + that the exchange can't forge signatures to obtain an incriminating + set of deposit-permissions and/or refresh-records. +\end{proof} |