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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/system/taler/implementation.tex | 106 |
1 files changed, 92 insertions, 14 deletions
diff --git a/doc/system/taler/implementation.tex b/doc/system/taler/implementation.tex index 26bc23fca..4bed97fd1 100644 --- a/doc/system/taler/implementation.tex +++ b/doc/system/taler/implementation.tex @@ -239,6 +239,7 @@ denomination keys to different customers in an attempt to deanonymize them. \subsubsection{Coins and Denominations}\label{sec:implementation:denoms} + Denominations are the RSA public keys used to blindly sign coins of a fixed amount, together with information about their validity and associated fees. The following information is signed by the exchanges master key for every denomination: \begin{itemize} @@ -1005,41 +1006,109 @@ row IDs that were last seen. \subsubsection{The \texttt{taler-helper-auditor-aggregation}} -FIXME: describe! +This tool checks that the exchange properly aggregates +individual deposits into wire transfers +(see Figure~\ref{fig:deposit:states}). The list of invariants checked by this tool thus includes: \begin{itemize} - \item FIXME +\item That the fees charged by the exchange are those + the exchange provided to the auditor earlier, and that the + fee calculations (deposit fee, refund fee, wire fee) + are correct. Refunds are relevant because refunded amounts + are not included in the aggregate balance. +\item The sanity of fees, as fees may not exceed the contribution + of a coin (so the deposit fee cannot be larger than the + deposited value, and the wire fee cannot exceed the + wired amount). Similarly, a coin cannot receive refunds + that exceed the deposited value of the coin, and the + deposit value must not exceed the coin's denomination value. +\item That the start and end dates for the wire + fee structure are sane, that is cover the timeframe without + overlap or gaps. +\item That denomination signatures on the coins are valid + and match denomination keys known to the auditor. +\item That the target account of the outgoing aggregate wire + transfer is well-formed and matches the account specified + in the deposit. +\item That coins that have been claimed in an aggregation have + a supporting history. +\item That coins which should be aggregated are listed in an + aggregation list, and that the timestamps match the + expected dates. \end{itemize} \subsubsection{The \texttt{taler-helper-auditor-coins}} -FIXME: describe! +This helper focuses on checking the history of individual coins (as described +in Figure~\ref{fig:coin:states}), ensuring that the coin is not double-spent +(or over-spent) and that refreshes, refunds and recoups are processed +properly. + +Additionally, this tool includes checks for denomination key abuse by +verifying that the value and number of coins deposited in any denomination +does not exceed the value and number of coins issued in that denomination. + +Finally, the auditor will also complain if the exchange processes +denominations that it did not properly report (with fee structure) to the +auditor. The list of invariants checked by this tool thus includes: \begin{itemize} - \item FIXME +\item emergency on denominations because the value or number + of coins deposited exceeds the value or number of coins + issued; if this happens, the exchange should revoke the + respective denomination. +\item various arithmetic inconsistencies from exchanges + not properly calculating balances or fees during the + various coin operations (withdraw, deposit, melt, refund); +\item signatures being wrong for denomination key revocation, + coin denomination signature, + or coin operations (deposit, melt, refund, recoup) +\item denomination keys not being known to the auditor +\item denomination keys being actually revoked if a recoup + is granted +\item coins being melted but not (yet) recouped + (this can be harmless and no fault of the exchange, but + could also be indicative of an exchange failing to process + certain requests in a timely fashion) \end{itemize} \subsubsection{The \texttt{taler-helper-auditor-deposits}} -FIXME: describe! - -The list of invariants checked by this tool thus includes: -\begin{itemize} - \item FIXME -\end{itemize} - +This tool verifies that the deposit confirmations reported by merchants +directly to the auditor are also included in the database we got from the +exchange. This is to ensure that the exchange cannot defraud merchants by +simply not reporting deposits to the auditor or an +exchange signing key being compromised (as described in +Section~\label{sec:signkey:compromise}). \subsubsection{The \texttt{taler-helper-auditor-reserves}} -FIXME: describe! +This figure checks the exchange's processing of the +balance of an individual reserve, as described +in Figure~\ref{fig:reserve:states}. The list of invariants checked by this tool thus includes: \begin{itemize} - \item FIXME +\item Correctness of the signatures that legitimized + withdraw and recoup operations. +\item Correct calculation of the reserve balance given + the history of operations (incoming wire transfers, + withdraws, recoups and closing operations) + involving the reserve. +\item That the exchange closed reserves when required, + and that the exchange wired the funds back to the + correct (originating) wire account. +\item Knowledge of the auditor of the denomination keys + involved in withdraw operations and of the + applicable closing fee. +\item That denomination keys were valid for use in a + withdraw operation at the reported time of withdrawal. +\item That denomination keys were eligible for recoup + at the time of a recoup. \end{itemize} @@ -1077,7 +1146,16 @@ the wrong wire transfers should be obvious. The list of invariants checked by this tool thus includes: \begin{itemize} - \item FIXME +\item The exchange correctly listing all incoming wire transfers. +\item The bank/Nexus having correctly suppressed incoming wire + transfers with non-unique wire transfer subjects, and having + assigned each wire transfer a unique row ID/offset. +\item The exchange correctly listing all outgoing wire transfers + including having the appropriate justifications (aggregation + or reserve closure) for the respective amounts and target accounts. +\item Wire transfers that the exchange has failed to execute that + were due. Note that small delays here can be normal as + wire transfers may be in flight. \end{itemize} |