auction done. v1 ready
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@ -311,11 +311,12 @@ content of the mentioned website with recommended concepts of youth protection.
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GNU Taler is going to be evaluated for the category ``holistic youth protection
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GNU Taler is going to be evaluated for the category ``holistic youth protection
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concept''. The KJM uses this category only for concepts that are widely
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concept''. The KJM uses this category only for concepts that are widely
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accessible to the public and do not only serve a closed user group
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accessible to the public and \textit{do not} serve a closed user group. Here,
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(closed user group means: access to content or goods is granted only after age
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\textit{serving a closed user group} means granting access to content or goods
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verification by presenting an official ID card, driving licenses or the
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only after ID-based verification of the membership in a particular group, such
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like---which is endangering privacy, data security, and informational
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as: proof of belonging to a certain age-group by presenting an official ID
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self-determination).
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card, driving licenses or the like---a type of verification which is
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endangering privacy, data security, and informational self-determination.
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\subsection{Future Works}
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\subsection{Future Works}
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@ -569,15 +570,143 @@ locations under \url{https://git.taler.net/wallet-core.git/tree/packages/}
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\newpage
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\newpage
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\section{Brandt-Vickrey Auctions}
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\section{Brandt-Vickrey Auctions}
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\TODO{}
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\href{https://pub.dss.in.tum.de/brandt-research/ijis2006.pdf}{In 2006, Felix
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Brandt} designed cryptographic Vickrey-style auction protocols that only yield
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the winners’ identities and the selling price. Losing bidders learn no
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information at all, except that they lost. This approach does not rely on
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trusted third parties, e.g., auctioneers or---in our case---the payment service
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provider.
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\href{https://grothoff.org/christian/teich2017ms.pdf}{In 2017, Marcus Teich}
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updated the cryptographic primitives in the Brandt-Vickrey protocols to use
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elliptic curves and provided an implementation in
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\url{https://git.gnunet.org/libbrandt.git/}.
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Based on that work, we implemented a Proof-of-Concept for \textsc{NGI Pointer}
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of conditional payments in GNU Taler in the form of sealed-bid auctions of type
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Brandt-Vickrey:
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Bidders put coins in escrow with the exchange in order to participate in a
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particular auction. The coins are locked and can only be unlocked by timeout
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or by winning the auction. After successfully running the Brandt-Vickrey
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auction, the seller has to provide the transcript of all (signed) messages
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received from all bidders. The exchange then replays the transcript and
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determines the winning bidder(s) and price(s) and pays the seller accordingly.
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Non-winning coins and rest amounts can be claimed by the bidders.
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\subsection{Technical details}
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\subsection{Technical details}
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\TODO{}
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We designed and implemented a general framework for conditional payments with
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GNU Taler---so-called \textit{policies}. Our proof-of-concept of sealed-bid
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auction support is implemented as an policy extension to GNU Taler. In
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particular, we implemented the following parts:
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\begin{description}
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\item[Transcript generation:] \texttt{libbrandt} has been extended to
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generate a transcript of the auction including all
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cryptographically signed messages from all bidders in
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JSON-encoding.
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\item[Transcript replay:] An external program to replay a transcript
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has been implemented as part of \texttt{libbrandt}. It
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consumes transcript of an auction in JSON-encoding, generates
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an Brandt-Vickrey-auction and replays all provided messages.
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On success, it returns the winning bidder(s) and price(s)
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according the transcript.
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\item[Policy extension for auctions:] A policy extension for GNU Taler
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has been implemented that handles deposit requests with set
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policy of type \texttt{\small
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policy\_brandt\_vickrey\_auction}. It locks the coins and
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persists the policy details under a hash-code, that it
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generates by calculating the hash $H(h_a || p_b)$, where $h_a$
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is the hash of the auction meta data and $p_b$ is the public
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key of the bidder. Both parameters are part of the policy
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structure provided during a deposit.
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\item[POST handler for auction transcripts:] A POST handler for the
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policy extension of that type has been implemented that expects
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a valid transcript of a Brandt-Vickrey-auction. It uses the
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external program to perform a replay of the auction and
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determine the winning bidder(s) and price(s). Based on the
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outcome information, the exchange unlocks the corresponding
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winning coins' value for transfer to the seller---minus an
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auction fee---and the rest value of all coins for refresh.
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\end{description}
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\subsection{Future Works}
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\subsection{Future Works}
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\TODO{}
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For a fully functional and maintainable solution, further development is needed
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in the following areas:
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\begin{description}
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\item[libbrandt upgrade:] The code base of this library is from 2017 and doesn't
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compile with the latest version of
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\href{https://git.gnunet.org/gnunet.git}{GNUnet}. It also
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uses \href{https://gnupg.org/software/libgcrypt/index.html}%
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{\ttfamily libgcrypt} as cryptographic library, which is quite
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slow compared to its modern alternative
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\href{https://doc.libsodium.org/}{\ttfamily libsodium}, at
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least with respect to the primitives used in libbrandt.
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For future work we plan to refactor libbrandt to use libsodium
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and the current version of GNUnet.
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\item[Brandt-Vickrey-auction continuation:] The current code is a
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proof-of-concept. The following known problem exist:
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\begin{itemize}
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\item Signature verification of the transcript and its messages
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is missing
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\item Unit- and integration-tests with the exchange are missing
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\item A fully featured auction(er) system, including billboard
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and client software, is missing.
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\end{itemize}
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We will address at least the first two issues and plan to
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address the lack of an auction system once we find volunteers
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and funding for it.
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\item[Policy framework continuation:] Based on the current design of policy
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extensions for deposit---aka conditional payments---we plan to add
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following policy extensions to the GNU Taler exchange:
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\begin{itemize}
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\item{\itshape Merchant refunds:} Merchant can grant customers refundable
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payments. Right now, this policy is implicit and optional in
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the usual deposit-flow. Future work on Taler will lift
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this into a policy-extension.
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\item{\itshape Escrowed payments:} A trustor puts coins into escrow
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with the exchange. It can be claimed by a beneficiary until a
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certain deadline, when the claim is signed by
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both, the beneficiary’s and the trustor’s keys.
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\end{itemize}
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\end{description}
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\subsection{Links}
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\subsection{Links}
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\TODO{}
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\begin{description}
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\item[Changes to libbrandt:]
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\href{https://git.kesim.org/oec/libbrandt/src/branch/transcript/test\_brandt.c}{\ttfamily test\_brandt.c}
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has been extended to generate and print a transcript in JSON
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encoding for each auction. The new file
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\href{https://git.kesim.org/oec/libbrandt/src/branch/transcript/replay.c}{\ttfamily
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replay.c} implements a standalone program to replay an auction.
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\item[Changes to the Exchange:]
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The changes to the exchange can be found at\\
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\url{https://git.kesim.org/taler/exchange/src/branch/auction\_brandt/},\\
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in particular:
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\begin{description}
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\item[\href{https://git.kesim.org/taler/exchange/src/branch/auction\_brandt/src/extensions/policy\_brandt\_vickrey\_auction/policy\_brandt\_vickrey\_auction.c\#L767-L821}{\ttfamily auction\_create\_policy\_details}]
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This implements the {\ttfamily create\_policy\_details}
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function of the policy extension interface.
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\item[\href{https://git.kesim.org/taler/exchange/src/branch/auction\_brandt/src/extensions/policy\_brandt\_vickrey\_auction/policy\_brandt\_vickrey\_auction.c\#L694-L764}{\ttfamily auction\_policy\_post\_handler}]
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This implements the {\ttfamily policy\_post\_handler} function
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of the policy extension interface.
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\end{description}
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\end{description}
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\newpage
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\newpage
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