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\begin{document}

\title{AP³\\
Report for Milestone III\\
NGI Pointer}
\author{Özgür Kesim\\
Christan Grothoff\\
Florian Dold\\
Stefan Kügel\\
Emmanuel Benoist\\[\bigskipamount]
\normalsize Mentor: Mirko Ross \href{mailto:m.ross@digital-worx.de}{<m.ross@digital-worx.de>}\\[\medskipamount]
}

\date{October 15, 2022}

\maketitle

\section*{Management summary}
\begin{abstract}
The AP³ project presents here the report for the milestone III for NGI Pointer.
	The deliverables for this milestone are:

\begin{description}
	\item[P2P payments] -- 
	\item[Anonymous auction] -- 
\end{description}
\end{abstract}

\vfill
\hfill {\footnotesize Version: 1.0}

\thispagestyle{empty}
\newpage

\tableofcontents

\newpage

\section{P2P payments}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\newpage
\section{Anonymous auctions}


\subsection{Transscript and Replay for libbrandt}

At the beginning of our project, the most recent implementation of
Brandt-Vickrey auctions was from Markus Teich
(\url{https://git.gnunet.org/libbrandt.git/}).  In our own fork at
\url{https://git.kesim.org/oec/libbrandt}, we added the following functionality:

\begin{description}
	\item[Transscript generation] The unit-test file 
		\href{https://git.kesim.org/oec/libbrandt/src/branch/transcript/test\_brandt.c}{test\_brandt.c}
		has been extended to generate and print a transscript for each
		auction, containing parameters of the auction---such as number
		of bidders, prices and auction type---and the list of all
		messages that the seller has received during the protocol
		execution.

		The definition of the transcript structure is given in appendix
		\ref{transcript}.

	\item[Replay of transscript] The new file 
		\href{https://git.kesim.org/oec/libbrandt/src/branch/transcript/replay.c}{replay.c}
		reads a transcript from stdin, parses it and executes an
		auction, replaying all messages from the transcript.

		On success, it prints a result in JSON form to stdout:

		\begin{lstlisting}[language=typescript]
interface BrandtVickreyAuctionWinner {
  // The index of the bidder into the
  // `BrandtVickreyAuctionTranscript`.bidder array.
  bidder: number;

  // The index of the winning price into the
  // `BrandtVickreyAuction`.prices array.
  price_idx: number;

  // The winning price
  price: Amount;
}
		\end{lstlisting}

\end{description}

\subsection{Policy extensions framework for GNUN Taler}

General policy extension framework

\subsection{Brandt-Vickrey-auction extension for GNU Taler}

Extension \verb|policy_brandt_vickrey_auction| added

\begin{itemize}
	\item \verb|get_policy_details| generates hash-code for
		a policy by building the hash $H(h_a || p_b)$,
		where $h_a$ is the hash of the auction meta
		data and $p_b$ is the public key of the bidder.
		Both parameters are part of the policy
		structure provided during a deposit.
	\item the POST-handler receives the transcript and the
		list of policy-details of former
		deposit-operations.  It parses the transcript
		and calls an external program to replay the
		auction and determine the winners and winning
		price.
\end{itemize}

\subsection{Future work}

\subsubsection{libbrandt}

use libsodium

make it compatible with current version of GNUNET

\subsubsection{policy framework}

add escrow policy and merge refund to it

\subsubsection{brandt-vickrey-auction}

verify signatures of transscript


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\newpage
\part*{Appendix}
\addcontentsline{toc}{part}{Appendix}
\appendix

\section{Definition of a Transcript of Brandt-Vickrey-Auctions}
\label{transcript}

The following definition is provided in TypeScript and taken from 
\url{https://docs.taler.net/core/api-exchange.html#tsref-type-BrandtVickreyAuction}.

\begin{lstlisting}[language=typescript]
// This structure defines an auction of Brandt-Vickory kind.
// It is used for the PolicyBrandtVickreyAuction.
interface BrandtVickreyAuction {
  // Start date of the auction
  time_start: Timestamp;

  // Maximum duration per round.  There are four rounds in an auction of
  // Brandt-Vickrey kind.
  time_round: RelativeTime;

  // This integer m refers to the (m+1)-type of the Brandt-Vickrey-auction.
  // - Type 0 refers to an auction with one highest-price winner,
  // - Type 1 refers to an auction with one winner, paying the second
  //   highest price,
  // - Type 2 refers to an auction with two winners, paying
  //   the third-highest price,
  // - etc.
  auction_type: number;

  // The vector of prices for the Brandt-Vickrey auction.  The values MUST
  // be in strictly increasing order.
  prices: Amount[];

  // The type of outcome of the auction.
  // In case the auction is declared public, each bidder can calculate the
  // winning price.  This field is not relevant for the replay of a
  // transcript, as the transcript must be provided by the seller who sees
  // the winner(s) and winning price of the auction.
  outcome_public: boolean;

  // The public key of the seller.
  pubkey: EddsaPublicKey;

  // The seller's account details.
  payto_uri: string;
}

// This structure defines the transcript of an auction
// of Brandt-Vickrey kind.
interface BrandtVickreyAuctionTranscript {
  // The auction definition.
  auction: BrandtVickreyAuction;

  // The public keys of the bidders, in Crockford Base32 encoding.
  bidders: EddsaPublicKey[];

  // Signatures of the auction in Crockford Base32 encoding.
  // One signature per bidder.
  signatures: EddsaSignature[];

  // List of policy hash codes that identify policy details associated with
  // each bidder.  Those codes were generated by the policy extension
  // policy_brandt_vickrey_auction during the deposit of coins for this
  // auction.
  policy_hash_codes: HashCode[];

  // The transcript of all messages received by the seller.
  transcript: BrandtVickreyAuctionMessage[];

  // Optionally, the seller can provide the winners it had calculated.
  winners?: BrandtVickreyAuctionWinner[];

  // The signature over the hash of this JSON object, without the
  // key ``sig`` and in normalized form, basically over
  //   H(auction, bidders, signatures, transcripts, winners?)
  // It is signed by the private key that corresponds to the public key
  // in `BrandtVickreyAuction`.``pubkey``.
  // This signature is in Crockford Base32 encoding.
  sig: EddsaSignature;
}

interface BrandtVickreyAuctionMessage {
  // The index of the bidder into the
  // `BrandtVickreyAuctionTranscript`.``bidders`` array.
  bidder: number;

  // The raw message in Crockford Base32 encoding.
  msg: string;

  // The signature over the message.  The signature is in Crockford Base32
  // encoding.  It must be signed by the private key corresponding to the
  // bidder's public key in `BrandtVickreyAuctionTranscript`.``bidders``.
  sig: EddsaSignature;
}
\end{lstlisting}

\newpage
%\includepdf[pagecommand=\section{Age restriction and Legal Issues}\label{legal},frame=true,pages=1,scale=.9]{Age_restriction_and_legal_issues.pdf}
%\includepdf[pages=2-,scale=.9,frame=true]{Age_restriction_and_legal_issues.pdf}

\end{document}