70 lines
4.9 KiB
TeX
70 lines
4.9 KiB
TeX
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\chapter{Conclusion}
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This section provides a summary of this work, presents the results and gives an outlook on future work.
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\section{Summary}
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In the beginning of the project good knowledge on the current state in research about Blind Schnorr signatures was needed.
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Therefore, various papers were read and then the paper "Blind Schnorr Signatures and Signed ElGamal Encryption in the Algebraic Group Model" \cite{cryptoeprint:2019:877} was chosen as basis for the redesign of the Taler protocols.\\
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The next step was to analyze the current Taler protocols and understand the required properties including \textit{\gls{abort-idempotency}}.\\
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With the gathered knowledge (see chapter \ref{chap:preliminaries}) the Taler protocols were redesigned to support \gls{CSBS} (see chapter \ref{chap:design}).
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These redesigned protocols were then further specified (chapter \ref{chap:spec}) and then implemented (chapter \ref{chap:implement}).
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The implementation includes the main protocols, key management, cryptographic utilities in Taler and the \gls{CSBS} cryptographic routines.\\
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The \gls{CSBS} scheme was analyzed and compared in detail to the RSA Blind Signature scheme (see \ref{chap:disc}).
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\section{Results}
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The thesis provides several results to add support for Schnorr's blind signature in Taler, including:
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\begin{itemize}
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\item Redesigned Taler protocols to support \gls{CSBS}
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\item Implementation of cryptographic routines
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\item Implementation of Taler protocols in Exchange
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\begin{itemize}
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\item Key Management and security module
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\item Cryptographic utilities
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\item Withdraw protocol
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\item Deposit protocol
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\end{itemize}
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\item Comparison and Analysis
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\begin{itemize}
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\item Performance (speed, space, latency \& bandwith)
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\item Security
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\item Scheme Comparison
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\end{itemize}
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\item Fixing a minor security issue in Taler's current protocols
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\end{itemize}
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The code is tested, and those tests are integrated in the existing testing framework.
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Benchmarks are added for the cryptographic routines and the security module.
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\section{Future Work}
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Like in any other project, there is always more that could be done.
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This section provides an outlook on what can be done in future work.
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\begin{itemize}
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\item Implement wallet
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\item Implementing remaining \gls{CSBS} protocols (refresh, tipping protocol, refund etc.)
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\item Implementing merchant
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\item Security audit of CS implementation
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\item Find a solution for withdraw loophole
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\item Evaluating \& implementing \gls{CSBS} on other curves
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\end{itemize}
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There are some remaining protocols to implement, which were out of scope for this thesis.
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To run \gls{CSBS} in production, these protocols have to be implemented too.
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Further, the merchant needs to support \gls{CSBS} too.
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The merchant implementation can be done fast, as the merchant only verifies denomination signatures in most cases. \\
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Currently, the exchange runs both security modules, the \gls{CSBS} and the RSA security modules.
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To reduce unnecessary overhead, this should be changed so that only one security has to be running.
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To run \gls{CSBS} in production a security audit from an external company is recommended (as done for other parts in the exchange, see \cite{codeblau:taler-audit}).
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A security audit should always be made when implementing big changes like these.\\
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As mentioned in the scope section, the optional goal to find and implement a good solution for the withdraw loophole was dropped.
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This was due to the scope shift and because the analysis of the problem showed that finding a good solution needs more research and is a whole project in itself (see \ref{sec:scope} for more information).\\
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Furthermore, \gls{CSBS} could be implemented on other curves.
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For example Curve448 \cite{cryptoeprint:2015:625} could be used, as it provides 224 bits of security, wheras \gls{25519} \cite{bern:curve25519} provides about 128 bits of security.
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Curve secp256k1 could further improve \gls{CSBS} performance.
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While providing support for Curve448 should not be problematic, a potential implementation for secp256k1 needs further analysis (see \cite{bernlange:safecurves} and \cite{bip:schnorr-bitc} for more information).
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\section{Personal Conclusion}
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This thesis includes understanding, analyzing, integrating and implementing a recent academic paper \cite{cryptoeprint:2019:877} containing a modern cryptographic scheme.
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Furthermore, the implementation is done in Taler, an intuitive and modern solution for a social responsible payment system with high ethical standards.
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Although there was a lot of work, we enjoyed working on such a modern and very interesting topic.
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Especially the first successful signature verification and the signature scheme performance benchmarks motivated us to push the implementation and integration into Taler forward.\\
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We are happy to provide an implementation of a modern scheme and making it available as free software.
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