27 lines
2.6 KiB
TeX
27 lines
2.6 KiB
TeX
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\chapter*{Abstract}
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GNU Taler is an intuitive, fast and socially responsible digital payment system implemented as free software.
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While preserving the customers privacy, GNU Taler is still compliant to regulations.
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The goal of this thesis is to improve Taler's performance and provide cipher agility by adding support for Schnorr's blind signatures.
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To achieve this goal, the current state in research for Schnorr signatures needs to be analyzed.
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After choosing a signature scheme, it has to be integrated into the Taler protocols.
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Besides implementing the redesigned protocols in Taler, an implementation of the cryptographic routines is needed.
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The paper "Blind Schnorr
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Signatures and Signed ElGamal Encryption in the Algebraic Group Model" \cite{cryptoeprint:2019:877} from 2019 (updated in 2021) introducing \gls{CSBS} is used as theoretical basis for our improvements.
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The paper explains why simple Blind Schnorr Signatures are broken and how the Clause Schnorr Blind Signature scheme is secured against this attack.\\
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Compared to the currently used \gls{RSABS}, the new scheme has an additional request, two blinding factors instead of one and many calculations are done twice to prevent attacks.
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The Taler protocols were redesigned to support the Clause Blind Schnorr Signature scheme, including slight alterations to ensure \textit{abort-idempotency}, and then further specified.
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Before starting with the implementation of the redesigned protocols, the cryptographic routines for \gls{CSBS} were implemented as part of the thesis. \\
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All of the implemented code is tested and benchmarks are added for the cryptographic routines.
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Multiple results were achieved during this thesis:
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The redesigned protocols Taler protocols with support for \gls{CSBS}, the implementation of the cryptographic routines, the implementation of Talers core protocols and a detailed comparison between \gls{RSABS} and \gls{CSBS}.
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Overall, the \gls{CSBS} are significantly faster, require less disk space, and bandwidth and provide \textit{cipher agility} for Taler.
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\section*{Acknowledgement}
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We would like to kindly thank Christian Grothoff (Bern University of Applied Sciences) for his extensive advice, support and very helpful feedback during our whole thesis.\\
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We also kindly thank Jeffrey Burdges (Web 3, Switzerland) for reviewing the proposal containing the redesigned protocols and giving feedback.\\
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Further, we kindly thank Jacob Appelbaum (Bern University of Applied Sciences, Eindhoven University of Technology) for further results for the performance measurements of our cryptographic routines and the insightful conversations.
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