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author | Gian Demarmels <gian@demarmels.org> | 2022-02-14 00:03:06 +0100 |
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committer | Gian Demarmels <gian@demarmels.org> | 2022-02-14 00:03:06 +0100 |
commit | 9e694994681b0b2861553d0a50bca6623b546dd2 (patch) | |
tree | d8ebb10d7707bc5d4e48d09911e217ff9e993ebb /doc/cs/content/1_introduction.tex | |
parent | 9b8c350d4dc38256fe746ef31c480bc4f50ac4c8 (diff) | |
download | exchange-9e694994681b0b2861553d0a50bca6623b546dd2.tar.xz |
CS thesis
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diff --git a/doc/cs/content/1_introduction.tex b/doc/cs/content/1_introduction.tex new file mode 100644 index 000000000..1ed9e0589 --- /dev/null +++ b/doc/cs/content/1_introduction.tex @@ -0,0 +1,72 @@ +\chapter{Introduction} + +\section{Motivation} +Public key cryptography based on elliptic curves allows smaller key sizes compared to other cryptographic systems. +While still providing equivalent security, the smaller key size leads to huge performance benefits. +\\ +Blind Signatures are one of the key components upon which Taler's privacy is built upon. +Our thesis adds support for a modern cryptographic scheme called the Clause Blind Schnorr Signature scheme \cite{cryptoeprint:2019:877}.\\ +Additionally to the benefits of ellicptic curve cryptography, adding a second blind signature scheme makes Taler independent of a single cryptographic scheme and thus provides \textit{cipher agility}. + + +\section{Goals} +\label{sec:goals} +The project definition is as follows \cite{project-definition}: + +The students will implement the blind Schnorr signature inside Taler. +Taler is a system for the management of virtual money. +Taler is based on coins that need to be signed by an exchange (for instance a bank). +In the actual version of the system, coins are signed by the exchange using Schaum's bind-signature protocol. +This allows users to have signed coins, without the exchange knowing what it signed. +This step is fundamental for the privacy protection of the system. +\\The students have to insert the Schnorr blind signature algorithm inside the protocol for the creation of coins. +But they also need to change the Taler subsystems where the verification of the signature is done. +\\The actual Taler system allows people to let an exchange sign a coin for which they do not have the private key. +This is a security issue (for misuse of coins on the dark-net for instance). +An optional task for the project is to prevent a user to let an exchange sign a public key when the client does not have access to the corresponding private key. +\\Here is a list of the tasks that the students must do: +\begin{itemize} + \item Design a protocol integrating Schnorr blind signature in the creation of Taler coins. + \item Implement the protocol inside the exchange application and the wallet app. + \item Analyze the different Taler subsystems to find where the blind signature is verified. + \item Replace verification of the blind signature everywhere it occurs. + \item Compare both blind signature systems (Schaum's and Schnorr's), from the point of view of security, privacy protection, speed, \dots + \item Write tests for the written software. + \item Conduct tests for the written software. + \item Transfer the new software the Taler developers team +\end{itemize} +Here is a list of optional features: +\begin{itemize} + \item Design a protocol, such that the exchange can verify that the user knows the private key corresponding to the coin that is to be signed. + \item Implement that protocol. +\end{itemize} + +\section{Scope} +\label{sec:scope} +In scope are all necessary changes on the protocol(s) and components for the following tasks: +\begin{itemize} + \item Research the current state of Blind Schnorr Signature schemes + \item Redesign the Taler protocols to support Blind Schnorr signatures + \item Add support for a Blind Schnorr Signature Scheme in the exchange, merchant, wallet-core, wallet web-extension and optionally on the android mobile wallet + \item design and implement a protocol where the user proves to the exchange the knowledge of the coin that is to be signed (optional) +\end{itemize} + +Out of scope is production readyness of the implementation. +This is because changes in the protocos and code need to be thoroughly vetted to ensure that no weaknesses or security vulnerabilities were introduced. +Such an audit is out of scope for the thesis and is recommended to be performed in the future. +The iOS wallet will not be considered in this work. +\\ +It is not unusual that a scope changes when a project develops. +Due to different reasons, the scope needed to be shifted. +Since there are no libraries supporting \gls{CSBS}, the signature scheme has to be implemented and tested before integrating it into Taler. +While this is still reasonable to do in this project, it will affect the scope quite a bit. +The analysis of the optional goal showed, that a good solution that aligns with Taler's goals and properties needs more research and is a whole project by itself. + +Scope changes during the project: +\begin{itemize} + \item \textbf{Added:} Implement the cryptographic routines in GNUnet + \item \textbf{Removed: } design and implement a protocol where the user proves to the exchange the knowledge of the coin that is to be signed (optional) + \item \textbf{Adjusted: } Focus is on the implementation of the exchange protocols (Withdraw, Spend, Refresh and cryptographic utilities) + \item \textbf{Adjusted: } Implementation of the refresh protocol and wallet-core are nice-to-have goals + \item \textbf{Removed: } The Merchant and the android wallet implementations are out of scope +\end{itemize}
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