143 lines
3.8 KiB
TeX
143 lines
3.8 KiB
TeX
\documentclass[a4paper]{article}
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\usepackage[english]{babel}
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\usepackage{amsmath,amssymb,amsthm}
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\usepackage{color}
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\newcommand{\TODO}{\textcolor{red}{TO DO}}
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\begin{document}
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\begin{center}
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\textbf{\Large NWI-IMC061 -- Applied Cryptography}\\[4pt]
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\textbf{\large Final Exam, Academic Year 2021--2022}
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\end{center}
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\bigskip
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\hrule
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\bigskip
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\noindent \textbf{Last Name:} Eidelpes
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\medskip\noindent \textbf{First Name:} Tobias
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\medskip\noindent \textbf{Student Number:} s1090746
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\medskip\noindent \textbf{Personalized Appendix Sequence Number:} 30
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\bigskip
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\hrule
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\bigskip
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\begin{enumerate}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%% SYMMETRIC - LITERATURE %%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\item \textbf{(18 points)}
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\begin{enumerate}
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\item EWCDM stands for \emph{Encrypted Wegman-Carter with Davies-Meyer}. As
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the name implies, EWCDM is based on a Wegman-Carter construction which
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takes the hash of a message $M$ and XORes it with the application of a
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pseudorandom function (PRF) to a nonce $N$. This construction is very
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efficient and also has a strong security bound. However, it is very
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vulnerable to \emph{nonce-misuse}. To deal with that problem, the
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Wegman-Carter construction is wrapped by another call to the PRF with a
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different key. Another disadvantage is the fact that PRFs are hard to get
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by and instead pseudorandom permutations are used. If a pseudorandom
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permutation (i.e. block cipher) is used, the security bound of the
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construction drops to the birthday bound ($2^{n/2}$). The authors replace
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the inner call to the PRF with the \emph{Davies-Meyer} construction
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\[ \mathrm{DM}[E]_K(N) = E_K(N)\oplus N \]
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and then encrypt that (with the hashed message) in another call to the
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block cipher. The resulting EWCDM construction looks like this
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\[ E_{K'}(E_K(N)\oplus N\oplus H_{K_h}(M)) \]
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and is secure \emph{beyond} the birthday bound against nonce-respecting
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adversaries while still offering birthday bound security against
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nonce-misusing adversaries.
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\item The type of symmetric cryptographic scheme introduced is a Message
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Authentication Code (MAC).
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\end{enumerate}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%% SYMMETRIC - KEYED %%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\item \textbf{(16 points)}
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\begin{enumerate}
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\item \TODO
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\end{enumerate}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%% SYMMETRIC - UNKEYED %%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\item \textbf{(16 points)}
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\begin{enumerate}
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\end{enumerate}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%% ASYMMETRIC - LITERATURE %%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\item \textbf{(17 points)}
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\begin{enumerate}
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\end{enumerate}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%% ASYMMETRIC - SECURITY %%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\item \textbf{(33 points)}
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\begin{enumerate}
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\end{enumerate}
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\end{enumerate}
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\end{document}
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