Solving Classical Ciphers with CrypTool 2

Nils Kopal
Applied Information Security, University of Kassel, Kassel, Germany

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Ingår i: Proceedings of the 1st International Conference on Historical Cryptology HistoCrypt 2018

Linköping Electronic Conference Proceedings 149:10, s. 29-38

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Publicerad: 2018-06-13

ISBN: 978-91-7685-252-1

ISSN: 1650-3686 (tryckt), 1650-3740 (online)


The difficulty of solving classical ciphers varies between very easy and very hard. For example, monoalphabetic substitution ciphers can be solved easily by hand. More complex ciphers like the polyalphabetic Vigenère cipher, are harder to solve and the solution by hand takes much more time. Machine ciphers like the Enigma rotor machine, are nearly impossible to be solved only by hand. To support researchers, cryptanalysts, and historians analyzing ciphers, the open-source software CrypTool 2 (CT2) was implemented. It contains a broad set of tools and methods to automate the cryptanalysis of different (classical and modern) ciphers. In this paper, we present a step-by-step approach for analyzing classical ciphers and breaking these with the help of the tools in CT2. The primary goals of this paper are: (1) Introduce historians and non-computer scientists to classical encryption, (2) give an introduction to CT2, enabling them to break ciphers by their own, and (3) present our future plans for CT2 with respect to (automatic) cryptanalysis of classical ciphers. This paper does not describe the used analysis methods in detail, but gives the according references.


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