Dr. Deyan Mihaylov, Assist. Prof.
University of Economics – Varna
https://doi.org/10.53656/math2022-1-4-kri
Absract. This paper provides implementations of three well-known ciphers –Caesar Cipher, Vigenere Cipher and Hill Cipher in Microsoft Excel. It is shown howthe ciphers can be broken by using Brute-force Attack, Frequency Analysis Attack and Known-plaintext Attack. For the purpose of the cryptanalysis the relative
occurrence frequencies of the letters and the index of coincidence (κ ) in Bulgarian language are determined. The classical Frequency Analysis Attack is modified using
the cross-correlation between frequencies of letters in the natural language and the cipher text. Modular matrix operations in MS Excel are shown.
Keywords: cryptanalysis; MS Excel
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