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Tools for breaking a substitution cipher

Sašo Kodrič (2013) Tools for breaking a substitution cipher. EngD thesis.

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    Digital communication is becoming an essential part of modern way of life. In some cases it is desired, that message stays secret, while in some other cases it is required to be revealed. Simplified, cryptography is a theory that studies techniques to enable secret communication with the use of encryption and the use of decryption to obtain back the original message. This thesis deals with cryptoanalysis, in particular, it explains mathematical background for breaking the substitution cipher based on statistics of pairs of letters. It presents our implementation of algorithms, which encrypt a clear text with the use of random substitution cipher, calculate the frequencies of pairs of letters in corpus and encrypted text and stores them in two matrices. It permutes the substitution cipher in matrix of the encrypted text and calculates the distance with corresponding matrix of corpus. The algorithm is running, until the distance is decreasing. As result we get substitution cipher, which was used to encrypt the clear text.

    Item Type: Thesis (EngD thesis)
    Keywords: cryptography, cryptoanalysis, substitution cipher
    Number of Pages: 33
    Language of Content: Slovenian
    Mentor / Comentors:
    Name and SurnameIDFunction
    prof. dr. Aleksandar Jurišić1118Mentor
    Link to COBISS: http://www.cobiss.si/scripts/cobiss?command=search&base=50070&select=(ID=9688148)
    Institution: University of Ljubljana
    Department: Faculty of Computer and Information Science
    Item ID: 1976
    Date Deposited: 04 Feb 2013 08:19
    Last Modified: 01 Mar 2013 09:54
    URI: http://eprints.fri.uni-lj.si/id/eprint/1976

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