Sirvi Autor "Schmeh, Klaus" järgi

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French encrypted newspaper advertisements in the 19th century
(Tartu University Library, 2024) Schmeh, Klaus; Müller, Didier; Dunin, Elonka; Waldispühl, Michelle; Megyesi, Beáta
We present a ciphertext database created by one of the authors. It contains over 3700 encrypted newspaper advertisements published in the French newspaper Le Figaro between 1875 and 1897. The collection includes over 2300 solved messages, which have been encrypted in almost 90 different crypto systems, as well as over 1400 unsolved cryptograms. We introduce some of the most interesting solved and unsolved advertisements, including messages based on ciphers, codes, and steganography. It will become clear that in addition to the messages contained in the database so far, thousands more encrypted advertisements from French newspapers remain to be catalogued and deciphered.
Solving a 750-Letter General Bigram Substitution Challenge
(Tartu University Library, 2025) Schmeh, Klaus; Dunin, Elonka; Van Eycke, Jarl; Helm, Louie; Antal, Eugen; Marák, Pavol
The general bigram substitution cipher is an encryption method originating in the Renaissance. It operates using a substitution table that maps each possible letter pair (bigram) to a unique replacement. While conceptually straightforward, this cipher is notably challenging to break, particularly when dealing with short ciphertexts. To inspire further research, one of the authors initiated a bigram substitution challenge featuring a 750-character ciphertext. In this paper, we present the solution to that challenge, achieved by two other authors using a hill climbing algorithm combined with a scoring function based on 8-gram (eight-letter sequence) frequencies. Since no prior 8-gram frequency statistics existed for the English language, one of the authors developed a comprehensive dataset by analyzing 2 terabytes of text, including 5.8 million books and the entire content of Wikipedia. This achievement, to our knowledge, marks the shortest bigram substitution ciphertext ever successfully decrypted. Furthermore, we propose a new challenge based on a 600-character ciphertext and invite readers to tackle it, setting the stage for future advancements in this field.