Proceedings of the 8th International Conference on Historical Cryptology (HistoCrypt 2025)

Selle kollektsiooni püsiv URIhttps://hdl.handle.net/10062/109727

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Sirvi Proceedings of the 8th International Conference on Historical Cryptology (HistoCrypt 2025) Autor "Helm, Louie" järgi

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  • Pisipilt
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    New records for Playfair solutions
    (Tartu University Library, 2025) Bean, Richard; Helm, Louie; Antal, Eugen; Marák, Pavol
    We give solutions to the 24 letter and 22 letter Playfair challenges proposed in Dunin et al. (2022) A number of methods were tried combining successful approaches of previous solvers, introducing new ideas while using letter-level and word-level approaches. We used vanilla and positional n-gram models for n values from 6 up to 10. However, these did not greatly assist to distinguish the intended solution from other high-scoring solutions. The most effective discriminative approach involved using a multi-terabyte-scale, unpruned large language model from Buck, Heafield, and Van Ooyen (2014) which moved the solution in each case into the top 5,000 ranked possibilities.
  • Pisipilt
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    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.