Sirvi Autor "Lasry, George" järgi

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An early French digit cipher: deciphering a letter from the King of France to the Duke of Nevers (1592)
(Tartu University Library, 2024) Desenclos, Camille; Lasry, George; Waldispühl, Michelle; Megyesi, Beáta
We deciphered a single letter written in 1592 by Henry IV, King of France, to Louis de Gonzague, Duke of Nevers, held in the Bibliothèque Nationale de France (BnF). The ciphertext mostly consists of contiguous digits, and demonstrates an early use of digit ciphers in 16th-century France. In this letter, Henri IV exposes some parts of his current military strategy against the Catholic League. After deciphering the letter, we were able to locate the original cipher table in another BnF manuscript, illustrating how codebreaking may assist historical research both to reconstruct the content of encrypted letters and to identify anonymous cipher tables.
Antonio Elio “Cipher” and his Polyphonic-Syllabic Cipher
(Tartu University Library, 2025) Lasry, George; Biermann, Norbert; Simonetta, Marcello; Antal, Eugen; Marák, Pavol
Antonio Elio (Helius) (1506–1576) was a Roman Catholic prelate who served as Bishop of Capodistria and Pola and Titular Patriarch of Jerusalem. Also a prolific cryptographer in the service of Pope Paul III, he is credited for the invention of polyphonic ciphers. In this article, we provide an overview of his career and work in cryptography and describe an ingenious polyphonic-syllabic cipher he designed. Although several matching plaintext-ciphertext segments were available, reconstructing the cipher key required a significant and unusual amount of time, underscoring the cipher’s high level of security. Ciphertext-only cryptanalysis for such a cipher would be extremely difficult and nearly impossible, even with modern computing, without prior knowledge of the principles of its complex design.
Cryptanalytic and historical challenges with unidentified encrypted documents from the early modern era
(Tartu University Library, 2025) Desenclos, Camille; Lasry, George; Antal, Eugen; Marák, Pavol
In most cases, historical encrypted documents include some parts in cleartext, such as headers, dates, signatures, or addresses, which allows the origin, date, and language of these documents to be established. An attached decrypted text, similar documents (same encryption, homogeneity of date or origin) in the same volume or box, or the catalog description may assist in that process. However, in a few cases, none of these are available, posing several challenges both from cryptanalytic and historical perspectives. Based on three 16th-century case studies, this paper aims to discuss a multidisciplinary method to proceed from an unidentified encrypted document to a workable transcription – decipherment and identification.
Deciphering Historical Syllabic Ciphers
(Tartu University Library, 2024) Lasry, George; Waldispühl, Michelle; Megyesi, Beáta
Historical ciphers with syllabic elements are significantly more challenging for cryptanalysis than regular homophonic ciphers. We present here a novel computerized technique which recovers significant parts of the keys, allowing for the remaining parts to be manually completed. We solved several previously undeciphered French, Spanish, and Italian syllabic ciphers, and we also evaluated the performance of this method against a series of additional historical syllabic ciphers.
What Encryption Errors Can Reveal: Cross-Cipher Errors in Mary Queen of Scots’ Letters
(Tartu University Library, 2024) Biermann, Norbert; Tomokiyo, Satoshi; Lasry, George; Waldispühl, Michelle; Megyesi, Beáta
In the recently deciphered letters from Mary Queen of Scots, a large number of systematic encryption errors were found and attributed to confusion as a result of concurrently using at least one other cipher key to communicate with a different recipient. In this paper, we further analyze such cross-cipher errors in those letters and identify additional cipher keys involved. This analysis also reveals valuable insights on the secret communications of Mary, Queen of Scots. We employ several techniques including statistical analysis, which may be applied to the analysis of encryption errors in other collections of historical enciphered documents.