Proceedings of the 7th International Conference on Historical Cryptology (HistoCrypt 2024)

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A new perspective on Dutch WWI codebreaking with its international ramifications
(Tartu University Library, 2024) Jacobs, Bart; van Kampen, Florentijn; Waldispühl, Michelle; Megyesi, Beáta
During the First World War, the Netherlands maintained a stance of carefully guarded neutrality. International tele communications in the form of telephone and telegraph were closely monitored and censored by so-called censorbureaus. In 2019 new files were declassified and released to the Dutch National Archive about the secensorship bureaus at Amsterdam and Rotterdam, covering 1914 to 1918. They provide detailed insight in the day-to-day business, the codebreaking efforts and specific cryptanalytic results. The material provides a completely new perspective on the genesis of modern Dutch codebreaking. This article gives a first survey of the development of these interception bureaus. It analyses their pioneering codebreaking activities and presents historic material on German diplomatic ciphers. Also, it provides new insight into the mysterious sale in 1919 of German codebooks from the Netherlands to the United States, as reported earlier in the literature.
A Typology for Cipher Key Instructions in Early Modern Times
(Tartu University Library, 2024) Megyesi, Beáta; Láng, Benedek; Kopal, Nils; Mikhalev, Vasily; Tudor, Crina; Waldispühl, Michelle; Waldispühl, Michelle; Megyesi, Beáta
We present an empirical study on instructions found in historical cipher keys dating back to early modern times in Europe. The study reveals that instructions in historical cipher keys are prevalent, covering a wide range of themes related to the practical application of ciphers. These include general information about the structure or usage of the cipher key, as well as specific instructions on their application. Being a hitherto neglected genre, these texts provide insight into the practice of cryptographic operations.
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.
Artificial neural network for hoax cryptogram identification
(Tartu University Library, 2024) Foxon, Floe; Waldispühl, Michelle; Megyesi, Beáta
Numerous putative cryptograms remain unsolved. Some, including the Dorabella cryptogram, have been suggestedas hoaxes, i.e., some sort of gibberish with no meaningful underlying plaintext.The statistical properties of a putative cryptogram may be modelled to determine whether the cryptogram groups moreclosely with real or with randomly generated plaintext. Ten thousand plaintexts from an English-language corpus, and ten thousand (pseudo-)randomly generated English-alphabet gibberish texts were studied through their statistical properties, including the alphabet length; the frequency, separation, and entropy of n-grams; the index of coincidence; Zipf’slaw, and mean associated contact counts. An artificial neural network (deep learning) model was fitted to these data, with a cross-validated mean accuracy of 99.8% (standard deviation: 0.1%). This model correctly predicted that arbitrary, out-of-sample simple substitution ciphers represented meaningful English plaintext (as opposed to gibberish) with probabilities close to 1; correctly predicted that arbitrary, out-of-sample gibberish texts were gibberish (as opposed to simple substitution ciphers) with probabilities close to 1; and assigned a probability of meaningful English plaintext of 0.9996 to the Dorabella cryptogram.
Bringing Cryptology into the Secondary Education Classroom
(Tartu University Library, 2024) Murphy, Catherine; Wootton, Aaron; Waldispühl, Michelle; Megyesi, Beáta
Cryptology is becoming increasingly commonplace in undergraduate mathematics curricula as a way to motivate abstract mathematics. However, it is still typically absent in secondary education (students aged 11 to 18). In the following, we discuss why we think it would be advantageous to bring cryptology, both historical and modern, to the secondary education classroom. Additionally, we discuss some of the barriers we perceive to doing so and suggest, in our opinion, how they might be overcome. We illustrate implementation with a specific example of a topic in cryptology that could be included in a secondary education classroom.
Can Artificial Intelligence solve the mysterious anagram from the church of the Poor Clares in Bratislava?
(Tartu University Library, 2024) Antal, Eugen; Zajac, Pavol; Waldispühl, Michelle; Megyesi, Beáta
A mysterious anagram was found in the Church of the Poor Clares in Bratislava, but as far as we know it has never been successfully solved. The anagram contains81 symbols, including specific diphthongsAE, CH, and GY. Unlike other anagramstypical of that age, the symbolsare not ordered alphabetically. We suspectthat a specific order of symbols is relatedto the original order of symbols in theplain text. Even with the suspected orderof letters, the number of possible plain textcandidates is too high to obtain the originaltext with standard methods. We examinealternative scoring methods based onmodern AI text similarity to improve thequality of the candidate plain text candidates.
Cryptanalysis of Hagelin M-209 Cipher Machine with Artificial Neural Networks: A Known-Plaintext Attack
(Tartu University Library, 2024) Mikhalev, Vasily; Kopal, Nils; Esslinger, Bernhard; Lampesberger, Harald; Hermann, Eckehard; Waldispühl, Michelle; Megyesi, Beáta
This paper introduces a machine learning (ML) approach for cryptanalysis of the ciphermachine Hagelin M-2091. For recovering the part of the secret key, represented by the wheel pins, we use Artificial Neural Networks (ANN) which take as input the pseudo-random displacement values generated by the internal mechanism of the machine. The displacement values can be easily obtained when ciphertext and plaintext are known. In particular, we are using several distinct ANNs, each recovering exactly one pin. Thus, to recover all the 131 pins, we utilize 131 model seach solving a binary classification problem. By experimenting with various ANN architectures and ciphertext lengths, ranging from 52 to 200 characters, we identified an ANN architecture that outperforms others in accuracy. This model, inspired by the architecture by Gohr used for attacking modern ciphers, achieved the following accuracies in recovering the pins of the first wheel of the machine: approximately 71% for 52-characters sequences, 88% for 104-characters, 96% for 200-characters. The first wheel has the largest size and hence represents the most complicated case. For the other wheels, these accuracies are slightly higher. To the best of our knowledge, this is the first time when ANNs are used in a key-recovery attack against such machines.
Cryptology and redaction – a strange symbiosis
(Tartu University Library, 2024) Turing, Dermot; Waldispühl, Michelle; Megyesi, Beáta
This paper explores the relationship between cryptology and redaction. Redaction can be a frustration to historical cryptology research. Examples of redactions of historical papers relevant to cryptology are presented. It is concluded that the practice of redaction is often ineffective and the policy rationale behind redactions difficult to understand.
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.
Decipherment of a German encrypted letter sent from Sigismund Heusner von Wandersleben to Axel Oxenstierna in 1637
(Tartu University Library, 2024) Waldispühl, Michelle; Kopal, Nils; Waldispühl, Michelle; Megyesi, Beáta
We present our work on an encrypted letter from the Thirty Years’ War written by the ally of the Swedish Empire, Sigismund Heusner von Wandersleben in 1637 and sent from Kassel to the Swedish High Lord Chancellor Axel Oxenstierna. We describe our analysis of the ciphertext including information on the cipher type, the process of cryptanalysis and challenges for the decipherment. We include the edition of the letter in the current state of decipherment and summarize its content.
Decipherment of an Encrypted Letter from 1724 Found in UCL Special Collections’ Brougham Archive
(Tartu University Library, 2024) Kopal, Nils; Makin, Katy; Waldispühl, Michelle; Megyesi, Beáta
This paper shows the decipherment of a 1724 encrypted letter, discovered recently in the Brougham Archive at University College London (UCL) Special Collections. The letter’s content hints at political intrigue and possibly relates to the Jacobite movement during George I’s reign in Great Britain. However, as all individuals mentioned in the letter are referred to bycode names, except for Madame de Prie, their true identities remain unknown to the authors. Therefore, any connection to the Jacobites remains speculative. The paper covers the cipher’s security, historical context, and unresolved inquiries surrounding the letter.
Demystifying La Buse’s Cryptogram and the Fiery Cross of Goa
(Tartu University Library, 2024) Dahlke, Carola; Waldispühl, Michelle; Megyesi, Beáta
The field of cryptology alone offers a multitude of exciting exhibits and stories for a museum of science and technology. But when secret ciphers meet seaborne piracy and rich treasures, it sounds like a perfect mix for a successful storytelling. However,an extensive study of an eyewitness account and contemporary reports on the legend of la Buse led to sobering contexts related to colonialism, inquisition and, apart from a small kernel of truth, to a large spool full of seaman’s yarn.
Development of the Block Cipher LAMBDA1 in 1990
(Tartu University Library, 2024) Stephan, Winfried; Waldispühl, Michelle; Megyesi, Beáta
In 1990, it became apparent that the German Democratic Republic (GDR) would leave the socialist community of states. This involved the gradual reduction of cooperation between the cipher services of these countries and the separation of cipher connections. LAMBDA1 is a block cipher developed in East Germany in 1990. It was designed for a cipher device for which a Soviet algorithm was originally intended. The plan was to use a predecessor of the Soviet block cipher algorithm, called GOST. This now had to be replaced. The aim was to provide a cipher algorithm that could not be easily decrypted by either the Warsaw Treaty countries states or the NATO countries. The background to these considerations was the assumption that the GDR would confirm to exist as an independent state for an extended period in a kind of transitional phase. The article describes the circumstances under which the LAMBDA1 algorithm was developed in just one month. It was based on the results of previous projects and was then intensively analyzed. The project was only abandoned when it became clear that the unification of the two German countries would take place at short notice and was imminent. The algorithm below is described only to the extent necessary to understand the development process.
Exploring the Alignment of Transcriptions to Images of Encrypted Manuscripts
(Tartu University Library, 2024) García, Goio; Torras, Pau; Fornés, Alicia; Megyesi, Beáta; Waldispühl, Michelle; Megyesi, Beáta
The automatic transcription of encrypted manuscripts is a challenge due to the different handwriting styles and the often invented symbol alphabets. Many transcription methods require annotated sources, including symbol locations. However, most existing transcriptions are provided at line or page level, making it necessary to find the bounding boxes of the transcribed symbols in the image, a process referred to as alignment. So, in this work, we develop several alignment methods, and discuss their performance on encrypted documents with various symbol sets.
Fake or real? A mysterious metal book on the market
(Tartu University Library, 2024) Király, Levente Zoltán; Láng, Benedek; Tokai, Gábor; Waldispühl, Michelle; Megyesi, Beáta
A newly emerged gilded folio metal book containing illustrations and unreadable character strings raises the question of authenticity. The article describes the object and examines on what grounds can be claimed with relative confidence that such a book is a forgery. The examination includes a structural analysis of the symbol sets and a comparison with similar, analogous metal books.
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.
How the MachinesWere Assisted by Women
(Tartu University Library, 2024) Fricker, Elizabeth S.D.; Waldispühl, Michelle; Megyesi, Beáta
The following paper analyzes nature of skill in the cryptographic work performed by female employees of the World War II British cryptography program at Bletchley Park. Using anecdotes from women who worked to decrypt the Lorenz cipher, I show the hidden skills which were integral to their work and to the war effort. This paper aims to reconstruct their experiences and deepen our understanding of what it took to operate decryption machines, especially focusing on the Colossus computer.
Lost in Translation: Missing Background, Contextual Blindspots, and Editing Mishaps in Translated Intelligence Content
(Tartu University Library, 2024) Jaskoski, Stephen; Waldispühl, Michelle; Megyesi, Beáta
This article examines the content as rendered by a small sample of intelligence reports issued by the UK Government Code and Cypher School (GC&CS) at Bletchley Park that address the initial indications in Italian communications of Italian regime change after Mussolini and considers how higher meaning in the texts may not have been fully appreciated in the context when they were written. The episode offers lessons in grasping context and significance in translated material.
Musician Cryptologists: The Band of the USS California at Pearl Harbor and Beyond
(Tartu University Library, 2024) Prescott, Kyle; Waldispühl, Michelle; Megyesi, Beáta
Working from the basement of US Pacific Fleet Headquarters in Pearl Harbor from 1941, a small team of navy cryptanalysts and linguists known as the Combat Intelligence Unit (CIU) provided the US Pacific Fleet Command with timely details of the capabilities and intentions of the Japanese Imperial Navy (IJN) in the Pacific. A substantial portion of the CIU was comprised of 20 enlisted musicians of US Navy Unit Band 16, the band of the USS California (BB-44), who survived the sinking of their ship in the attack of December 7, 1941. The musicians were recruited to Combat Intelligence, retrained to perform tasks related to the deciphering of Japanese Naval Code JN-25b, and contributed to that unit’s celebrated intelligence successes of 1942. As the war waged on, several musicians from Band 16 transferred to the Naval Communications Complex at Nebraska Avenue in Washington DC, and three eventually joined the National Security Agency (NSA) and served through the height of the Cold War.
On the tracks of Félix-Marie Delastelle
(Tartu University Library, 2024) Géraud-Stewart, Rémi; Naccache, David; Waldispühl, Michelle; Megyesi, Beáta
“Can not find any info on Delastelle— Nothing on record in this country.” (William Friedman, 18 Jan 1955, NSA Archives A63734) Following these words, the then-director of the US National Security Agency hailed contacts in Europe, hoping that someone would fill in this missing information. The initial inquiry was sent to Friedman by amateur American cryptographer William Maxwell Bowers; in 1963, Bowers would publish under a pseudonym all that he could find on the matter (The Cryptogram 1963, preserved under reference VF 54-30 at the US National Cryptologic Museum). Since this document, which had a very limited audience, almost no new information on Delastelle was published, and indeed most of the information available widely today on Delastelle is at best fragmentary. In this paper we reopen that case, reviewing information about the life and work of Félix-Marie Delastelle, establishing data overlooked by earlier historians, correcting several oft-repeated errors and bringing novel documents to public awareness.

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