Fakultät 3

In this paper, we present an empirical study on plaintext entities in historical cipher keys from the 15th to the 18th century to shed light on what linguistic entities have been chosen for encryption. We focus mainly on the nomenclature part of the keys describing longer elements than the plaintext alphabet. We show that the chosen plaintext entities to be encoded varied over time. Nomenclatures developed from short lists consisting of names for persons and/or locations to longer, more advanced dictionaries and eventually to codebooks containing a highly diverse and advanced set of linguistic entities.

The Enigma machines were a series of electromechanical rotor cipher machines developed in Germany and used in the first half of the twentieth century to protect commercial, diplomatic, and military communications. Until 1938, the German Army used the so-called double-indicator procedure to transmit Enigma-encoded messages. It was replaced in September 1938 by a new procedure also involving double indicators. Both procedures enabled a team of mathematicians from the Polish Cipher Bureau to recover the wiring of the rotors and to develop cryptanalytic methods for the recovery of the daily keys. The double-indicator procedure was discontinued by the German Army in May 1940, and new methods were developed by the British at Bletchley Park, who were assisted by the knowledge transferred to them by the Polish cryptanalysts. In this article, the authors introduce two new algorithms that build on the historical cryptanalytic attacks on the two variants of the double-indicator procedures. Those attacks are based on hill climbing, divide-and-conquer, and specialized scoring functions, and they can recover the daily key using a number of indicators significantly smaller than the number of indicators required for the historical methods. Unlike the historical methods, the new algorithms produce unique and unambiguous results, including for scenarios with turnover of the middle rotor, and they also fully recover the plugboard settings. With these algorithms we won an international Enigma contest organized in 2015 by the City of Poznan, in memory of the Polish Cipher Bureau mathematicians.

Many historians and linguists are working individually and in an uncoordinated fashion on the identification and decryption of historical ciphers. This is a time-consuming process as they often work without access to automatic methods and processes that can accelerate the decipherment. At the same time, computer scientists and cryptologists are developing algorithms to decrypt various cipher types without having access to a large number of original ciphertexts. In this paper, we describe the DECRYPT project aiming at the creation of resources and tools for historical cryptology by bringing the expertise of various disciplines together for collecting data, exchanging methods for faster progress to transcribe, decrypt and contextualize historical encrypted manuscripts. We present our goals and work-in progress of a general approach for analyzing historical encrypted manuscripts using standardized methods and a new set of state-of-the-art tools. We release the data and tools as open-source hoping that all mentioned disciplines would benefit and contribute to the research infrastructure of historical cryptology.

The Hagelin M-209 was a mechanical encryption device used by the U.S. Army during World War 2 (WWII) and the Korean War, as well as by other armies and diplomatic services. The Hagelin M-209 has been the focus of extensive research by codebreaking agencies. Several ciphertext-only attacks have been published, but, those attacks are applicable only to the case of long cryptograms. In this article, the authors present a nested hill-climbing and simulated annealing algorithm for recovering the full key settings from ciphertext only, with ciphertexts as short as 500 letters, compared to a minimum of 750 to 1,250 letters with prior methods. With this method, the authors have solved the last problem of a public Hagelin M-209 challenge contest.

In Meister's 1906 landmark study, "Die Geheimschrift im Dienste der p€ apstlichen Kurie von ihren Anf€ angen bis zum Ende des XVI Jahrhunderts", the 16th Century papal cryptographic service is described as a vibrant, highly professional organization, at the forefront of the science of cryptography in the Late Renaissance. In his work from 1993, Alvarez concluded that by the 19th Century, "the reputation of papal cryptography, once so lustrous, has sadly faded." However, until now, very little was known about the evolution of papal cryptography from the 16th to the 18th Century. In this article, we describe how we obtained a large collection of original papal ciphertexts from the Vatican archives, transcribed them, and how we were able to recover most of the keys, and to decipher the original plaintexts using novel cryptanalysis methods and the open-source e-learning CrypTool platform. The recovered keys and decipherments provide unique insights into papal cryptographic practices from the 16th to the 18th Century. The 16th Century is characterized by innovation and a high level of sophistication, with a primary focus on cryptographic security. From the 17th Century, only the simpler but also less secure forms of ciphers remain in use, and papal cryptography significantly lags behind other European states.

In volunteer computing, participants donate computational resources in exchange for credit points. Cheat detection is necessary to prevent dishonest participants from receiving credit points, without actually providing these resources. We suggest a novel, scalable approach for cheat detection in decentralized volunteer computing systems using gossip communication. Each honest participant adapts its detection effort dynamically subject to the number of active participants, which we estimate based on observed system performance. This enables minimizing the detection overhead for each participant, while still achieving a high preselected detection rate for the overall system. Systems based on majority voting usually produce at least 100% overhead, whereas our approach, e.g. requires only 50.6% overhead in a network with 1 000 participants to achieve a 99.9% detection rate. Since our approach does not require trusted entities or an active cooperation between participants, it is robust even against colluding cheaters.

Cryptanalysis of enciphered documents typically starts with identifying the cipher type. A large number of encrypted historical documents exists, whose decryption can potentially increase the knowledge of historical events. This paper investigates whether machine learning can support the cipher type classification task when only ciphertexts are given. A selection of engineered features for historical ciphertexts and various machine-learning classifiers have been applied for 56 different cipher types specified by the American Cryptogram Association. Different neuronal network models were empirically evaluated. Our best-performing model achieved an accuracy of 80.24% which improves the current state of the art by 37%. Accuracy is calculated by dividing the total number of samples by the number of true positive predictions. The software-suite is published under the name ”Neural Cipher Identifier (NCID)”.

This paper presents the work on two encrypted diplomatic letters sent by the Lithuanian nobleman Jan Chodkiewicz to emperor Maximilian II in 1574 and 1575. It describes the decipherment process as well as the content and the context of the letters. Furthermore, it provides linguistic aspects of the used plaintext language. It continues our previous work on Habsburg ciphers where we analyzed and contextualized three diplomatic letters sent by Maximilian II. All presented and analyzed letters relate to the Polish-Lithuanian election in 1575, where Maximilian II, his son Ernst, and his brother Ferdinand were amongst the candidates. The deciphered German plaintexts of all five letters can be accessed via the DECODE database, a storage for historical encrypted manuscripts, which is maintained by members of the DECRYPT project.

After publishing data on the Internet, the data publisher loses control over it. However, there are several situations where it is desirable to remove published information. To support this, the European Union proposed the General Data Protection Regulation (GDPR) which states that providers must remove the data when the corresponding owner requests it. However, the data might already have been copied by third parties. Therefore, Article 17 of the GDPR includes the regulation that the provider must also inform all third parties about the users request. Hence, the providers would need to track every access, which is hard to achieve. This technical infeasibility is a gap between the legislation and the current technical possibilities. To close this gap, we propose a novel service which gives the data owner the possibility to inform simultaneously all providers about her removal request.

Messaging applications are among the most popular internet applications and people use them worldwide on a daily basis. Their supporting infrastructure, though consisting of a multitude of servers, is typically under central control. This enables censorship and seamless user profiling. A fully decentralized infrastructure, with decentralized control and redundant data storage, can mitigate these dangers. In this paper we evaluate the basic ability of decentralized networks created by the network overlay and data storage protocol Kademlia to serve as a short-term data cache for messaging applications. Our results show, that reliable retrieval of up to 20 replicas is possible.

In this paper, we discuss new additions (components) for cryptography and cryptanalysis added to the CrypTool 2 (CT2) software over the course of the last two years. We mainly focus on components for classical and historical ciphers, but also keep an eye on other updates of CT2, e.g. the CrypConsole, which allows the users to execute CT2 workspaces in the Windows command prompt. The Chaocipher as well as Josse's cipher were added to CT2. The Symbol Cipher component already allows the user to create musical ciphers. We implemented a new Playfair Analyzer as well as a Josse Cipher Analyzer. The Enigma Analyzer component has been rewritten completely and now features six different computerized attacks on Enigma. Two historical ciphers were successfully deciphered with the help of CT2: five ciphertexts from and to the Holy Roman Emperor Maximilian II as well as the Ramanacoil transcript. Both ciphers from the 16th and 17th century were analyzed and deciphered using the Homophonic Substitution Analyzer component as well as the substitution component. Finally, we take a brief look at how CT2 is used for teaching and e-learning cryptology.

There are many (historical) unsolved ciphertexts from which we don’t know the type of cipher which was used to encrypt these. A first step each cryptanalyst does is to try to identify their cipher types using different (statistical) methods. This can be difficult, since a multitude of cipher types exist. To help cryptanalysts, we developed a first version of an artificial neural network that is right now able to differentiate between five classical ciphers: simple monoalphabetic substitution, Vigenère, Playfair, Hill, and transposition. The network is based on Google’s TensorFlow library as well as Keras. This paper presents the current progress in the research of using such networks for detecting the cipher type. We tried to classify all ciphers of a new MysteryTwister C3 challenge called “Cipher ID” created by Stamp in 2019. The network is able to classify about 90% of the ciphertexts of the challenge correctly. Furthermore, the paper presents the current state-of-the-art of ciphe...

This German paper was written entirely at the University of Duisburg-Essen in 2011 for a 3D modeling masters course in applied computer science. We publish this paper, thus, interested people can acquire a first impression of the topic "volume raycasting". In addition to writing this paper, we developed a functioning open-source OpenCL raycaster. A video of this raycaster is available: this http URL. Additionally, we archived and published the complete source code of the raycaster in the Google Code Archive: this http URL. If this is no longer the case, those who are interested can also write an email to the author, hence, we can provide the source code. This paper provides an introduction and overview of the topic "volume ray casting with OpenCL". We show how volume data can be loaded, manipulated, and visualized by modern GPUs in real time. In addition, we present basic algorithms and data structures that are necessary for building such a raycaster. Then, we de...

In this German seminar paper, which was written in the year 2011 at the University of Duisburg for a Bachelor Colloquium in Applied computer science, we show a brief overview of the Rational Unified Process (RUP). Thus, interested students or generally interested people in software development gain a first impression of RUP. The paper includes a survey and overview of the underlying process structure, the phases of the process, its workflows, and describes the always by the RUP developers postulated "best practices" of software development.

The difficulty of solving classical ciphers varies between very easy and very hard. For example, monoalphabetic substitution ciphers can be solved easily by hand. More complex ciphers like the polyalphabetic Vigenère cipher, are harder to solve and the solution by hand takes much more time. Machine ciphers like the Enigma rotor machine, are nearly impossible to be solved only by hand. To support researchers, cryptanalysts, and historians analyzing ciphers, the open-source software CrypTool 2 (CT2) was implemented. It contains a broad set of tools and methods to automate the cryptanalysis of different (classical and modern) ciphers. In this paper, we present a step-by-step approach for analyzing classical ciphers and breaking these with the help of the tools in CT2. The primary goals of this paper are: (1) Introduce historians and non-computer scientists to classical encryption, (2) give an introduction to CT2, enabling them to break ciphers by their own, and (3) present our future p...

This paper describes the current progress of our research in the area of breaking homophonic substitution ciphers. Furthermore, it presents the state-of-the-art of cryptanalyzing this kind of cipher. There is a huge gap between the success rate of methods published in according research papers and the success rate of already available tools on the Internet. This paper also presents a small general taxonomy of monoalphabetic substitution ciphers. Finally, it shows how we broke different homophonic substitution ciphers in an automatic as well as in a semi-automatic way.

The deciphered Ramanacoil ciphertext reveals two Dutch East India Company letters, from 1674 that are, in retrospect, already known in the National Archives as plaintext letters. The letters are written in Dutch. We have been able to relate them. The first letter, from Van Goens senior from Sri Lanka to the Lords Seventeen in The Netherlands, was most important to the sender. He sent his personal secretary Leeuwenson overland with the ciphertext in his pocket and its key in his head. And with additional oral information that had to be delivered in person. Van Goens senior requested to conquer the whole of Sri Lanka, the island Ramanacoil and coastal area around it along with 1,000 more soldiers. This paper shows that by sending Leeuwenson, Van Goens senior wanted to repeat his most successful 'Vertoog' from 1655. Substantiate his strategic goals and get approval for them from the Lords Seventeen. In 1655 he got a 'Go!' and twenty years later in 1675 he got a 'No!'. The zeitgeist of expansion had changed. Ramanacoil was a bridge too far.