Cellular automata for dynamic S-boxes in cryptography.

In today\u27s world of private information and mass communication, there is an ever increasing need for new methods of maintaining and protecting privacy and integrity of information. This thesis attempts to combine the chaotic world of cellular automata and the paranoid world of cryptography to enhance the S-box of many Substitution Permutation Network (SPN) ciphers, specifically Rijndael/AES. The success of this enhancement is measured in terms of security and performance. The results show that it is possible to use Cellular Automata (CA) to enhance the security of an 8-bit S-box by further randomizing the structure. This secure use of CA to scramble the S-box, removes the 9-term algebraic expression [20] [21] that typical Galois generated S-boxes share. This cryptosystem securely uses a Margolis class, partitioned block, uniform gas, cellular automata to create unique S-boxes for each block of data to be processed. The system improves the base Rijndael algorithm in the following ways. First, it utilizes a new S-box for each block of data. This effectively limits the amount of data that can be gathered for statistical analysis to the blocksize being used. Secondly, the S-boxes are not stored in the compiled binary, which protects against an S-box Blanking [22] attack. Thirdly, the algebraic expression hidden within each galois generated S-box is destroyed after one CA generation, which also modifies key expansion results. Finally, the thesis succeeds in combining Cellular Automata and Cryptography securely, though it is not the most efficient solution to dynamic S-boxes

Generating secret in a network

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 247-253) and index.This monograph studies the theory of information through the multiuser secret key agreement problem. A general notion of mutual dependence is established for the secrecy capacity, as a natural generalization of Shannon's mutual information to the multivariate case. Under linear-type source models, this capacity can be achieved practically by linear network codes. In addition to being an unusual application of the network coding solution to a secrecy problem, it gives secrecy capacity an interpretation of network information flow and partition connectivity, further confirming the intuitive meaning of secrecy capacity as mutual dependence. New identities in submodular function optimization and matroid theory are discovered in proving these results. A framework is also developed to view matroids as graphs, allowing certain theory on graphs to generalize to matroids. In order to study cooperation schemes in a network, a general channel model with multiple inputs is formulated. Single-letter secrecy capacity upper bounds are derived using the Shearer-type lemma. Lower bounds are obtained with a new cooperation scheme called the mixed source emulation. In the same way that mixed strategies may surpass pure strategies in zero-sum games, mixed source emulation outperforms the conventional pure source emulation approach in terms of the achievable key rate. Necessary and sufficient conditions are derived for tightness of these secrecy bounds, which shows that secrecy capacity can be characterized for a larger class of channels than the broadcast-type channels considered in previous work. The mixed source emulation scheme is also shown to be unnecessary for some channels while insufficient for others. The possibility of a better cooperative scheme becomes apparent, but a general scheme remains to be found.by Chung Chan.Ph.D

Soft Processing Techniques for Quantum Key Distribution Applications

This thesis deals with soft-information based information reconciliation and data sifting for Quantum Key Distribution (QKD). A novel composite channel model for QKD is identified, which includes both a hard output quantum channel and a soft output classic channel. The Log-Likelihood Ratios, - also called soft-metrics - derived from the two channels are jointly processed at the receiver, exploiting capacity achieving soft-metric based iteratively decoded block codes. The performance of the proposed mixed-soft-metric algorithms are studied via simulations as a function of the system parameters. The core ideas of the thesis are employing Forward Error Correction (FEC) coding as opposed to two-way communication for information reconciliation in QKD schemes, exploiting all the available information for data processing at the receiver including information available from the quantum channel, since optimized use of this information can lead to significant performance improvement, and providing a security versus secret-key rate trade-off to the end-user within the context of QKD system

Digital rights management (DRM) - watermark encoding scheme for JPEG images

The aim of this dissertation is to develop a new algorithm to embed a watermark in JPEG compressed images, using encoding methods. This encompasses the embedding of proprietary information, such as identity and authentication bitstrings, into the compressed material. This watermark encoding scheme involves combining entropy coding with homophonic coding, in order to embed a watermark in a JPEG image. Arithmetic coding was used as the entropy encoder for this scheme. It is often desired to obtain a robust digital watermarking method that does not distort the digital image, even if this implies that the image is slightly expanded in size before final compression. In this dissertation an algorithm that combines homophonic and arithmetic coding for JPEG images was developed and implemented in software. A detailed analysis of this algorithm is given and the compression (in number of bits) obtained when using the newly developed algorithm (homophonic and arithmetic coding). This research shows that homophonic coding can be used to embed a watermark in a JPEG image by using the watermark information for the selection of the homophones. The proposed algorithm can thus be viewed as a ‘key-less’ encryption technique, where an external bitstring is used as a ‘key’ and is embedded intrinsically into the message stream. The algorithm has achieved to create JPEG images with minimal distortion, with Peak Signal to Noise Ratios (PSNR) of above 35dB. The resulting increase in the entropy of the file is within the expected 2 bits per symbol. This research endeavor consequently provides a unique watermarking technique for images compressed using the JPEG standard.Dissertation (MEng)--University of Pretoria, 2008.Electrical, Electronic and Computer Engineeringunrestricte

Soft Processing Techniques for Quantum Key Distribution Applications

This thesis deals with soft-information based information reconciliation and data sifting for Quantum Key Distribution (QKD). A novel composite channel model for QKD is identified, which includes both a hard output quantum channel and a soft output classic channel. The Log-Likelihood Ratios, - also called soft-metrics - derived from the two channels are jointly processed at the receiver, exploiting capacity achieving soft-metric based iteratively decoded block codes. The performance of the proposed mixed-soft-metric algorithms are studied via simulations as a function of the system parameters. The core ideas of the thesis are employing Forward Error Correction (FEC) coding as opposed to two-way communication for information reconciliation in QKD schemes, exploiting all the available information for data processing at the receiver including information available from the quantum channel, since optimized use of this information can lead to significant performance improvement, and providing a security versus secret-key rate trade-off to the end-user within the context of QKD systems

Towards a Theory of Symmetric Encryption

Motivée par le commerce et l'industrie, la recherche publique dans le domaine du chiffrement symétrique s'est considérablement développée depuis vingt cinq ans si bien qu'il est maintenant possible d'en faire le bilan. La recherche a tout d'abord progressé de manière empirique. De nombreux algorithmes de chiffrement fondés sur la notion de réseau de substitutions et de permutations ont été proposés, suivis d'attaques dédiées contre eux. Cela a permis de définir des stratégies générales: les méthodes d'attaques différentielles, linéaires et statistiques, et les méthodes génériques fondées sur la notion de boîte noire. En modélisant ces attaques on a trouvé en retour des règles utiles dans la conception d'algorithmes sûrs: la notion combinatoire de multipermutation pour les fonctions élémentaires, le contrôle de la diffusion par des critères géométriques de réseau de calcul, l'étude algébrique de la non-linéarité, ... Enfin, on montre que la sécurité face à un grand nombre de classes d'attaques classiques est assurée grâce à la notion de décorrélation par une preuve formelle. Ces principes sont à l'origine de deux algorithmes particuliers: la fonction CS-Cipher qui permet un chiffrement à haut débit et une sécurité heuristique, et le candidat DFC au processus de standardisation AES, prototype d'algorithme fondé sur la notion de décorrélation

The Cultural Contradictions of Cryptography

This dissertation examines the origins of political and scientific commitments that currently frame cryptography, the study of secret codes, arguing that these commitments took shape over the course of the twentieth century. Looking back to the nineteenth century, cryptography was rarely practiced systematically, let alone scientifically, nor was it the contentious political subject it has become in the digital age. Beginning with the rise of computational cryptography in the first half of the twentieth century, this history identifies a quarter-century gap beginning in the late 1940s, when cryptography research was classified and tightly controlled in the US. Observing the reemergence of open research in cryptography in the early 1970s, a course of events that was directly opposed by many members of the US intelligence community, a wave of political scandals unrelated to cryptography during the Nixon years also made the secrecy surrounding cryptography appear untenable, weakening the official capacity to enforce this classification. Today, the subject of cryptography remains highly political and adversarial, with many proponents gripped by the conviction that widespread access to strong cryptography is necessary for a free society in the digital age, while opponents contend that strong cryptography in fact presents a danger to society and the rule of law. I argue that cryptography would not have become invested with these deep political commitments if it had not been suppressed in research and the media during the postwar years. The greater the force exerted to dissuade writers and scientists from studying cryptography, the more the subject became wrapped in an aura of civil disobedience and public need. These positive political investments in cryptography have since become widely accepted among many civil libertarians, transparency activists, journalists, and computer scientists who treat cryptography as an essential instrument for maintaining a free and open society in the digital age. Likewise, even as opponents of widespread access to strong cryptography have conceded considerable ground in recent decades, their opposition is grounded in many of the same principles that defined their stance during cryptography’s public reemergence in the 1970s. Studying this critical historical moment reveals not only the origins of cryptography’s current politics, but also the political origins of modern cryptography

The Poetry of Logical Ideas: Towards a Mathematical Genealogy of Media Art

In this dissertation I chart a mathematical genealogy of media art, demonstrating that mathematical thought has had a significant influence on contemporary experimental moving image production. Rather than looking for direct cause and effect relationships between mathematics and the arts, I will instead examine how mathematical developments have acted as a cultural zeitgeist, an indirect, but significant, influence on the humanities and the arts. In particular, I will be narrowing the focus of this study to the influence mathematical thought has had on cinema (and by extension media art), given that mathematics lies comfortably between the humanities and sciences, and that cinema is the object par excellence of such a study, since cinema and media studies arrived at a time when the humanities and sciences were held by many to be mutually exclusive disciplines. It is also shown that many media scholars have been implicitly engaging with mathematical concepts without necessarily recognizing them as such. To demonstrate this, I examine many concepts from media studies that demonstrate or derive from mathematical concepts. For instance, Claude Shannon's mathematical model of communication is used to expand on Stuart Hall's cultural model, and the mathematical concept of the fractal is used to expand on Rosalind Krauss' argument that video is a medium that lends itself to narcissism. Given that the influence of mathematics on the humanities and the arts often occurs through a misuse or misinterpretation of mathematics, I mobilize the concept of a productive misinterpretation and argue that this type of misreading has the potential to lead to novel innovations within the humanities and the arts. In this dissertation, it is also established that there are many mathematical concepts that can be utilized by media scholars to better analyze experimental moving images. In particular, I explore the mathematical concepts of symmetry, infinity, fractals, permutations, the Axiom of Choice, and the algorithmic to moving images works by Hollis Frampton, Barbara Lattanzi, Dana Plays, T. Marie, and Isiah Medina, among others. It is my desire that this study appeal to scientists with an interest in cinema and media art, and to media theorists with an interest in experimental cinema and other contemporary moving image practices