Distributed pre-computation for a cryptanalytic time-memory trade-off

Cryptanalytic tables often play a critical role in decryption efforts for ciphers where the key is not known. Using a cryptanalytic table allows a time-memory tradeoff attack in which disk space or physical memory is traded for a shorter decryption time. For any N key cryptosystem, potential keys are generated and stored in a lookup table, thus reducing the time it takes to perform cryptanalysis of future keys and the space required to store them. The success rate of these lookup tables varies with the size of the key space, but can be calculated based on the number of keys and the length of the chains used within the table. The up-front cost of generating the tables is typically ignored when calculating cryptanalysis time, as the work is assumed to have already been performed. As computers move from 32 bit to 64 bit architectures and as key lengths increase, the time it takes to pre-compute these tables rises exponentially. In some cases, the pre-computation time can no longer be ignored because it becomes infeasible to pre-compute the tables due to the sheer size of the key space. This thesis focuses on parallel techniques for generating pre-computed cryptanalytic tables in a heterogeneous environment and presents a working parallel application that makes use of the Message Passing Interface (MPI). The parallel implementation is designed to divide the workload for pre-computing a single table across multiple heterogeneous nodes with minimal overhead incurred from message passing. The result is an increase in pre-computational speed that is close to that which can be achieved by adding the computational ability of all processors together

Plasticity in second language (L2) learning: perception of L2 phonemes by native Greek speakers of English

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Understanding the process of language acquisition is a challenge that many researchers spanning different disciplines (e.g. linguistics, psychology, neuroscience) have grappled with for centuries. One which has in recent years attracted a lot of attention has been in the area of non-native phoneme acquisition. Speech sounds that contain multiple phonetic cues are often difficult for foreign-language learners, especially if certain cues are weighted differently in the foreign and native languages. Greek adult and child speakers of English were studied to determine which cues (duration or spectral) they were using to make discrimination and identification judgments for an English vowel contrast pair. To this end, two forms of identification and discrimination tasks were used: natural (unedited) stimuli and another ‘modified’ vowel duration stimuli which were edited so that there were no duration differences between the vowels. Results show the Greek speakers were particularly impaired when they were unable to use the duration cue as compared to the native English speakers. Similar results were also obtained in control experiments where there was no orthographic representation or where the stimuli were cross-spliced to modify the phonetic neighborhood. Further experiments used high-variability training sessions to enhance vowel perception. Following training, performance improved for both Greek adult and child groups as revealed by post training tests. However the improvements were most pronounced for the child Greek speaker group. A further study examined the effect of different orthographic cues that might affect rhyme and homophony judgment. The results of that study showed that Greek speakers were in general more affected by orthography and regularity (particularly of the vowel) in making these judgments. This would suggest that Greek speakers were more sensitive to irrelevant orthographic cues, mirroring the results in the auditory modality where they focused on irrelevant acoustic cues. The results are discussed in terms of current theories of language acquisition, with particular reference to acquisition of non-native phonemes.School of Social Sciences, Brunel Universit

Case board, traces, & chicanes: Diagrams for an archaeology of algorithmic prediction through critical design practice

This PhD thesis utilises diagrams as a language for research and design practice to critically investigate algorithmic prediction. As a tool for practice-based research, the language of diagrams is presented as a way to read algorithmic prediction as a set of intricate computational geometries, and to write it through critical practice immersed in the very materials in question: data and code. From a position rooted in graphic and interaction design, the research uses diagrams to gain purchase on algorithmic prediction, making it available for examination, experimentation, and critique. The project is framed by media archaeology, used here as a methodology through which both the technical and historical "depths" of algorithmic systems are excavated. My main research question asks: How can diagrams be used as a language to critically investigate algorithmic prediction through design practice? This thesis presents two secondary questions for critical examination, asking: Through which mechanisms does thinking/writing/designing in diagrammatic terms inform research and practice focused on algorithmic prediction? As algorithmic systems claim to produce objective knowledge, how can diagrams be used as instruments for speculative and/or conjectural knowledge production? I contextualise my research by establishing three registers of relations between diagrams and algorithmic prediction. These are identified as: Data Diagrams to describe the algorithmic forms and processes through which data are turned into predictions; Control Diagrams to afford critical perspectives on algorithmic prediction, framing the latter as an apparatus of prescription and control; and Speculative Diagrams to open up opportunities for reclaiming the generative potential of computation. These categories form the scaffolding for the three practice-oriented chapters where I evidence a range of meaningful ways to investigate algorithmic prediction through diagrams. This includes, the 'case board' where I unpack some of the historical genealogies of algorithmic prediction. A purpose-built graph application materialises broader reflections about how such genealogies might be conceptualised, and facilitates a visual and subjective mode of knowledge production. I then move to producing 'traces', namely probing the output of an algorithmic prediction system|in this case YouTube recommendations. Traces, and the purpose-built instruments used to visualise them, interrogate both the mechanisms of algorithmic capture and claims to make these mechanisms transparent through data visualisations. Finally, I produce algorithmic predictions and examine the diagrammatic "tricks," or 'chicanes', that this involves. I revisit a historical prototype for algorithmic prediction, the almanac publication, and use it to question the boundaries between data-science and divination. This is materialised through a new version of the almanac - an automated publication where algorithmic processes are used to produce divinatory predictions. My original contribution to knowledge is an approach to practice-based research which draws from media archaeology and focuses on diagrams to investigate algorithmic prediction through design practice. I demonstrate to researchers and practitioners with interests in algorithmic systems, prediction, and/or speculation, that diagrams can be used as a language to engage critically with these themes

Review of the ACT Government's harm minimisation measures

This report outlines research on the effects of three harm minimisation measures introduced between 1993 and 2002 in the ACT: • a $10 maximum bet on EGMs (electronic gaming machines, or ‘poker’ machines); • a mandatory three-hour shutdown of gaming machines each day; • restriction on cash payment of winnings. The Gambling and Racing Control (Code of Practice) Regulations require that winnings above$1,000 must be paid by non-cash means such as a cheque or electronic transfer. ¶ The report also provides a summary of the ACT gambling and regulatory environment and a policy chronology, with particular focus on the history and objectives of the ACT harm minimisation measures under review.This report was commisioned by ACT GAmbling and Racing Commissio

Bitcoin and the Japanese Retail Investor

The objective of this research is to examine the Bitcoin rally of 2017 as it occurred in Japan and establish a greater context for why it was the Japanese retail investors that propelled the nation to being the largest trader of the cryptocurrency at the end of the year. This dissertation begins with the examination of the technical and economical properties of Bitcoin by classifying it as fulfilling two roles: that of a means of payment and that of an investment commodity. Following that is a description of Bitcoin’s roots and the history of its non-speculative usage. These chapters serve as a base for examining the cryptocurrency’s role in Japan. The third chapter examines the Japanese retail investor and the Japanese retail investment landscape with a focus on the question of the low rates of risk-asset participation in face of a favorable investment environment. Historical context is drawn upon to argue that the present situation, wherein most financial assets are kept as cash, is rather the result of the historical path dependence than the present-day conditions in which Japanese retail investors operate. The final chapter addresses the question of high-risk activities in the form of gambling and margin trading by a group of predominantly middle-aged men and connects this propensity to engage in zero-sum games with Bitcoin’s success in Japan. The author argues that the solitary practice of high-risk financial activities enabled by trusted institutions is separate from the general savings tradition that suffered shocks following the low interest-rate regime and that it was the high-risk gambles that became the primary cause for the popularity of Bitcoin. The dissertation concludes with the argument that the success of Bitcoin in 2017 had been in no small part achieved precisely by inverting the hard-line libertarian values of its creators and making it a centrally-held commodity offered by a banking-like institution with a strong public presence