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A measurement study of peer-to-peer bootstrapping and implementations of delay-based cryptography
Get PDFThis thesis researches two distinct areas of study in both peer-to-peer networking formodern cryptocurrencies and implementations of delay-based cryptography.The first part of the thesis researches elements of peer-to-peer network mechanisms,with a specific focus on the dependencies on centralised infrastructure required for theinitial participation in such networks.Cryptocurrencies rely on decentralised peer-to-peer networks, yet the method bywhich new peers initially join these networks, known as bootstrapping, presents a significantchallenge. Our original research consists of a measurement study of 74 cryptocurrencies.Our study reveals a prevalent reliance on centralised infrastructure which leadsto censorship-prone bootstrapping techniques leaving networks vulnerable to censorshipand manipulation.In response, we explore alternative bootstrapping methods seeking solutions lesssusceptible to censorship. However, our research demonstrates operational challengesand limitations which hinder their effectiveness, highlighting the complexity of achievingcensorship-resistance in practice.Furthermore, our global measurement study uncovers the details of cryptocurrencypeer-to-peer networks, revealing instances outages and intentional protocol manipulationimpacting bootstrapping operations. Through a volunteer network of probes deployedacross 42 countries, we analyse network topology, exposing centralisation tendencies andunintentional peer exposure.Our research also highlights the pervasive inheritance of legacy bootstrapping methods,perpetuating security vulnerabilities and censorship risks within cryptocurrencysystems. These findings illuminate broader concerns surrounding decentralisation andcensorship-resistance in distributed systems.In conclusion, our study offers valuable insights into cryptocurrency bootstrappingtechniques and their susceptibility to censorship, paving the way for future research andinterventions to enhance the resilience and autonomy of peer-to-peer networks.In the second part of the thesis, attention shifts towards delay-based cryptography,where the focus lies on the creation and practical implementations of timed-release encryptionschemes. Drawing from the historical delay-based cryptographic protocols, thisthesis presents two original research contributions.The first is the creation of a new timed-release encryption scheme with a propertytermed implicit authentication. The second contribution is the development of a practicalconstruction called TIDE (TIme Delayed Encryption) tailored for use in sealed-bidauctions.Timed-Release Encryption with Implicit Authentication (TRE-IA) is a cryptographicprimitive which presents a new property named implicit authentication (IA). This propertyensures that only authorised parties, such as whistleblowers, can generate meaningfulciphertexts. By incorporating IA techniques into the encryption process, TRE-IAaugments a new feature in standard timed-release encryption schemes by ensuring thatonly the party with the encryption key can create meaningful ciphertexts. This propertyensures the authenticity of the party behind the sensitive data disclosure. Specifically, IAenables the encryption process to authenticate the identity of the whistleblower throughthe ciphertext. This property prevents malicious parties from generating ciphertextsthat do not originate from legitimate sources. This ensures the integrity and authenticityof the encrypted data, safeguarding against potential leaks of information not vettedby the party performing the encryption.TIDE introduces a new method for timed-release encryption in the context of sealedbidauctions by creatively using classic number-theoretic techniques. By integratingRSA-OEAP public-key encryption and the Rivest Shamir Wagner time-lock assumptionwith classic number theory principles, TIDE offers a solution that is both conceptuallystraightforward and efficient to implement.Our contributions in TIDE address the complexities and performance challengesinherent in current instantiations of timed-release encryption schemes. Our researchoutput creates a practical timed-release encryption implementation on consumer-gradehardware which can facilitate real-world applications such as sealed-bid auctions withclear steps for implementation.Finally, our thesis concludes with a review of the prospects of delay-based cryptographywhere we consider potential applications such as leveraging TIDE for a publicrandomness beacon.<br/
Thermal Working Paper #1:Heat Stress in the Cambodian Brick Sector
Get PDFWorkers in the Cambodian brick sector face an exceptionally high risk of heat stress due to undertaking heavy work in high temperatures and humidities, as well as working around very hot environments during and after brick firing. Under climate change, this risk is increasing, as very hot days become more common. In Cambodia, the number of very hot days – meaning days over 35˚C or a Heat Index of 55+ assuming average humidity of 77% (UNICEF, 2022) – have increased by 46 days per year since 1990 (World Bank, 2021). This working paper presents data from a survey of 30 brick workers in three kilns undertaken from 25th of March to May 5th 2023
The unaccounted effects of digital transformation:Participatory accountability in a humanitarian organisation
Get PDFModelling the Longitudinal Dynamics of Paranoia in Psychosis:A Temporal Network Analysis Over 20 Years
Get PDFParanoia is a highly debilitating, core element of psychosis, although is poorly managed. Theories of paranoia mostly interface with short-scale or cross-sectional data models, leaving the longitudinal course of paranoia underspecified. Here, we develop an empirical characterisation of two aspects of paranoia - persecutory and referential delusions - in individuals with psychosis over 20 years. We examine delusional dynamics by applying a Graphical Vector Autoregression Model to data collected from the Chicago Follow-up Study. We adjusted for age, sex, IQ, and antipsychotic use. We found that referential and persecutory delusions are central themes, supported by other primary delusions, and are strongly autoregressive. In a second analysis we demonstrate that social factors influence the severity of referential, but not persecutory, delusions. We suggest that persecutory delusions represent central, resistant states in the cognitive landscape, whereas referential beliefs are more flexible, offering an important window of opportunity for intervention. Our data models can be collated with prior biological, computational, and social work to contribute toward a more complete theory of paranoia and provide more time-dependent evidence for optimal treatment targets
The seed morphospace, a new contribution towards the multidimensional study of angiosperm sexual reproductive biology
Get PDF• Background. The evolutionary success of flowering plants is associated with the vast diversity of their reproductive structures. Despite recent progress in understanding angiosperm-wide trends of floral structure and evolution, a synthetic view of the diversity in seed form and function across angiosperms is lacking.• Scope. Here we present a roadmap to synthesise the diversity of seed forms in extant angiosperms, relying on the morphospace concept, i.e. a mathematical representation which relates multiple traits and describes the realised morphologies. We provide recommendations on how to broaden the range of measurable traits beyond mass, by using key morphological traits representative of the embryo, endosperm, and seed coat but also fruit attributes (e.g., dehiscence, fleshiness). These key traits were used to construct and analyse a morphospace to detect evolutionary trends and gain insight into how morphological traits relate to seed functions. Finally, we outline challenges and future research directions, combining the morphospace with macroevolutionary comparative methods to underline the drivers that gave rise to the diversity of observed seed forms.• Conclusions. We conclude that this multidimensional approach has the potential, although still untapped, to improve our understanding of covariation among reproductive traits, and further elucidate angiosperm reproductive biology as a whole
The dimorphic diaspore model Aethionema arabicum (Brassicaceae):Distinct molecular and morphological control of responses to parental and germination temperatures
Get PDFPlants in habitats with unpredictable conditions are often characterized by diversifying their bet-hedging strategies that ensure fitness over a wider range of variable environmental factors. A striking example is the diaspore (seed and fruit) heteromorphism that evolved to maximize species survival in Aethionema arabicum (Brassicaceae) in which external and endogenous triggers allow the production of two distinct diaspores on the same plant. Using this dimorphic diaspore model, we identified contrasting molecular, biophysical, and ecophysiological mechanisms in the germination responses to different temperatures of the mucilaginous seeds (M+ seed morphs), the dispersed indehiscent fruits (IND fruit morphs), and the bare non-mucilaginous M- seeds obtained by pericarp (fruit coat) removal from IND fruits. Large-scale comparative transcriptome and hormone analyses of M+ seeds, IND fruits, and M- seeds provided comprehensive datasets for their distinct thermal responses. Morph-specific differences in co-expressed gene modules in seeds, as well as seed and pericarp hormone contents identified a role of the IND pericarp in imposing coat dormancy by generating hypoxia affecting ABA sensitivity. This involved expression of morph-specific transcription factors, hypoxia response and cell wall-remodeling genes, as well as altered abscisic acid (ABA) metabolism, transport, and signaling. Parental temperature affected ABA contents and ABA-related gene expression and altered IND pericarp biomechanical properties. Elucidating the molecular framework underlying the diaspore heteromorphism can provide insight into developmental responses to globally changing temperatures
Neural Inference Search for Multiloss Segmentation Models
Get PDFSemantic segmentation is vital for many emerging surveillance applications, but current models cannot be relied upon to meet the required tolerance, particularly in complex tasks that involve multiple classes and varied environments. To improve performance, we propose a novel algorithm, Neural Inference Search (NIS), for hyperparameter optimisation pertaining to established deep learning segmentation models in conjunction with a new multi-loss function. It incorporates three novel search behaviours, i.e. Maximised Standard Deviation Velocity Prediction, Local Best Velocity Prediction, and n-dimensional Whirlpool Search. The first two behaviours are exploratory, leveraging Long Short-Term Memory (LSTM)-(Convolutional Neural Network) CNN based velocity predictions, while the third employs n-dimensional matrix rotation for local exploitation. A scheduling mechanism is also introduced in NIS to manage the contributions of these three novel search behaviours in stages. NIS optimises learning and multi-loss parameters simultaneously. Compared with state-of-the-art segmentation methods and those optimised with other well-known search algorithms, NIS-optimised models show significant improvements across multiple performance metrics on five segmentation datasets. NIS also reliably yields better solutions as compared with a variety of search methods for solving numerical benchmark functions
Enacted Offstage Images, Reported Onstage Action, and Parallel Fictional Worlds in Dead Centre’s Chekhov’s First Play (2015) and Tim Crouch and Rachana Jadhav’s Total Immediate Collective Imminent Terrestrial Salvation (2019)
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Pred-Pol-Pov:Visibility, data flows and the predictive policing of poverty
Get PDFPredictive and data-driven policing systems continue to proliferate around the world enticing police forces with promises of improvements in efficiency and the ability to offer various ways of addressing the future to pre-empt, predict, or prevent crime. As more of these systems become operationalised in England and Wales, this paper takes up Duarte's (2021) observation of a lack of description as to what such systems actually are. It adapts a social network methodology to explore what a data-driven policing system is. Using a police force in England, UK, as a case study, we provide a visualisation of a data-driven policing system based on the data flows it requires to operate. We show how a disparate network of affiliate organisations act as collators of specific data types which are then used in a range of policing applications. The paper makes visible how data travels from its source through various nodes and the different potential points of translation that occur. We uncover how certain groups are made visible to the police due to the data being shared within a network of institutions and organisations, and as others have argued before us, how the data points that make this network visibility possible are often proxies for poverty. This makes certain groups and sections of society highly visible to the digital system whilst other groups become less visible – and potentially even hidden
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