233 research outputs found
Line-Point Zero Knowledge and Its Applications
No full textWe introduce and study a simple kind of proof system called line-point zero knowledge (LPZK). In an LPZK proof, the prover encodes the witness as an affine line (t) : = at + in a vector space ⁿ, and the verifier queries the line at a single random point t = α. LPZK is motivated by recent practical protocols for vector oblivious linear evaluation (VOLE), which can be used to compile LPZK proof systems into lightweight designated-verifier NIZK protocols.
We construct LPZK systems for proving satisfiability of arithmetic circuits with attractive efficiency features. These give rise to designated-verifier NIZK protocols that require only 2-5 times the computation of evaluating the circuit in the clear (following an input-independent preprocessing phase), and where the prover communicates roughly 2 field elements per multiplication gate, or roughly 1 element in the random oracle model with a modestly higher computation cost. On the theoretical side, our LPZK systems give rise to the first linear interactive proofs (Bitansky et al., TCC 2013) that are zero knowledge against a malicious verifier.
We then apply LPZK towards simplifying and improving recent constructions of reusable non-interactive secure computation (NISC) from VOLE (Chase et al., Crypto 2019). As an application, we give concretely efficient and reusable NISC protocols over VOLE for bounded inner product, where the sender’s input vector should have a bounded L₂-norm
Interview: Jason Dittmer Interviewed by Steven M. Schnell, Editor, The Geographical Bulletin
No full textJason Dittmer is from Jacksonville, Florida, received his PhD from Florida State University in 2003, and has taught at University College London in the United Kingdom since 2007. He is the author of Popular Culture, Geopolitics, and Identity (Rowman and Littlefield, 2010) and the co-editor of Mapping the End Times: American Evangelical Geopolitics and Apocalyptic Visions (Ashgate, 2010). He is married to the lovely Stephanie and has two cats. They all live in southeast London
Improving Line-Point Zero Knowledge: Two Multiplications for the Price of One
No full textRecent advances in fast protocols for \textit{vector oblivious linear evaluation} (VOLE) have inspired a family of new VOLE-based lightweight designated-verifier NIZK protocols (Weng et al., S\&P 2021, Baum et al., Crypto 2021, Dittmer et al., ITC 2021, Yang et al., CCS 2021). In particular, the Line-Point Zero Knowledge (LPZK) protocol of Dittmer et al.\ has the advantage of being entirely non-cryptographic given a single instance of a random VOLE correlation.
We present improvements to LPZK through the introduction of additional structure to the correlated randomness. Using an efficiently realizable variant of the VOLE correlation, we reduce the online proof size of LPZK by roughly 2x: from roughly 2 field elements per multiplication gate, or 1 element in the random oracle variant, to only 1 or elements respectively. In particular, we get the first practical VOLE-based NIZK that breaks the 1-element-per-multiplication barrier.
We implemented an optimized version of our protocol and compared it with other recent VOLE-based NIZK protocols. In the typical case where communication is the bottleneck, we get at least 2x performance improvement over all previous VOLE-based protocols. When prover computation is the bottleneck, we outperform all non-LPZK protocols by at least -x and (our optimized implementation of) LPZK by roughly 30%, obtaining a -x slowdown factor compared to plain circuit evaluation
Characterisation of organic materials for photovoltaic devices
No full textThis thesis presents an investigation into a wide range of potential materials
for organic photovoltaic (PV) devices. A variety of optical techniques
are used to define physical parameters for each material such
as the photoluminescence quantum yield (PLQY), absorption coefficient
and exciton diffusion length. Electrical characterisation is used to determine
the optimal structure for devices fabricated with these materials.
A number of novel materials are presented in this thesis. These include
new polymers, both soluble and precursor, and a relatively new class
of material, the conjugated dendrimer. These are highly configurable
branching molecular structures that enable fine tuning of material properties.
Work on polymers presented in this thesis investigates how such materials
can be improved by testing the effect of small changes to their
molecular structure. One of these changes had significant effects upon
the overall material characteristics. The introduction of a dipole across
a polymer successfully created a charge separating material without the
need for an extra species such as C60 to be present.
The introduction of the conjugated dendrimer to PV applications allows
significant scope for molecular engineering. Dendrimers enable tight
control over certain aspects of the molecular properties. Small changes
can be made such as colour tuning or solubility that enable optimisation
to be performed on the molecular level, rather than on device structure.
Such changes produced significantly higher internal quantum efficiencies
(> 90%) than typical polymer devices and offer the prospect of power
conversion efficiencies in excess of 10%.
Time-resolved luminescence (TRL) spectroscopy was used to characterise
the behaviour of photogenerated excitons within organic films. The investigation
of exciton diffusion length was performed upon two polymers,
each utilising two different time-resolved methods; diffusion to a quencher
and exciton-exciton annihilation. It was found that diffusion in
polythiophene films is anisotropic and the photoluminescence lifetime
is dependent upon film thickness. This is explained by the formation of
self-ordered microstructures during the spin coating process. Data modelling
was performed which took into account both the thickness variation
and the interaction of excitons with a quenching interface producing
a much more realistic approach than previously published work
Mapping the political geographies of Europeanization: National discourses, external perceptions and the question of popular culture
No full textPolitical geographers have significantly contributed to understandings of the spatialities of Europeanization. We review some of this work, while also highlighting research themes where further political-geographic research would be insightful. We note the importance of work that captures both the diverse expressions and meanings attributed to Europe, European integration and 'European power' in different places within and beyond the EU, and the variegated manifestations of 'Europeanizing' processes across these different spaces. We also suggest that political-geographic research can add crucial input to reconceptualizing European integration as well as Europeanization as it now unfolds in a time of 'crisis'. © The Author(s) 2012
A year in Labour: rethinking political parties, campaigns and elections through assemblage and affect
No full textThis thesis argues for a different approach towards the study of elections, campaigns and political parties than has conventionally been pursued in political and electoral geography. I argue that approaches in electoral geography have neglected the everyday lived experience of elections, and in political geography of recent there has been a distinct lack of consideration of the 'political party'. These issues have not gone unnoticed in either field and so I am answering several calls for renewal. To do this, I theorise campaigns, elections and parties through the Deleuzo-Guattarian (2013a, 2013b) concepts of assemblage and affect, highlighting the themes of people, materials and technology in my analysis. Starting with Labour's 2014 Manchester Conference and ending at their 2015 Brighton Conference, I conducted an ethnographical study of the British Labour Party and its relationship to the 7 May 2015 UK General Election. During this period, I participated in Labour's campaign for Hove in the south coast, interviewed participants of the wider Brighton and Hove Labour Party campaigns, recorded how social media related to the election and the subsequent Labour leadership election and lastly, conducted a discourse analysis. By focusing on the themes of leadership, people and materials through relations and experience, I show that there is a different iteration of the party that is becoming in each moment. I conclude by drawing out some theoretical discussions around assemblage and affect, specifically the notion of the 'abstract machine', arborescent/rhizomatic structures and the 'war machine'. I contribute to both electoral geography and political geography by reconceptualising elections, campaigns and political parties as entangled in a bodied, material, emotional and relational world
Oblivious Tight Compaction In O(n) Time with Smaller Constant
No full textOblivious compaction is a crucial building block for hash-based oblivious RAM. Asharov et al. recently gave a O(n) algorithm for oblivious tight compaction. Their algorithm is deterministic and asymptotically optimal, but it is not practical to implement because the implied constant is . We give a new algorithm for oblivious tight compaction that runs in time . As part of our construction, we give a new result in the bootstrap percolation of random regular graphs
Challenges to Chinese Foreign Policy: Diplomacy, Globalization, and the Next World Power
No full textWhen Beijing hosted the 2008 Summer Olympics, China symbolically asserted its role as an emerging world power—a position it is not likely to relinquish anytime soon. China’s growing economy, military reforms, and staggering productivity have contributed to its ascendancy as a major player in international affairs. Western scholars have attempted to explain Chinese foreign policy using historical or theoretical evidence, but until this volume, few studies from a Chinese perspective have been published in English.
In Challenges to Chinese Foreign Policy: Diplomacy, Globalization, and the Next World Power, editors Yufan Hao, C. X. George Wei, and Lowell Dittmer reveal how Chinese scholars view their nation’s rise to global dominance. Drawing from a wealth of foreign relations experts including scholars native to the region, this volume examines the unique challenges China faces as it adapts in its role as a world leader, and it analyzes how China’s evolving international relationships are shaping the global landscape of the twenty-first century.
Yufan Hao is professor of political science at Colgate University, as well as professor and dean of the Faculty of Social Sciences and Humanities, the University of Macau.
George Wei is associate professor of history at Susquehanna University, PA, as well as associate professor and coordinator of the History Program, the Faculty of Social Sciences and Humanities, the University of Macau.
Lowell Dittmer is professor of political science at the University of California at Berkeley.
This is an important and timely work. It increases our understanding of PRC foreign policy and the factors that shape it. —Dennis V. Hickey, author of Foreign Policy Making in Taiwan: From Principles to Pragmatism
This volume makes a significant contribution to scholarship in Chinese foreign policy by examining challenging theoretical and policy issues. The authors ask important questions and help to solve multiple puzzles in Chinese foreign policy. —Guoli Liu
“This collection . . . seeks to offer an alternative approach to western views of China’s rapidly developing international relations in light of sweeping changes to its global role...as well as fresh insights on some of the most important past and present issues relating to the country’s ongoing opening to the world.”—International Affairs
“The essays afford insight into China’s aims and attitudes. There are equally useful chapters on the questions of Taiwan, Hong Kong and Macao, and North Korea. —Asian Affairs
“Empirically rich . . . this book is one of the very few in English that present the perspectives of Chinese scholars on China\u27s foreign policy.”—China Review International
“Eight highly knowledgeable scholars have jointly made this book exemplary.”—Journal of Chinese Political Science
“The volume is a great resource for students and researchers working on Chinese diplomatic history, as it gives a useful survey of the various topics in Chinese foreign relations. —China Quarterlyhttps://uknowledge.uky.edu/upk_political_science_international_relations/1008/thumbnail.jp
1-private n-party AND from 5 random bits
No full textIn the field of information-theoretic cryptography, randomness complexity is a key metric for protocols for private computation, that is, the number of random bits needed to realize the protocol. Although some general bounds are known, even for the relatively simple example of -party AND, the exact complexity is unknown.
We improve the upper bound from Couteau and Ros\\u27en in Asiacrypt 2022 on the (asymptotic) randomness complexity of -party AND from 6 to 5 bits, that is, we give a -private protocol for computing the AND of parties\u27 inputs requiring bits of additional randomness, for all . Our construction, like that of Couteau and Ros\\u27en, requires a single source of randomness.
Additionally, we consider the modified setting of Goyal, Ishai, and Song (Crypto \u2722) where helper parties without any inputs are allowed to assist in the computation. In this setting, we show that the randomness complexity of computing a general boolean circuit -privately is exactly 2 bits, and this computation can be performed with seven helper parties per gate
Characterisation of materials for organic photovoltaics
No full textOrganic solar cells offer the possibility for lightweight,
flexible, and inexpensive photovoltaic devices. This thesis
studies the physics of a wide range of materials designed for use
in organic solar cells. The materials investigated include
conjugated polymers, conjugated dendrimers, and inorganic
nanocrystals.
The materials studied in this thesis fall into five categories:
conjugated polymers blended with a buckminsterfullerene derivative
PCBM, nanocrystals synthesised in a conjugated polymer matrix,
conjugated polymers designed for intramolecular charge separation,
conjugated dendrimers blended with PCBM, and nanocrystals
synthesised in a matrix of conjugated small molecules or dendrimers.
Conjugated polymers blended with PCBM have been extensively
studied for photovoltaic applications, and hence form an ideal
test bed for new experiments. In this thesis this blend was used
to achieve the first pulsed electrically detected magnetic
resonance experiments on organic solar cells.
Nanocrystals are attractive for photovoltaics because it is
possible to tune their band gap across the solar spectrum. In this
thesis a one-pot synthesis is used to grow PbS and CdS
nanocrystals in conjugated polymers, soluble small molecules, and
dendrimers, and characterisation is performed on these composites.
Previous work on dendrimer: nanocrystal composites has been
limited to non-conjugated molecules, and the synthesis developed
in this thesis extends this work to a conjugated oligomer and a
conjugated dendrimer. This synthesis can potentially be extended
to a variety of conjugated soluble small molecule: nanocrystal and
dendrimer: nanocrystal systems.
Conjugated dendrimers have been successfully employed in organic
light emitting diodes, and in this thesis they are applied to
organic solar cells. Materials based on fluorene and cyanine dye
cores show excellent absorption tunability across the solar
spectrum.
A set of electronically asymetric polymers designed for
intramolecular charge separation were investigated. Quenching of
the luminescence was observed, and light induced electron
paramagnetic resonance measurements revealed that photoexcitation
led to approximately equal numbers of positive polarons and nitro
centred radical anions. This indicates that charge separation is
occurring in these molecules
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