2,333 research outputs found

    Size-efficient interval time stamps

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    http://www.ester.ee/record=b4338625~S1*es

    Post-Quantum Secure Time-Stamping

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    Krüptograafilisi ajatempliprotokolle kasutatakse tõestusena, et üks dokument eksisteeris enne teist. Postkvantkrüptograafiliselt turvalised ajatempliprotokollid uurivad, kas neid tõestusi on võimalik võltsida kasutades kvantarvuteid. Tegu on suuresti uurimata alaga, kuna võtmeta ajatempliprotokollides kasutatavates primitiivides pole seni leitud kvantarvutite kontekstis tõsiseid nõrkusi. Selles töös me defineerime, mis on post-kvant turvalised ajatempliprotokollid ning uurime kuidas klassikalised tulemused muutuvad uues raamistikus. Suur erinevus kvantvastaste puhul on see, et meil ei ole võimalik saada suvalise kvantalgoritmi mitut erinevat käivitust. Tänapäeval teadaolevad tagasipööramise võtted võimaldavad kvantalgoritmi tagasi pöörata ainult väga kindlatel tingimustel. Me uurime nende võtete kombineerimise võimalikkust ühe teoreemi tõestamiseks. Sellele teoreemile ei ole hetkel post-kvant standardmudelis ühtegi tõestust. Me pakume tõestuseta ühe tagasipööramise konstruktsiooni, mille abil võib osutuda teoreemi tõestamine võimalikuks. Me lisaks pakume välja ka minimaalse lahendamata probleemi, mis on esimene samm teoreemi formaalse tõestamiseni.Cryptographic timestamps are used as proof that a certain document existed before another. Post-quantum secure time-stamping examines whether these proofs can be forged using a quantum computer. The field is very unexplored as the primitives used in keyless time-stamping have not shown any serious weakness towards quantum computers. Until now no effort had been made towards formally defining post-quantum secure time-stamping. In this work, we define the notion of post-quantum time-stamping and examine how contemporary classical results change in this new framework. A key difference in the post-quantum setting is that we cannot retrieve multiple separate executions of an arbitrary quantum adversary. Currently known rewinding techniques allow an adversary to be ran again only under very specific conditions. We examine the possibility of combining existing rewinding techniques to prove a theorem for which there is currently no proof in the standard post-quantum model. We conjecture a rewinding construction which could possibly prove the theorem and establish a minimal open problem for formally proving the theorem

    Better Prefix Authentication

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    We present new schemes for solving prefix authentication and secure relative timestamping. By casting a new light on antimonotone linking schemes, we improve upon the state of the art in prefix authentication, and in timestamping with rounds of bounded length. Our designs can serve as more efficient alternatives to certificate transparency logs.Comment: 11 pages, 14 figure

    Engineering poly(ethylene glycol) nanogel coatings: Developments in achieving ultralow protein adsorption and applications as substrates for stem cell culture

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    The biocompatibility of biomaterials is primarily dictated by the interactions that occur at the material\u27s interface with its biological environment. Proteins irreversibly adsorb to these interfaces within seconds to minutes of exposure, altering their structural conformation, inducing cell adhesion, and activating various cellular responses. To this end, surface modification strategies have been designed in attempts to develop stealth biomaterials or even biomaterials that modulate this response by inducing specific biological reactions. We sought to advance the design of biomaterial surfaces by quantitatively studying protein adsorption to ultralow protein adsorbing surfaces formed from poly(ethylene glycol) nanogel coatings of variable structural and chemical properties. We found that resistance to protein adsorption can be improved by increasing the nanogel coating\u27s surface packing density, which is achievable using orthogonal cross-linking chemistries, such as click chemistry, under phase separation conditions. We also confirmed that PEG and albumin act synergistically within nanogel coatings to resist protein adsorption. As a demonstration of the utility for such protein resistant surfaces, we fabricated improved cell culture substrates with nanogel coatings, by spatially patterning cell adhesion and functionalizing surfaces with specific ligands. These surfaces showed superior potential for driving the direct reprogramming of fibroblasts to cardiomyocytes over the standard stem cell substratum of Matrigel and revealed insight into optimal cellular organizations for cardiomyocyte differentiation. However, we also unexpectedly found that adsorption of laminin to mercaptosilanated glass promotes a relatively high efficiency of cardiomyocyte differentiation. The findings outlined in this dissertation demonstrate that consideration of often overlooked material design parameters, in addition to the choice of material, provides further opportunity for improving biocompatibility. We further demonstrated that the precision control of cell adhesion and substratum signaling provided by these materials has broad potential in biological applications, including stem cell culture

    A New Approach to Constructing Digital Signature Schemes (Extended Paper)

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    A new hash-based, server-supported digital signature scheme was proposed recently. We decompose the concept into forward-resistant tags and a generic cryptographic time-stamping service. Based on the decomposition, we propose more tag constructions which allow efficient digital signature schemes with interesting properties to be built. In particular, the new schemes are more suitable for use in personal signing devices, such as smart cards, which are used infrequently. We define the forward-resistant tags formally and prove that (1) the discussed constructs are indeed tags and (2) combining such tags with time-stamping services gives us signature schemes

    Overview of blockchain technology cryptographic security

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    This thesis work is aimed at developing understanding of the hash functions and algorithms being used in blockchain technologies Bitcoin in comparison to Ethereum and private blockchain hash functions. This study attempts to answer one fundamental research question: “What considerations are important in assessing blockchain cryptographic security, with an emphasis on hash functions”. The study was carried out qualitatively using a desk research approach and combining this approach with using two public blockchains-based cryptocurrencies; Ethereum and Bitcoin as case studies. The research aims to provide a holistic view of blockchain cryptographic security comparing Bitcoin and Ethereum as use cases, and thus providing a consolidated document which students studying cryptography can access to obtain a better understanding of what is involved in blockchain security. From an academic perspective, the research aims at providing a model which can be used in assessing what is important to consider in the cryptographic security of blockchains. Three main categories of factors considered were presented in the proposed model which were strategical factors, complexity attributes and technical drivers. This results in a base crucial metrics such as absence of secret seeds, efficiency of verification, preimage collision resistance, fixed output size, low collision probability, and even distribution of preimages in output
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