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Contributions to Provable Security of Digital Signatures in AGM
No full textDigital signatures allow digital documents to be signed in a secure manner. Unlike electronic signatures (handwritten), in a digital signature scheme, a signer has a pair of keys: a secret key and a public key. The signer uses the secret key to create signatures on messages, and these signatures are publicly verifiable under the corresponding public key.In cryptography, provable security is important because it provides a formal and reliable way to ensure the security of cryptographic schemes. One can prove and measure the security of a scheme based on three factors: security models, hardness assumptions, and reduction probability. In the security proofs, we use reduction techniques to construct a reduction algorithm that runs an efficient adversary under a pre-defined security model, which is assumed to break the scheme, to successfully solve some hard problems. Based on the reduction, the security of the signature scheme is related to the hard problem and the probability of success in solving the problem - the contradiction concludes that the scheme must be secure. A signature scheme achieves ideal security, which provides the highest level of security, if its security is proven under a standard security model, namely existential unforgeability under chosen-message attacks (EUF-CMA), and the hardest problem, which is the weakest of the standard computational assumptions in cryptography, with a tight reduction known as the constant probability of success without dependence on the number of queries made by the adversary.While a signature scheme can theoretically provide robust security, it is equally important that it is practical for real-world applications. A signature scheme is considered practical if the size of its signature element remains constant, regardless of external factors such as the message size or the limited number of signatures the scheme can generate. In the context of group-based signatures, several practical signature schemes have been proposed under the hardest (fundamental) problem, known as the discrete logarithm (DL) problem. However, none of them achieves the ideal security because the existing proof techniques suffer from the inherent reduction loss. To achieve this goal, security reductions in the algebraic group model (AGM), which idealises the adversary’s computation to be algebraic, with random oracles (hash function behaves like a random function) are one of the candidates in the cyclic group settings.The first half of this thesis focuses on the adoption of AGM only to achieve practical digital signature schemes that can be tightly reduced to the DL problem under EUF-CMA.• In Chapter 3, we show for the first time how to use AGM to prove security without random oracles by obtaining a new tightly EUF-CMA secure signature scheme under the DL assumption. Since the introduction of AGM, some practical signature schemes can now achieve ideal security in AGM with random oracles. In this chapter, we study the challenge of proving signature schemes without random oracles in AGM. We revisit the security of a practical signature scheme derived from Boneh-Boyen’s (BB) ID-based encryption scheme at Eurocrypt’04, namely BB signatures, and show that the public key size of the scheme can be reduced to a single group element. By carefully embedding the DL problem instance (without random oracles), the proposed security reduction manages to obtain a modular quadratic equation due to the algebraic adversary, allowing for the extraction of the DL solution with an overwhelming success probability.• In Chapter 4, we adopt AGM to obtain a new randomisable signature scheme that is as secure as the DL problem under the EUF-CMA without random oracles features with constant signature element size and it is instantiable to the anonymous credential systems. The Camenisch-Lysyanskaya (CL) signature scheme has been widely adopted in many privacy-preserving systems, i.e. anonymous credential systems, due to its randomisability, i.e. signatures can be randomised by anyone holding the signatures. Unfortunately, the size of the CL signature elements grows with the size of the messages to be signed, and its EUF-CMA security is not tight under DL assumptions even in AGM. In this chapter, we propose a new variant, namely CL+ signatures, which have randomisability without the linear size disadvantage. This means that the signature size remains constant at three group elements, regardless of the size of the messages. Furthermore, we prove that the EUF-CMA security of CL+ signatures can tightly reduce the DL problem in AGM with a loss factor of 3. Finally, we show how CL+ signatures can serve as a building block for anonymous credential systems.The second half of this thesis is the study of identity (ID)-based signatures (IBS). The need for a public key infrastructure (PKI) arises from its role in binding the public key to a signer, ensuring the authenticity and integrity of communications. However, managing a PKI can be costly and complex due to key management and certificate issuance. To address these challenges, the notion of IBS has been introduced. IBS replaces the signer’s public key with a user’s identity (e.g., email and ID number), thereby eliminating the need for a PKI and substantially reducing the associated costs. The standard EUF-CMA security model for IBS, namely existential unforgeability under chosen identity-and-message attacks (EUF-ID-CMA), additionally captures the chosen identity attacks. In the second aspect of this thesis, we study how the adoption of the AGM can help achieve the ideal security of IBS schemes.• In Chapter 5, we show for the first time how to use AGM to prove the EUF-IDCMA security of IBS schemes as secure as the DL problem. To date, none of the existing IBS are tightly secure under the EUF-ID-CMA and DL assumption. Unlike the EUF-CMA for digital signatures, the most challenging part of achieving a tight reduction in IBS is that extra cautions are needed while simulating the user’s private key due to the chosen identity-and-message attacks. In this chapter, we obtain two IBS schemes with and without random oracles, respectively. The first scheme is derived based on well-known BLS signatures with random oracles and features a signature size of two group elements. The second scheme is obtained based on the aforementioned EUF-CMA secure BB signatures without random oracles, and it features a signature size of three group elements. This demonstrates the trade-offs between efficiency and security. While proving their EUF-ID-CMA security under DL assumption, we identify additional measures required to address the chosen identity attacks. Fortunately, the security proofs can be achieved through two indistinguishable simulations, allowing the simulator to extract the DL solution by randomly running one of them. Both of the schemes feature a reduction loss factor of two.• In Chapter 6, we utilise AGM to obtain the first pairing-free, tightly EUF-ID-CMA secure IBS under DL assumption. Although the introduction of pairing-based cryptography is powerful enough to achieve tight reduction under weak assumptions (but not the DL assumption) for IBS schemes, pairing-free cryptography is desirable because it avoids the computationally expensive operations of pairing-based schemes and ensures compatibility with existing cryptographic standards. The Schnorr-like IBS at AfricaCrypt’09 is known to be the most efficient IBS based on the DL problem, without the need for computationally expensive operations, and it is compatible with existing Schnorr signatures. However, the EUF-ID-CMA security of Schnorr-like IBS is not tight under the DL assumption. In this chapter, we first study the fact that why the Schnorr-like IBS is hard to be tightly secure under EUF-ID-CMA and DL assumption - even in AGM with random oracles. We then resolve this challenge, in AGM with random oracles, by using the OR-proof technique to generate the user’s private key containing the DL of either one of the two random group elements, leading to a new pairing-free IBS scheme that can be tightly reduced to the DL problem under EUF-ID-CMA.</p
Qualitative case studies in suicide research: a novice researcher's reflections
No full textBACKGROUND: The suicide process is a complex and uniquely individual phenomenon. The need to understand and bring meaning to individual experiences of suicide is burgeoning amidst the growing global impacts of suicide. Qualitative case-study research uses multiple forms of evidence to investigate a phenomenon in a certain context. AIM: To present critical reflections on the lead author's doctoral project, which uses a case-study design to investigate people who have experience of suicide and are educating preregistration nurses on clinical placement. DISCUSSION: The lead author reflects critically on, and provides insights into, adopting the qualitative case-study methodology for suicide research, including: defining the role of the researcher; the appropriate use of methods of collecting data; and ensuring participants are safe. Reflexivity played an important role in ensuring the participants' and the lead author's well-being throughout the project, and the authors posit it as a central strategy in future research. CONCLUSION: Qualitative case-study research is a novel approach to suicide research that aligns with global suicide prevention frameworks and includes people's experiences in the formation of policies, design of interventions and education. Reflection should be a central strategy in such research. IMPLICATIONS FOR PRACTICE: Suicide research requires careful consideration and planning at every stage. Researchers must plan and evaluate participants' safety, the role of the researcher and data collection methods before, during and after the research.</p
Novel Mass Spectrometry Technologies for Enhancing Structural Characterisation and Imaging of Lipids in Biological Systems
No full textThe abstract for this item has not been populated.</p
Organic matter production and accumulation along tidal gradients of Australian coastal wetlands
No full textCoastal wetlands can store substantial carbon through organic matter accumulation, thereby influencing substrate volume. These processes collectively contribute to climate change mitigation through carbon sequestration and climate change adaptation by increasing the vertical position of substrates while sea level rises. Although, uncertainty about carbon fluxes via organic matter production and the contribution of sequestered carbon to surface elevation change remain. Variation in tidal behaviour along tidal gradients influences spatial vegetation structure, sedimentation and organic matter production. However, relationships between these factors and tidal position are not well defined. Holocene sea-level history partly underpins carbon storage and the contemporary position of coastal wetlands in the tidal frame, but limited information of organic matter accumulation processes in some settings reduces capacity to account for variability. Information about variation in organic matter production along tidal gradients is required, particularly for coastlines where sea level has been relatively stable for millennia.The aim of this thesis was to quantify spatiotemporal variation in organic matter production and stocks along tidal gradients in coastal wetlands, providing crucial information regarding associations between organic matter accumulation and relative sea-level rise (RSLR). The objectives of this thesis are, to: (1) characterise the influence of vegetation zonation and tidal position on root mass and volume dynamics within substrates; (2) characterise relationships between above-ground biomass, production, forest age and tidal position on a coral reef island; and (3) examine mangrove substrates and organic matter accumulation in the context of decadal- to millennial-scale sea-level history on a coral reef island. Short-term contributions of below-ground root mass and volume to production, standing stock and turnover were quantified using the root ingrowth technique and sediment coring along a tidal gradient at Kooweerup, Victoria, Australia. Root zone dynamics were primarily explained by variation in vegetation structure and composition, whereas tidal position imposed a secondary influence. Field-based mangrove structural measurements, and LiDAR and multispectral data were used on Low Isles, Great Barrier Reef, to investigate mangrove above-ground biomass production and canopy production. Above-ground biomass was positively correlated with forest age and tidal position, whereas above-ground biomass production and canopy production declined along this gradient. Substrate organic matter accumulation patterns were also examined using radiometric dating techniques (analysis of 210Pb, 239+240Pu, 236U and 14C dating), across mangrove age zones and tidal positions on Low Isles. Mangroves established on Low Isles within the past -200 years, and shallower below-ground carbon stores contrast sites where RSLR for millennia encouraged the development of deep mangrove peats.Mangrove age and/or structure influenced organic matter production at Kooweerup and Low Isles; sites where mangrove shoreline progradation established conditions for forest age and/or structure to co-relate to tidal gradients. Links to tidal gradients may be less defined elsewhere, particularly where tidal position and forest age are not coupled. At Kooweerup and Low Isles, below-ground organic matter production peaked in older, taller mangroves at higher tidal positions, indicating capacity for root volume storage and vertical adjustment with RSLR is enhanced at optimal tidal positions. Continued above-ground biomass accumulation in the oldest stand on Low Isles (-135 years old) contrasts to previous studies indicating mangrove biomass asymptotes at younger forest ages. Despite being positioned in a setting optimal for production (i.e., wet tropics), mineral sediment supply may constrain carbon accumulation patterns on Low Isles. Older, taller forests at sites where mangroves are expanding seaward continue to accumulate above- and below-ground organic matter and store carbon. Ongoing carbon accumulation at both sites demonstrates resilience to recent rates of RSLR. However, resilience under accelerating RSLR may be tested sooner on Low Isles where processes increasing mangrove substrate elevation are dominated by plant organic matter inputs. Knowledge of organic matter dynamics along tidal gradients is important, allowing for space-for-time substitution and modelling of coastal wetland substrate development with RSLR. Moreover, information about above- and below-ground carbon fluxes will improve accuracy of net ecosystem production accounts and forecasting potential carbon additions associated with blue carbon restoration initiatives.</p
Optimised nanobody-based quenchbodies for enhanced protein detection
No full textQuenchbodies, antibodies labelled with fluorophores that increase in intensity upon antigen binding, offer great promise for biosensor development. Nanobody-based quenchbodies are particularly attractive due to their small size, ease of expression, high stability, rapid evolvability, and amenability to protein engineering. However, existing designs for protein detection show limited dynamic range, with fluorescence increases of only 1.1–1.4 fold. Here we identify the tryptophan residues in the nanobody complementarity-determining regions (CDRs) that are critical to quenchbody performance. Using a combination of rational design and molecular dynamics simulations, we developed an optimised nanobody scaffold with tryptophans introduced at key positions. We used this scaffold in an in vitro directed-evolution screen against human inflammatory cytokine interleukin-6 (IL-6). This yielded quenchbodies with 1.5–2.4-fold fluorescence increases, enabling IL-6 detection down to 1–2 nM. Our scaffold provides a valuable platform for developing biosensors for diverse protein targets, with applications in research, diagnostics, and environmental monitoring. (Figure presented.)</p
The late Quaternary filling of Lake George, Australia: evidence from the Winderadeen Embankment
No full textLake George is the largest endorheic lake of eastern New South Wales, often thought of as the benchmark for southeastern Australia palaeoclimate reconstructions. Abandoned shoreline features surrounding the lake, show a history of lake level fluctuations and climate variability during the late Quaternary. To address the ongoing discussion of a wet versus arid Last Glacial Maximum (LGM), this study aims to revisit the classic Lake George palaeoclimate work of Coventry (1976), applying updated coring and dating techniques to create a more reliable depositional history of the largest abandoned shoreline feature, the Winderadeen Embankment. It is hypothesised that the embankment was deposited prior to the LGM, and therefore previous water balance studies may have provided unreliable estimates for precipitation predictions during the LGM.Two deep cores (LGWS1 = 19.3 m and LGWS2 = 14.4 m) were collected from the Winderadeen Embankment; a site of previous sedimentary investigations. Three dominant lacustrine facies units were identified: coarse- grained beach facies (sand and gravel), near shore facies (muddy gravel) and deep water facies (silt and clay). Twenty samples were chosen from each core to undergo a particle size analysis, and a total of five single-grain optically stimulated luminescence (OSL) samples were analysed as part of a broader project on Lake George. The results indicate that the bulk of the embankment was deposited from 43 to 58 ka, during Marine Isotope Stage (MIS) 3. The stratigraphy of the embankment suggests that the water level fluctuated between a maximum depth of 30 m and a minimum depth of 18 m during this time. Subsequently, the lake experienced an overall regression, with an estimated average depth of around 11 meters during the LGM. The updated water balance analysis, using simple water balance equations, suggests that this depth could be maintained during the LGM with less than half the modern mean precipitation. It was also shown that a depth of 11 m could be produced in modern times with a 18% decrease in annual evaporation or a 21% increase in precipitation or 17 years of a continuous La Niña.The palaeoenvironmental record shows a history of fluctuating climates and water levels during the late Quaternary, with the highest lake levels during MIS3. Although the LGM experienced exceptional depths, they were significantly lower than those in MIS3. The study suggests that southeastern Australia maintained a positive moisture balance during the LGM despite reduced precipitation, contributing significantly to the ongoing discussion of the region's climatic conditions during the late Quaternary. The implication of this research underscores the need for further investigation into the timing of lake level fluctuations during the deposition of the Winderadeen Embankment and to perform a sensitivity analysis of the water balance results.</p
Assessing Soil Properties Following a Cultural Burn in Southeast Australia
No full textSustaining soil health is necessary for supporting the structure and functioning of aboveground ecosystems (Neary et al. 1999). When exposed to fire, the soil’s physical, chemical, and biological constituents considered essential for these processes are susceptible to a range of functional changes. In southeast Australia, Traditional Custodians have utilised fire as a land management tool for thousands of years, with the purpose of protecting and enhancing the health and biodiversity of the landscape (Firesticks Alliance Indigenous Corporation 2022). Although the impact of bushfires and prescribed burns on soil properties is understood, little is known about the effect of cultural burning. Through a range of field- and laboratory-based experiments on NSW’s south coast, this study has shown Indigenous-led fire practices improves soil health, when contrasted with a government organised “cool” burn. The cultural burn’s low severity caused minimal volatilisation to soil organic matter, allowing for additional inputs to existing nutrient pools, this resulted in >1.5 times more carbon and nitrogen. Through this incorporation, bulk density and moisture content were enhanced, which are trends directly linked to improved soil functionality (Al-Shammary et al. 2018). Additionally, soil pH remained within the regions naturally occurring range (5.1-5.5), while salinity was found to be >57% lower. Although no differences in biological activity were observed, the culturally burnt environment is expected to benefit from improvements to the soil’s physiochemical parameters. Furthermore, this research demonstrates the benefit of cultural burn practices applied to Country for belowground ecosystems, in a region left largely untouched from Traditional Land Management for decades.</p
Impact of the Black Summer Bushfires on Coastal Wetlands of Wonboyn Lake, NSW
No full textThe 2019 / 2020 bushfires were the largest fire event in Australia’s recorded history, resulting in over 5.6 million hectares of land burnt in New South Wales alone, including extensive damage to mangroves and saltmarsh. This project focussed on Wonboyn Lake of NSW and assessed the coastal wetland vegetation dynamics pre-fire, extent of coastal wetland vegetation impacted post-fire, and quantifying the recovery of such vegetation post-fire. The study further produced a fire risk mapping method, examining the likelihood of a highly intense fire occurring (HIFO) across the catchment. While Wonboyn supports a relatively small area of mangroves in comparison to other estuaries, it supports a substantial area of saltmarsh. This study utilised remotely piloted aircraft surveys using spectral and LiDAR sensors, in-field elevation data collection, and remotely sensed datasets, that were processed using various analytical approaches. Pre-fire coastal wetland dynamics mapping indicated a generally stable state of vegetation extents, with saltmarsh area declining as mangrove area increased in 2013 and 2018, suggesting the encroachment of mangroves into saltmarsh as a result of sea level rise. Saltmarsh communities across the lake were comprehensively impacted by fire, with ~77% (34 ha) of the total saltmarsh population recorded as burnt in 2020. Mangrove populations were less affected immediately post-fire, with ~3% (45 m2) of the total 2020 mangrove population recorded as dead. Dead mangrove cover increased to 1016 m2 in 2023. Saltmarsh made a major recovery within one year post fire, with complete recovery observed by 2023. While mangrove mortality increased to 2023, recovery was slow with some recruitment of seedlings observed. The HIFO map visualises area’s most at risk within the Wonboyn catchment. Fire risk was observed to increase on westerly aspects and where elevation declines. Validation of the map against fire frequency shows promising results, where high and low thresholds overlap appropriately. Overall, this study provides important insights into the impact fires have on coastal wetland vegetation structure and recovery following a severe fire. Future research should consider monitoring implications the extended recovery of coastal wetlands has on other physical properties such as tidal frame positioning and soil structure. Consideration into the maps production and validation should also be undertaken, where a multiplicative method and comprehensive validation approach may improve map accuracy, allowing for future applications in management.</p
“Differences in Virtual and Physical Head Pose” Predict Cybersickness When Naturalistic Head-Movements are Made in VR
No full textWhen we move during virtual reality (VR) display lag produces Differences in our Virtual and Physical head pose (DVP). Research suggests that DVP can be used to predict cybersickness during head-mounted display (HMD) based VR. However, these studies always had participants make unusual (continuous oscillatory) head-movements. This study examined whether DVP also predicts cybersickness during more typical VR conditions. After assessing their susceptibility to real-world motion sickness (using the MSSQ-Revised), 67 participants repeatedly moved their heads to “target” objects that appeared inside a virtual room (under different experimentally imposed display lags). We found that cybersickness was more likely and severe when: (1) participants had higher MSSQ scores; (2) the spatial magnitudes and the detrended fluctuation analysis α values of their DVP increased. Based on these findings we believe that real-time estimates of the DVP could be used to warn users about the imminent onset of sickness during consumer HMD VR
The Associations Between Dietary Anthocyanins, Cognitive Performance and Mood
No full textFlavonoids are a diverse class of dietary polyphenols comprising several subclasses, including flavonols, flavanones, flavan-3-ols, and anthocyanins. Anthocyanins are naturally occurring compounds responsible for the red, purple, and blue pigmentation in fruits and vegetables, and although they are typically consumed in relatively small quantities, they have distinct structural and biological properties that may influence neurocognitive processes. While other flavonoid subclasses have been extensively investigated in relation to cognitive outcomes, evidence specific to anthocyanins remains comparatively limited. Recent studies have advanced methods for assessing flavonoid intake, with emerging data suggesting potential neuroprotective effects of anthocyanins. To determine whether these associations can be translated into meaningful dietary strategies, further evidence is required to clarify their role in cognitive function and mood, particularly among populations at increased risk of age-related cognitive decline.This thesis adopts a multi-method approach to address inconsistencies in the current clinical trials regarding anthocyanins and cognitive performance in adults. It also develops and validates a flavonoid-specific dietary assessment tool (FLAV-Q), explores associations between habitual anthocyanin consumption and cognitive outcomes, and assesses the feasibility of increasing anthocyanin intake through food-based interventions.The thesis comprises four main components. First, a systematic review and meta-analysis of randomised controlled trials was conducted to evaluate the cognitive effects of anthocyanins. The review revealed suggestive benefits for cognitive and mood outcomes, but high study heterogeneity and methodological differences limited the ability to draw definitive conclusions.Second, a shortened version of the Kent & Charlton Flavonoid Food Frequency Questionnaire (FLAV-Q) was developed and validated to rank flavonoid intake in the Australian population. While the tool demonstrated moderate to low validity for estimating absolute intake, it performed adequately in ranking individuals according to flavonoid intake and identifying key dietary sources, making it a practical tool for large-scale epidemiological studies but less so for clinical trials.The third component involved a 24-week, multi-center randomised controlled trial with older adults (aged 60–85) experiencing self-reported memory complaints. Cross-sectional analysis of baseline data suggested a potential association between higher habitual anthocyanin intake and lower depressive symptoms, though no significant relationship with cognitive performance was observed. The subsequent trial which forms the fourth component included three arms: a diet intervention arm aiming to increase anthocyanin intake through dietary change, a supplement arm providing 250 mg/day of anthocyanins, and a control arm receiving a placebo. The diet intervention arm demonstrated that structured dietary counselling, combined with tailored educational materials (e.g., cookbook, shopping guide), successfully increased anthocyanin intake by an average of 114 mg/day. Although this fell short of the 250 mg/day target provided in the supplement arm, the results confirm the feasibility of food-based strategies to enhance anthocyanin intake in older adults.This doctoral research makes several key contributions. It highlights the need for improved dietary assessment tools and calls for more rigorous studies to clarify the cognitive and mood-related effects of anthocyanins. It also addresses a critical gap in current dietary guidelines, which advocate fruit and vegetable intake but fail to recognize specific bioactive compounds like anthocyanins. The findings support the use of validated, flavonoid-focused dietary tools in future research and promote the integration of colourful, anthocyanin-rich foods into public health recommendations aimed at improving cognitive, mood and emotional well-being in ageing populations.</p