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School Mathematics, Statistics and Computer Science

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Browsing School Mathematics, Statistics and Computer Science by SDG "SDG9"

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    Post-quantum cloud security and data exchange using artificial intelligence.
    (2023) Mosola, Napo Nathnael.; Blackledge, Jonathan Michael.; Dombeu, Jean Vincent Fonou.
    This thesis investigates the application of plausible modern-day cryptographic solutions for securing the cloud and exchanging confidential data. The context followed is such that the strength of an encryption algorithm is based on the difficulty to cryptanalyse it. This means the more difficult the crypto-system is to cryptanalyse, the stronger and more trusted it is. The success of cryptanalysis on a cryptographic algorithm has been a function of the computational power available at the time of performing the cryptanalysis, without consideration of future innovations, specifically, without careful consideration of Moore’s law. A significant number of public-key crypto-systems can and will be compromised by a quantum computer coupled with the implementation of Shor’s algorithm. This has brought a lot of focus regarding research on cryptographic solutions post quantum computing (PQC) due to the following: ˆ cryptographic algorithms are based on the intractability of prime number factorisation using a conventional computing power; ˆ a quantum computer can factorize prime numbers with relative ease. In the past, the quantum computing paradigm was a hypothetical concept. Thus, cryptanalysis using quantum resources was a theoretical idea. This is no longer the case with the loom of quantum computers eminent. Consequently, prime number based encryption is becoming increasingly irrelevant. Low Qubit quantum computers now exist. Research and development in this area is growing. Hence the existence of the post-quantum cryptography paradigm. This paradigm is based on encryption algorithms developed and considered secure enough to withstand quantum attacks. Thus, the National Institute of Standards and Technology made a call for projects clustered under the Open Quantum Safe project (OQSP), which began in 2016. The ultimate goal of this project is development of future quantum resistant cryptographic algorithms for secure communication and data exchange. The OQSP aims to gather open source libraries which can be standalone or integrated into the public key encryption schemes to improve their security against ii quantum attacks in the quest to achieve quantum resistance. The major focus is placed on quantum key exchange (QKE). It is against this background that the material presented in this thesis reports on a spectrum of algorithms that are thought to be quantum resistant based on a coherence of ideas, methods, models and software implementation, trying to meet the NIST requirements and contributing to new knowledge in the field of cryptography. The aim is to provide confidentiality guarantees on cloud-hosted data as well as secure data exchange between communicating entities, while also tackling the cumbersome key exchange and management problem. The results show that the algorithms presented in this thesis introduce new ideas in cryptography and can be tested to withstand cryptanalytic quantum attacks, while a plausible encryption key distribution and management solution is proposed. In this context, the material presented in this thesis report on a spectrum of algorithms that are proposed to be quantum resistant based on a coherence of ideas, methods and software implementation, aimed at providing security of cloud-hosted data as well as data exchange between communicating entities. The cloud has a flexible, scalable and low cost properties. This is due to two concepts which are fundamental to cloud computing: ˆ virtualization; ˆ multi-occupancy. These above concepts have brought infinitely many benefits which make the cloud an attractive paradigm. Among the benefits are reduced capital and maintenance costs, high processing power, enormous storage facilities etc. However, security concerns affecting confidentiality of cloud-hosted data still plague bring concerns when it comes to cloud adoption. Data confidentiality can be achieved through encryption, which is in turn implemented by cryptographic algorithms. Hence, this thesis proposes and puts into practice cryptographic algorithms to solve issues of confidentiality, specifically in the cloud.
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    Star formation as a function of environment in the MeerKAT Galaxy Clusters Legacy Survey=Ulwazibunkanyezi Njengethuluzi Lokuhlola isiqoqzinkanyezi iMeerKAT Galaxy Clusters Legacy.
    (2023) Kesebonye, Kabelo Calvin.; Hilton, Matthew James.; Knowles, Kenda Leigh.
    Probing the star formation (SF) activity of cluster galaxies paves an important path towards the understanding of cluster evolution. This thesis presents the study of star formation rates (SFR) in clusters using dustunbiased radio luminosities from the MeerKAT Galaxy Clusters Legacy Survey (MGCLS). Our radio data is complemented by optical data from the Dark Energy Camera Legacy Survey (DECaLS), for photometric redshifts, and also Sunyaev-Zel’dovich (SZ) effect-derived cluster masses from the Atacama Cosmology Telescope (ACT). We present the first statistical study of SFR in clusters using MeerKAT-detected galaxies which takes advantage of MeerKAT’s large field of view to investigate the relation between SF activity and cluster environments out to 2R200. Using radio diffuse emission in the form of haloes and relics as a proxy for cluster merger activity, we divide our cluster sample between disturbed/merger clusters and relaxed clusters. We observe a higher fraction of star-forming galaxies (fSF) in disturbed clusters than in relaxed clusters. Disturbed clusters also have higher masses (M200) and total SFR (ΣSFR) in contrast to relaxed clusters. On analysing the redshift evolution of the massnormalised ΣSFR, we observe a ≈ 4× decline in the SF activity of clusters from the redshift of 0.35 to 0.15, corresponding to ≈ 2 Gyr in look-back time. Our result is roughly consistent with the one from cluster studies that used infrared-derived SFR (≈ 5× decline) at a similar redshift slice as our sample. We use a subsample of double relic-hosting clusters to investigate the relation between cluster SF activity and the time that has passed since the merger started (tmerger) estimated from the relic distances from cluster cores. We observe an anti-correlation between ΣSFR and merger, suggesting that younger mergers have a higher SF activity. However, we see no clear correlation in the mass-normalised ΣSFR with tmerger. We also investigate for differences in the SF activity of galaxies closer to radio relics and those away from the relics and observe no significant differences between the two populations. Iqoqa Ukuhlola kokusebenza kolwazi-bunkanyezi ( star formation -SF) kwesixhobo sezinkanyezi cluster galaxies kucabe indlela emqoka ukuqonda kokukhula kwalamaqoqo (cluster evolution). Lolu cwaningo lwethula ukuhlolwa lwe star (formation rates -SFR) kuma-clusters kusetshenziswa i dust-unbiased radio luminosities kuMeerKAT Galaxy Clusters Legacy Survey (MGCLS). Imininingo ye-radio isebenzisana ne-optical data yeDark Energy Camera Legacy Survey (DECaLS), ukuhlola iphotometric redshifts, ne Sunyaev-Zel'dovich (SZ) nomthelela odalwa yicluster masses esuka kwiAtacama Cosmology Telescope (ACT). Kube sekwethulwa ucwaningo lokuqala lwezibalo lweSFR in clusters kusetshenziswa iMeerKAT-detected galaxies. Kusetshenziswe ithuba lobukhulu bomkhakha lokubonakala kahle kweMeerKAT ukuhlola ubudlelwane phakathi kwe-SFR nemvelo yamaclusters ezinhlobonhlobo zedynamical states. Kusetshenziswe iradio diffuse emission eyizinhlobo zehaloes nerelics njengegunya lokuhlola ukuhlangana kwamacluster , amasampula ama-cluster ahlukaniswe phakathi kwamadisturbed/merger clusters namarelaxed clusters. Okutholakele ukuthi ihigher fraction of star-forming galaxies (fSF) kumaclusters aphazamisekile (disturbed clusters) kunama clusters akhululekile (relaxed clusters). Amaclusters aphazamisekile anama masi aphezulu (M200) kanti isamba sonke siwuSFR (∑SFR) uma eqhathaniswa namaclusters aphazamisekile . Sekucutshungulwa iredshift evolution yemass-normalised ∑SFR, kutholakale ukuthi aphindwe kawu ≅4 times decline ekusebenzeni kwe SF esukela kwiredshift of 0.35 to 0.15, ahlobana ne ≅2 Gyr kwi look-back time. Imiphumela ilinganiselwe ngokuhambisana nezifundo zamacluster kusetshenziswa i-infrared-derived SFR (≅5 times decline) ngokufanayo neredshift slice njengamasampula ocwaningo lolu .Kusetshenziswe elinye isampula esigabeni sesibili ukuze kwenziwe idouble relic-hosting clusters ukuhlola ubudlelwane okusebenza kwama clusters (SF activity) kanye nesikhathi esisuke sidlulile ehlanganiswe (t_merger) kulinganiselwe kusukela ebangeni lerelic distances kucluster ewumsuka (cluster cores). Kutholakale ukungadlelani phakathi kwe ∑SFR ne t_merger, okuchaza ukuthi ukuhlanganiswa kwalawo asemancane kusebenzisa izinga eliphezulu (SF activity). Yize-kunjalo , akubonakali ubudlelwane obucacile kumass-normalised ∑SFR ne t_merger. Kuphinde kwahlolwa ukusebenza okungefani kumagalaxies asondelene neradio relics nalawo aqhelile kumarelics kwase kwangatholakala mehluko otheni kule miphakathi yomibili.