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Differential attacks using alternative operations and block cipher design
Full text linkBlock ciphers and their security are the main subjects of this work.
In the first part it is described the impact of differential cryptanalysis, a powerful statistical attack against block ciphers, when operations different from the one used to perform the key addition are considered on the message space. It is proven that when an alternative difference operation is carefully designed, a cipher that is proved secure against classical differential cryptanalysis can instead be attacked using this alternative difference.
In the second part it is presented a new design approach of round functions for block ciphers. The proposed round functions can give to the cipher a potentially better level of resistance against statistical attacks. It is also shown that the corresponding ciphers can be proven secure against a well-known algebraic attack, based on the action of the permutation group generated by the round functions of the cipher
Formal Proofs of Security for Privacy-Preserving Blockchains and other Cryptographic Protocols
Full text linkCryptography is used to protect data and communications.
The basic tools are cryptographic primitives, whose security and efficiency are widely studied.
But in real-life applications these primitives are not used individually, but combined inside complex protocols.
The aim of this thesis is to analyse various cryptographic protocols and assess their security in a formal way.
In chapter 1 the concept of formal proofs of security is introduced and the main categorisation of attack scenarios and types of adversary are presented, and the protocols analysed in the thesis are briefly introduced with some motivation.
In chapter 2 are presented the security assumptions used in the proofs of the following chapters, distinguishing between the hardness of algebraic problems and the strength of cryptographic primitives.
Once that the bases are given, the first protocols are analysed in chapter 3, where two Attribute Based Encryption schemes are proven secure.
First context and motivation are introduced, presenting settings of cloud encryption, alongside the tools used to build ABE schemes.
Then the first scheme, that introduces multiple authorities in order to improve privacy, is explained in detail and proven secure.
Finally the second scheme is presented as a variation of the first one, with the aim of improving the efficiency performing a round of collaboration between the authorities.
The next protocol analysed is a tokenization algorithm for the protection of credit cards.
In chapter 4 the advantages of tokenization and the regulations required by the banking industry are presented, and a practical algorithm is proposed, and proven secure and compliant with the standard.
In chapter 5 the focus is on the BIX Protocol, that builds a chain of certificates in order to decentralize the role of certificate authorities.
First the protocol and the structure of the certificates are introduced, then two attack scenarios are presented and the protocol is proven secure in these settings.
Finally a viable attack vector is analysed, and a mitigation approach is discussed.
In chapter 6 is presented an original approach on building a public ledger with end-to-end encryption and a one-time-access property, that make it suitable to store sensitive data.
Its security is studied in a variety of attack scenarios, giving proofs based on standard algebraic assumptions.
The last protocol presented in chapter 7 uses a proof-of-stake system to maintain the consistency of subchains built on top of the Bitcoin blockchain, using only standard Bitcoin transactions.
Particular emphasis is given to the analysis of the refund policies employed, proving that the naive approach is always ineffective whereas the chosen policy discourages attackers whose stake falls below a threshold, that may be adjusted varying the protocol parameters
La legittimazione dell'intervento penale tra offensività e harm principle
Full text linkIl presente lavoro, attraverso una prospettiva comparata, indaga le più recenti tendenze in tema di dannosità sociale in Italia e nel sistema anglo-americano. Si interroga, quindi, sulla definizione e sui limiti della legittimazione dell’intervento penale dello Stato. In particolare, la tesi prende atto delle prospettive attuali sul principio di offensività nel nostro ordinamento, verificando le sue radici, le sue fonti e il suo ruolo, per poi vagliare la teoria del bene giuridico che ne costituisce il sostrato materiale. Come è noto, tale teoria si è sviluppata, in Italia, attraverso una lettura costituzionalmente orientata indicando così le caratteristiche fondamentali che il bene doveva avere per dirsi legittimo. Negli anni, un aggiramento del principio di offensività ha portato a una smaterializzazione del concetto di bene giuridico fino a far dubitare della natura effettivamente forte del principio stesso. Il dibattito anglo-americano sui criteri di legittimazione dell’intervento punitivo si è caratterizzato per degli spunti interpretativi notevolmente diversi, specie in virtù delle caratteristiche proprie dei sistemi di common law. Le radici dell’harm e offence principle, infatti, partono dall’ottica liberale di J.S. Mill, ma ricevono una vera e propria nuova definizione con J. Feinberg il quale, in un’ottica di liberalismo cauto, riempie di contenuto le nozioni alla base dei liberty-limiting principles. La più recente dottrina di common law ha poi fornito nuovi spunti di riflessione specie se di considera quello che è stato definito il “collapse” dell’harm principle.
Il recente interesse della dottrina italiana per i criteri anglo-americani ha dato spunto, nel presente lavoro, per una verifica della rilevanza dell’harm e dell’offence principle in relazione alle scelte del legislatore italiano. Per dimostrare questo assunto si sono così presi in esame due case study e, in particolare, quello degli atti osceni, con la recente opera di depenalizzazione e quello dell’omofobia, che si caratterizza per un costante dibattito in merito alla sua possibile criminalizzazione. Nel presente elaborato, infatti, si mostra come il principio anglo-americano del danno e della molestia possa contribuire a superare l’impasse sul principio di offensività proprio in seguito a una valutazione dei fenomeni in tema di atti osceni e omofobia, in chiave di necessaria causazione di un danno o una molestia ad altri.
In ragione di tali considerazioni si è cercato di creare le basi per una ri-legittimazione, da un punto di vista dogmatico, dell’intervento penale dello Stato. Il concetto di bene giuridico, infatti, presenta non poche insufficienze tali da considerare plausibile un suo abbandono per un accoglimento del principle of harm, nella visione di J. Feinberg. Questo passaggio si mostra quanto mai opportuno specie ove si ritenga di dover combinare i criteri in tema di dannosità sociale ai modelli (procedurali) di democrazia, nonché a un’attenzione ai tipi di morale emergenti nella società. L’accettazione di una teoria aperta in tema di criminalizzazione permette, così, di dare un nuovo futuro all’offensività e all’harm principle, tale da rimettere al centro del dibattito penale la domanda alla quale il legislatore deve rispondere nelle scelte in tema di meritevolezza e sussidiarietà penale e, cioè, se la condotta sottoposta al suo vaglio provochi o meno un danno o una molestia ad altri
Campaign and network effects on electoral participation: The various facets of mobilization and interpersonal influence
Full text linkThe thesis investigates the impact of extra-individual factors on electoral participation, by providing a comprehensive theoretical framework aimed at highlighting the role of context. In particular, it analyzes the key-concepts of mobilization and interpersonal influence, with a focus on the Italian case. Both experimental and survey data are employed to answer the research questions. Concerning mobilization, main findings show that personal forms of contact, such as face-to-face interactions with party members, are more successful than impersonal forms, which prove to be ineffective. When looking at the interpersonal influence, the thesis shows that the exposure to political disagreement has differentiated effects on turnout, depending on the level of cohesiveness of the social circle where disagreement is experienced
Modeling and simulations of low dimensional and nanostructured materials systems at the nanoscale
Full text linkThe properties of a broad range of materials are due to processes which occur at the nanoscale. Recently, an increasing interest has been devoted to nanostructured materials, in which the basic components are nanoscopic, and low-dimensional nanomaterials such as nanoparticles, nanowires and layered materials, in which one or more dimensions are confined. This thesis deals with nanostructured materials, in particular based on graphene, such as Graphene Nanofoams and Pillared Graphene Frameworks, and low dimensional nanomaterials such as SiC/SiO2 core/shell nanowires and graphene layers. The work is divided in four parts treating four different topics with the underlying theme of material modeling, the first two parts deal with mechanical properties and gas treatment applications, for which a description at the atomistic level is adequate, while the third and the forth focus on X-ray spectra and electron holography simulations for which electronic structure calculations are needed. The present thesis gives a general overview on various computational approaches that are useful in modeling novel low dimensional and nanostructured materials, using these approaches in dealing with specific systems
Slow dynamics in colloids and network glasses close to the structural arrest: the Stress-relaxation as a root to equilibrium
Full text linkMicroscopically disordered materials are at the core of an increasing number of new material technologies, but crucial limitations in their applications come from the physical aging of their properties and the extreme sensitivity on the system's history, which stem from the their intrinsically out of equilibrium nature. A clear understanding of the aging phenomenon, as well as the effects of the release of internal stresses acting at different length-scales, are still lacking. In this Thesis the slow dynamics of disordered systems is investigated at different length-scales ranging from the micrometre length-scale probed in optical experiments to length-scales of few angstroms probed in wide angle X-ray experiments. The time evolution of the probed out of equilibrium dynamics is thoroughly studied in different glasses exploiting the multi speckle photon correlation technique with different sources. The investigated materials are a set of strong glass-formers (materials that can be found in a wide variety of common glassware) and colloidal suspensions at high volume fractions in an arrested state. The latter class of materials are known as soft glasses and in recent years they are earning great interest and can be found in a lot of industrial products (e.g. wall paint, ink, chocolate) or in production processes (e.g. ceramics). Despite the differences between the probed systems and their production protocols, it is here shown that in all the studied materials the microscopic dynamics displays common trends and that it is strongly connected to the relaxation of the stresses that have remained trapped in these systems after their production
Resource allocation and modeling in spectrally and spatially flexible optical transport networks
Full text linkThe world's hunger for connectivity appears to be endlessly growing, yet the capacity of the networks that underpin that connectivity is anything but endless. This thesis explores both short and long term solutions for increasing the capacity of the largest and most capacious of these networks, the backbones upon which the Internet is built: optical transport networks. In the short term, Flexi-grid technology has emerged as the evolution of fixed-grid WDM optical networks, providing higher potential throughput but suffering from an aggravated form of the spectrum ragmentation problem that affects fixed-grid networks.
A novel path-based metric to better evaluate the fragmentation of spectral resources in flexi-grid networks is presented, which considers both the fact that free spectrum slices may not be available on all the links of a path, and the likelihood that an end-to-end spectral void is usable to route incoming connections, and tested by means of simulations, finding that it outperforms existing ones from literature. For the longer term, Space Division Multiplexing (SDM) is a promising solution to overcome the looming fiber capacity crunch, and, perhaps more importantly, can offer a beneficial ratio between the expected capacity gains and the resulting increase in the cost of the network thanks to Joint and Fractional Joint Switching architectures and integrated transceivers and amplifiers. A model for such network is presented, and multiple heuristics for solving the Routing, Space and Spectrum Allocation problem are described, studied via simulations and iteratively improved, with the objective of quantifying the likely performance of several SDM architectures under multiple traffic scenarios.
In addition, possible improvements to joint switching architectures, and an experimental SDN control plane for SDM networks, are presented and characterized, again by means of simulations. SDM is shown to be an attractive technology for increasing future transport networks capacity, at a reasonable cost
Participatory Design For Community Energy - Designing the Renewable Energy Commons
Full text linkThe energy sector is facing a major paradigm shift from centralised production and management to distributed energy generation and management. Digital technologies play a crucial role in enabling such scenario; emphasis and attention has been given to Smart Grids and new energy management systems both for final users and companies. Energy, its consumption, and its production are at the centre of our everyday lives and are connected to everyday practices and habits. However, while this scenario can be seen as mundane, new spaces can be created for citizens and communities to participate and be empowered. This thesis presents the work done by the author within a three-years European Project used as his main research field. The focal points were: (i) the participatory design process of a community energy digital platform; and (ii) the advantages and disadvantages of a commons based approach to renewable energy management on the development and empowerment of local communities. First will be presented how a participatory design process opens a new space for citizen participation to design as an alternative energy management model. Then will be presented the energy budgeting framework designed within this process, discussing how social acceptance of technology affected the design and how energy has been translated to a new kind of value within this framework. Afterwards, it will be discussed how the participatory process and the framework contributed to the construction-in-practice of energy justice, and how this process reconfigured the relationships among civil society, the energy sector, and politics. Finally, the whole three years project experience will be analysed retrospectively using the interaction spaces framework, highlighting how participatory configurations evolved over time and how cross-participation is crucial for the boundary-spanning of design issues. Therefore, concluding reflections will be drawn based on this content, they will consider lessons learned, limitations of the experience and possible future work to continue explore the relationship between energy, digital technologies and participatory design
Semi-implicit schemes for compressible fluids in elastic pipes and a-posteriori sub-cell finite volume limiting techniques for semi-implicit Discontinuous Galerkin schemes for hyperbolic conservation laws on staggered meshes
Full text linkIn the present work we solve systems of partial differential equations (PDE) for hyperbolic conservation laws using semi-implicit numerical methods on staggered meshes applied both to the class of finite volume (FV) and both to the family of high order Discontinuous Galerkin (DG) finite elements schemes. In particular, we want to show that these new semi-implicit schemes can be applied in several fields of applied sciences, such as in geophysical flows and compressible fluids in compliant tubes. Inside this thesis we distinguish two big parts. First, we consider staggered semi-implicit
schemes for compressible viscous fluids flowing in elastic pipes. This topic is very important in several practical applications of civil, environmental, industrial and biomedical engineering. Here, we analyse the accuracy and the computational efficiency of fully explicit and semi-implicit 1D and 2D finite volume schemes for the simulation of highly unsteady viscous compressible flows in laminar regime in axially symmetric rigid and elastic pipes. We consider two families of differential models that can be used to predict the pressure and velocity distribution along the tube. One is the so called 2Dxr PDE model which is derived from the full compressible Navier-Stokes equations under the assumptions of a hydrostatic pressure and an axially symmetric geometry. The second family is a simple 1D non-conservative PDE system based on the cross-sectionally
averaged version of the Navier-Stokes equations in cylindrical coordinates. In this last case, the use of a simple steady friction model is not enough to simulate the wall friction phenomena in highly transient regime. As a consequence the wall friction model has to be frequency dependent and, following previous studies present in the literature, we consider the classes of convolution integral (CI) models and instantaneous acceleration (IA) models.
We carry out a rather complete analysis of the previously-mentioned methods for the simulation of flows characterized by fast transient regime in rigid and compliant tubes.
The numerical results show that the convolution integral models are clearly better than instantaneous acceleration models concerning accuracy. Moreover, for CI models,
instead of computing the convolution integrals, which is very time- and memoryconsuming, we express these methods via a set of additional ODEs for appropriate auxiliary
variables. This trick improves the computational efficiency of these methods substantially, since it avoids the direct computation of the convolution integral. In addition,
semi-implicit finite volume methods are significantly superior to classical explicit finite volume schemes in terms of computational efficiency, however, providing the same level of accuracy. We then proceed by extending the finite volume discretization of the 1D and 2Dxr PDE
models to arbitrary high-order of accuracy in space introducing a new SIDG scheme on staggered meshes. Both models include the effects of the viscosity and of the wall
motion. The nonlinear convective terms are discretized explicitly by using a classical RKDG scheme of arbitrary high-order of accuracy in space and third order of accuracy
in time. The continuity equation is integrated over the elements that belong to the main grid, while the momentum equation is integrated over the control volumes of the edgebased staggered dual grid. Inserting the discrete momentum equation into the discrete continuity leads to a mildly nonlinear algebraic system for the degrees of freedom of the pressure, which is solved by using the (nested) Newton method of Brugnano, Casulli and Zanolli. We use the -method in order to get second order of accuracy in time for the implicit part of the scheme. In addition, the schemes have to obey only a mild CFL condition based on the fluid velocity and not based on the sound speed; consequently these schemes work also in the low Mach number regime and even in the incompressible limit of the Navier-Stokes equations. This is a very important property, which is the so-called asymptotic preserving (AP) property of the scheme. We carry out several numerical tests in order to validate this novel family of numerical methods against available exact solutions and experimental data. We also report numerical convergence tables in order to show that the new schemes indeed achieve high order of accuracy in space.
In the second part of the thesis, we present a new class of a posteriori sub-cell finite volume limiters for spatially high order accurate semi-implicit discontinuous Galerkin
schemes on staggered Cartesian grids for the solution of the 1D and 2D shallow water equations (SWE) and of the Euler equations both expressed in conservative form.
Here, the starting point is the unlimited arbitrary high order accurate staggered SIDG scheme proposed by Dumbser and Casulli (2013). For this metho d, the mass conservation
equation and the momentum equations are integrated using a discontinuous finite element strategy on staggered control volumes, where the discrete free surface elevation
is defined on the main grid and the discrete momentum is defined on edge-based staggered
dual control volumes. According to the semi-implicit approach, pressure terms
are discretized implicitly, while the nonlinear convective terms are discretized explicitly.
Inserting the momentum equations into the discrete continuity equation leads to a well
conditioned block diagonal linear system for the free surface elevation which can be efficiently
solved with modern iterative methods.
Furthermore, the staggered SIDG is also extended to the Euler equations of compressible
gasdynamics. Here, the governing PDE are rewritten using a flux vector splitting technique. The convective terms are updated using an explicit Runge-Kutta DG integrator.
Then, the discrete momentum equation, which is integrated again on the dual grid,
is coupled with the discrete energy equation that is discretized on the control volumes
of the main grid. The pressure is efficiently obtained solving a linear system combined
with an iterative Picard iteration procedure
Illiberal Secularism: A Critical Approach to the Study of Social and Religious Governance in Liberal Democracies
Full text linkTaking note of the emergence of illiberal forms of governance across Western Europe, a liberal and democratic region, this thesis endeavors to unravel one particular manifestation of this tendency, illiberal secularism. Specifically, it asks how secularism has been discursively (trans)formed in political contexts so as to allow for the emergence of illiberal forms of social and religious governance. To address this question, this thesis analyzes the discursive enactment of ideological secularism by Italian state actors in three cases—the Crucifix, the Burqa, and the Charter cases. Building on critical and discursive perspectives, this thesis argues that secularism is an ideology that shapes thinking and action and provides a conceptualization of, and an answer to, the problem of diversity. Thus, it proposes to study secularism as a political category that works as a stake in, and as a means through which contemporary contests over religion and diversity are conducted. In methodological terms, these considerations lead to a combined analytical endeavor, which focuses on both the conceptual grammar of secularism and the discursive practices through which state actors (re)construct this ideological formation. Conducting conceptual and critical discourse analyses, this thesis reveals the argumentative structures and the main ideational and relational assumptions of Italian state actors’ discourses. It demonstrates that, in all three cases, these actors revise secular–religious demarcations in ways that expand the secular power of the state over the religious realm and, moreover, allow for the revision of liberal entitlements and for the resetting of the boundaries that define the political community. Notably, this thesis finds that it is through the secularization of Christianity, the culturalization of liberalism, and the othering of Muslims that some state actors reconcile secularism and illiberalism, thereby promoting practices that restrict and violate important liberal values and achievements, such as religious freedom and political unity