2,218 research outputs found
Resonant-Tunnelling Diodes as PUF building blocks
Resonant-Tunnelling Diodes (RTDs) have been proposed as building blocks for Physical Unclonable Functions (PUFs). In this paper we show how the unique RTD current-voltage (I-V) spectrum can be translated into a robust digital representation. We analyse 130 devices and show that RTDs are a viable PUF building block
Program Synthesis and Linear Operator Semantics
For deterministic and probabilistic programs we investigate the problem of
program synthesis and program optimisation (with respect to non-functional
properties) in the general setting of global optimisation. This approach is
based on the representation of the semantics of programs and program fragments
in terms of linear operators, i.e. as matrices. We exploit in particular the
fact that we can automatically generate the representation of the semantics of
elementary blocks. These can then can be used in order to compositionally
assemble the semantics of a whole program, i.e. the generator of the
corresponding Discrete Time Markov Chain (DTMC). We also utilise a generalised
version of Abstract Interpretation suitable for this linear algebraic or
functional analytical framework in order to formulate semantical constraints
(invariants) and optimisation objectives (for example performance
requirements).Comment: In Proceedings SYNT 2014, arXiv:1407.493
A static analysis framework for security properties in mobile and cryptographic systems
We introduce a static analysis framework for detecting instances of security breaches in infinite mobile and cryptographic systems specified using the languages of the 7r-calculus and its cryptographic extension, the spi calculus. The framework is composed from three components: First, standard denotational semantics of the 7r-calculus and the spi calculus are constructed based on domain theory. The resulting model is sound and adequate with respect to transitions in the operational semantics. The standard semantics is then extended correctly to non-uniformly capture the property of term substitution, which occurs as a result of communications and successful cryptographic operations. Finally, the non-standard semantics is abstracted to operate over finite domains so as to ensure the termination of the static analysis. The safety of the abstract semantics is proven with respect to the nonstandard semantics. The results of the abstract interpretation are then used to capture breaches of the secrecy and authenticity properties in the analysed systems. Two initial prototype implementations of the security analysis for the 7r-calculus and the spi calculus are also included in the thesis.
The main contributions of this thesis are summarised by the following. In the area of denotational semantics, the thesis introduces a domain-theoretic model for the spi calculus that is sound and adequate with respect to transitions in the structural operational semantics. In the area of static program analysis, the thesis utilises the denotational approach as the basis for the construction of abstract interpretations for infinite systems modelled by the 7r-calculus and the spi calculus. This facilitates the use of computationally significant mathematical concepts like least fixed points and results in an analysis that is fully compositional. Also, the thesis demonstrates that the choice of the term-substitution property in mobile and cryptographic programs is rich enough to capture breaches of security properties, like process secrecy and authenticity. These properties are used to analyse a number of mobile and cryptographic protocols, like the file transfer protocol and the Needham-Schroeder, SPLICE/AS, Otway-Rees, Kerberos, Yahalom and Woo Lam authentication protocols
Resonant-Tunnelling Diodes as PUF Building Blocks
Resonant-Tunnelling Diodes (RTDs) have been proposed as building blocks for Physical Unclonable Functions (PUFs). In this paper we show how the unique RTD current-voltage (I-V) spectrum can be translated into a robust digital representation. We analyse 130 devices and show that RTDs are a viable PUF building block
Development and study of a high performance protective solution against blast loads
The increasing use of improvised explosive devices in terrorist attacks against civil targets
has challenged the scientific community to find new strengthening or protective solutions
able to mitigate the effects of the blast loads. As a response to this demand, the main
purpose of the present thesis is the development and study of a high performance protective
solution based on the concept of sacrificial claddings. Due to the high flexibility,
precision and relatively low costs, additive manufacturing has been increasingly used in
the search of new material disposition patterns that improve the mitigation capabilities
of crushable cores.
The presentwork assesses the performance of a PLA crushable core manufactured through
fused deposition modelling 3D printing. An experimental campaign is conducted to determine
the mechanical behaviour of the PLA. These results allow the selection and
calibration of an adequate numerical constitutive model, which considers the anisotropy
and compressive/tensile asymmetry exhibited in additively manufactured materials.
Once the constitutive material calibrated, the results of a second experimental campaign
resorting to an explosive driven shock tube are used to validate a numerical model that
allows the deterministic design of a sacrificial cladding which successfully improves the
blast resistant capabilities of a given structural element.
However, when verified taking into account the model’s uncertainties and the probabilistic
distribution of the structural element’s properties, the cladding solution might, for
certain blast scenarios, negatively impact the performance of the structural element it
intends to protect.
Therefore, one may conclude that the use of a probabilistic approach in the design of such
protective solutions is recommended, as the deterministic approach might yields results
against safety
Cyber-security protection techniques to mitigate memory errors exploitation
Tesis por compendio[EN] Practical experience in software engineering has demonstrated that the goal of
building totally fault-free software systems, although desirable, is impossible
to achieve. Therefore, it is necessary to incorporate mitigation techniques in
the deployed software, in order to reduce the impact of latent faults.
This thesis makes contributions to three memory corruption mitigation
techniques: the stack smashing protector (SSP), address space layout
randomisation (ASLR) and automatic software diversification.
The SSP is a very effective protection technique used against stack buffer
overflows, but it is prone to brute force attacks, particularly the dangerous
byte-for-byte attack. A novel modification, named RenewSSP, has been proposed
which eliminates brute force attacks, can be used in a completely transparent
way with existing software and has negligible overheads. There are two
different kinds of application for which RenewSSP is especially beneficial:
networking servers (tested in Apache) and application launchers (tested on
Android).
ASLR is a generic concept with multiple designs and implementations. In this
thesis, the two most relevant ASLR implementations of Linux have been analysed
(Vanilla Linux and PaX patch), and several weaknesses have been found. Taking
into account technological improvements in execution support (compilers and
libraries), a new ASLR design has been proposed, named ASLR-NG, which
maximises entropy, effectively addresses the fragmentation issue and removes a
number of identified weaknesses. Furthermore, ASLR-NG is transparent to
applications, in that it preserves binary code compatibility and does not add
overheads. ASLR-NG has been implemented as a patch to the Linux kernel 4.1.
Software diversification is a technique that covers a wide range of faults,
including memory errors. The main problem is how to create variants,
i.e. programs which have identical behaviours on normal inputs but
where faults manifest differently. A novel form of automatic variant
generation has been proposed, using multiple cross-compiler suites and
processor emulators.
One of the main goals of this thesis is to create applicable results.
Therefore, I have placed particular emphasis on the development of real
prototypes in parallel with the theoretical study. The results of this thesis
are directly applicable to real systems; in fact, some of the results have
already been included in real-world products.[ES] La creación de software supone uno de los retos más complejos para el
ser humano ya que requiere un alto grado de abstracción. Aunque se ha
avanzado mucho en las metodologías para la prevención de los fallos
software, es patente que el software resultante dista mucho de ser
confiable, y debemos asumir que el software que se produce no está
libre de fallos. Dada la imposibilidad de diseñar o implementar
sistemas libres de fallos, es necesario incorporar técnicas de
mitigación de errores para mejorar la seguridad.
La presente tesis realiza aportaciones en tres de las principales
técnicas de mitigación de errores de corrupción de memoria: Stack
Smashing Protector (SSP), Address Space Layout Randomisation (ASLR) y
Automatic Software Diversification.
SSP es una técnica de protección muy efectiva contra
ataques de desbordamiento de buffer en pila, pero es sensible a ataques de
fuerza bruta, en particular al peligroso ataque denominado byte-for-byte.
Se ha propuesto una novedosa modificación del SSP, llamada RenewSSP,
la cual elimina los ataques de fuerza bruta. Puede ser usada
de manera completamente transparente con los programas existentes sin
introducir sobrecarga. El RenewSSP es especialmente beneficioso en dos áreas de
aplicación: Servidores de red (probado en Apache) y
lanzadores de aplicaciones eficientes (probado en Android).
ASLR es un concepto genérico, del cual hay multitud de diseños e
implementaciones. Se han analizado las dos implementaciones más
relevantes de Linux (Vanilla Linux y PaX patch), encontrándose en
ambas tanto debilidades como elementos mejorables. Teniendo en cuenta
las mejoras tecnológicas en el soporte a la ejecución (compiladores y
librerías), se ha propuesto un nuevo diseño del ASLR, llamado
ASLR-NG, el cual: maximiza la entropía, soluciona el problema de la
fragmentación y elimina las debilidades encontradas. Al igual que la
solución propuesta para el SSP, la nueva propuesta de ASLR es
transparente para las aplicaciones y compatible a nivel
binario sin introducir sobrecarga. ASLR-NG ha sido implementado como
un parche del núcleo de Linux para la versión 4.1.
La diversificación software es una técnica que cubre una amplia gama
de fallos, incluidos los errores de memoria. La principal dificultad
para aplicar esta técnica radica en la generación de las
"variantes", que son programas que tienen un comportamiento idéntico
entre ellos ante entradas normales, pero tienen un comportamiento
diferenciado en presencia de entradas anormales. Se ha propuesto una
novedosa forma de generar variantes de forma automática a partir de un
mismo código fuente, empleando la emulación de sistemas.
Una de las máximas de esta investigación ha sido la aplicabilidad de
los resultados, por lo que se ha hecho especial hincapié en el
desarrollo de prototipos sobre sistemas reales a la par que se llevaba
a cabo el estudio teórico. Como resultado, las propuestas de esta
tesis son directamente aplicables a sistemas reales, algunas de ellas
ya están siendo explotadas en la práctica.[CA] La creació de programari suposa un dels reptes més complexos per al ser humà ja
que requerix un alt grau d'abstracció. Encara que s'ha avançat molt en les
metodologies per a la prevenció de les fallades de programari, és palès que el
programari resultant dista molt de ser confiable, i hem d'assumir que el
programari que es produïx no està lliure de fallades. Donada la impossibilitat
de dissenyar o implementar sistemes lliures de fallades, és necessari
incorporar tècniques de mitigació d'errors per a millorar la seguretat.
La present tesi realitza aportacions en tres de les principals tècniques de
mitigació d'errors de corrupció de memòria: Stack Smashing Protector (SSP),
Address Space Layout Randomisation (ASLR) i Automatic Software
Diversification.
SSP és una tècnica de protecció molt efectiva contra atacs de desbordament de
buffer en pila, però és sensible a atacs de força bruta, en particular al
perillós atac denominat byte-for-byte.
S'ha proposat una nova modificació del SSP, RenewSSP, la qual elimina els atacs
de força bruta. Pot ser usada de manera completament transparent amb els
programes existents sense introduir sobrecàrrega. El RenewSSP és especialment
beneficiós en dos àrees d'aplicació: servidors de xarxa (provat en Apache) i
llançadors d'aplicacions eficients (provat en Android).
ASLR és un concepte genèric, del qual hi ha multitud de dissenys i
implementacions. S'han analitzat les dos implementacions més rellevants de
Linux (Vanilla Linux i PaX patch), trobant-se en ambdues tant debilitats com
elements millorables. Tenint en compte les millores tecnològiques en el suport
a l'execució (compiladors i llibreries), s'ha proposat un nou disseny de
l'ASLR: ASLR-NG, el qual, maximitza l'entropia, soluciona el problema de
la fragmentació i elimina les debilitats trobades. Igual que la solució
proposada per al SSP, la nova proposta d'ASLR és transparent per a les
aplicacions i compatible a nivell binari sense introduir sobrecàrrega. ASLR-NG
ha sigut implementat com un pedaç del nucli de Linux per a la versió 4.1.
La diversificació de programari és una tècnica que cobrix una àmplia gamma de
fa\-llades, inclosos els errors de memòria. La principal dificultat per a aplicar
esta tècnica radica en la generació de les "variants", que són programes que
tenen un comportament idèntic entre ells davant d'entrades normals, però tenen
un comportament diferenciat en presència d'entrades anormals. S'ha proposat una
nova forma de generar variants de forma automàtica a partir d'un mateix codi
font, emprant l'emulació de sistemes.
Una de les màximes d'esta investigació ha sigut l'aplicabilitat dels resultats,
per la qual cosa s'ha fet especial insistència en el desenrotllament de
prototips sobre sistemes reals al mateix temps que es duia a terme l'estudi
teòric. Com a resultat, les propostes d'esta tesi són directament aplicables
a sistemes reals, algunes d'elles ja estan sent explotades en la pràctica.Marco Gisbert, H. (2015). Cyber-security protection techniques to mitigate memory errors exploitation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/57806TESISCompendi
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Finite element characterisation of photonic crystal fibres
Rigorous numerical simulations have been carried out by using the Finite Element Method (FEM) in order to calculate bending and leakage losses of Photonic Crystal Fibres (PCF). A modal solution approach including the implementations of the conformal transformation and the Perfectly Matched Layer (PML) were undertaken to determine the bending and leakage losses of several designs of Photonic Crystal Fibres. This was carried out by varying key parameters such as the pitch (Λ), diameter (d) and air-filling fraction (d/Λ). Output modal parameters including the effective indices, spot sizes, leakage and bending losses as well as the mode field profiles were obtained. These output parameters were obtained by varying the bending radius (R) from very large values to very low values for different dimensions of the PCF, with results being obtained for Transverse Magnetic and Transverse Electric (quasi-TM and quasi-TE) polarizations. These parameters were calculated by solving the Maxwell’s equations using the H-field vector formulation and with the inclusion of PML to solve complex eigenvalue equations. Generally, it was observed that for all Λ, d/Λ and the polarization considered, as R is reduced from a very high value to lower values, the bending losses increase and there is a sharp increase at some lower values of R. At some very low values of R, some oscillatory behaviour was observed in the curves obtained for the fibre losses, where further investigations were carried out. These oscillations appeared due to degeneration of the fundamental mode with the cladding modes. In most of the cases investigated, there was a correlation in the variation of effective indices the loss values and also in the variation of spot sizes. PCFs with non-identical air-holes were also investigated in which case the d ≠ d2 (diameter of 4 larger air-holes in the first ring) and knowing the values for TM and TE polarizations, it was possible to determine the birefringence, which is the difference between the effective indices for the TM and TE modes and also the loss ratio, which is the ratio of TM loss to that of the TE loss. All the input and output parameters that were considered with the symmetric air-holes were also considered in the case with fibre with asymmetric air-holes study. The results obtained are very important in the design of Single Mode Single Polarization PCF. Results have also been obtained from the studies done of asymmetric arrangement of air-holes which lead to the design of Single Mode Single Polarization PCF. Work was carried out on the design of a tapered PCF that could be efficiently coupled to a single mode fibre, SMF. This was achieved by increasing the number rings up to 10 rings of air-holes in the cladding and having the outermost ring with larger air-holes, the inner rings were near cutoff. This fibre was coupled to a conventional SMF to allow for better tolerance to fabrication errors. There has also been work carried out in polymer fibre namely Teflon and TOPAS in the terahertz regime. The conventional hexagonal arrangement of PCF was simulated and compared to spiral PCF in THz. An improved PCF design having a porous core with hexagonal arrangement and cladding was designed and analysed and low-loss guidance in THz was achieved. Thus overall a number of different PCF designs were considered and their properties evaluated and detailed knowledge has been obtained on potential performance of such fibres
The failure of a tungsten carbide-cobalt cored projectile penetrating a hard target
Experimental results are presented from an investigation of the parameters of a ceramic-faced armour system that are required to induce damage in a tungsten carbide - cobalt (WC-Co) penetrator. A WC-Co material model has been successfully developed and implemented within the numerical hydrocode AUTODYN 2D. The understanding of penetration mechanisms was used to guide a parametric investigation, validating the WC-Co material failure model with experimental results.
A series of experiments has been conducted firing the Russian 14.5 mm BS41 WC-Co cored projectile into various thicknesses and types of alumina (Al2O3) and silicon carbide (SiC), backed by aluminium alloy or mild steel semi-infinite witness blocks. Results demonstrated that SiC B out-performed standard monolithic armours and a selection of other armour ceramics including PS 5000 SiC and Sintox-CL. After comminution, the SiC B consisted of particles of closely interlocked grains. These appeared to provide considerable resistance to deviatoric stresses. Results suggest that it is not only increased hardness but also the nature of the fracture of the ceramic ahead of the penetrator that improves the armour’s ballistic performance at defeating WC-Co penetrators. If such superior ballistic response can be controlled and incorporated into practical armour systems, it will provide the basis for an advance in armour protective capability against WC-Co penetrators.
In addition, a numerical material model derived from experimental data was developed to provide a preliminary tool to study the WC-Co failure. It was demonstrated that the numerical estimation of WC-Co behaviour using a shock Equation Of State (EOS), a piecewise linear strength model and a principle stress failure model provides a good method to estimate spall behaviour under dynamic loading in AUTODYN 2D. Successful numerical simulation of the material model used demonstrated the future potential of the technique
Grazing among carnivores: Managing cattle depredation across the Western-world
Large carnivores such as wolves and bears may prey on cattle. With the recent recovery of large carnivore populations in the Western world, cattle depredation is expected to increase. To mitigate potential conflicts, it is therefore important to find best practice for cattle grazing in carnivore-exposed areas. In my thesis I examined depredation rates of cattle by carnivores in different regions of Europe and North America and performed a survey and an interview study on cattle farming practices, losses to carnivores and other causes of mortality, and mitigation techniques to reduce depredation.
My objectives were (1) to examine cattle depredation over time in carnivore-exposed areas across different countries; (2) to understand the possible geographical variation in cattle depredation in relation to carnivore species present, cattle and carnivore densities, grazing system and preventive measure(s) applied; and (3) subsequently, make recommendations. I hypothesised that predator density influences cattle depredation. Further, I hypothesised higher depredation rates for herds in extensive and free-ranging systems than in systems where cattle grazes in close vicinity to the farm. I expected to see differences between continents and areas both in depredation rates and commonness and effectiveness of measures applied, due to differences in habitat, farming practices, carnivore densities and carnivore management.
Depredation statistics, cattle- and carnivore densities were collected from 25 areas in Europe and North America. The survey was carried out in 18 areas and the interview with eight of the survey participants. I mapped depredation trends over time and modelled depredation of cattle as a function of carnivore presence and density, year, and forest cover. To analyse the social data, I performed a descriptive and inferential analysis, using non-parametric tests.
Cattle depredation increased over time in 70% of the areas in Europe and 60% of the study areas in North America. Cattle depredation was positively related to wolf density in Europe, but only weakly in North America. The social study results aligned with this finding and also showed that depredation occurred more often in extensive and free-grazing systems. Lastly, measures to prevent cattle depredation differed greatly between the continents. While electric fencing was most common in Europe, Americans used lethal control, avoidance and herding to a larger extent. In general, a higher number of preventive measures are commonly used in North America than in Europe.
There is urgent need of a standardised, uniform method to monitor livestock depredation. Especially throughout Europe, where cattle depredation has increased the most and, according to the interviewees, the problem of cattle depredation has become more urgent. I wrote recommendations about: I) the carnivore species, II) replacement of electric fencing and avoiding carnivores, III) carnivores avoiding cattle, IV) lethal control of carnivores
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