475 research outputs found
Efficient implementation of hybrid encryption from coding theory
No full textIn this work we present an efficient implementation of the Hybrid Encryption scheme based on the Niederreiter PCKS proposed by E. Persichetti. To achieve IND-CCA2 security (in the random oracle model), we use an HMAC function of the message and the symmetric key, and then apply AES128-CBC as the data encapsulation part of this hybrid scheme. The HMAC function is based on SHA3-512. In addition, we introduce a modification in the decapsulation algorithm, to resist a reaction attack first proposed by Bernstein et al. The implementation is done in C on Intel core i3 CPU and 4 GB RAM and 64 bit OS. The code is running Debian/Linux 3.5.2, where the source has been compiled with gcc 4.7
Order and randomness in Kolmogorov–Johnson–Mehl–Avrami-type phase transitions
No full textThe distribution of points on a 2D domain influences the kinetics of its coverage when a
growth law is attached at each point. This implies that the kinetics of space filling can be
adopted as a descriptor of the degree of order of the initial point distribution. In this paper, the
degree of order of an initial array of points has been changed following two paths: (i) from a
regular square lattice, through increasing displacement assigned to each point, towards
Poissonian disorder; (ii) from a Poissonian distribution, by introducing a hard core potential
with increasing correlation lengths, towards a more ordered lattice. A linear growth law has
been attached to the points of the initial array and the kinetics X.Xe/, where Xe is the extended
coverage as defined in the Kolmogorov–Johnson–Mehl–Avrami model, has been monitored.
The quantitative analysis has been performed by fitting the kinetics to an equation which we
propose for the first time and which has proved to be, in fact, highly suitable for the purpose.
The results demonstrate that the gross of variation from order to disorder is obtained for point
displacements, u, of the order of a, the latter being the constant of a square lattice. Vice versa,
the introduction of a correlation distance in a random distribution provokes at most an order
limited to the first neighbors and no real order can ever be reached. Others descriptors have
been investigated, all confirming our results. We also developed an analytical description
based on the use of the f -functions, as have been defined by Van Kampen, up to the second
order terms. Such a description has been shown to work well for u=a < 1 within an interval
1Xe which depends on the value
Efficient implementation of a CCA2-secure variant of McEliece using generalized Srivastava codes
No full textIn this paper we present efficient implementations of McEliece variants using quasi-dyadic codes. We provide secure parameters for a classical McEliece encryption scheme based on quasi-dyadic generalized Srivastava codes, and successively convert our scheme to a CCA2-secure protocol in the random oracle model applying the Fujisaki-Okamoto transform. In contrast with all other CCA2-secure code-based cryptosystems that work in the random oracle model, our conversion does not require a constant weight encoding function. We present results for both 128-bit and 80-bit security level, and for the latter we also feature an implementation for an embedded device. © 2012 International Association for Cryptologic Research
Size-dependent reversal of the elastic interaction energy between misfit nanostructures
No full textBy exploiting a fully three-dimensional finite-element modeling of strain fields, we investigate
the spatial dependence of the elastic interaction energy between misfitting nanostructures
beyond the point-dipole approximation. When interacting islands are finite in size, the detailed
shape of the elastic strain field around and under the islands may convert the repulsive
interactions, usually experienced between equal-sized islands, into an attractive basin between
a large island and a population of neighboring clusters smaller than a critical size. The results
of the simulations applied to large Ge islands grown on a Si(111) substrate have significant
implications for the understanding of the strain-mediated coarsening of quantum dots around
the islands
Order and randomness in Kolmogorov-Johnson-Mehl-Avrami-type phase transitions
No full textThe distribution of points on a 2D domain influences the kinetics of its coverage when a growth law is attached at each point. This implies that the kinetics of space filling can be adopted as a descriptor of the degree of order of the initial point distribution. In this paper, the degree of order of an initial array of points has been changed following two paths: (i)from a regular square lattice, through increasing displacement assigned to each point, towards Poissonian disorder; (ii)from a Poissonian distribution, by introducing a hard core potential with increasing correlation lengths, towards a more ordered lattice. A linear growth law has been attached to the points of the initial array and the kinetics X(X e), where X e is the extended coverage as defined in the Kolmogorov-Johnson-Mehl-Avrami model, has been monitored. The quantitative analysis has been performed by fitting the kinetics to an equation which we propose for the first time and which has proved to be, in fact, highly suitable for the purpose. The results demonstrate that the gross of variation from order to disorder is obtained for point displacements, u, of the order of a, the latter being the constant of a square lattice. Vice versa, the introduction of a correlation distance in a random distribution provokes at most an order limited to the first neighbors and no real order can ever be reached. Others descriptors have been investigated, all confirming our results. We also developed an analytical description based on the use of the f-functions, as have been defined by Van Kampen, up to the second order terms. Such a description has been shown to work well for u/a<1 within an interval ΔX e which depends on the value. © 2012 IOP Publishing Ltd
The entangled role of strain and diffusion in driving the spontaneous formation of atolls and holes in Ge/Si(111) heteroepitaxy
No full textWe investigate the interdependent processes of strain and diffusion in the formation of holes and atolls obtained by rapid annealing of Ge/Si(111) islands at T ≈ 970 °C. We show that the shape evolution from islands to atolls and holes is closely captured by an analytical model including strain-driven diffusion. In the model, strain profiles obtained by finite element solutions of continuum elasticity equations are introduced in the diffusion equation as the source of a diffusion flux driven by the strain gradient. When the shape of the elastic field in Ge/Si(111) islands is coupled to diffusion, the morphology of the SiGe nanostructures observed after annealing is reproduced. © 2013 IOP Publishing Ltd
Heteroepitaxy of Ge on singular and vicinal Si surfaces: Elastic field symmetry and nanostructure growth
No full textStarting with the basic definition, a short description of a few relevant physical quantities playing a role in the growth process of heteroepitaxial strained systems, is provided. As such, the paper is not meant to be a comprehensive survey but to present a connection between the Stranski-Krastanov mechanism of nanostructure formation and the basic principles of nucleation and growth. The elastic field is described in the context of continuum elasticity theory, using either analytical models or numerical simulations. The results are compared with selected experimental results obtained on GeSi nanostructures. In particular, by tuning the value of quantities such as vicinality, substrate orientation and symmetry of the diffusion field, we elucidate how anisotropic elastic interactions determine shape, size, lateral distribution and composition of quantum dots
Pair interaction between Ge islands on vicinal Si(001) surfaces
No full textThe pair interaction between Ge islands on vicinal Si(001) substrates is investigated by scanning tunneling microscopy measurements as a function of the miscut angle. By the analysis of the nearest-neighbor island distributions, we assess the dependence of the local strain field on the substrate misorientation. We support our results by modeling elastic relaxation for different shapes and arrangements of islands with finite element calculations. © 2010 The American Physical Society
Driving Ge island ordering on nanostructured Si surfaces
No full textSemiconductor epitaxial nanostructures have been recently proposed as the key building blocks of many innovative applications in materials science and technology. To bring their tremendous potential to fruition, a fine control of nanostructure size and placement is necessary. We present a detailed investigation of the self-ordering process in the prototype case of Ge/Si heteroepitaxy. Starting from a bottom-up strategy (step-bunching instabilities), our analysis moves to lithographic techniques (scanning tunneling lithography, nanomechanical stamping, focused ion beam patterning) with the aim of developing a hybrid approach in which the exogenous intervention is specifically designed to suit and harness the natural self-organization dynamics of the system
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