2,916 research outputs found
Lengths May Break Privacy – Or How to Check for Equivalences with Length
Security protocols have been successfully analyzed using symbolic models, where messages are represented by terms and protocols by processes. Privacy properties like anonymity or untraceability are typically expressed as equivalence between processes. While some decision procedures have been proposed for automatically deciding process equivalence, all existing approaches abstract away the information an attacker may get when observing the length of messages.
In this paper, we study process equivalence with length tests. We first show that, in the static case, almost all existing decidability results (for static equivalence) can be extended to cope with length tests.
In the active case, we prove decidability of trace equivalence with length tests, for a bounded number of sessions and for standard primitives. Our result relies on a previous decidability result from Cheval et al (without length tests). Our procedure has been implemented and we have discovered a new flaw against privacy in the biometric passport protocol
Analisis Kestabilan dan Bifurkasi Solusi Sistem Autoparametrik dengan Osilator Tipe Rayleigh
Masalah resonansi autoparametrik pada sistem tereksitasi sendiri banyak terjadi pada struktur-struktur mekanika. Paper ini akan menganalisis model rekayasa dari struktur mekanika yang sesungguhnya. Sistem autoparametrik tipe Rayleigh dipelajari untuk melihat perilaku solusinya, kasus-kasus bifurkasi solusi yang mungkin
Sharp error terms for return time statistics under mixing conditions
We describe the statistics of repetition times of a string of symbols in a
stochastic process. Denote by T(A) the time elapsed until the process spells
the finite string A and by S(A) the number of consecutive repetitions of A. We
prove that, if the length of the string grows unbondedly, (1) the distribution
of T(A), when the process starts with A, is well aproximated by a certain
mixture of the point measure at the origin and an exponential law, and (2) S(A)
is approximately geometrically distributed. We provide sharp error terms for
each of these approximations. The errors we obtain are point-wise and allow to
get also approximations for all the moments of T(A) and S(A). To obtain (1) we
assume that the process is phi-mixing while to obtain (2) we assume the
convergence of certain contidional probabilities
The Hierarchical Formation of the Galactic Disk
I review the results of recent cosmological simulations of galaxy formation
that highlight the importance of satellite accretion in the formation of
galactic disks. Tidal debris of disrupted satellites may contribute to the disk
component if they are compact enough to survive the decay and circularization
of the orbit as dynamical friction brings the satellite into the disk plane.
This process may add a small but non-negligible fraction of stars to the thin
and thick disks, and reconcile the presence of very old stars with the
protracted merging history expected in a hierarchically clustering universe. I
discuss various lines of evidence which suggest that this process may have been
important during the formation of the Galactic disk.Comment: paper to be read at the "Penetrating Bars through Masks of Cosmic
Dust" conference in South Afric
Smarter Data Availability Checks in the Cloud: Proof of Storage via Blockchain
Cloud computing offers clients flexible and cost-effective resources. Nevertheless, past incidents indicate that the cloud may misbehave by exposing or tampering with clients' data. Therefore, it is vital for clients to protect the confidentiality and integrity of their outsourced data. To address these issues, researchers proposed cryptographic protocols called “proof of storage” that let a client efficiently verify the integrity or availability of its data stored in a remote cloud server. However, in these schemes, the client either has to be online to perform the verification itself or has to delegate the verification to a fully trusted auditor. In this chapter, a new scheme is proposed that lets the client distribute its data replicas among multiple cloud servers to achieve high availability without the need for the client to be online for the verification and without a trusted auditor's involvement. The new scheme is mainly based on blockchain smart contracts. It illustrates how a combination of cloud computing and blockchain technology can resolve real-world problems
Pengenalan Algoritma Pemrograman melalui Simulasi Robot
Programming algorithms is one discipline that became the basic of learning a programming language. Everyone who will makes the creation of applications or information systems need to know the algorithm or the flow of the system to be made in advance. During this time the usual way of learning may seem difficult and less attractive. We will try another, more interesting way to learn a programming algorithms through a robotsimulation. In this way we are sure to make learning more attractive so that will foster interest in learning
The low mass end of the neutral gas mass and velocity width functions of galaxies in CDM
We use the high-resolution Aquarius cosmological dark matter simulations
coupled to the semi-analytic model by Starkenburg et al. (2013) to study the HI
content and velocity width properties of field galaxies at the low mass end in
the context of CDM. We compare our predictions to the observed ALFALFA
survey HI mass and velocity width functions, and find very good agreement
without fine-tuning, when considering central galaxies. Furthermore, the
properties of the dark matter halos hosting galaxies, characterised by their
peak velocity and circular velocity at 2 radial disk scalelengths overlap
perfectly with the inferred values from observations. This suggests that our
galaxies are placed in the right dark matter halos, and consequently at face
value, we do not find any discrepancy with the predictions from the
CDM model. Our analysis indicates that previous tensions, apparent
when using abundance matching models, arise because this technique cannot be
straightforwardly applied for objects with masses .Comment: Accepted for publication in MNRAS, 9 pages, 8 figure
Formal Verification of Security Protocol Implementations: A Survey
Automated formal verification of security protocols has been mostly focused on analyzing high-level abstract models which, however, are significantly different from real protocol implementations written in programming languages. Recently, some researchers have started investigating techniques that bring automated formal proofs closer to real implementations. This paper surveys these attempts, focusing on approaches that target the application code that implements protocol logic, rather than the libraries that implement cryptography. According to these approaches, libraries are assumed to correctly implement some models. The aim is to derive formal proofs that, under this assumption, give assurance about the application code that implements the protocol logic. The two main approaches of model extraction and code generation are presented, along with the main techniques adopted for each approac
On the statistical distribution of first--return times of balls and cylinders in chaotic systems
We study returns in dynamical systems: when a set of points, initially
populating a prescribed region, swarms around phase space according to a
deterministic rule of motion, we say that the return of the set occurs at the
earliest moment when one of these points comes back to the original region. We
describe the statistical distribution of these "first--return times" in various
settings: when phase space is composed of sequences of symbols from a finite
alphabet (with application for instance to biological problems) and when phase
space is a one and a two-dimensional manifold. Specifically, we consider
Bernoulli shifts, expanding maps of the interval and linear automorphisms of
the two dimensional torus. We derive relations linking these statistics with
Renyi entropies and Lyapunov exponents.Comment: submitted to Int. J. Bifurcations and Chao
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