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

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

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

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

The low mass end of the neutral gas mass and velocity width functions of galaxies in Λ\LambdaCDM

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 $\Lambda$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 $\Lambda$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 $M_{vir} < 10^{10} M_{\odot}$.Comment: Accepted for publication in MNRAS, 9 pages, 8 figure

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

Pemodelan Penentuan Keasaman Dan Kebasaan Suatu Molekul Menggunakan Sistem Fuzzy Berdasarkan Data Muatan H Dan N Yang Diperoleh Dari Metode Semiempirik

Tujuan penulisan artikel ini untuk mendapatkan model penetuan keasaman dan kebasaan molekul berdasarkan muatan pada H untuk kelompok asam dan muatan pada N untuk kelompok basa menggunakan analisis metode regresi linear dan sistem fuzzy. berdasarkan data nilai pKa dan pKb hasil hitungan secara regresi linear maupun sistem samar kemudian dihitung besarnya selisih atau deviasi nilai pKa/pKb hitungan dengan pKa/pKb hasil eksperimen. hasil analisis menunjukkan bahwa permodelan dengan sistem fuzzy mempunyai tingkat kesalahan yang lebih kecil dibandingkan permodelan dengan metode regresi linear. kelebihan dari permodelan dengan sistem fuzzy adalah dapat diperoleh model sesuai dengan tingkat kesalahan yang diinginkan dengan cara memilih parameter yang sesuai pada model sistem fuzzy tersebut

Perbandingan Keefektifan Pembelajaran Cooperative Learning Type Stad Dan Type Tps Pada Pembelajaran Bangun Ruang Siswa SMP

Penelitian ini bertujuan untuk mendeskripsikan keefektifan pembelajaran cooperative learning (type student team achiement division dan type think-pair-share) dan keefektifan pembelajaran coope-rative learning type student team achiement division dibandingkan dengan pembelajaran cooperative lerning type think-pair-share ditinjau dari aspek ketercapaian standar kompetensi, kemampuan komunikasi matematika, dan berpikir matematis siswa SMP. Jenis penelitian ini adalah quasi experiment dengan pretest-posttest nonequivalent group design. Populasi dan sampelnya adalah siswa Kelas VIII SMP Negeri 7 Yogyakarta dan siswa Kelas VIII A dan VIII B.Untuk menguji keefektifan metode (type student team achiement division dan type think-pair-share), data dianalisis menggunakan uji one sample t-test. Untuk menguji bahwa metode type student team achiement division lebih efektif daripada metode think-pair-share, data dianalisis menggunakan MANOVA yang dilanjutkan dengan uji t-Benferroni. Hasil penelitian menunjukkan bahwa metode pembelajaran (type student team achiement division dan type think-pair-share) efektif dan metode type student team achiement division lebih efektif daripada metode type think-pair-share ditinjau dari aspek ketercapaian standar kompetensi, kemampuan komunikasi matematika, dan berpikir matematis siswa SMP