GraphSE2^2: An Encrypted Graph Database for Privacy-Preserving Social Search

In this paper, we propose GraphSE$^2$, an encrypted graph database for online social network services to address massive data breaches. GraphSE$^2$ preserves the functionality of social search, a key enabler for quality social network services, where social search queries are conducted on a large-scale social graph and meanwhile perform set and computational operations on user-generated contents. To enable efficient privacy-preserving social search, GraphSE$^2$ provides an encrypted structural data model to facilitate parallel and encrypted graph data access. It is also designed to decompose complex social search queries into atomic operations and realise them via interchangeable protocols in a fast and scalable manner. We build GraphSE$^2$ with various queries supported in the Facebook graph search engine and implement a full-fledged prototype. Extensive evaluations on Azure Cloud demonstrate that GraphSE$^2$ is practical for querying a social graph with a million of users.Comment: This is the full version of our AsiaCCS paper "GraphSE$^2$: An Encrypted Graph Database for Privacy-Preserving Social Search". It includes the security proof of the proposed scheme. If you want to cite our work, please cite the conference version of i

The Galois Complexity of Graph Drawing: Why Numerical Solutions are Ubiquitous for Force-Directed, Spectral, and Circle Packing Drawings

Many well-known graph drawing techniques, including force directed drawings, spectral graph layouts, multidimensional scaling, and circle packings, have algebraic formulations. However, practical methods for producing such drawings ubiquitously use iterative numerical approximations rather than constructing and then solving algebraic expressions representing their exact solutions. To explain this phenomenon, we use Galois theory to show that many variants of these problems have solutions that cannot be expressed by nested radicals or nested roots of low-degree polynomials. Hence, such solutions cannot be computed exactly even in extended computational models that include such operations.Comment: Graph Drawing 201

On formal verification of arithmetic-based cryptographic primitives

Cryptographic primitives are fundamental for information security: they are used as basic components for cryptographic protocols or public-key cryptosystems. In many cases, their security proofs consist in showing that they are reducible to computationally hard problems. Those reductions can be subtle and tedious, and thus not easily checkable. On top of the proof assistant Coq, we had implemented in previous work a toolbox for writing and checking game-based security proofs of cryptographic primitives. In this paper we describe its extension with number-theoretic capabilities so that it is now possible to write and check arithmetic-based cryptographic primitives in our toolbox. We illustrate our work by machine checking the game-based proofs of unpredictability of the pseudo-random bit generator of Blum, Blum and Shub, and semantic security of the public-key cryptographic scheme of Goldwasser and Micali.Comment: 13 page

Stock assessment of red Pandora Pagellus Bellottii (Steindachner, 1882) in the Ivorian continental shelf (West Africa)

Population parameters of Red Pandora Pagellus bellottii (Steindachner, 1882) were collected in the Ivorian continental shelf from March 2016 to February 2018. 799 specimens of P. bellottii used in this study. Their fork length ranging from 9.9 to 25 cm was measured. The length frequency data were analyzed using ELEFAN I in the software package FiSAT II. Estimated Von Bertalanffy parameters for the whole population were: L = 31.73 cm, k = 0.42 year-1 and t 0 = - 0.38 year-1. The length-weight relationship all  individuals of P. bellottii was described by the following parameters: a = 0.0186, b = 2.9796. Negative allometric was observed. The rates of total (Z) and natural mortalities (M) were 2.88 and 0.96 year-1, respectively. The annual instantaneous fishing mortality rate (F) was 1.92 year-1. The recruitment pattern was continuous with one recruitment pulse. The estimated length at first capture (Lc) was 14.39  cm. The exploitation rate (E= 0.67) and the results from the yield-per-recruit analysis indicated that the resource has been heavily over exploited. Therefore, some measures of management should be imperatively implemented to protect the Red Pandora population in  the Ivorian continental shelf. Keywords: Population parameters, stock assessment, Pagellus bellottii, continental shelf, Côte d’Ivoire. English Title: Evaluation du stock du pageot à tache rouge <i>Pagellus bellottii </i> (Steindachner, 1882) sur le plateau continental Ivoirien (Afrique de l’ouest) Les paramètres de population du Pageot à tache rouge Pagellus bellottii (Steindachner, 1882) ont été étudiés au niveau du plateau continental ivoirien de mars 2016 à février 2018. Au total, 799 spécimens de P. bellottii ont été utilisés dans cette étude. Leur longueur à la fourche varie de 9,9 à 25 cm. Les données de fréquence de taille ont été analysées à l’aide du programme ELEFAN I du logiciel FiSAT II. Les paramètres de croissance selon le modèle de Von Bertalanffy pour toute la population sont les suivants : L = 31,73 cm, k = 0,42 an-1 et t0 = -0,38 an-1. La relation longueur poids chez les deux sexes confondus de P. bellottii est décrite par les paramètres suivants : a = 0.0186, b = 2,9796. Ainsi, chez les sexes confondus, P. bellottii présente une allométrie négative. Les taux de mortalité totale (Z) etnaturelle (M) ont été de 2,88 et 0,96 an-1, respectivement. Le taux instantané annuel de mortalité par pêche (F) obtenu est de 1,92 an-1. Le recrutement est continu est avec un seul pic. La taille de première capture (Lc) est de 14,39 cm. Le taux d’exploitation (E = 0,67) et les résultats de l’analyse du rendement par recrue indiquent que la ressource est fortement surexploitée. De ce fait, certaines mesures degestion doivent être impérativement mises en œuvre pour protéger la population du Pageot à tache rouge sur le plateau continental ivoirien. Mots clés : Paramètres de population, évaluation du stock, Pagellus bellottii, plateau continental, Côte d’Ivoire

Compositional closure for Bayes Risk in probabilistic noninterference

We give a sequential model for noninterference security including probability (but not demonic choice), thus supporting reasoning about the likelihood that high-security values might be revealed by observations of low-security activity. Our novel methodological contribution is the definition of a refinement order and its use to compare security measures between specifications and (their supposed) implementations. This contrasts with the more common practice of evaluating the security of individual programs in isolation. The appropriateness of our model and order is supported by our showing that our refinement order is the greatest compositional relation --the compositional closure-- with respect to our semantics and an "elementary" order based on Bayes Risk --- a security measure already in widespread use. We also relate refinement to other measures such as Shannon Entropy. By applying the approach to a non-trivial example, the anonymous-majority Three-Judges protocol, we demonstrate by example that correctness arguments can be simplified by the sort of layered developments --through levels of increasing detail-- that are allowed and encouraged by compositional semantics

Error-Correcting Tournaments

We present a family of pairwise tournaments reducing $k$-class classification to binary classification. These reductions are provably robust against a constant fraction of binary errors. The results improve on the PECOC construction \cite{SECOC} with an exponential improvement in computation, from $O(k)$ to $O(\log_2 k)$, and the removal of a square root in the regret dependence, matching the best possible computation and regret up to a constant.Comment: Minor wording improvement

Universally Composable Quantum Multi-Party Computation

The Universal Composability model (UC) by Canetti (FOCS 2001) allows for secure composition of arbitrary protocols. We present a quantum version of the UC model which enjoys the same compositionality guarantees. We prove that in this model statistically secure oblivious transfer protocols can be constructed from commitments. Furthermore, we show that every statistically classically UC secure protocol is also statistically quantum UC secure. Such implications are not known for other quantum security definitions. As a corollary, we get that quantum UC secure protocols for general multi-party computation can be constructed from commitments

Bounds and optimisation of orbital angular momentum bandwidths within parametric down-conversion systems

The measurement of high-dimensional entangled states of orbital angular momentum prepared by spontaneous parametric down-conversion can be considered in two separate stages: a generation stage and a detection stage. Given a certain number of generated modes, the number of measured modes is determined by the measurement apparatus. We derive a simple relationship between the generation and detection parameters and the number of measured entangled modes.Comment: 6 pages, 4 figure

Bit-parallel search algorithms for long patterns

Peer reviewe

Effect of meniscus modelling assumptions in a static tibiofemoral finite element model: importance of geometry over material

Finite element studies of the tibiofemoral joint have increased use in research, with attention often placed on the material models. Few studies assess the effect of meniscus modelling assumptions in image-based models on contact mechanics outcomes. This work aimed to assess the effect of modelling assumptions of the meniscus on knee contact mechanics and meniscus kinematics. A sensitivity analysis was performed using three specimen-specific tibiofemoral models and one generic knee model. The assumptions in representing the meniscus attachment on the tibia (shape of the roots and position of the attachment), the material properties of the meniscus, the shape of the meniscus and the alignment of the joint were evaluated, creating 40 model instances. The values of material parameters for the meniscus and the position of the root attachment had a small influence on the total contact area but not on the meniscus displacement or the force balance between condyles. Using 3D shapes to represent the roots instead of springs had a large influence in meniscus displacement but not in knee contact area. Changes in meniscus shape and in knee alignment had a significantly larger influence on all outcomes of interest, with differences two to six times larger than those due to material properties. The sensitivity study demonstrated the importance of meniscus shape and knee alignment on meniscus kinematics and knee contact mechanics, both being more important than the material properties or the position of the roots. It also showed that differences between knees were large, suggesting that clinical interpretations of modelling studies using single geometries should be avoided