Franck Leprévost

Safe Distributed Architecture for Image-based Computer Assisted Diagnosis

Existing electronic healthcare systems based on PACS and Hospital IS are designed for clinical practice. Yet, both for security, technical and legacy reasons, they are often weakly connected to computing infrastructures and data networks. In the context of the RAGTIME project, grid infrastructures are studied to propose a cheap and reliable infrastructure enabling computerized medical applications. This raises various concerns, in particular in terms of security and data privacy. This paper presents the results of this study and proposes a complete grid-based architecture able to process medical image for assisted diagnosis in a secured way. Using this infrastructure, care practitioner are able to execute the application from any machine connected to the Internet, therefore improving their mobility. Medical image analysis jobs are certified to be correct using the latest advances in result checking and fault-tolerant algorithms. The architecture has been successfully deployed and validated on the Grid5000 large scale infrastructure.

Torsion sur des familles de courbes de genre g

We construct here, forl=2g2+2g+1 or2g2+3g+1, a family with one parameter of hyperelliptic curves of genusg overQ such that its jacobian has a point of orderl rational overQ(t). Wheng=2 the method allows to construct, forl=17, 19 or 21 a family with one parameter of hyperelliptic curves of genus 2 overQ such that its jacobian has a point of orderl rational overQ(t).

FlowCert : probabilistic certification for peer-to-peer computations

Large scale cluster, peer-to-peer computing systems and grid computer systems gather thousands of nodes for computing parallel applications. At this scale, it raises the problem of the result checking of the parallel execution of a program on an unsecured grid. This domain is the object of numerous works, either at the hardware or at the software level. We propose here an original software method based on the dynamic computation of the data-flow associated to a partial execution of the program on a secure machine. This data-flow is a summary of the execution: any complete execution of the program on an unsecured remote machine with the same inputs supplies a flow which summary has to correspond to the one obtained by partial execution.

5-TORSION POINTS ON CURVES OF GENUS 2

Let C be a smooth proper curve of genus 2 over an algebraically closed field k . Fix a Weierstrass point ∞in C ( k ) and identify C with its image in its Jacobian J under the Albanese embedding that uses ∞ as base point. For any integer N [ges ]1, we write J N for the group of points in J ( k ) of order dividing N and J * N for the subset of J N of points of order N . It follows from the Riemann–Roch theorem that C ( k )∩ J 2 consists of the Weierstrass points of C and that C ( k )∩ J * 3 and C ( k )∩ J * are empty (see [ 3 ]). The purpose of this paper is to study curves C with C ( k )∩ J * 5 non-empty.

Jacobians of Genus-2 Curves with a Rational Point of Order 11

On the one hand, it is well known that Jacobians of (hyper) elliptic curves defined over ℚ having a rational point of order I can be used in many applications, for instance in the construction of class groups of quadratic fields with a nontrivial l-rank. On the other hand, it is also well known that 11 is the least prime number that is not the order of a rational point of an elliptic curve defined over ℚ. It is therefore interesting to look for curves of higher genus whose Jacobians have a rational point of order 11. This problem has already been addressed, and Flynn found such a family 𝔉 t of genus-2 curves. Now it turns out that the Jacobian J 0(23) of the modular genus-2 curve X 0(23) has the required property, but does not belong to 𝔉 t . The study of X 0(23) leads to a method giving a partial solution of the considered problem. Our approach allows us to recover X 0(23) and to construct another 18 distinct explicit curves of genus 2 defined over ℚ whose Jacobians have a rational point of order 11. Of these 19 curves, 10 do not have any rational Weierstrass point, and 9 have a rational Weierstrass point. None of these curves are ℚ̄-isomorphic to each other, nor ℚ̄-isomorphic to an element of Flynns family 𝔉 t . Finally, the Jacobians of these new curves are absolutely simple.

Distributed authentication in GRID5000

Between high-performance clusters and grids appears an intermediate infrastructure called cluster grid that corresponds to the interconnection of clusters through the Internet. Cluster grids are not only dedicated to specific applications but should allow the users to execute programs of different natures. This kind of architecture also imposes additional constraints as the geographic extension raises availability and security issues. In this context, authentication is one of the key stone by providing access to the resources. Grid5000 is a french project based on a cluster grid topology. This article expounds and justifies the authentication system used in Grid5000. We first show the limits of classical approaches that are local files and NIS in such configurations. We then propose a scalable alternative based on the LDAP protocol allowing to meet the needs of cluster grids, either in terms of availability, security and performances. Finally, among the various applications that can be executed in the Grid5000 platform, we present μgrid, a minimal middleware used for medical data processing.

Sur certains sous-groupes de torsion de jacobiennes de courbes hyperelliptiques de genreg ≥ 1

We construct a family of hyperelliptic curves of genusg defined over Q whose Jacobians have a rational point of order 2g(2g+1). Forl = 2g2 + 5g + 5, we construct a family of genusg hyperelliptic curves defined over Q, such that their Jacobians have a rational point of orderl orl / 2 orl / 4. We also construct a hyperelliptic curve of genusg defined over Q, which does not belong to the previous family, and whose Jacobian has a rational point of orderl.

Courbes modulaires et 11-rang de corps quadratiques

Nous construisons 53 corps quadratiques imaginaires ayant un ll-rang egal a 3, et sept corps quadratiques reels de ll-rang egal a 2. Ce sont, a notre connaissance, les premiers exemples de tels corps. We construct 53 imaginary quadratic fields of ll -rank equal to 3, and seven quadratic fields of ll-rank equal to 2. These appear to be the first examples of such fields.

On the Computation of Class Polynomials with “Thetanullwerte” and Its Applications to the Unit Group Computation

The classical class invariants of Weber are introduced as quotients of Thetanullwerte, enabling the computation of these invariants more efficiently than as quotients of values of the Dedekind η-function. We show also how to compute the unit group of suitable ring class fields by proving the fact that most of the invariants introduced by Weber are actually units in the corresponding ring class fields.

How to bypass the Wassenaar arrangement: a new application for watermarking

The scope of this article is to clarify the current legal and political situation related to electronic surveillance on the one hand, and to export regulations for encryption software on the other hand. We will look at different international agreements, such as the UKUSA agreement and the Wassenaar arrangement, and elaborate on current encryption techniques falling under these regulations. This discussion is then followed by introducing the basic concepts of steganography and digital watermarking which could be used for secret communication. As a consequence, we propose an original way to legally bypass the international export regulations using these technologies. To this end a new watermarking technique is proposed, which is robust to JPEG2000 compression and provides a good channel capacity. The efficiency of the proposed technique is analyzed by means of simulations to allow for secure communications.