4,411 research outputs found
Towards an Information Theoretic Analysis of Searchable Encryption (Extended Version)
Searchable encryption is a technique that allows a client to store
data in encrypted form on a curious server, such that data can be
retrieved while leaking a minimal amount of information to the
server. Many searchable encryption schemes have been proposed and
proved secure in their own computational model. In this paper we
propose a generic model for the analysis of searchable
encryptions. We then identify the security parameters of
searchable encryption schemes and prove information theoretical
bounds on the security of the parameters. We argue that perfectly
secure searchable encryption schemes cannot be efficient. We
classify the seminal schemes in two categories: the schemes that
leak information upfront during the storage phase, and schemes
that leak some information at every search. This helps designers
to choose the right scheme for an application
Adaptively Secure Computationally Efficient Searchable Symmetric Encryption
Searchable encryption is a technique that allows a client to store documents on a server in encrypted form. Stored documents can be retrieved selectively while revealing as little information as\ud
possible to the server. In the symmetric searchable encryption domain, the storage and the retrieval are performed by the same client. Most conventional searchable encryption schemes suffer\ud
from two disadvantages.\ud
First, searching the stored documents takes time linear in the size of the database, and/or uses heavy arithmetic operations.\ud
Secondly, the existing schemes do not consider adaptive attackers;\ud
a search-query will reveal information even about documents stored\ud
in the future. If they do consider this, it is at a significant\ud
cost to updates.\ud
In this paper we propose a novel symmetric searchable encryption\ud
scheme that offers searching at constant time in the number of\ud
unique keywords stored on the server. We present two variants of\ud
the basic scheme which differ in the efficiency of search and\ud
update. We show how each scheme could be used in a personal health\ud
record system
XMM-Newton observations of two transient millisecond X-ray pulsars in quiescence
We report on XMM-Newton observations of two X-ray transient millisecond
pulsars (XRTMSPs). We detected XTE J0929-314 with an unabsorbed luminosity of
\~7x10^{31} erg/s. (0.5-10 keV) at a fiducial distance of 10 kpc. The quiescent
spectrum is consistent with a simple power law spectrum. The upper limit on the
flux from a cooling neutron star atmosphere is about 20% of the total flux. XTE
J1807-294 instead was not detected. We can put an upper limit on the source
quiescent 0.5-10 keV unabsorbed luminosity <4x10^{31} erg/s at 8 kpc. These
observations strenghten the idea that XRTMSPs have quiescent luminosities
significantly lower than classical neutron star transients.Comment: 4 pages including 1 figures. Accepted for publication in A&A Letter
Authentieke contexten in wiskundemethoden in het vmbo
Centrale vraag
Zijn de bestaande wiskundemethoden die gebruikt worden in de beroepsgerichte leerwegen van het vmbo bruikbaar in verband met authentiek leren en wat is daarvoor eventueel nog extra nodig.
Belangrijkste conclusies
De bestaande wiskundemethoden bevatten enkele authentieke leertaken, maar over het algemeen bevatten de opdrachten weinig kenmerken passend bij authentiek leren. Wel bevatten de boeken diverse aangrijpingspunten om, dicht bij de methode, meer authentieke leertaken te ontwikkelen. In deze publicatie worden aanbevelingen gedaan en enkele mogelijkheden daartoe beschreven. Dit is een Ico-Isor rapport
LOFT as a discovery machine for jetted Tidal Disruption Events
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of jetted tidal disruption events.
For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timin
The optical counterpart of IGR J00291+5934 in quiescence
The recent (December 2004) discovery of the sixth accretion-powered
millisecond X-ray pulsar IGR J00291+5934 provides a very good chance to deepen
our knowledge of such systems. Although these systems are well studied at high
energies, poor informations are available for their optical/NIR counterparts
during quiescence. Up to now, only for SAX J1808.4-3658, the first discovered
system of this type, we have a secure multiband detection of its optical
counterpart in quiescence. Among the seven known system IGR J00291+5934 is the
one that resembles SAX J1808.4-3658 more closely. With the Italian 3.6 m TNG
telescope, we have performed deep optical and NIR photometry of the field of
IGR J00291+5934 during quiescence in order to look for the presence of a
variable counterpart. We present here the first multiband () detection
of the optical and NIR counterpart of IGR J00291+5934 in quiescence as well as
a deep upper limit in the band. We obtain an optical light curve that shows
variability consistent with a sinusoidal modulation at the known 2.46 hr
orbital period and present evidence for a strongly irradiated companion.Comment: 6 pages, 5 figures. Accepted for publication in Astronomy and
Astrophysic
Low Temperature Magnetic Properties of the Double Exchange Model
We study the {\it ferromagnetic} (FM) Kondo lattice model in the strong
coupling limit (double exchange (DE) model). The DE mechanism proposed by Zener
to explain ferromagnetism has unexpected properties when there is more than one
itinerant electron. We find that, in general, the many-body ground state of the
DE model is {\it not} globally FM ordered (except for special filled-shell
cases). Also, the low energy excitations of this model are distinct from spin
wave excitations in usual Heisenberg ferromagnets, which will result in unusual
dynamic magnetic properties.Comment: 5 pages, RevTeX, 5 Postscript figures include
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