24,890 research outputs found
Lattice-Based Group Signatures: Achieving Full Dynamicity (and Deniability) with Ease
In this work, we provide the first lattice-based group signature that offers
full dynamicity (i.e., users have the flexibility in joining and leaving the
group), and thus, resolve a prominent open problem posed by previous works.
Moreover, we achieve this non-trivial feat in a relatively simple manner.
Starting with Libert et al.'s fully static construction (Eurocrypt 2016) -
which is arguably the most efficient lattice-based group signature to date, we
introduce simple-but-insightful tweaks that allow to upgrade it directly into
the fully dynamic setting. More startlingly, our scheme even produces slightly
shorter signatures than the former, thanks to an adaptation of a technique
proposed by Ling et al. (PKC 2013), allowing to prove inequalities in
zero-knowledge. Our design approach consists of upgrading Libert et al.'s
static construction (EUROCRYPT 2016) - which is arguably the most efficient
lattice-based group signature to date - into the fully dynamic setting.
Somewhat surprisingly, our scheme produces slightly shorter signatures than the
former, thanks to a new technique for proving inequality in zero-knowledge
without relying on any inequality check. The scheme satisfies the strong
security requirements of Bootle et al.'s model (ACNS 2016), under the Short
Integer Solution (SIS) and the Learning With Errors (LWE) assumptions.
Furthermore, we demonstrate how to equip the obtained group signature scheme
with the deniability functionality in a simple way. This attractive
functionality, put forward by Ishida et al. (CANS 2016), enables the tracing
authority to provide an evidence that a given user is not the owner of a
signature in question. In the process, we design a zero-knowledge protocol for
proving that a given LWE ciphertext does not decrypt to a particular message
Search for signatures of dust in the Pluto-Charon system using Herschel/PACS observations
In this letter we explore the environment of Pluto and Charon in the far
infrared with the main aim to identify the signs of any possible dust ring,
should it exist in the system. Our study is based on observations performed at
70 um with the PACS instrument onboard the Herschel Space Observatory at 9
epochs between March 14 and 19, 2012. The far-infrared images of the
Pluto-Charon system are compared to those of the point spread function (PSF)
reference quasar 3C454.3. The deviation between the observed Pluto-Charon and
reference PSFs are less then 1 sigma indicating that clear evidence for an
extended dust ring around the system was not found. Our method is capable of
detecting a hypothetical ring with a total flux of ~3.3 mJy at a distance of
~153 000 km (~8.2 Pluto-Charon distances) from the system barycentre. We place
upper limits on the total disk mass and on the column density in a reasonable
disk configuration and analyse the hazard during the flyby of NASAs New
Horizons in July 2015. This realistic model configuration predicts a column
density of 8.7x10^(-10) gcm^(-2) along the path of the probe and an impactor
mass of 8.7x10^(-5) g.Comment: 10 pages, 4 figures, 2 table
Still Wrong Use of Pairings in Cryptography
Several pairing-based cryptographic protocols are recently proposed with a
wide variety of new novel applications including the ones in emerging
technologies like cloud computing, internet of things (IoT), e-health systems
and wearable technologies. There have been however a wide range of incorrect
use of these primitives. The paper of Galbraith, Paterson, and Smart (2006)
pointed out most of the issues related to the incorrect use of pairing-based
cryptography. However, we noticed that some recently proposed applications
still do not use these primitives correctly. This leads to unrealizable,
insecure or too inefficient designs of pairing-based protocols. We observed
that one reason is not being aware of the recent advancements on solving the
discrete logarithm problems in some groups. The main purpose of this article is
to give an understandable, informative, and the most up-to-date criteria for
the correct use of pairing-based cryptography. We thereby deliberately avoid
most of the technical details and rather give special emphasis on the
importance of the correct use of bilinear maps by realizing secure
cryptographic protocols. We list a collection of some recent papers having
wrong security assumptions or realizability/efficiency issues. Finally, we give
a compact and an up-to-date recipe of the correct use of pairings.Comment: 25 page
The Earth as an extrasolar transiting planet: Earth's atmospheric composition and thickness revealed by Lunar eclipse observations
An important goal within the quest for detecting an Earth-like extrasolar
planet, will be to identify atmospheric gaseous bio-signatures. Observations of
the light transmitted through the Earth's atmosphere, as for an extrasolar
planet, will be the first step for future comparisons. We have completed
observations of the Earth during a Lunar eclipse, a unique situation similar to
that of a transiting planet. We aim at showing what species could be detected
in its atmosphere at optical wavelengths, where a lot of photons are available
in the masked stellar light. We present observations of the 2008 August 16 Moon
eclipse performed with the SOPHIE spectrograph at the Observatoire de
Haute-Provence. Locating the spectrograph fibers in the penumbra of the
eclipse, the Moon irradiance is then a mix of direct, unabsorbed Sun light and
solar light that has passed through the Earth's limb. This mixture essentially
reproduces what is recorded during the transit of an extrasolar planet. We
report here the clear detection of several Earth atmospheric compounds in the
transmission spectra, such as ozone, molecular oxygen, and neutral sodium as
well as molecular nitrogen and oxygen through the Rayleigh signature. Moreover,
we present a method that allows us to derive the thickness of the atmosphere
versus the wavelength for penumbra eclipse observations. We quantitatively
evaluate the altitude at which the atmosphere becomes transparent for important
species like molecular oxygen and ozone, two species thought to be tightly
linked to the presence of life. The molecular detections presented here are an
encouraging first attempt, necessary to better prepare for the future of
extremely-large telescopes and transiting Earth-like planets. Instruments like
SOPHIE will be mandatory when characterizing the atmospheres of transiting
Earth-like planets from the ground and searching for bio-marker signatures.Comment: 15 pages, 14 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
Planet Signatures in Collisionally Active Debris Discs: scattered light images
Planet perturbations are often invoked as a potential explanation for many
spatial structures that have been imaged in debris discs. So far this issue has
been mostly investigated with collisionless N-body numerical models. We
numerically investigate how the coupled effect of collisions and radiation
pressure can affect the formation and survival of radial and azimutal
structures in a disc perturbed by a planet. We consider two set-ups: a planet
embedded within an extended disc and a planet exterior to an inner debris ring.
We use the DyCoSS code of Thebault(2012) and derive synthetic images of the
system in scattered light. The planet's mass and orbit, as well as the disc's
collisional activity are explored as free parameters.
We find that collisions always significantly damp planet-induced structures.
For the case of an embedded planet, the planet's signature, mostly a density
gap around its radial position, should remain detectable in head-on images if
M_planet > M_Saturn. If the system is seen edge-on, however, inferring the
presence of the planet is much more difficult, although some planet-induced
signatures might be observable under favourable conditions.
For the inner-ring/external-planet case, planetary perturbations cannot
prevent collision-produced small fragments from populating the regions beyond
the ring: The radial luminosity profile exterior to the ring is close to the
one it should have in the absence of the planet. However, a Jovian planet on a
circular orbit leaves precessing azimutal structures that can be used to
indirectly infer its presence. For a planet on an eccentric orbit, the ring is
elliptic and the pericentre glow effect is visible despite of collisions and
radiation pressure, but detecting such features in real discs is not an
unambiguous indicator of the presence of an outer planet.Comment: Accepted for Publication in A&A (NOTE: Abridged abstract and
(very)LowRes Figures. Better version, with High Res figures and full abstract
can be found at http://lesia.obspm.fr/perso/philippe-thebault/planpapph.pdf
Discovering habitable Earths, hot Jupiters and other close planets with microlensing
Searches for planets via gravitational lensing have focused on cases in which
the projected separation, a, between planet and star is comparable to the
Einstein radius, R_E. This paper considers smaller orbital separations and
demonstrates that evidence of close-orbit planets can be found in the
low-magnification portion of the light curves generated by the central star. We
develop a protocol to discover hot Jupiters as well as Neptune-mass and
Earth-mass planets in the stellar habitable zone. When planets are not
discovered, our method can be used to quantify the probability that the lens
star does not have planets within specified ranges of the orbital separation
and mass ratio. Nearby close-orbit planets discovered by lensing can be subject
to follow-up observations to study the newly-discovered planets or to discover
other planets orbiting the same star. Careful study of the low-magnification
portions of lensing light curves should produce, in addition to the discoveries
of close-orbit planets, definite detections of wide-orbit planets through the
discovery of "repeating" lensing events. We show that events exhibiting
extremely high magnification can effectively be probed for planets in close,
intermediate, and wide distance regimes simply by adding several-time-per-night
monitoring in the low-magnification wings, possibly leading to gravitational
lensing discoveries of multiple planets occupying a broad range of orbits, from
close to wide, in a single planetary system.Comment: 21 pages, 5 figures, submitted to the Astrophysical Journa
Grain Size segregation in debris discs
In most debris discs, dust grain dynamics is strongly affected by stellar
radiation pressure. As this mechanism is size-dependent, we expect dust grains
to be spatially segregated according to their sizes. However, because of the
complex interplay between radiation pressure, collisions and dynamical
perturbations, this spatial segregation of the particle size distribution (PSD)
has proven difficult to investigate with numerical models. We propose to
explore this issue using a new-generation code that can handle some of the
coupling between dynamical and collisional effects. We investigate how PSDs
behave in both unperturbed discs "at rest" and in discs pertubed by planetary
objects. We use the DyCoSS code of Thebault(2012) to investigate the coupled
effect of collisions, radiation pressure and dynamical perturbations in systems
having reached a steady state. We consider 2 setups: a narrow ring perturbed by
an exterior planet, and an extended disc into which a planet is embedded. For
both setups we consider an additional unperturbed case with no planet. We also
investigate how possible spatial size segregation affect disc images at
different wavelengths. We find that PSDs are always strongly spatially
segregated. The only case for which they follow a standard dn/dr = C.r**(-3.5)
law is for an unperturbed narrow ring, but only within the parent body ring
itself. For all other configurations, the PSD can strongly depart from such
power laws and have strong spatial gradients. As an example, the geometrical
cross section of the disc is rarely dominated by the smallest grains on bound
orbits, as it is expected to be in standard PSDs in s**q with q<-3. Although
the exact profiles and spatial variations of PSDs are a complex function of the
considered set-up, we are however able to derive some robust results that
should be useful for image-or-SED-fitting models of observed discs.Comment: Accepted in A&A // Figure quality has been downgraded. A high-res
version of the paper can be found at
http://lesia.obspm.fr/perso/philippe-thebault/sizepap_rev.pdf /V2: typos
correcte
Tidally-driven Roche-Lobe Overflow of Hot Jupiters with MESA
Many exoplanets have now been detected in orbits with ultra-short periods,
very close to the Roche limit. Building upon our previous work, we study the
possibility that mass loss through Roche lobe overflow (RLO) may affect the
evolution of these planets, and could possibly transform a hot Jupiter into a
lower-mass planet (hot Neptune or super-Earth). We focus here on systems in
which the mass loss occurs slowly ("stable mass transfer" in the language of
binary star evolution) and we compute their evolution in detail with the binary
evolution code MESA. We include the effects of tides, RLO, irradiation and
photo-evaporation of the planet, as well as the stellar wind and magnetic
braking. Our calculations all start with a hot Jupiter close to its Roche
limit, in orbit around a sun-like star. The initial orbital decay and onset of
RLO are driven by tidal dissipation in the star. We confirm that such a system
can indeed evolve to produce lower-mass planets in orbits of a few days. The
RLO phase eventually ends and, depending on the details of the mass transfer
and on the planetary core mass, the orbital period can remain around a few days
for several Gyr. The remnant planets have a rocky core and some amount of
envelope material, which is slowly removed via photo-evaporation at nearly
constant orbital period; these have properties resembling many of the observed
super-Earths and sub-Neptunes. For these remnant planets we also predict an
anti-correlation between mass and orbital period; very low-mass planets
() in ultra-short periods (<1d) cannot be produced through this type of evolution.Comment: 14 pages, 7 figures, 2 tables. Accepted by ApJ. The manuscript has
been revised significantly to address the referee's comments. A link to MESA
inlist files is now provided on page
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