6,858 research outputs found
Physical Randomness Extractors: Generating Random Numbers with Minimal Assumptions
How to generate provably true randomness with minimal assumptions? This
question is important not only for the efficiency and the security of
information processing, but also for understanding how extremely unpredictable
events are possible in Nature. All current solutions require special structures
in the initial source of randomness, or a certain independence relation among
two or more sources. Both types of assumptions are impossible to test and
difficult to guarantee in practice. Here we show how this fundamental limit can
be circumvented by extractors that base security on the validity of physical
laws and extract randomness from untrusted quantum devices. In conjunction with
the recent work of Miller and Shi (arXiv:1402:0489), our physical randomness
extractor uses just a single and general weak source, produces an arbitrarily
long and near-uniform output, with a close-to-optimal error, secure against
all-powerful quantum adversaries, and tolerating a constant level of
implementation imprecision. The source necessarily needs to be unpredictable to
the devices, but otherwise can even be known to the adversary.
Our central technical contribution, the Equivalence Lemma, provides a general
principle for proving composition security of untrusted-device protocols. It
implies that unbounded randomness expansion can be achieved simply by
cross-feeding any two expansion protocols. In particular, such an unbounded
expansion can be made robust, which is known for the first time. Another
significant implication is, it enables the secure randomness generation and key
distribution using public randomness, such as that broadcast by NIST's
Randomness Beacon. Our protocol also provides a method for refuting local
hidden variable theories under a weak assumption on the available randomness
for choosing the measurement settings.Comment: A substantial re-writing of V2, especially on model definitions. An
abstract model of robustness is added and the robustness claim in V2 is made
rigorous. Focuses on quantum-security. A future update is planned to address
non-signaling securit
Predictable arguments of knowledge
We initiate a formal investigation on the power of predictability for argument of knowledge systems for NP. Specifically, we consider private-coin argument systems where the answer of the prover can be predicted, given the private randomness of the verifier; we call such protocols Predictable Arguments of Knowledge (PAoK).
Our study encompasses a full characterization of PAoK, showing that such arguments can be made extremely laconic, with the prover sending a single bit, and assumed to have only one round (i.e., two messages) of communication without loss of generality.
We additionally explore PAoK satisfying additional properties (including zero-knowledge and the possibility of re-using the same challenge across multiple executions with the prover), present several constructions of PAoK relying on different cryptographic tools, and discuss applications to cryptography
2DPHOT: A Multi-purpose Environment for the Two-dimensional Analysis of Wide-field Images
We describe 2DPHOT, a general purpose analysis environment for source
detection and analysis in deep wide-field images. 2DPHOT is an automated tool
to obtain both integrated and surface photometry of galaxies in an image, to
perform reliable star-galaxy separation with accurate estimates of
contamination at faint flux levels, and to estimate completeness of the image
catalog. We describe the analysis strategy on which 2DPHOT is based, and
provide a detailed description of the different algorithms implemented in the
package. This new environment is intended as a dedicated tool to process the
wealth of data from wide-field imaging surveys. To this end, the package is
complemented by 2DGUI, an environment that allows multiple processing of data
using a range of computing architectures.Comment: Accepted to PAS
Hubble Space Telescope Photometry of Globular Clusters in M81
We perform aperture photometry and profile fitting on 419 globular cluster
(GC) candidates with mV \leq 23 mag identified in Hubble Space Telescope
Advanced Camera for Surveys BVI imaging, and estimate the effective radii of
the clusters. We identify 85 previously known spectroscopically-confirmed
clusters, and newly identify 136 objects as good cluster candidates within the
3{\sigma} color and size ranges defined by the spectroscopically confirmed
clusters, yielding a total of 221 probable GCs. The luminosity function peak
for the 221 probable GCs with estimated total dereddening applied is V ~(20.26
\pm 0.13) mag, corresponding to a distance of ~3.7\pm0.3 Mpc. The blue and red
GC candidates, and the metal-rich (MR) and metal-poor (MP) spectroscopically
confirmed clusters, are similar in half-light radius, respectively. Red
confirmed clusters are about 6% larger in median half-light radius than blue
confirmed clusters, and red and blue good GC candidates are nearly identical in
half-light radius. The total population of confirmed and "good" candidates
shows an increase in half-light radius as a function of galactocentric
distance.Comment: 42 figures, 14 pages, accepted to A
Concurrently Non-Malleable Zero Knowledge in the Authenticated Public-Key Model
We consider a type of zero-knowledge protocols that are of interest for their
practical applications within networks like the Internet: efficient
zero-knowledge arguments of knowledge that remain secure against concurrent
man-in-the-middle attacks. In an effort to reduce the setup assumptions
required for efficient zero-knowledge arguments of knowledge that remain secure
against concurrent man-in-the-middle attacks, we consider a model, which we
call the Authenticated Public-Key (APK) model. The APK model seems to
significantly reduce the setup assumptions made by the CRS model (as no trusted
party or honest execution of a centralized algorithm are required), and can be
seen as a slightly stronger variation of the Bare Public-Key (BPK) model from
\cite{CGGM,MR}, and a weaker variation of the registered public-key model used
in \cite{BCNP}. We then define and study man-in-the-middle attacks in the APK
model. Our main result is a constant-round concurrent non-malleable
zero-knowledge argument of knowledge for any polynomial-time relation
(associated to a language in ), under the (minimal) assumption of
the existence of a one-way function family. Furthermore,We show time-efficient
instantiations of our protocol based on known number-theoretic assumptions. We
also note a negative result with respect to further reducing the setup
assumptions of our protocol to those in the (unauthenticated) BPK model, by
showing that concurrently non-malleable zero-knowledge arguments of knowledge
in the BPK model are only possible for trivial languages
[OII] emitters in the GOODS field at z~1.85: a homogeneous measure of evolving star formation
We present the results of a deep, near-infrared, narrow band imaging survey
at a central wavelength of 1.062 microns (FWHM=0.01 microns) in the GOODS-South
field using the ESO VLT instrument, HAWK-I. The data are used to carry out the
highest redshift search for [OII]3727 emission line galaxies to date. The
images reach an emission line flux limit (5 sigma) of 1.5 x 10^-17 erg cm^-2
s^-1, additionally making the survey the deepest of its kind at high redshift.
In this paper we identify a sample of [OII]3727 emission line objects at
redshift z~1.85 in a co-moving volume of ~4100 Mpc^3. Objects are selected
using an observed equivalent width (EW_obs) threshold of EW_obs = 50 angstroms.
The sample is used to derive the space density and constrain the luminosity
function of [OII] emitters at z=1.85. We find that the space density of objects
with observed [OII] luminosities in the range log(L_[OII]) > 41.74 erg s^-1 is
log(rho)=-2.45+/-0.14 Mpc^-3, a factor of 2 greater than the observed space
density of [OII] emitters reported at z~1.4. After accounting for completeness
and assuming an internal extinction correction of A_Halpha=1 mag (equivalent to
A_[OII]=1.87), we report a star formation rate density of rho* ~0.38+/-0.06
Msun yr^-1 Mpc^-3. We independently derive the dust extinction of the sample
using 24 micron fluxes and find a mean extinction of A_[OII]=0.98+/-0.11
magnitudes (A_Halpha=0.52). This is significantly lower than the A_Halpha=1
(A[OII]=1.86) mag value widely used in the literature. Finally we incorporate
this improved extinction correction into the star formation rate density
measurement and report rho*~0.24+/-0.06 Msun yr^-1 Mpc^-3.Comment: 11 pages, 10 figures, accepted for publication in MNRA
Efficient public-key cryptography with bounded leakage and tamper resilience
We revisit the question of constructing public-key encryption and signature schemes with security in the presence of bounded leakage and tampering memory attacks. For signatures we obtain the first construction in the standard model; for public-key encryption we obtain the first construction free of pairing (avoiding non-interactive zero-knowledge proofs). Our constructions are based on generic building blocks, and, as we show, also admit efficient instantiations under fairly standard number-theoretic assumptions.
The model of bounded tamper resistance was recently put forward by Damgård et al. (Asiacrypt 2013) as an attractive path to achieve security against arbitrary memory tampering attacks without making hardware assumptions (such as the existence of a protected self-destruct or key-update mechanism), the only restriction being on the number of allowed tampering attempts (which is a parameter of the scheme). This allows to circumvent known impossibility results for unrestricted tampering (Gennaro et al., TCC 2010), while still being able to capture realistic tampering attack
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