82 research outputs found
Hot exciton transport in ZnSe quantum wells
The in-plane transport of excitons in ZnSe quantum wells is investigated
directly by microphotoluminescence in combination with a solid immersion lens.
Due to the strong Froehlich coupling, the initial kinetic energy of the
excitons is well controlled by choosing the excess energy of the excitation
laser. When increasing the laser excess energy, we find a general trend of
increasing transport length and more importantly a pronounced periodic
quenching of the transport length when the excess energy corresponds to
multiples of the LO-phonon energy. Such features show the dominant role of the
kinetic energy of excitons in the transport process. Together with the
excitation intensity dependence of the transport length, we distinguish the
phonon wind driven transport of cold excitons and defect-limited hot exciton
transport.Comment: 4 pages, 4 figure
Generic Decoding of Restricted Errors
Several recently proposed code-based cryptosystems base their security on a
slightly generalized version of the classical (syndrome) decoding problem.
Namely, in the so-called restricted (syndrome) decoding problem, the error
values stem from a restricted set. In this paper, we propose new generic
decoders, that are inspired by subset sum solvers and tailored to the new
setting. The introduced algorithms take the restricted structure of the error
set into account in order to utilize the representation technique efficiently.
This leads to a considerable decrease in the security levels of recently
published code-based cryptosystems
Numerical study on the application of vacuum insulation panels and a latent heat storage for refrigerated vehicles with a large Eddy lattice Boltzmann method
How to Lose Some Weight - A Practical Template Syndrome Decoding Attack
We study the hardness of the Syndrome Decoding problem, the base of most code-based cryptographic schemes, such as Classic McEliece, in the presence of side-channel information. We use ChipWhisperer equipment to perform a template attack on Classic McEliece running on an ARM Cortex-M4, and accurately classify the Hamming weights of consecutive 32-bit blocks of the secret error vector. With these weights at hand, we optimize Information Set Decoding algorithms. Technically, we show how to speed up information set decoding via a dimension reduction, additional parity-check equations, and an improved information set search, all derived from the Hamming weight information.
Consequently, using our template attack, we can practically recover an error vector in dimension n=2197 in a matter of seconds. Without side-channel information, such an instance has a complexity of around 88 bit.
We also estimate how our template attack affects the security of the proposed McEliece parameter sets. Roughly speaking, even an error-prone leak of our Hamming weight information leads for n=3488 to a security drop of 89 bits
A nearly symmetric double-image gravitational lens
We report the discovery of a new double-image gravitational lens resulting
from our search for lenses in the southern sky. Radio source PMN J2004-1349 is
composed of two compact components separated by 1.13 arcseconds in VLA, MERLIN
and VLBA images. The components have a flux ratio of 1:1 at radio frequencies
ranging from 5 GHz to 22 GHz. The I-band optical counterpart is also an equal
double, with roughly the same separation and position angle as the radio
double. Upon subtraction of the components from the I-band image, we identify a
dim pattern of residuals as the lens galaxy. While the present observations are
sufficient to establish that J2004-1349 is a gravitational lens, additional
information will be necessary (such as the redshifts of the galaxy and quasar,
and precise astrometry and photometry of the lens galaxy) before constructing
detailed mass models.Comment: 17 pp., 5 bitmapped figs. (contact [email protected] for nicer figs), in
press, A.J. (substantially revised
Zero Knowledge Protocols and Signatures from the Restricted Syndrome Decoding Problem
The Restricted Syndrome Decoding Problem (R-SDP) cor-
responds to the Syndrome Decoding Problem (SDP) with the additional
constraint that entries of the solution vector must live in a desired sub-
set of a finite field. In this paper we study how this problem can be
applied to the construction of signatures derived from Zero-Knowledge
(ZK) proofs. First, we show that R-SDP appears to be well suited for
this type of applications: almost all ZK protocols relying on SDP can be
modified to use R-SDP, with important reductions in the communication
cost. Then, we describe how R-SDP can be further specialized, so that
solutions can be represented with a number of bits that is slightly larger
than the security parameter (which clearly provides an ultimate lower
bound), thus enabling the design of ZK protocols with tighter and rather
competitive parameters. Finally, we show that existing ZK protocols can
greatly benefit from the use of R-SDP, achieving signature sizes in the
order of 7 kB, which are smaller than those of several other schemes ob-
tained from ZK protocols. For instance, this beats all schemes based on
the Permuted Kernel Problem (PKP), almost all schemes based on SDP
and several schemes based on rank metric problems
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Prevalence of SARS-CoV-2 antibodies in healthy blood donors from the state of Tyrol, Austria, in summer 2020.
BACKGROUND: Seroepidemiological studies provide important insight into the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV‑2) in our society. We aimed to determine seropositivity of SARS-CoV‑2 antibodies and its cross-sectional correlates in a large cohort of blood donors. METHODS: In this observational cohort study, we tested healthy blood donors residing in Tyrol, Austria, for SARS-CoV‑2 antibodies using the Abbott SARS-CoV‑2 IgG chemiluminescent microparticle immunoassay. We estimated 95% confidence intervals (95% CI) of seroprevalences using bootstrapping and tested for differences by participant characteristics using logistic regression. FINDINGS: Between 8 June and 4 September 2020, we screened 5345 healthy individuals at local blood donor sessions (mean age 42.7 years, SD 13.5 years, 46.7% female). Overall seroprevalence was 3.1% (95% CI 2.7-3.6%, 165 cases), which is 5.1-fold higher (95% CI 4.5-6.0%) than the case number identified by the health authorities in the state-wide testing program (0.6%; 4536 out of 757,634). Seroprevalence was higher in the district Landeck (16.6%, P < 0.001) and in individuals aged < 25 years (4.7%, P = 0.043), but did not differ by gender, blood types, or medication intake. The odds ratio for seropositivity was 2.51 for participants who had travelled to Ischgl (1.49-4.21, P = 0.001), 1.39 who had travelled to other federal states (1.00-1.93, P = 0.052), and 2.41 who had travelled abroad (1.61-3.63, P < 0.001). Compared to participants who had a suspected/confirmed SARS-CoV‑2 infection but were seronegative, seropositive participants more frequently reported loss of smell (odds ratio = 2.49, 1.32-4.68, P = 0.005) and taste (odds ratio = 2.76, 1.54-4.92, P = 0.001). CONCLUSION: In summer 2020, SARS-CoV‑2 seroprevalence in Tyrolean blood donors was 3.1%. Our study revealed regional variation and associations with young age, travel history and specific symptoms
FuLeeca: A Lee-based Signature Scheme
In this work we introduce a new code-based signature scheme, called \textsf{FuLeeca}, based on the NP-hard problem of finding codewords of given Lee-weight. The scheme follows the Hash-and-Sign approach applied to quasi-cyclic codes. Similar approaches in the Hamming metric have suffered statistical attacks, which revealed the small support of the secret basis. Using the Lee metric, we are able to thwart such attacks. We use existing hardness results on the underlying problem and study adapted statistical attacks. We propose parameters for \textsf{FuLeeca}~and compare them to an extensive list of proposed post-quantum secure signature schemes including the ones already standardized by NIST. This comparison reveals that \textsf{FuLeeca}~is competitive. For example, for NIST category I, i.e., 160 bit of classical security, we obtain an average signature size of 1100 bytes and public key sizes of 1318 bytes. Comparing the total communication cost, i.e., the sum of the signature and public key size, we see that \textsf{FuLeeca} is only outperformed by Falcon while the other standardized schemes Dilithium and SPHINCS+ show larger communication costs than \textsf{FuLeeca}
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