A proposal for founding mistrustful quantum cryptography on coin tossing

A significant branch of classical cryptography deals with the problems which arise when mistrustful parties need to generate, process or exchange information. As Kilian showed a while ago, mistrustful classical cryptography can be founded on a single protocol, oblivious transfer, from which general secure multi-party computations can be built. The scope of mistrustful quantum cryptography is limited by no-go theorems, which rule out, inter alia, unconditionally secure quantum protocols for oblivious transfer or general secure two-party computations. These theorems apply even to protocols which take relativistic signalling constraints into account. The best that can be hoped for, in general, are quantum protocols computationally secure against quantum attack. I describe here a method for building a classically certified bit commitment, and hence every other mistrustful cryptographic task, from a secure coin tossing protocol. No security proof is attempted, but I sketch reasons why these protocols might resist quantum computational attack.Comment: Title altered in deference to Physical Review's fear of question marks. Published version; references update

A Fourier approach to cloud motion estimation

A Fourier technique is described for estimating cloud motion from pairs of pictures using the phase of the cross spectral density. The method allows motion estimates to be made for individual spatial frequencies, which are related to cloud pattern dimensions. Results obtained are presented and compared with the results of a Fourier domain cross correlation scheme. Using both artificial and real cloud data show that the technique is relatively sensitive to the presence of mixtures of motions, changes in cloud shape, and edge effects

Beating the PNS attack in practical quantum cryptography

In practical quantum key distribution, weak coherent state is often used and the channel transmittance can be very small therefore the protocol could be totally insecure under the photon-number-splitting attack. We propose an efficient method to verify the upper bound of the fraction of counts caused by multi-photon pluses transmitted from Alice to Bob, given whatever type of Eve's action. The protocol simply uses two coherent states for the signal pulses and vacuum for decoy pulse. Our verified upper bound is sufficiently tight for QKD with very lossy channel, in both asymptotic case and non-asymptotic case. The coherent states with mean photon number from 0.2 to 0.5 can be used in practical quantum cryptography. We show that so far our protocol is the $only$ decoy-state protocol that really works for currently existing set-ups.Comment: So far this is the unique decoy-state protocol which really works efficiently in practice. Prior art results are commented in both main context and the Appendi

Furniture Stability: A Review of Data and Testing Results

This report by Kids In Danger (KID) and Shane's Foundation focuses on tip-overs of dressers and chests. ASTM International, which has developed thousands of voluntary industry consensus technical standards, has a standard in place to test furniture stability. However, furniture on the market is not required to conform, resulting in widespread non-compliance. Additionally, these standards are too lenient and require reform, as testing protocols have remained virtually unchanged for over a decade, despite continuing injuries and deaths. Units may pass the standard, but still present a significant risk. KID advocates for a two-pronged approach to decreasing tip-over incidents:Increasing consumer awareness of the danger of furniture tip-overs and knowledge of the actions needed to keep children safe, andImproving furniture stability by strengthening standards, making those standards mandatory and enforceable and promoting changes in furniture design.KID compiled data from incidents reported to the U.S. Consumer Product Safety Commission (CPSC) by various sources and from the National Electronic Injury Surveillance System (NEISS). These include reports from January 1, 2010 to October 14, 2015. Findings of the data analysis include:Two-year-olds are the age group most affected by tip-overs, especially in regard to fatal incidents.Children age 2 to 5 accounted for 77% of total incidents.The age range of children injured is wider than the age range of children killed by tip-overs.Fatalities accounted for 12% of total incidents.Head injuries (37%) were the most common category of injury.Almost all (98.7%) of head injuries are related to a television tipping over on a child.KID conducted performance tests on a sample of 19 dressers and chests. Testing was run at the UL Furniture Center of Excellence in Holland, Michigan. UL laboratory technicians followed a testing protocol developed by KID. The protocol included tests based on the current voluntary standard for furniture stability. KID added tests that, among other things, evaluated for tip-overs when more weight was added (simulating larger children), drawers were full of clothes, furniture was placed on carpeting as opposed to bare flooring, televisions were placed on top of the furniture, and additional drawers were opened simultaneous with weighting one drawer. These additional tests were intended to be more representative of real-world scenarios.Test results include:Only nine of the 19 units passed performance tests based on the current tip-over safety standard, ASTM F2057.Only two units passed all tests, including the additional testing protocols added by KID.The weight of a television or any type placed on top of the unit did not decrease the stability of furniture.Furniture placed on carpet is less stable than furniture placed on hard floors.Many units remained stable when more than 70 pounds was placed on an open drawer, while others tipped with less than half that weight

Detection of low energy single ion impacts in micron scale transistors at room temperature

We report the detection of single ion impacts through monitoring of changes in the source-drain currents of field effect transistors (FET) at room temperature. Implant apertures are formed in the interlayer dielectrics and gate electrodes of planar, micro-scale FETs by electron beam assisted etching. FET currents increase due to the generation of positively charged defects in gate oxides when ions (121Sb12+, 14+, Xe6+; 50 to 70 keV) impinge into channel regions. Implant damage is repaired by rapid thermal annealing, enabling iterative cycles of device doping and electrical characterization for development of single atom devices and studies of dopant fluctuation effects

Similarity transformations approach for a generalized Fokker-Planck equation

By using similarity transformations approach, the exact propagator for a generalized one-dimensional Fokker-Planck equation, with linear drift force and space-time dependent diffusion coefficient, is obtained. The method is simple and enables us to recover and generalize special cases studied through the Lie algebraic approach and the Green function technique.Comment: 8 pages, no figure

Insecurity of position-based quantum cryptography protocols against entanglement attacks

Recently, position-based quantum cryptography has been claimed to be unconditionally secure. In contrary, here we show that the existing proposals for position-based quantum cryptography are, in fact, insecure if entanglement is shared among two adversaries. Specifically, we demonstrate how the adversaries can incorporate ideas of quantum teleportation and quantum secret sharing to compromise the security with certainty. The common flaw to all current protocols is that the Pauli operators always map a codeword to a codeword (up to an irrelevant overall phase). We propose a modified scheme lacking this property in which the same cheating strategy used to undermine the previous protocols can succeed with a rate at most 85%. We conjecture that the modified protocol is unconditionally secure and prove this to be true when the shared quantum resource between the adversaries is a two- or three- level system

On the communication cost of entanglement transformations

We study the amount of communication needed for two parties to transform some given joint pure state into another one, either exactly or with some fidelity. Specifically, we present a method to lower bound this communication cost even when the amount of entanglement does not increase. Moreover, the bound applies even if the initial state is supplemented with unlimited entanglement in the form of EPR pairs, and the communication is allowed to be quantum mechanical. We then apply the method to the determination of the communication cost of asymptotic entanglement concentration and dilution. While concentration is known to require no communication whatsoever, the best known protocol for dilution, discovered by Lo and Popescu [Phys. Rev. Lett. 83(7):1459--1462, 1999], requires a number of bits to be exchanged which is of the order of the square root of the number of EPR pairs. Here we prove a matching lower bound of the same asymptotic order, demonstrating the optimality of the Lo-Popescu protocol up to a constant factor and establishing the existence of a fundamental asymmetry between the concentration and dilution tasks. We also discuss states for which the minimal communication cost is proportional to their entanglement, such as the states recently introduced in the context of ``embezzling entanglement'' [W. van Dam and P. Hayden, quant-ph/0201041].Comment: 9 pages, 1 figure. Added a reference and some further explanations. In v3 some arguments are given in more detai