8,647 research outputs found
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
Coin Tossing is Strictly Weaker Than Bit Commitment
We define cryptographic assumptions applicable to two mistrustful parties who
each control two or more separate secure sites between which special relativity
guarantees a time lapse in communication. We show that, under these
assumptions, unconditionally secure coin tossing can be carried out by
exchanges of classical information. We show also, following Mayers, Lo and
Chau, that unconditionally secure bit commitment cannot be carried out by
finitely many exchanges of classical or quantum information. Finally we show
that, under standard cryptographic assumptions, coin tossing is strictly weaker
than bit commitment. That is, no secure classical or quantum bit commitment
protocol can be built from a finite number of invocations of a secure coin
tossing black box together with finitely many additional information exchanges.Comment: Final version; to appear in Phys. Rev. Let
A Fast and Efficient Algorithm for Slater Determinant Updates in Quantum Monte Carlo Simulations
We present an efficient low-rank updating algorithm for updating the trial
wavefunctions used in Quantum Monte Carlo (QMC) simulations. The algorithm is
based on low-rank updating of the Slater determinants. In particular, the
computational complexity of the algorithm is O(kN) during the k-th step
compared with traditional algorithms that require O(N^2) computations, where N
is the system size. For single determinant trial wavefunctions the new
algorithm is faster than the traditional O(N^2) Sherman-Morrison algorithm for
up to O(N) updates. For multideterminant configuration-interaction type trial
wavefunctions of M+1 determinants, the new algorithm is significantly more
efficient, saving both O(MN^2) work and O(MN^2) storage. The algorithm enables
more accurate and significantly more efficient QMC calculations using
configuration interaction type wavefunctions
Effects of Domain Wall on Electronic Transport Properties in Mesoscopic Wire of Metallic Ferromagnets
We study the effect of the domain wall on electronic transport properties in
wire of ferromagnetic 3 transition metals based on the linear response
theory. We considered the exchange interaction between the conduction electron
and the magnetization, taking into account the scattering by impurities as
well. The effective electron-wall interaction is derived by use of a local
gauge transformation in the spin space. This interaction is treated
perturbatively to the second order. The conductivity contribution within the
classical (Boltzmann) transport theory turns out to be negligiblly small in
bulk magnets, due to a large thickness of the wall compared with the fermi
wavelength. It can be, however, significant in ballistic nanocontacts, as
indicated in recent experiments. We also discuss the quantum correction in
disordered case where the quantum coherence among electrons becomes important.
In such case of weak localization the wall can contribute to a decrease of
resistivity by causing dephasing. At lower temperature this effect grows and
can win over the classical contribution, in particular in wire of diameter
, being the inelastic diffusion
length. Conductance change of the quantum origin caused by the motion of the
wall is also discussed.Comment: 30 pages, 4 figures. Detailed paper of Phys. Rev. Lett. 78, 3773
(1997). Submitted to J. Phys. Soc. Jp
Survey Research in Finance: Views from Journal Editors
We survey editors from 15 core and 35 non-core finance journals to learn their views about specific issues involving survey research. Based on responses from 25 editors, none of their journals has an established policy involving the publication of survey research. The evidence shows that survey-based manuscripts typically go through the same review process as other manuscripts. However, editors of core versus non-core journals have mixed views about the role that survey research should play in the finance literature. The editors provide their views about the strengths and weaknesses of survey research as well as topic areas that would benefit from using this approach. A review of a finance journals shows that the publication of survey-based papers is an infrequent event for most journals
Survey Research in Finance: Views from Journal Editors
We survey editors from 15 core and 35 non-core finance journals to learn their views about specific issues involving survey research. Based on responses from 25 editors, none of their journals has an established policy involving the publication of survey research. The evidence shows that survey-based manuscripts typically go through the same review process as other manuscripts. However, editors of core versus non-core journals have mixed views about the role that survey research should play in the finance literature. The editors provide their views about the strengths and weaknesses of survey research as well as topic areas that would benefit from using this approach. A review of a finance journals shows that the publication of survey-based papers is an infrequent event for most journals
Cheat Sensitive Quantum Bit Commitment
We define cheat sensitive cryptographic protocols between mistrustful parties
as protocols which guarantee that, if either cheats, the other has some nonzero
probability of detecting the cheating. We give an example of an unconditionally
secure cheat sensitive non-relativistic bit commitment protocol which uses
quantum information to implement a task which is classically impossible; we
also describe a simple relativistic protocol.Comment: Final version: a slightly shortened version of this will appear in
PRL. Minor corrections from last versio
Unconditionally Secure Bit Commitment
We describe a new classical bit commitment protocol based on cryptographic
constraints imposed by special relativity. The protocol is unconditionally
secure against classical or quantum attacks. It evades the no-go results of
Mayers, Lo and Chau by requiring from Alice a sequence of communications,
including a post-revelation verification, each of which is guaranteed to be
independent of its predecessor.Comment: Typos corrected. Reference details added. To appear in Phys. Rev.
Let
Rasch analysis of the 23-item version of the Roland Morris Disability Questionnaire
Objective: To determine the psychometric properties of the 23-item version of the Roland Morris Disability Questionnaire (RMDQ-23) and to quantify their stability across 2 cultures/languages and 2 types of care-settings. Methods: Rasch analysis of data from 1,000 patients with low back pain from primary care (UK and Denmark) and secondary care (Denmark). Results: The RMDQ-23 is unidimensional if local item dependency issues are accommodated, but contains several misfitting or overdiscriminating items, some poor targeting of items, and the scoring of 4-5 items is differentially affected by common clinical characteristics (such as age, gender, pain intensity, pain duration and care setting), depending on the country. Conclusion: As similar results have been found for the RMDQ-24, we believe it is timely to reconsider whether: (i) the RMDQ should be reconstructed using an item-response theory-based approach that includes consideration of new items and response options; or (ii) the use of alternative questionnaires should be recommended, such as the Oswestry Disability Index, that have shown evidence of fitting the Rasch model; or (iii) a completely new condition-specific questionnaire should be developed, perhaps utilizing a computerized adaptive testing platform
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