15,755 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
Commentary on session I: The migration, trade, and development nexus
Summary and discussion of the three papers in this session: "The trade, migration, and development nexus" by Philip L. Martin; "External and internal determinants of development" by Thomas Osang; and "Globalization and Mexican labor markets" by Raymond Robertson.Emigration and immigration ; International trade ; Economic development ; Developing countries
Nonlinearity without Superluminality
Quantum theory is compatible with special relativity. In particular, though
measurements on entangled systems are correlated in a way that cannot be
reproduced by local hidden variables, they cannot be used for superluminal
signalling. As Czachor, Gisin and Polchinski pointed out, this is not true for
general nonlinear modifications of the Schroedinger equation. Excluding
superluminal signalling has thus been taken to rule out most nonlinear versions
of quantum theory. The no superluminal signalling constraint has also been used
for alternative derivations of the optimal fidelities attainable for imperfect
quantum cloning and other operations.
These results apply to theories satisfying the rule that their predictions
for widely separated and slowly moving entangled systems can be approximated by
non-relativistic equations of motion with respect to a preferred time
coordinate. This paper describes a natural way in which this rule might fail to
hold. In particular, it is shown that quantum readout devices which display the
values of localised pure states need not allow superluminal signalling,
provided that the devices display the values of the states of entangled
subsystems as defined in a non-standard, but natural, way. It follows that any
locally defined nonlinear evolution of pure states can be made consistent with
Minkowski causality.Comment: References update
Engine condition monitoring: CF6 family 60's through the 80's
The on condition program is described in terms of its effectiveness as a maintenance tool both at the line station as well as at home base by the early detection of engine faults, erroneous instrumentation signals and by verification of engine health. The system encompasses all known methods from manual procedures to the fully automated airborne integrated data system
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
SAGE 2 satellite data set validation
The results of a validation study of data obtained by the Stratospheric Aerosol and Gas Experiment 2 satellite experiment (SAGE 2) are given. Preliminary SAGE 2 data have been available for the period October, 1984 to May, 1985. In addition, the results of two correlative experimental measurement series have been studied in detail, as well as climatological data obtained by other techniques, including ground-based and airborne lidar. The study shows the SAGE 2 data to be of great potential value to studies of the microphyiscs of stratospheric aerosols, the chemistry of trace gases and stratospheric dynamics. A small number of unidentified errors in the current preliminary data set are described. These will be removed from the next version of the data set which is anticipated to be of archival quality
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