843 research outputs found
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
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
Does Social Presence or the Potential for Interaction reduce Social Gaze in Online Social Scenarios? Introducing the "Live Lab" paradigm.
Research has shown that peopleâs gaze is biased away from faces in the real-world but
towards them when they are viewed onscreen. Non-equivalent stimulus conditions may have
represented a confound in this research however, as participants viewed onscreen stimuli as
pre-recordings where interaction was not possible, compared to real-world stimuli which
were viewed in real-time where interaction was possible. We assessed the independent
contributions of online social presence and ability for interaction on social gaze by
developing the âlive labâ paradigm. Participants in three groups (N = 132) viewed a
confederate either as a) a live webcam stream where interaction was not possible (one-way),
b) a live webcam stream where an interaction was possible (two-way) or c) as a prerecording.
Potential for interaction, rather than online social presence, was the primary
influence on gaze behaviour: Participants in the pre-recorded and one-way conditions looked
more to the face than those in the two-way condition, particularly when the confederate made
âeye contactâ. Fixation durations to the face were shorter when the scene was viewed live,
particularly during a bid for eye contact
Our findings support the dual function of gaze, but suggest that online social presence alone
is not sufficient to activate social norms of civil inattention. Implications for the
reinterpretation of previous research are discussed
Location-Oblivious Data Transfer with Flying Entangled Qudits
We present a simple and practical quantum protocol involving two mistrustful
agencies in Minkowski space, which allows Alice to transfer data to Bob at a
spacetime location that neither can predict in advance. The location depends on
both Alice's and Bob's actions. The protocol guarantees unconditionally to
Alice that Bob learns the data at a randomly determined location; it guarantees
to Bob that Alice will not learn the transfer location even after the protocol
is complete.
The task implemented, transferring data at a space-time location that remains
hidden from the transferrer, has no precise analogue in non-relativistic
quantum cryptography. It illustrates further the scope for novel cryptographic
applications of relativistic quantum theory.Comment: References updated. Published versio
11 beta-hydroxysteroid dehydrogenase type 1 regulates glucocorticoid-induced insulin resistance in skeletal muscle
OBJECTIVE: Glucocorticoid excess is characterized by increased adiposity, skeletal myopathy, and insulin resistance, but the precise molecular mechanisms are unknown. Within skeletal muscle, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) converts cortisone (11-dehydrocorticosterone in rodents) to active cortisol (corticosterone in rodents). We aimed to determine the mechanisms underpinning glucocorticoid-induced insulin resistance in skeletal muscle and indentify how 11beta-HSD1 inhibitors improve insulin sensitivity. \ud
RESEARCH DESIGN AND METHODS: Rodent and human cell cultures, whole-tissue explants, and animal models were used to determine the impact of glucocorticoids and selective 11beta-HSD1 inhibition upon insulin signaling and action. \ud
RESULTS: Dexamethasone decreased insulin-stimulated glucose uptake, decreased IRS1 mRNA and protein expression, and increased inactivating pSer insulin receptor substrate (IRS)-1. 11beta-HSD1 activity and expression were observed in human and rodent myotubes and muscle explants. Activity was predominantly oxo-reductase, generating active glucocorticoid. A1 (selective 11beta-HSD1 inhibitor) abolished enzyme activity and blocked the increase in pSer IRS1 and reduction in total IRS1 protein after treatment with 11DHC but not corticosterone. In C57Bl6/J mice, the selective 11beta-HSD1 inhibitor, A2, decreased fasting blood glucose levels and improved insulin sensitivity. In KK mice treated with A2, skeletal muscle pSer IRS1 decreased and pThr Akt/PKB increased. In addition, A2 decreased both lipogenic and lipolytic gene expression.\ud
CONCLUSIONS: Prereceptor facilitation of glucocorticoid action via 11beta-HSD1 increases pSer IRS1 and may be crucial in mediating insulin resistance in skeletal muscle. Selective 11beta-HSD1 inhibition decreases pSer IRS1, increases pThr Akt/PKB, and decreases lipogenic and lipolytic gene expression that may represent an important mechanism underpinning their insulin-sensitizing action
General theory for decoy-state quantum key distribution with arbitrary number of intensities
We develop a general theory for quantum key distribution (QKD) in both the
forward error correction and the reverse error correction cases when the QKD
system is equipped with phase-randomized coherent light with arbitrary number
of decoy intensities. For this purpose, generalizing Wang's expansion, we
derive a convex expansion of the phase-randomized coherent state. We also
numerically check that the asymptotic key generation rates are almost saturated
when the number of decoy intensities is three.Comment: This manuscript has been revised extensivel
Experimental quantum tossing of a single coin
The cryptographic protocol of coin tossing consists of two parties, Alice and
Bob, that do not trust each other, but want to generate a random bit. If the
parties use a classical communication channel and have unlimited computational
resources, one of them can always cheat perfectly. Here we analyze in detail
how the performance of a quantum coin tossing experiment should be compared to
classical protocols, taking into account the inevitable experimental
imperfections. We then report an all-optical fiber experiment in which a single
coin is tossed whose randomness is higher than achievable by any classical
protocol and present some easily realisable cheating strategies by Alice and
Bob.Comment: 13 page
One-way quantum key distribution: Simple upper bound on the secret key rate
We present a simple method to obtain an upper bound on the achievable secret
key rate in quantum key distribution (QKD) protocols that use only
unidirectional classical communication during the public-discussion phase. This
method is based on a necessary precondition for one-way secret key
distillation; the legitimate users need to prove that there exists no quantum
state having a symmetric extension that is compatible with the available
measurements results. The main advantage of the obtained upper bound is that it
can be formulated as a semidefinite program, which can be efficiently solved.
We illustrate our results by analysing two well-known qubit-based QKD
protocols: the four-state protocol and the six-state protocol. Recent results
by Renner et al., Phys. Rev. A 72, 012332 (2005), also show that the given
precondition is only necessary but not sufficient for unidirectional secret key
distillation.Comment: 11 pages, 1 figur
Universal teleportation with a twist
We give a transfer theorem for teleportation based on twisting the
entanglement measurement. This allows one to say what local unitary operation
must be performed to complete the teleportation in any situation, generalizing
the scheme to include overcomplete measurements, non-abelian groups of local
unitary operations (e.g., angular momentum teleportation), and the effect of
non-maximally entangled resources.Comment: 4 pages, 1 figur
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