1,228 research outputs found
Unconditional security from noisy quantum storage
We consider the implementation of two-party cryptographic primitives based on
the sole assumption that no large-scale reliable quantum storage is available
to the cheating party. We construct novel protocols for oblivious transfer and
bit commitment, and prove that realistic noise levels provide security even
against the most general attack. Such unconditional results were previously
only known in the so-called bounded-storage model which is a special case of
our setting. Our protocols can be implemented with present-day hardware used
for quantum key distribution. In particular, no quantum storage is required for
the honest parties.Comment: 25 pages (IEEE two column), 13 figures, v4: published version (to
appear in IEEE Transactions on Information Theory), including bit wise
min-entropy sampling. however, for experimental purposes block sampling can
be much more convenient, please see v3 arxiv version if needed. See
arXiv:0911.2302 for a companion paper addressing aspects of a practical
implementation using block samplin
Continuous-variable quantum enigma machines for long-distance key distribution
Quantum physics allows for unconditionally secure communication through
insecure communication channels. The achievable rates of quantum-secured
communication are fundamentally limited by the laws of quantum physics and in
particular by the properties of entanglement. For a lossy communication line,
this implies that the secret-key generation rate vanishes at least
exponentially with the communication distance. We show that this fundamental
limitation can be violated in a realistic scenario where the eavesdropper can
store quantum information for only a finite, yet arbitrarily long, time. We
consider communication through a lossy bononic channel (modeling linear loss in
optical fibers) and we show that it is in principle possible to achieve a
constant rate of key generation of one bit per optical mode over arbitrarily
long communication distances.Comment: 13 pages. V2: new title, new result on active attacks, increased
rigour in the security proo
Entanglement sampling and applications
A natural measure for the amount of quantum information that a physical
system E holds about another system A = A_1,...,A_n is given by the min-entropy
Hmin(A|E). Specifically, the min-entropy measures the amount of entanglement
between E and A, and is the relevant measure when analyzing a wide variety of
problems ranging from randomness extraction in quantum cryptography, decoupling
used in channel coding, to physical processes such as thermalization or the
thermodynamic work cost (or gain) of erasing a quantum system. As such, it is a
central question to determine the behaviour of the min-entropy after some
process M is applied to the system A. Here we introduce a new generic tool
relating the resulting min-entropy to the original one, and apply it to several
settings of interest, including sampling of subsystems and measuring in a
randomly chosen basis. The sampling results lead to new upper bounds on quantum
random access codes, and imply the existence of "local decouplers". The results
on random measurements yield new high-order entropic uncertainty relations with
which we prove the optimality of cryptographic schemes in the bounded quantum
storage model.Comment: v3: fixed some typos, v2: fixed minor issue with the definition of
entropy and improved presentatio
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