17,810 research outputs found
Quantum Key Distribution with Classical Bob
Secure key distribution among two remote parties is impossible when both are
classical, unless some unproven (and arguably unrealistic)
computation-complexity assumptions are made, such as the difficulty of
factorizing large numbers. On the other hand, a secure key distribution is
possible when both parties are quantum.
What is possible when only one party (Alice) is quantum, yet the other (Bob)
has only classical capabilities? We present a protocol with this constraint,
and prove its robustness against attacks: we prove that any attempt of an
adversary to obtain information (and even a tiny amount of information)
necessarily induces some errors that the legitimate users could notice.Comment: 4 and a bit pages, 1 figure, RevTe
Semiquantum key distribution using entangled states
Recently, Boyer et al. presented a novel semiquantum key distribution
protocol [M. Boyer, D. Kenigsberg, and T. Mor, Phys. Rev. Lett. 99, 140501
(2007)], by using four quantum states, each of which is randomly prepared by Z
basis or X basis. Here we present a semiquantum key distribution protocol by
using entangled states in which quantum Alice shares a secret key with
classical Bob. We also show the protocol is secure against eavesdropping.Comment: 6 page
A simple proof of the unconditional security of quantum key distribution
Quantum key distribution is the most well-known application of quantum
cryptography. Previous proposed proofs of security of quantum key distribution
contain various technical subtleties. Here, a conceptually simpler proof of
security of quantum key distribution is presented. The new insight is the
invariance of the error rate of a teleportation channel: We show that the error
rate of a teleportation channel is independent of the signals being
transmitted. This is because the non-trivial error patterns are permuted under
teleportation. This new insight is combined with the recently proposed quantum
to classical reduction theorem. Our result shows that assuming that Alice and
Bob have fault-tolerant quantum computers, quantum key distribution can be made
unconditionally secure over arbitrarily long distances even against the most
general type of eavesdropping attacks and in the presence of all types of
noises.Comment: 13 pages, extended abstract. Comments will be appreciate
Unifying classical and quantum key distillation
Assume that two distant parties, Alice and Bob, as well as an adversary, Eve,
have access to (quantum) systems prepared jointly according to a tripartite
state. In addition, Alice and Bob can use local operations and authenticated
public classical communication. Their goal is to establish a key which is
unknown to Eve. We initiate the study of this scenario as a unification of two
standard scenarios: (i) key distillation (agreement) from classical
correlations and (ii) key distillation from pure tripartite quantum states.
Firstly, we obtain generalisations of fundamental results related to
scenarios (i) and (ii), including upper bounds on the key rate. Moreover, based
on an embedding of classical distributions into quantum states, we are able to
find new connections between protocols and quantities in the standard scenarios
(i) and (ii).
Secondly, we study specific properties of key distillation protocols. In
particular, we show that every protocol that makes use of pre-shared key can be
transformed into an equally efficient protocol which needs no pre-shared key.
This result is of practical significance as it applies to quantum key
distribution (QKD) protocols, but it also implies that the key rate cannot be
locked with information on Eve's side. Finally, we exhibit an arbitrarily large
separation between the key rate in the standard setting where Eve is equipped
with quantum memory and the key rate in a setting where Eve is only given
classical memory. This shows that assumptions on the nature of Eve's memory are
important in order to determine the correct security threshold in QKD.Comment: full versio
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