158,412 research outputs found
Adaptive real time selection for quantum key distribution in lossy and turbulent free-space channels
The unconditional security in the creation of cryptographic keys obtained by quantum key distribution (QKD) protocols will induce a quantum leap in free-space communication privacy in the same way that we are beginning to realize secure optical fiber connections. However, free-space channels, in particular those with long links and the presence of atmospheric turbulence, are affected by losses, fluctuating transmissivity, and background light that impair the conditions for secure QKD. Here we introduce a method to contrast the atmospheric turbulence in QKD experiments. Our adaptive real time selection (ARTS) technique at the receiver is based on the selection of the intervals with higher channel transmissivity. We demonstrate, using data from the Canary Island 143-km free-space link, that conditions with unacceptable average quantum bit error rate which would prevent the generation of a secure key can be used once parsed according to the instantaneous scintillation using the ARTS technique
Experimental Demonstration of Post-Selection based Continuous Variable Quantum Key Distribution in the Presence of Gaussian Noise
In realistic continuous variable quantum key distribution protocols, an
eavesdropper may exploit the additional Gaussian noise generated during
transmission to mask her presence. We present a theoretical framework for a
post-selection based protocol which explicitly takes into account excess
Gaussian noise. We derive a quantitative expression of the secret key rates
based on the Levitin and Holevo bounds. We experimentally demonstrate that the
post-selection based scheme is still secure against both individual and
collective Gaussian attacks in the presence of this excess noise.Comment: 4 pages, 4 figure
SANNS: Scaling Up Secure Approximate k-Nearest Neighbors Search
The -Nearest Neighbor Search (-NNS) is the backbone of several
cloud-based services such as recommender systems, face recognition, and
database search on text and images. In these services, the client sends the
query to the cloud server and receives the response in which case the query and
response are revealed to the service provider. Such data disclosures are
unacceptable in several scenarios due to the sensitivity of data and/or privacy
laws.
In this paper, we introduce SANNS, a system for secure -NNS that keeps
client's query and the search result confidential. SANNS comprises two
protocols: an optimized linear scan and a protocol based on a novel sublinear
time clustering-based algorithm. We prove the security of both protocols in the
standard semi-honest model. The protocols are built upon several
state-of-the-art cryptographic primitives such as lattice-based additively
homomorphic encryption, distributed oblivious RAM, and garbled circuits. We
provide several contributions to each of these primitives which are applicable
to other secure computation tasks. Both of our protocols rely on a new circuit
for the approximate top- selection from numbers that is built from comparators.
We have implemented our proposed system and performed extensive experimental
results on four datasets in two different computation environments,
demonstrating more than faster response time compared to
optimally implemented protocols from the prior work. Moreover, SANNS is the
first work that scales to the database of 10 million entries, pushing the limit
by more than two orders of magnitude.Comment: 18 pages, to appear at USENIX Security Symposium 202
Breaking barriers in two-party quantum cryptography via stochastic semidefinite programming
In the last two decades, there has been much effort in finding secure
protocols for two-party cryptographic tasks. It has since been discovered that
even with quantum mechanics, many such protocols are limited in their security
promises. In this work, we use stochastic selection, an idea from stochastic
programming, to circumvent such limitations. For example, we find a way to
switch between bit commitment, weak coin flipping, and oblivious transfer
protocols to improve their security. We also use stochastic selection to turn
trash into treasure yielding the first quantum protocol for Rabin oblivious
transfer.Comment: 42 pages, 2 figure
Quantum authentication of classical messages
Although key distribution is arguably the most studied context on which to
apply quantum cryptographic techniques, message authentication, i.e.,
certifying the identity of the message originator and the integrity of the
message sent, can also benefit from the use of quantum resources. Classically,
message authentication can be performed by techniques based on hash functions.
However, the security of the resulting protocols depends on the selection of
appropriate hash functions, and on the use of long authentication keys. In this
paper we propose a quantum authentication procedure that, making use of just
one qubit as the authentication key, allows the authentication of binary
classical messages in a secure manner.Comment: LaTeX, 6 page
QuickSync: A Quickly Synchronizing PoS-Based Blockchain Protocol
To implement a blockchain, we need a blockchain protocol for all the nodes to
follow. To design a blockchain protocol, we need a block publisher selection
mechanism and a chain selection rule. In Proof-of-Stake (PoS) based blockchain
protocols, block publisher selection mechanism selects the node to publish the
next block based on the relative stake held by the node. However, PoS
protocols, such as Ouroboros v1, may face vulnerability to fully adaptive
corruptions.
In this paper, we propose a novel PoS-based blockchain protocol, QuickSync,
to achieve security against fully adaptive corruptions while improving on
performance. We propose a metric called block power, a value defined for each
block, derived from the output of the verifiable random function based on the
digital signature of the block publisher. With this metric, we compute chain
power, the sum of block powers of all the blocks comprising the chain, for all
the valid chains. These metrics are a function of the block publisher's stake
to enable the PoS aspect of the protocol. The chain selection rule selects the
chain with the highest chain power as the one to extend. This chain selection
rule hence determines the selected block publisher of the previous block. When
we use metrics to define the chain selection rule, it may lead to
vulnerabilities against Sybil attacks. QuickSync uses a Sybil attack resistant
function implemented using histogram matching. We prove that QuickSync
satisfies common prefix, chain growth, and chain quality properties and hence
it is secure. We also show that it is resilient to different types of
adversarial attack strategies. Our analysis demonstrates that QuickSync
performs better than Bitcoin by an order of magnitude on both transactions per
second and time to finality, and better than Ouroboros v1 by a factor of three
on time to finality
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