1,240 research outputs found
Optimal Coding Functions for Pairwise Message Sharing on Finite-Field Multi-Way Relay Channels
This paper considers the finite-field multi-way relay channel with pairwise
message sharing, where multiple users exchange messages through a single relay
and where the users may share parts of their source messages (meaning that some
message parts are known/common to more than one user). In this paper, we design
an optimal functional-decode-forward coding scheme that takes the shared
messages into account. More specifically, we design an optimal function for the
relay to decode (from the users on the uplink) and forward (back to the users
on the downlink). We then show that this proposed function-decode-forward
coding scheme can achieve the capacity region of the finite-field multi-way
relay channel with pairwise message sharing. This paper generalizes our
previous result for the case of three users to any number of users.Comment: Author's final version (accepted for presentation at the 2014 IEEE
International Conference on Communications [ICC 2014]
Reliable Physical Layer Network Coding
When two or more users in a wireless network transmit simultaneously, their
electromagnetic signals are linearly superimposed on the channel. As a result,
a receiver that is interested in one of these signals sees the others as
unwanted interference. This property of the wireless medium is typically viewed
as a hindrance to reliable communication over a network. However, using a
recently developed coding strategy, interference can in fact be harnessed for
network coding. In a wired network, (linear) network coding refers to each
intermediate node taking its received packets, computing a linear combination
over a finite field, and forwarding the outcome towards the destinations. Then,
given an appropriate set of linear combinations, a destination can solve for
its desired packets. For certain topologies, this strategy can attain
significantly higher throughputs over routing-based strategies. Reliable
physical layer network coding takes this idea one step further: using
judiciously chosen linear error-correcting codes, intermediate nodes in a
wireless network can directly recover linear combinations of the packets from
the observed noisy superpositions of transmitted signals. Starting with some
simple examples, this survey explores the core ideas behind this new technique
and the possibilities it offers for communication over interference-limited
wireless networks.Comment: 19 pages, 14 figures, survey paper to appear in Proceedings of the
IEE
The Engineering of a Scalable Multi-Site Communications System Utilizing Quantum Key Distribution (QKD)
Quantum Key Distribution (QKD) is a means of generating keys between a pair
of computing hosts that is theoretically secure against cryptanalysis, even by
a quantum computer. Although there is much active research into improving the
QKD technology itself, there is still significant work to be done to apply
engineering methodology and determine how it can be practically built to scale
within an enterprise IT environment. Significant challenges exist in building a
practical key management service for use in a metropolitan network. QKD is
generally a point-to-point technique only and is subject to steep performance
constraints. The integration of QKD into enterprise-level computing has been
researched, to enable quantum-safe communication. A novel method for
constructing a key management service is presented that allows arbitrary
computing hosts on one site to establish multiple secure communication sessions
with the hosts of another site. A key exchange protocol is proposed where
symmetric private keys are granted to hosts while satisfying the scalability
needs of an enterprise population of users. The key management service operates
within a layered architectural style that is able to interoperate with various
underlying QKD implementations. Variable levels of security for the host
population are enforced through a policy engine. A network layer provides key
generation across a network of nodes connected by quantum links. Scheduling and
routing functionality allows quantum key material to be relayed across trusted
nodes. Optimizations are performed to match the real-time host demand for key
material with the capacity afforded by the infrastructure. The result is a
flexible and scalable architecture that is suitable for enterprise use and
independent of any specific QKD technology
Uplink User-Assisted Relaying in Cellular Networks
We use stochastic geometry to analyze the performance of a partial
decode-and-forward (PDF) relaying scheme applied in a user-assisted relaying
setting, where an active user relays data through another idle user in uplink
cellular communication. We present the geometric model of a network deploying
user-assisted relaying and propose two geometric cooperation policies for fast
and slow fading channels. We analytically derive the cooperation probability
for both policies. This cooperation probability is further used in the
analytical derivation of the moments of inter-cell interference power caused by
system-wide deployment of this user-assisted PDF relaying. We then model the
inter-cell interference power statistics using the Gamma distribution by
matching the first two moments analytically derived. This cooperation and
interference analysis provides the theoretical basis for quantitatively
evaluating the performance impact of user-assisted relaying in cellular
networks. We then numerically evaluate the average transmission rate
performance and show that user-assisted relaying can significantly improve
per-user transmission rate despite of increased inter-cell interference. This
transmission rate gain is significant for active users near the cell edge and
further increases with higher idle user density, supporting user-assisted
relaying as a viable solution to crowded population areas.Comment: 32 pages, 13 figures, revised version submitted to IEEE Transactions
on Wireless Communication
The two-unicast problem
We consider the communication capacity of wireline networks for a two-unicast
traffic pattern. The network has two sources and two destinations with each
source communicating a message to its own destination, subject to the capacity
constraints on the directed edges of the network. We propose a simple outer
bound for the problem that we call the Generalized Network Sharing (GNS) bound.
We show this bound is the tightest edge-cut bound for two-unicast networks and
is tight in several bottleneck cases, though it is not tight in general. We
also show that the problem of computing the GNS bound is NP-complete. Finally,
we show that despite its seeming simplicity, the two-unicast problem is as hard
as the most general network coding problem. As a consequence, linear coding is
insufficient to achieve capacity for general two-unicast networks, and
non-Shannon inequalities are necessary for characterizing capacity of general
two-unicast networks.Comment: 23 pages, 22 figure
A Survey of Distributed Consensus Protocols for Blockchain Networks
Since the inception of Bitcoin, cryptocurrencies and the underlying
blockchain technology have attracted an increasing interest from both academia
and industry. Among various core components, consensus protocol is the defining
technology behind the security and performance of blockchain. From incremental
modifications of Nakamoto consensus protocol to innovative alternative
consensus mechanisms, many consensus protocols have been proposed to improve
the performance of the blockchain network itself or to accommodate other
specific application needs.
In this survey, we present a comprehensive review and analysis on the
state-of-the-art blockchain consensus protocols. To facilitate the discussion
of our analysis, we first introduce the key definitions and relevant results in
the classic theory of fault tolerance which help to lay the foundation for
further discussion. We identify five core components of a blockchain consensus
protocol, namely, block proposal, block validation, information propagation,
block finalization, and incentive mechanism. A wide spectrum of blockchain
consensus protocols are then carefully reviewed accompanied by algorithmic
abstractions and vulnerability analyses. The surveyed consensus protocols are
analyzed using the five-component framework and compared with respect to
different performance metrics. These analyses and comparisons provide us new
insights in the fundamental differences of various proposals in terms of their
suitable application scenarios, key assumptions, expected fault tolerance,
scalability, drawbacks and trade-offs. We believe this survey will provide
blockchain developers and researchers a comprehensive view on the
state-of-the-art consensus protocols and facilitate the process of designing
future protocols.Comment: Accepted by the IEEE Communications Surveys and Tutorials for
publicatio
Onions in the Crosshairs: When The Man really is out to get you
We introduce and investigate *targeting adversaries* who selectively attack
users of Tor or other secure-communication networks. We argue that attacks by
such adversaries are more realistic and more significant threats to those most
relying on Tor's protection than are attacks in prior analyses of Tor security.
Previous research and Tor design decisions have focused on protecting against
adversaries who are equally interested in any user of the network. Our
adversaries selectively target users---e.g., those who visit a particular
website or chat on a particular private channel---and essentially disregard Tor
users other than these. We present a model of such adversaries and investigate
three example cases where particular users might be targeted: a cabal
conducting meetings using MTor, a published Tor multicast protocol; a cabal
meeting on a private IRC channel; and users visiting a particular .onion
website. In general for our adversaries, compromise is much faster and provides
more feedback and possibilities for adaptation than do attacks examined in
prior work. We also discuss selection of websites for targeting of their users
based on the distribution across users of site activity. We describe
adversaries both attempting to learn the size of a cabal meeting online or of a
set of sufficiently active visitors to a targeted site and attempting to
identify guards of each targeted user. We compare the threat of targeting
adversaries versus previously considered adversaries, and we briefly sketch
possible countermeasures for resisting targeting adversaries.Comment: 16 pages, 10 figure
DFINITY Technology Overview Series, Consensus System
The DFINITY blockchain computer provides a secure, performant and flexible
consensus mechanism. At its core, DFINITY contains a decentralized randomness
beacon which acts as a verifiable random function (VRF) that produces a stream
of outputs over time. The novel technique behind the beacon relies on the
existence of a unique-deterministic, non-interactive, DKG-friendly threshold
signatures scheme. The only known examples of such a scheme are pairing-based
and derived from BLS.
The DFINITY blockchain is layered on top of the DFINITY beacon and uses the
beacon as its source of randomness for leader selection and leader ranking. A
"weight" is attributed to a chain based on the ranks of the leaders who propose
the blocks in the chain, and that weight is used to select between competing
chains. The DFINITY blockchain is layered on top of the DFINITY beacon and uses
the beacon as its source of randomness for leader selection and leader ranking
blockchain is further hardened by a notarization process which dramatically
improves the time to finality and eliminates the nothing-at-stake and selfish
mining attacks.
DFINITY consensus algorithm is made to scale through continuous quorum
selections driven by the random beacon. In practice, DFINITY achieves block
times of a few seconds and transaction finality after only two confirmations.
The system gracefully handles temporary losses of network synchrony including
network splits, while it is provably secure under synchrony
A New Efficient Key Management Protocol for Wireless Sensor and Actor Networks
Research on sensor networks has become much more active and is currently
being applied to many different fields. However since sensor networks are
limited to only collecting and reporting information regarding a certain event,
and requires human intervention with that given information, it is often
difficult to react to an event or situation immediately and proactively. To
overcome this kind of limitation, Wireless Sensor and Actor Networks (WSANs)
with immediate-response actor nodes have been proposed which adds greater
mobility and activity to the existing sensor networks. Although WSANs share
many common grounds with sensor networks, it is difficult to apply existing
security technologies due to the fact that WSANs contain actor nodes that are
resource-independent and mobile. Therefore, this research seeks to demonstrate
ways to provide security, integrity, and authentication services for WSANs
secure operation, by separating networks into hierarchical structure by each
node's abilities and provides different encryption key based secure protocols
for each level of hierarchy, Pairwise key, node key, and region key for sensor
levels, and public key for actorComment: 8 pages IEEE format, International Journal of Computer Science and
Information Security, IJCSIS November 2009, ISSN 1947 5500,
http://sites.google.com/site/ijcsis
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