257,275 research outputs found
On-Line/Off-Line DCR-based Homomorphic Encryption and Applications
On-line/off-line encryption schemes enable the fast encryption of a message from a pre-computed coupon. The paradigm was put forward in the case of digital signatures.
This work introduces a compact public-key additively homomorphic encryption scheme. The scheme is semantically secure under the decisional composite residuosity (DCR) assumption. Compared to Paillier cryptosystem, it merely requires one or two integer additions in the on-line phase and no increase in the ciphertext size. This work also introduces a compact on-line/off-line trapdoor commitment scheme featuring the same fast on-line phase. Finally, applications to chameleon signatures are presented
A Secure and Efficient Off-line Electronic Payment System forWireless Networks
An electronic cash system allows the exchange of digital coins with value assured by the bank’s signature and with concealed user identity. In an electronic cash system, a user can withdraw coins from the bank and then spends each coin anonymously and unlinkably. In this paper we propose a secure and efficient off-line electronic payment system based on bilinear pairings and group signature schemes. The anonymity of the customer is revocable by a trustee in case of a dispute. Because the amount of communication in the payment protocol is about 480 bits, the proposed off-line electronic payment system can be used in wireless networks with limited bandwidth
Adaptive differential amplitude pulse-position modulation technique (DAPPM) using fuzzy logic for optical wireless communication channels
In the past few years, people have become increasingly demanding for high
transmission rate, using high-speed data transfer rate, the number of user increased
every year, therefore the high-speed optical wireless communication link have
become more popular. Optical wireless communication has the potential for
extremely high data rates of up to tens of Gigabits per second (Gb/s). An optical
wireless channel is usually a non-directed link which can be categorized as either
line-of-sight (LOS) or diffuses. Modulation techniques have attracted increasing
attention in optical wireless communication, therefore in this project; a hybrid
modulation technique named Differential Amplitude Pulse-Position Modulation
(DAPPM) is proposed to improve the channel immunity by utilizing optimized
modulation to channel. The average symbol length, unit transmission rate, channel
capacity, peak-to-average power ratio (PAPR), transmission capacity, bandwidth
requirement and power requirement of the DAPPM were determined and compared
with other modulation schemes such as On-Off Key (OOK), Pulse-Amplitude
Modulation (PAM), Pulse-Position Modulation (PPM), Differential Pulse-Position
Modulation (DPPM), and Multilevel Digital Pulse Interval Modulation (MDPIM).
Simulation result shows that DAPPM gives better bandwidth and power efficiency
depending on the number of amplitude level (A) and the maximum length (L) of a
symbol. In addition, the fuzzy logic module is developed to assist the adaptation
process of differential amplitude pulse-position modulation. Mamdani fuzzy logic
method is used in which the decisions made by the system will be approaching to
what would be decided by the user in the real world
On Randomizing Hash Functions to Strengthen the Security of Digital Signatures
Halevi and Krawczyk proposed a message randomization algorithm called RMX as a front-end tool to the hash-then-sign digital signature schemes such as DSS and RSA in order to free their reliance on the collision resistance property of the hash functions. They have shown that to forge a RMX-hash-then-sign signature scheme, one has to solve a cryptanalytical task which is related to finding second preimages for the hash function. In this article, we will show how to use Dean’s method of finding expandable messages for finding a second preimage in the Merkle-Damgård hash function to existentially forge a signature scheme based on a t-bit RMX-hash function which uses the Davies-Meyer compression functions (e.g., MD4, MD5, SHA family) in 2 t/2 chosen messages plus 2 t/2 + 1 off-line operations of the compression function and similar amount of memory. This forgery attack also works on the signature schemes that use Davies-Meyer schemes and a variant of RMX published by NIST in its Draft Special Publication (SP) 800-106. We discuss some important applications of our attack
Reliable Multi-Path Routing Schemes for Real-Time Streaming
In off-line streaming, packet level erasure resilient Forward Error
Correction (FEC) codes rely on the unrestricted buffering time at the receiver.
In real-time streaming, the extremely short playback buffering time makes FEC
inefficient for protecting a single path communication against long link
failures. It has been shown that one alternative path added to a single path
route makes packet level FEC applicable even when the buffering time is
limited. Further path diversity, however, increases the number of underlying
links increasing the total link failure rate, requiring from the sender
possibly more FEC packets. We introduce a scalar coefficient for rating a
multi-path routing topology of any complexity. It is called Redundancy Overall
Requirement (ROR) and is proportional to the total number of adaptive FEC
packets required for protection of the communication. With the capillary
routing algorithm, introduced in this paper we build thousands of multi-path
routing patterns. By computing their ROR coefficients, we show that contrary to
the expectations the overall requirement in FEC codes is reduced when the
further diversity of dual-path routing is achieved by the capillary routing
algorithm.Comment: Emin Gabrielyan, "Reliable Multi-Path Routing Schemes for Voice over
Packet Networks", ICDT'06, International Conference on Digital
Telecommunications, Cote d'Azur, France, 29-31 August 2006, pp. 65-7
Experimental demonstration of digital predistortion for orthogonal frequency-division multiplexing-radio over fibre links near laser resonance
Radio over fibre (RoF), an enabling technology for distribution of wireless broadband service signals through analogue optical links, suffers from non-linear distortion. Digital predistortion has been demonstrated as an effective approach to overcome the RoF non-linearity. However, questions remain as to how the approach performs close to laser resonance, a region of significant dynamic non-linearity, and how resilient the approach is to changes in input signal and link operating conditions. In this work, the performance of a digital predistortion approach is studied for directly modulated orthogonal frequency-division multiplexing RoF links operating from 2.47 to 3.7 GHz. It extends previous works to higher frequencies, and to higher quadrature amplitude modulation (QAM) levels. In addition, the resilience of the predistortion approach to changes in modulation level of QAM schemes, and average power levels are investigated, and a novel predistortion training approach is proposed and demonstrated. Both memoryless and memory polynomial predistorter models, and a simple off-line least-squares-based identification method, are used, with excellent performance improvements demonstrated up to 3.0 GHz
An overview of data acquisition, signal coding and data analysis techniques for MST radars
An overview is given of the data acquisition, signal processing, and data analysis techniques that are currently in use with high power MST/ST (mesosphere stratosphere troposphere/stratosphere troposphere) radars. This review supplements the works of Rastogi (1983) and Farley (1984) presented at previous MAP workshops. A general description is given of data acquisition and signal processing operations and they are characterized on the basis of their disparate time scales. Then signal coding, a brief description of frequently used codes, and their limitations are discussed, and finally, several aspects of statistical data processing such as signal statistics, power spectrum and autocovariance analysis, outlier removal techniques are discussed
Spatiotemporal heterodyne detection
We describe a scheme into which a camera is turned into an efficient tunable
frequency filter of a few Hertz bandwidth in an off-axis, heterodyne optical
mixing configuration, enabling to perform parallel, high-resolution coherent
spectral imaging. This approach is made possible through the combination of a
spatial and temporal modulation of the signal to reject noise contributions.
Experimental data obtained with dynamically scattered light by a suspension of
particles in brownian motion is interpreted
Power Line Communication Technologies: Modeling and Simulation of PRIME Physical Layer
Power Line Communications is a relatively new
area of telecommunication. PLC employs full duplex methods
for transmitting data over power lines as medium of
transmission of electrical signals over a grid. PLC technologies
are used in advanced meter reading, home automation and
Public street lighting. Several PLC technologies classified
based on the operational frequency range, are explored in this
paper. PRIME is a new NBPLC system, which uses OFDM in
its physical layer, for power line communication in the last
mile. This work also focused on PRIME’s physical
specifications, which was modeled in MATLAB/SIMULINK.
In this paper, the performance of PRIME when its data is
modulated using DQPSK and 4-QAM in four (4) channel
models is shown.
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