32826804
Generalized minimum distance decoding in Euclidean space: Performance analysis
We present a detailed analysis of generalized minimum distance (GMD) decoding algorithms for Euclidean space codes. In particular, we completely characterize GMD decoding regions in terms of receiver front-end properties. This characterization is used to show that GMD decoding regions have intricate geometry. We prove that although these decoding regions are polyhedral, they are essentially always nonconvex. We furthermore show that conventional performance parameters, such as error-correction radius and effective error coefficient, do not capture the essential geometric features of a GMD decoding region, and thus do not provide a meaningful measure of performance. As an alternative, probabilistic estimates of, and upper bounds upon, the performance of GMD decoding are developed. Furthermore, extensive simulation results, for both low-dimensional and high-dimensional sphere-packings, are presented. These simulations show that multilevel codes in conjunction with multistage GMD decoding provide significant coding gains at a very low complexity. Simulated performance, in both cases, is in remarkably close agreement with our probabilistic approximations.
43442738
The turbo decoding algorithm and its phase trajectories
This paper analyzes phase trajectories and fixed points of the turbo decoding algorithm as a function of the signal-to-noise ratio (SNR). By exploiting the large length of turbo codes, the turbo decoding algorithm is treated as a single-parameter dynamical system, parameterized (approximately) by the SNR. This parameterization, along "with" extensive simulations at practical SNRs and asymptotic analysis as SNR goes to zero and infinity, is used to subdivide the entire SNR range into three regions with the "waterfall region" in the middle. The turbo decoding algorithm has distinctive phase trajectories and convergence properties in these three SNR regions. This paper also investigates existence and properties of fixed points in these SNR regions. The main fixed points of the turbo decoding algorithm are classified into two categories. In a wide range of SNRs (corresponding to bit-error rates less than 10/sup -1/), the decoding algorithm has "unequivocal" fixed points which correspond to mostly correct decisions on the information bits. Within this range, toward the lower values of SNR, there is another fixed point which corresponds to many erroneous decision on the information bits. Fixed points of this type are referred to as "indecisive" fixed points. It turns out that the indecisive fixed points bifurcate and disappear for SNRs in the waterfall region. This paper associates the qualitative transition of phase trajectories in the waterfall region to the bifurcation of indecisive fixed points. These bifurcations also explain empirically observed quasi-periodic and periodic phase trajectories of the turbo decoding algorithm.
9570200
Templates as Master Keys
We introduce two new attacks: the single-bit template attack and the template-enhanced DPA attack. The single-bit template attack can be used very effectively to classify even single bits in a single side channel sample with a high probability of correctness. The template-enhanced DPA attack, combines traditional DPA with single-bit template attacks to show that if an adversary has access to a test card with even a slightly biased RNG, then he/she can break protected cryptographic implementations on a target card even if they have perfect RNGs. In support of our claim, we report results from experiments on breaking two implementations of DES and AES protected by the masking countermeasure running on smartcards of different manufacturers. 
 
In light of these results, the threat of template attacks, generally viewed as intrinsically difficult to mount, needs to be reconsidered.
14060994
On nearest neighbor indexing of nonlinear trajectories
In recent years, the problem of indexing mobile objects has assumed great importance because of its relevance to a wide variety of applications. Most previous results in this area have proposed indexing schemes for objects with linear trajectories in one or two dimensions. In this paper, we present methods for indexing objects with nonlinear trajectories. Specifically, we identify a useful condition called the convex hull property and show that any trajectory satisfying this condition can be indexed by storing a careful representation of these objects in a traditional index structure. Since a wide variety of relevant nonlinear trajectories satisfy this condition, our result significantly expands the class of trajectories for which nearest neighbor indexing schemes can be devised. We also show that even though many non-linear trajectories do not satisfy the convex hull condition, an approximate representation can often be found which satisfies it. We discuss examples of techniques which can be utilized to find representations that satisfy the convex hull property. We present empirical results to demonstrate the effectiveness of our indexing method.
45546568
Multi-channel Attacks
We introduce multi-channel attacks, i.e., side-channel attacks which utilize multiple side-channels such as power and EM simultaneously. We propose an adversarial model which combines a CMOS leakage model and the maximum-likelihood principle for performing and analyzing such attacks. This model is essential for deriving the optimal and very often counter-intuitive techniques for channel selection and data analysis. We show that using multiple channels is better for template attacks by experimentally showing a three-fold reduction in the error probability. Developing sound countermeasures against multi-channel attacks requires a rigorous leakage assessment methodology. Under suitable assumptions and approximations, our model also yields a practical assessment methodology for net information leakage from the power and all available EM channels in constrained devices such as chip-cards. Classical DPA/DEMA style attacks assume an adversary weaker than that of our model. For this adversary, we apply the maximum-likelihood principle to such design new and more efficient single and multiple-channel DPA/DEMA attacks.
15003245
Probabilistic treatment of MIXes to hamper traffic analysis
The goal of anonymity providing techniques is to preserve the privacy of users, who has communicated with whom, for how long, and from which location, by hiding traffic information. This is accomplished by organizing additional traffic to conceal particular communication relationships and by embedding the sender and receiver of a message in their respective anonymity sets. If the number of overall participants is greater than the size of the anonymity set and if the anonymity set changes with time due to unsynchronized participants, then the anonymity technique becomes prone to traffic analysis attacks. We are interested in the statistical properties of the disclosure attack, a newly suggested traffic analysis attack on the MIXes. Our goal is to provide analytical estimates of the number of observations required by the disclosure attack and to identify fundamental (but avoidable) 'weak operational modes' of the MIXes and thus to protect users against a traffic analysis by the disclosure attack.
43330192
Impact of bursty error rates on the performance of wireless local area network (WLAN)
Abstract With an increasing popularity of DCF based wireless LAN, the modeling of 802.11 distributed coordination function (DCF) has attracted lots of research attention. Existing analysis of 802.11 DCF has been focused on the determination of the throughput and the packet delay under saturated traffic and ideal channel conditions. Although some recent papers address the saturated performance under a simple uniform error model, they can hardly capture the impact of bursty characteristics of wireless fading on the performance of 802.11 DCF. This paper presents exact formulae for the throughput and the delay in DCF for various traffic conditions when either saturated or unsaturated traffic load is present. A two-state Markov channel model is incorporated to present the bursty characteristics of channel errors. With our analysis, the impact of bursty channel error on unsuccessful transmission probability and the DCF performance can be determined. The results of our analytical framework reveal that the four-way handshaking scheme does not improve throughput substantially for light traffic load. However, for heavy traffic load, the four-way handshaking scheme is advantageous as compared to the basic access scheme. Also, extensive simulation is done to substantiate the accuracy of our analytical model.
17596019
Performance Analysis of FFT Algorithms on Multiprocessor Systems
A decimation-in-time radix-2 fast Fourier transform (FFT) algorithm is considered here for implementation in multiprocessors with shared bus, multistage interconnection network (MIN), and in mesh connected computers. Results are derived for data allocation, interprocessor communication, approximate computation time, and speedup of an N point FFT on any P available processing elements (PE's). Further generalization is obtained for a radix-r FFT algorithm. An N X N point two-dimensional discrete Fourier transform (DFT) implementation is also considered when one or more rows of the input data matrix are allocated to each PE.
18245224
Distributed Pairwise Key Establishment in Wireless Sensor Networks
Abstract - Security is a big challenge when wireless sensor networks are deployed in a hostile environment. Due to the computational and storage overheads, traditional asymmetric-key based security protocols are not suitable for the resource-constrained wireless sensors. Several symmetric-key distribution protocols have been proposed in literature to establish shared cryptographic keys between sensor nodes, but most of them only work for small-scale networks due to their linearly increased communication overhead and key storage overhead. Furthermore, existing protocols are not secure when the number of compromised nodes exceeds a threshold value. In this paper, we propose a new distributed pairwise key establishment method for large-scale wireless sensor networks. Compared with existing key distribution protocols, our scheme guarantees any two sensors to establish a pairwise key between them with low overheads. A high level network security also can be achieved in our scheme even a large number of sensors are compromised.
12800245
Dynamic probabilistic broadcasting in MANETs
In mobile ad hoc networks (MANETs), the efficiency of broadcasting protocol can dramatically affect the performance of the entire network. Appropriate use of a probabilistic method can reduce the number of rebroadcasting, therefore reduce the chance of contention and collision among neighboring nodes. A good probabilistic broadcast protocol can achieve higher throughput and lower energy consumption, without sacrificing the reachability or having any significant degradation. In this paper, we propose a probabilistic approach that dynamically adjusts the rebroadcasting probability as per the node distribution and node movement. This is done based on locally available information and without requiring any assistance of distance measurements or exact location determination devices. We evaluate the performance of our approach by comparing it with the AODV protocol (which is based on simple flooding) as well as a fixed probabilistic approach. Simulation results show our approach performs better than both simple flooding and fixed probabilistic schemes.
1710599
Exploiting Mobility Patterns to Reduce Re-Authentication Overheads in Infrastructure WLAN Networks
The current EAP-TLS standard accounts for authentication delays of the order of one second for infrastructure 802.11 networks. This delay is clearly unacceptable for maintaining the QoS requirements for a mobile station which have frequent handoffs to different regions. Pre-authentication schemes have been proposed to reduce these delays. However, most of these schemes suffer from an increased network message overhead since they fail to appropriately model the mobility of each individual user. In this paper, we exploit the notion of predictability in user mobility patterns and propose a set of novel proactive key distribution algorithms to achieve low latencies while minimizing the message overhead. Our schemes involve pre-distributing keys in fewer necessary access points (APs) as opposed to all neighboring APs. We evaluate the performance of our schemes for three different mobility models; (i) predictable motion (ii) changing predictable motion and (iii) random motion. Almost under all scenarios, our schemes indicate up to 70% message reduction, while maintaining similar latencies