1021221
Inferring client response time at the web server
As businesses continue to grow their World Wide Web presence, it is becoming increasingly vital for them to have quantitative measures of the client perceived response times of their web services. We present Certes (CliEnt Response Time Estimated by the Server), an online server-based mechanism for web servers to measure client perceived response time, as if measured at the client. Certes is based on a model of TCP that quantifies the effect that connection drops have on perceived client response time, by using three simple server-side measurements: connection drop rate, connection accept rate and connection completion rate. The mechanism does not require modifications to http servers or web pages, does not rely on probing or third party sampling, and does not require client-side modifications or scripting. Certes can be used to measure response times for any web content, not just HTML. We have implemented Certes and compared its response time measurements with those obtained with detailed client instrumentation. Our results demonstrate that Certes provides accurate server-based measurements of client response times in HTTP 1.0/1.1 [14] environments, even with rapidly changing workloads. Certes runs online in constant time with very low overhead. It can be used at web sites and server farms to verify compliance with service level objectives.
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.
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.
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.
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.
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.
206573197
Efficient Deadlock-Free Wormhole Routing and Virtual-Channel Reduction in Shuffle-Based Networks
Many aspects of shuffle-based networks have recently been studied by numerous researchers. However, no attention has been paid to deadlock-free wormhole routing algorithms. In this paper, for a set of shuffle-based networks, we introduce a graph-partitioning technique that enables a deadlock-free routing algorithm with fewer virtual channels than the known algorithms. This is achieved for the de Bruijn digraphs which are shown to require a maximum ofm? ?(m? 1)/r? virtual channels per physical channel, wheremis the diameter andris the radix. Algorithms for the generalized de Bruijn graph, the de Bruijn Cube (dBCube) graph and the Shuffle?Exchange network are introduced, and virtual channel requirements are determined. The dBCube graph of size (r,Nb,n) requires a maximum ofm? ?(m? 1)/r? virtual channels for the outcluster channels, and a maximum ofm+ 1 ? ?m/r? virtual channels for the incluster channels in most cases, wherem= ?logrNb?,ris the radix of a generalized de Bruijn graph of sizeNb, andnrepresents the number of dimensions in a binary hypercube. We also show that a maximum ofm? ?(m? 1)/2? virtual channels are required in shuffle-exchange networks with 2mnodes.
6240384
On the application of traffic engineering over bluetooth ad hoc networks
The seamless communication of data and voice over short-range, point-to-multipoint wireless links between mobile and/or stationary devices is becoming a reality by newly introduced Bluetooth radio technology for Wireless Personal Area Networking, which can support only up to 1 Mbps of nominal bandwidth. It is based on a master-slave model where double the resources are allocated for any slave-to-slave communication via the master. In addition, it does not have any mechanism to serve demands exceeding this capacity. In this paper, we employ the concepts of Internet Traffic Engineering to maximize the channel utilization and optimize the performance of QoS-sensitive applications, with minimum possible interference. We introduce two novel techniques of Pseudo Role Switching (PRS) and Pseudo PaRtitioning (PPR) to alleviate bottlenecks in the existing schemes in a proactive manner. We propose a two-layered approach wherein we first achieve the maximum possible throughput in existing network using PRS technique, and then dynamically partition piconets using the PPR to satisfy the increased demands. It has been observed that combining both PRS and PPR drastically enhances the aggregate network throughput while minimizing the interference. Through extensive performance evaluations, we show that our proposed schemes reduce up to 50% of the network overhead and increase the overall throughput by 200%.
206414100
Parameters for System Effectiveness Evaluation of Distributed Systems
In a Distributed Computing System (DCS), the failure of one or more system components causes the degradation in its effectiveness to complete a given task as opposed to a complete network breakdown. This paper addresses the issue of degraded system effectiveness evaluation by introducing two static measures, namely, Distributed Program Performance Index (DPPI) and Distributed System Performance Index (DSPI). These metrics can be used to compare networks with different features for application execution. It can be used to determine if the network with high reliability and low capacity, or low reliability and high capacity is better for a given program execution. An algorithm is also developed for computing these indices, and it is shown to be not only efficient, but general enough to compute many other existing measures such as computer networks, distributed systems, transaction based systems, etc.
15029640
Improving scheduling of tasks in a heterogeneous environment
Optimal scheduling of parallel tasks with some precedence relationship, onto a parallel machine is known to be NP-complete. The complexity of the problem increases when task scheduling is to be done in a heterogeneous environment, where the processors in the network may not be identical and take different amounts of time to execute the same task. We introduce a task duplication-based scheduling algorithm for network of heterogeneous systems (TANH), with complexity O(V/sup 2/), which provides optimal results for applications represented by directed acyclic graphs (DAGs), provided a simple set of conditions on task computation and network communication time could be satisfied. The performance of the algorithm is illustrated by comparing the scheduling time with an existing "best imaginary level scheduling (BIL)" scheme for heterogeneous systems. The scalability for a higher or lower number of processors, as per their availability is also discussed. We have shown to provide substantial improvement over existing work on the task duplication-based scheduling algorithm (TDS).
36917414
Performance Analysis of Single Stage Interconnection Networks
A single-stage interconnection network (SSIN) consisting of only one stage of switches and recirculation through processors is studied. An analytical probability model for SSINs using 2*2 switches is introduced, and results obtained with the model are compared with simulation results. Four SSINs with different network sizes, loading, and routing strategies are discussed. Processors with and without buffers are considered, and three different routing strategies are applied to resolve conflicts. The analytical model is seen to be in close agreement with the simulation results while providing at least an order of magnitude reduction in CPU time. >