Abstract

Pattern discovery is at the heart of bioinformatics, and algorithms from computer science have been widely used for identifying biological patterns. The assumption behind pattern discovery approaches is that a pattern that occurs often enough in biological sequences/structures or is conserved across organisms is expected to play a role in defining the respective sequence’s or structure’s functional behavior and/or evolutionary relationships. The pattern recognition problem addressed here is at the genomic level and involves identifying horizontally transferred regions, called genomic islands. A horizontally transferred event is defined as the movement of genetic material between phylogenetically unrelated organisms by mechanisms other than parent to progeny inheritance. Increasing evidence suggests the importance of horizontal transfer events in the evolution of bacteria, influencing traits such as antibiotic resistance, symbiosis and fitness, virulence, and adaptation in general. In the genomic era, with the availability of large number of bacterial genomes, the identification of genomic islands also form the first step in the annotation of the newly sequenced genomes and in identifying the differences between virulent and non-virulent strains of a species. Considerable effort is being made in their identification and analysis and in this chapter a brief summary of various approaches used in the identification and validation of horizontally acquired regions is discussed.

Abstract

We study the problem of secure message transmission (SMT) in asynchronous directed graphs, where an unbounded Byzantine adversary can corrupt some subset of nodes specified via an adversary structure. We focus on the particular variant (0, δ)-SMT, where the message remains perfectly private, but there is a small chance that the receiver R may not obtain it. This variant can be of two kinds: Monte Carlo - where R may output an incorrect message with small probability; and Las Vegas - where R never outputs an incorrect message. For a Monte Carlo (0, δ)-SMT protocol to exist in an asynchronous directed graph, we show that the minimum connectivity required in the network does not decrease even when privacy of the message being transmitted is not required. In the case of Las Vegas (0, δ)-SMT, we show that the minimum connectivity required matches exactly with the minimum connectivity requirements of the zero-error variant of SMT – (0, 0)-SMT. For a network that meets the minimum connectivity requirements, we provide a protocol efficient in the size of the graph and the adversary structure. We also provide a protocol efficient in the size of the graph for an important family of graphs, when the adversary structure is threshold.

Abstract

In this paper, we give approximate algorithms for privacy preserving distance based outlier detection for both horizontal and vertical distributions, which scale well to large datasets of high dimensionality in comparison with the existing techniques. In order to achieve efficient private algorithms, we introduce an approximate outlier detection scheme for the centralized setting which is based on the idea of Locality Sensitive Hashing. We also give theoretical and empirical bounds on the level of approximation of the proposed algorithms.

Abstract

We consider AESOP Task as Topic based evaluation of information content. Means at first stage, we identify the topics covered in given model/reference summary and calculate their importance. At the next stage, we calculate the information coverage in test/machine generated summary, wrt every identified topic. We use the local importance of words in calculation of importance of topics. From experiments it is clear that use of different methods for identification of topics and calculation of information coverage in test documents wrt every identified topic, have different effect on the result. It is important to note that our devised system do not require any linguistic support or learning or training in entire execution of the system.

Abstract

In this paper, we give an approximate algorithm for distance based outlier detection using Locality Sensitive Hashing (LSH) technique. We propose an algorithm for the centralized case wherein the entire dataset is locally available for processing. However, in case of very large datasets collected from various input sources, often the data is distributed across the network. Accordingly, we show that our algorithm can be effectively extended to a constant round protocol with low communication costs, in a distributed setting with horizontal partitioning.

Abstract

Three decades ago, Pease et al. introduced the problem of Byzantine Agreement [PSL 80] where nodes need to maintain a consistent view of the world in spite of the challenge posed by Byzantine faults. Subsequently, it is well known that Byzantine agreement over a completely connected synchronous network of n nodes tolerating up to t faults is (efficiently) possible if and only if t < n/3. Pease et al. further empowered the nodes with the ability to authenticate themselves and their messages and proved that agreement in this new model (popularly known as authenticated Byzantine agreement (ABA)) is possible if and only if t < n. (which is a huge improvement over the bound of t < n/3 in the absence of authentication for the same functionality). To understand the utility, potential and limitations of using authentication in distributed protocols for agreement, Gupta et al. [GGBS10] studied ABA in new light. They generalize the existing models and thus, attempt to give a unified theory of agreements over the authenticated and non-authenticated domains. In this paper we extend their results to synchronous (undirected) networks and give a complete characterization of agreement protocols. As a corollary, we show that agreement can be strictly easier than all-pair point-to-point communication. It is well known that in a synchronous network over n nodes of which up to any t are corrupted by a Byzantine adversary, BA is possible only if all pair point-to-point reliable communication is possible [Dol82, DDWY93]. Thus, a folklore in the area is that maintaining global consistency (agreement) is at least as hard as the problem of all pair point-to-point communication. Equivalently, it is widely believed that protocols for BA over incomplete networks exist only if it is possible to simulate an overlay-ed complete network. Surprisingly, we show that the folklore is not always true. Thus, it seems that agreement protocols may be more fundamental to distributed computing than reliable communication.

Abstract

In the Perfectly Secure Message Transmission (PSMT) problem, a sender S and a receiver R are part of a distributed network and connected through node disjoint paths, also called as wires, among which at most wires are controlled by a static, Byzantine adversary , having unbounded computing power. S has a message , which S intends to send to R. The challenge is to design a protocol, such that at the end of the protocol, R should correctly output without any error (perfect reliability) and should not get any information about , whatsoever, in information theoretic sense (perfect security). The problem of Statistically Secure Message Transmission (SSMT) is same as PSMT, except that R should correctly output with very high probability. Sayeed and Abu-Amara (1995) [37] have given a PSMT protocol in an asynchronous network tolerating , where S and R are connected by wires. However, we show that their protocol does not provide perfect security. We then prove that in an asynchronous network, if all the wires are directed from S to R, then any PSMT protocol tolerating is possible iff . Surprisingly, we also prove that even if all the wires are bi-directional, then any PSMT protocol in asynchronous network tolerating is possible iff . This is quite surprising because for synchronous networks, by the results of Dolev et al. (1993) [16], if all the wires are unidirectional (directed from S to R), then PSMT tolerating is possible iff , where as if all the wires are bi-directional then PSMT tolerating is possible iff . This shows that asynchrony of the network demands higher connectivity of the network for the existence of PSMT protocols. Interestingly, we further show that wires are necessary and sufficient for the existence of any SSMT protocol in asynchronous network tolerating , irrespective of whether the wires are unidirectional from S to R or the wires are bi-directional. By the results of Franklin and Wright (2000) [18] and Kurosawa and Suzuki (2009) [22], wires are necessary and sufficient for the existence of SSMT in synchronous networks, irrespective of whether the wires are unidirectional from S to R or the wires are bi-directional. This shows that asynchrony of the network does not demand higher connectivity of the network for SSMT protocols.

Abstract

In this paper we give the minimal connectivity required in a synchronous directed network, which is under the influence of a computationally unbounded Byzantine adversary that can corrupt a subset of nodes, so that Secure Message Transmission is possible between sender S and receiver R. We also show that secure communication between a pair of nodes in a given synchronous directed network is possible in both directions if and only if reliable communication is possible between them. We assume that in a network, every node is capable of computation and we model the network along the lines of [14].

Abstract

In this paper we propose and evaluate Marasim, a novel Jigsaw based graphical authentication mechanism using tagging. Marasim is aimed at achieving the security of random images with the memorability of personal images. Our scheme relies on the human ability to remember a personal image and later recognize the alternate visual representations (images) of the concepts occurred in the image. These concepts are retrieved from the tags assigned to the image. We illustrate how a Jigsaw based approach helps to create a portfolio of system-chosen random images to be used for authentication. The paper describes the complete design of Marasim along with the empirical studies of Marasim that provide evidences of increased memorability. Results show that 93% of all participants succeeded in the authentication tests using Marasim after three months while 71% succeeded in authentication tests using Marasim after nine months. Our findings indicate that Marasim has potential applications, especially where text input is hard (e.g., PDAs or ATMs), or in situations where passwords are infrequently used (e.g., web site passwords).

Abstract

Graphical passwords are considered to be a secure and memorable alternative to text passwords. Users of such systems, authenticate themselves by identifying a subset of images from the set of displayed images. However, despite the impressive results of user studies on experimental graphical passwords schemes, their overall commercial adaptations have been relatively low. In this paper, we investigate the reasons behind the low commercial acceptance of graphical passwords and present recommendations to overcome the same. Based on these recommendations, we design a simple graphical password scheme, which we call as NAPTune. NAPTune is aimed to work as a cued recognition based graphical authentication scheme that allows users to choose both text as well as images as their password with the same underlying design and interaction. In doing so, we blend the strengths of Numbers, Alphabets and Pictures (NAP) together to effectively defeat prevalent forms of social hacking. We conducted a user study with 35 participants to evaluate the viability of our proposed design. Results of the study are encouraging which indicates that our proposed design is potentially secure and usable method of authentication.