EXPLOITING N-GRAM IMPORTANCE AND ADDITIONAL KNOWEDGE BASED ON WIKIPEDIA FOR IMPROVEMENTS IN GAAC BASED DOCUMENT CLUSTERING

This paper provides a solution to the issue: “How can we use Wikipedia based concepts in document\ud clustering with lesser human involvement, accompanied by effective improvements in result?” In the\ud devised system, we propose a method to exploit the importance of N-grams in a document and use\ud Wikipedia based additional knowledge for GAAC based document clustering. The importance of N-grams\ud in a document depends on several features including, but not limited to: frequency, position of their\ud occurrence in a sentence and the position of the sentence in which they occur, in the document. First, we\ud introduce a new similarity measure, which takes the weighted N-gram importance into account, in the\ud calculation of similarity measure while performing document clustering. As a result, the chances of topical similarity in clustering are improved. Second, we use Wikipedia as an additional knowledge base both, to remove noisy entries from the extracted N-grams and to reduce the information gap between N-grams that are conceptually-related, which do not have a match owing to differences in writing scheme or strategies. Our experimental results on the publicly available text dataset clearly show that our devised system has a significant improvement in performance over bag-of-words based state-of-the-art systems in this area

Secure Message Transmission In Asynchronous Directed Networks

We study the problem of information-theoretically secure message transmission (SMT) in asynchronous directed networks. In line with the literature, the distrust and failures of the network is captured via a computationally unbounded Byzantine adversary that may corrupt some subset of nodes. We give a characterization of networks over which SMT from sender S to receiver R is possible in both the well-known settings, namely perfect SMT (PSMT) and unconditional SMT (USMT). We distinguish between two variants of USMT: one in which R can output an incorrect message (with small probability) and another in which R never outputs a wrong message, but may choose to abort (with small probability). We also provide efficient protocols for an important class of networks

Unconditionally Reliable Message Transmission in Directed Neighbour Networks

The problem of unconditionally reliable message transmission (URMT) is to design a protocol which when run by players in a network enables a sender S to deliver a message to a receiver R with high probability, even when some players in the network are under the control of an unbounded adversary. Renault and Tomala [JoC2008] gave a characterization of undirected neighbour networks over which URMT tolerating Byzantine adversary is possible. In this paper, we generalize their result to the case of directed networks

Interplay between (Im)perfectness, Synchrony and Connectivity: The Case of Reliable Message Transmission

For unconditionally reliable message transmission (URMT) in synchronous directed networks of n nodes, a subset of which may be Byzantine faulty, it is well-known that the minimum connectivity requirements for zero-error (perfect) protocols to exist is strictly higher than those where a negligible yet non-zero error probability is allowed (Monte Carlo protocols). In this work, we study the minimum connectivity requirements for the existence of (a) synchronous Las Vegas protocols, (b) asynchronous Monte Carlo protocols, and (c) asynchronous Las Vegas protocols for URMT. Interestingly, we prove that in any network, synchronous Las Vegas URMT protocol exists if and only if asynchronous Monte Carlo URMT protocol exists too. We further show that asynchronous Las Vegas URMT protocols exist if and only if synchronous perfect protocols exist. We conclude with another interesting result: there exists networks where the number of critical edges for the ‘easier’ randomized variants are asymptotically higher than that for the perfect variant. Thus, our results establish an interesting interplay between (im)perfectness, synchrony and connectivity for the case of URMT

Authenticated Byzantine Generals in Dual Failure Model

Pease {\em et al.}\/ introduced the problem of Byzantine Generals (BGP) to study the effects of Byzantine faults in distributed protocols for reliable broadcast. It is well known that BGP among $n$ players tolerating up to $t$ faults is (efficiently) possible if and only if $n > 3t$. To overcome this severe limitation, Pease {\em et al.} introduced a variant of BGP, \emph{Authenticated Byzantine General} (ABG). Here players are supplemented with digital signatures (or similar tools) to thwart the challenge posed by Byzantine faults. Subsequently, they proved that with the use of authentication, fault tolerance of protocols for reliable broadcast can be amazingly increased to $n > t$ (which is a huge improvement over the $n > 3t$). Byzantine faults are the most generic form of faults. In a network not {\em all} faults are always malicious. Some faulty nodes may only leak their data while others are malicious. Motivated from this, we study the problem of ABG in ($t_b$,$t_p$)-mixed adversary model where the adversary can corrupt up to any $t_b$ players actively and control up to any other $t_p$ players passively. We prove that in such a setting, ABG over a completely connected synchronous network of $n$ nodes tolerating a ($t_b$,$t_p$)-adversary is possible if and only if $n > 2t_b$+min($t_b,t_p$) when $t_p > 0$. Interestingly, our results can also be seen as an attempt to unify the extant literature on BGP and ABG

On the Price of Proactivizing Round-Optimal Perfectly Secret Message Transmission

In a network of $n$ nodes (modelled as a digraph), the goal of a perfectly secret message transmission (PSMT) protocol is to replicate sender\u27s message $m$ at the receiver\u27s end without revealing any information about $m$ to a computationally unbounded adversary that eavesdrops on any $t$ nodes. The adversary may be mobile too -- that is, it may eavesdrop on a different set of $t$ nodes in different rounds. We prove a necessary and sufficient condition on the synchronous network for the existence of $r$-round PSMT protocols, for any given $r > 0$; further, we show that round-optimality is achieved without trading-off the communication complexity; specifically, our protocols have an overall communication complexity of $O(n)$ elements of a finite field to perfectly transmit one field element. Apart from optimality/scalability, two interesting implications of our results are: (a) adversarial mobility does not affect its tolerability: PSMT tolerating a static $t$-adversary is possible if and only if PSMT tolerating mobile $t$-adversary is possible; and (b) mobility does not affect the round optimality: the fastest PSMT protocol tolerating a static $t$-adversary is not faster than the one tolerating a mobile $t$-adversary

Unconditionally Reliable and Secure Message Transmission in Undirected Synchronous Networks: Possibility, Feasibility and Optimality

We study the interplay of network connectivity and the issues related to the ‘possibility’, ‘feasibility’ and ‘optimality’ for unconditionally reliable message transmission (URMT) and unconditionally secure message transmission (USMT) in an undirected synchronous network, under the influence of an adaptive mixed adversary having unbounded computing power, who can corrupt some of the nodes in the network in Byzantine, omission, fail-stop and passive fashion respectively. We consider two types of adversary, namely threshold and non-threshold. One of the important conclusions we arrive at from our study is that allowing a negligible error probability significantly helps in the ‘possibility’, ‘feasibility’ and ‘optimality’ of both reliable and secure message transmission protocols. To design our protocols, we propose several new techniques which are of independent interest