Computing geometric median to locate the sink node with the aim of extending the lifetime of wireless sensor networks

AbstractIn case of wireless sensor networks (WSNs) the sensed data which are collected by the ordinary senor nodes will have to be forwarded to the sink node (Base Station) in order to be accessible by the remote users. The location of the sink could significantly affect the energy dissipation and throughput of the network. This paper aims to investigate an optimal location for the sink node in such a way that the sum of distances from all the sensor nodes to the sink node is minimized. In an effort to place the sink node within the network our algorithm finds the geometric median of all the location associated with the sensor nodes. In a discrete set of points, the geometric median could be defined as the location which basically minimizes the sum of distances to all the points. Performance evaluation reveals that the proposed location for the sink node extends the network lifetime comparing with other possible location within the network field

Comparative Analysis of Structures And Attacks on Various Stream Ciphers

ABSTRCAT INTRODUCTION Does increased security provide comfort to paranoid people? Or does security provide some very basic protections that we are naive to believe that we don't need? Today when tens of millions of people rely on Internet for essential communication and trade & commerce between them, a secure system becomes a very important issue to deal with. Cryptography under such circumstances forms an essential aspect for secure communications. Cryptography deals with four major goals viz Confidentiality, Data integrity, Authentication and Nonrepudiation and thus is widely used to secure telephonic messages, e-mails, credit card information, and corporate data[1] but with all these applications under its sleeve, one must keep in mind that cryptography on its own does not suffice all the requirements of security. Cryptography systems can be broadly classified into symmetric-key systems (AES,RC4,DES) that use a single key that both the sender and recipient have, and public-key or asymmetric systems (ElGamal, McEliece, RSA) that use two keys, a public key known to everyone and a private key that only the recipient of messages uses t = O(S t , K c C ) t = E(P t , Z t S ) t+1 = U (P, S t , K c Where the encryption function E is such that it is easy to construct a decryption function D, the decryption process can be described as follows: ), Z t = O(S t ,K c P ) t = D(C t , Z t S ) t+1 = U(P t , S t As stated in , Kc) . Stream ciphers are generally much faster than block ciphers No or limited error propagation Low hardware complexity The keystream can be sometimes generated prior to encryption/decryption.(in the synchronous case) Further on, Stream ciphers can be classified based on internal state as being either synchronous or self synchronizing. If the change in state occurs independent of the plaintext or cipher text messages the cipher is categorized as a synchronous stream cipher. In contrast, self-synchronizing stream ciphers update their state based on previous cipher text digits. In case of synchronous ciphers, the keystream generated is dependent only on the key and the position i while as in case of selfsynchronous the keystream depends only on the key and a fixed amount of previous ciphertext. Synchronous ciphers are described as having no error propagation while error propagation is limited in self-synchronous With synchronous ciphers, synchronization is achieved with 'marker positions' in the transmission, in contrast self-synchronizing ciphers have the facility to resume correct decryption if the keystream falls out of synchronization. Though desirable properties are found in both the variations, various implications are found in both of these. During decryption, the synchronous cipher limits the opportunity of detecting an error and a more serious limitation is that the attacker is able to make controlled changes to parts of ciphertext knowing very well the effect being induced on the corresponding plaintext. Rueppe

How well they retrieve fresh news items: News search engine perspective

People are nowadays opting news search engines for searching news instead of traditional web search engines as, number of specialized news search services have been developed. So it becomes necessary to evaluate these news search systems and help users to select the best one. Lots of work has been done to measure the traditional effectiveness of web search engines, major work has been done for relevance based evaluation using precision based measures, where topical relevance is often the main selection criteria, but less work has been done to measure the time-sensitive effectiveness of the news search systems where freshness matters. In this paper we used a scheme using mathematical statistics to measure the time-sensitive effectiveness of four news search systems, i.e., how well they retrieve the fresh documents. To our knowledge there is a lack of a good measure that combines both time-independent effectiveness and the relative freshness of news items so our scheme, using top ten results for 100 news queries on four news search engines with the basic idea to pull all the relevant results from the news search systems we want to compare together into a single ranked list based on their recency and analyse the relative positions of these results, will be useful in stuffing this gap