Neelam Shekhawat et al, International Journal of Computer Science and Mobile Computing, Vol.3 Issue.4, April- 2014, pg. 717-721 © 2014, IJCSMC All Rights Reserved 717 Available Online at www.ijcsmc.com International Journal of Computer Science and Mobile Computing A Monthly Journal of Computer Science and Information Technology ISSN 2320–088X IJCSMC, Vol. 3, Issue. 4, April 2014, pg.717 – 721 RESEARCH ARTICLE Enhancement the Security of WSN using ALARM Protocol to Prevention from Reply Attack Neelam Shekhawat Faculty of Engineering Mody University of Science & Technology,Laxmangarh (Sikar), India er.neelamshekhawat@gmail.com Moumita Ghosh Faculty of Engineering Mody University of Science & Technology Laxmangarh (Sikar), India mom2001@gmail.com Abstract — The wireless Ad hoc network is the self configuring type of network. In self configuring type of networks mobile nodes can leave or join the network when they want .In such type of networks many inside and outside attacks are possible. Inside and outside attacks are broadly classified as active and passive attacks. To prevent inside and outside attacks trust relationship between the mobile nodes must be maintained. The trust relationship between the mobile nodes is provided by mutual authentication. ALARM is the protocol for providing trust relationship between the mobile nodes. In this protocol the clocks of the mobile nodes are weakly synchronized by using GPS. In such case reply attack is possible. To prevent reply attack clocks of the mobile nodes must be strongly synchronized. In our new proposed technique, we are enhancing t the ALARM protocol to provide strong clock synchronization between the mobile nodes. Our new technique will be based on the NTP (network time protocol). Keywords— ALARM, Attacks, clock Synchronization, GPS, NTP I. INTRODUCTION Ad hoc network is a decentralized type of wireless network. In ad hoc network there is no pre-existing infrastructure, such as routers in wired networks or access points in wireless networks. In ad hoc network each node participates in routing by forwarding data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity. Ad-hoc networks are a new paradigm of wireless communication for mobile hosts. Basically it’s a network which is used in emergency causes. Here is No fixed infrastructure in ad hoc network like base stations as mobile switching. Nodes