A Mobile Ad-hoc Network (MANET) is a kind of wireless ad-hoc network that keeps configuring continuously. The nodes of the MANET are dynamic in nature as they are mobile. Conventional ad-hoc routing protocols are aimed at finding optimum route from source to destination. Security in MANETs is challenging because of the infra-structure less feature and dynamic nature of nodes in MANET. There are many security attacks in MANETs the prominent ones being black hole attacks, gray hole attacks, worm hole attacks sink hole attacks etc.. This paper details a survey done on the existing mechanisms for preventing and tackling black hole attacks in MANETs and also puts forward a digital signature based authentication scheme to detect adversaries which send fake RREP packets to source. © 2016, International Journal of Pharmacy and Technology. All rights reserved.