The Wireless Sensor Networks (WSNs) have spread its roots in almost every application. Owing to their scattered nature of sensor nodes, they are more prone to attacks. There are certain applications e.g. military, where sensor data"s confidentiality requirement during transmission is essential. Cryptography has a vital role for achieving security in WSNs.WSN has resource constraints like memory size, processing speed and energy consumption which bounds the applicability of existing cryptographic algorithms for WSN. Any good security algorithms has higher energy consumption by the nodes, so it"s a need to choose most energy-efficient cryptographic encryption algorithms for WSNs. This paper surveys different asymmetric algorithms such as RSA, Diffie-Hellman, DSA, ECC, hybrid and DNA cryptography. These algorithms are compared based on their key size, strength, weakness, attacks and possible countermeasures in the form of The main components of sensor network are: sensing field, sensor nodes, base station and internet. The main components of sensor node are: controller, transceiver, power supply, memory and one or more sensors. These nodes have the sensing, processing and communication capabilities to monitor the real-world environment. WSNs have the advantage over the traditional networks in terms of scalability, deployment, applications, robustness, etc. As they are ad-hoc in nature, hence can be deployed in any area like military, environmental observation, syndrome surveillance, supply chain management, fire detection, vision enabling, energy automation, building administration, gaming, health and other commercial and home applications [1].Because of its broad usage in multifarious applications, security becomes the primary issue in WSN. When we provide security to sensor networks, it is more complicated than that of MANET because of the resource limitations of sensor nodes. There are some resource constraints such as energy and power supplies, limited memory, computation and communication capabilities. This is the reason that traditional cryptographic techniques cannot be applied on sensor networks, hence demand of more security in WSNs arises. The security requirements in WSN are authentication, confidentiality, availability, integrity and QoS. These conditions should be met while developing the security algorithm.