Review of Asymmetric Key Cryptography in Wireless Sensor Networks

In wireless sensor networks (WSN’s), our main aim is to ensure the confidentiality of the data which has been sensed , aggregated and communicated to the base node. This will be achieved using key management. Symmetric key management uses only one key for encryption and decryption.Symmetric key management is generally preferred in WSN, because it will consume less battery power, memory and induces less computation overhead. Asymmetric key cryptography uses two separate keys , for encryption and decryption but those two keys are interconnected with complex mathematical algorithm. Since it is using complex mathematical algorithms it will induce huge overhead on power , computation and memory Asymmetric key cryptography is not preferred in WSN. Asymmetrickey cryptography is more secured and efficient when compared to symmetric key cryptography, this paper analyzes various opportunities of implementing asymmetric cryptography in wireless sensor networks.(WSN : Wireless Sensor Networks) I.Introduction. A.Key Management. Key management is systematic process of generating , distributing keys to the various sensor nodes , if the nodes gets compromised we need to revocate the keys to those compromised nodes. The principal concerns regarding the key management framework are as follows:  Key deployment/pre-distribution: it is process of generating keys and deploying it in the individual nodes.  Key establishment: Here, the methods by which any pair of nodes or a group of nodes establishes a secure session are discussed.  Member/node addition: This process of adding a node to the network, extra node added must be able to establish secure connections with the other nodes.  Member/node eviction: This process eliminates the node from the network such that it will not again be able to establish secure sessions with any of the existing nodes in the network. Moreover, the node will not to decipher future congestion in the network .  Key Revocation: Process of re issuing fresh keys to the compromised nodes. B.Types of key Management. 1.Symmetric Key Management : Here only one type of key is preferred to authenticate the nodes. Key pre distribution is widely preferred in WSN. Symmetric key cryptography uses relatively simple mathematical operations and hence it demands less computation power , and eventually consumes less battery power. Since its using simpler keys it will give less overhead in terms of memory. Since its consuming fewer resources it is widely preferred in wireless sensor networks.[10] 2.Asymmetric Key Management : it uses two different keys , public key and private key for encryption and decryption. Two keys are mathematically linked with each other, Asymmetric key cryptography incurs huge overhead in terms of memory computation power and battery and hence its generally not preferred in WSN.In the rest of the paper , we discuss more about asymmetric key cryptography and the ways in which it can be implemented in WSN.[10] Asymmetric Key Cryptography was introduced first by W.Diffie and M. Hellman presents the main idea of a public key cryptosystem. e-ISSN : 0975-4024 U.SenthilKumaran et al. / International Journal of Engineering and Technology (IJET) p-ISSN : 2319-8613 Vol 8 No 2 Apr-May 2016 859 Figure 1: Public-key cryptosystem Asymmetric key cryptography prefers a pair of keys: a public key and a private key.public key can be broadcasted to all nodes whereas the private key was kept as secret.We use mathematical logic to link public and private keys. Though the public key was broadcasted to every node, hacker will not be able to retrieve private key only with the help of public key. Assume that messageMwas encrypted with the known public key. To decrypt the cipher textC we need private key.occasionally we prefer to encrypt using private key and decrypt using public key., We need to simplify this scheme to use it in the wireless scenario .we can replace the trusted third party by the network deployer. Network deployer can act as trusted third party and deploy nodes with an private/public key pair. Every node present in the network can broad cast its public key to its neighbors if requiredto encrypt messages. However, in order to authenticate the public key there is a need for a trusted Certificate Authority which issues appropriate certificates. Among all public key algorithms, there are three established families of practical relevance. The security of these systems is based on hard mathematic problems: RSA Is named after its inventorsRivest, Shamir and Adleman [6][8]. This algorithm employs two large prime numbers P and Q .The strength of this scheme is based on the difficulty of finding these large prime numbers which is essential to find the secret key whereas the public key can be distributed freely .this algorithm as variety of applications on the normal conventional network, and is widely used in e commerce. Since we use large prime numbers and factoring as process , it demands high operational requirements in terms of resources. It will take toll on computational power memory, and the longevity of the operation demands power supply as well. All three resources are crucial in wireless sensor networks and hence its very tedious employ this algorithm in wireless sensor network security. Discrete logarithm :Elgamal proposed another group of asymmetric cryptography algorithm which is widely used in the security of conventional networks.the strength of this scheme relies upon the difficulty in finding the logarithms on the finite field. Resource usage of these algorithm is comparable RSA algorithm, hence it is difficult to implement this algorithm in wireless sensor networks. Elliptic Curve Cryptography is based on the algebraic structure of elliptic curve used on the finite field , the size the key will depend upon the size of the curve preferred strength of this method relies on the difficulty of the discrete logarithm problem in this setting (ECDLP).it has smaller key size when compared to the non elliptical key methods. Therefore it is considered the most attractive family for embedded devices, however the use of this method in wireless sensor networks is still tedious due to resource constraints. As we discussed in the abstract, public key cryptography techniques are lot more tedious because of the scarcity of resources in wireless Sensor networks. Few researchers declared that implementation of Public Key Cryptography sensor nodes are not feasible Hence hard-ware support may be needed for public key operations. Researchers concentrated on improving the hardware quality in wireless sensor networks in order to fit asymmetric cryptography in wireless sensor networks.. None of the sensor node platforms currently available on the market provides hardware support for Public Key Cryptography. Any change in the hardware may influence the size of the sensors as well as the cost There is aserious demand for cost effective Public Key Cryptography hardware solutions for sensor nodes. Meanwhile researchers concentrated more on , software based solutions for asymmetric key management.With respect to wireless sensor networks , asymmetric key cryptography would seem to be the best method for key broadcasting process. It gives necessary security and also provides improved scalability and resilience when compared the symmetric key solutions. Despite all these advantages, the application of public key cryptography protocols in WSNs remains challenging. All three asymmetric cryptography algorithms discussed , require e-ISSN : 0975-4024 U.SenthilKumaran et al. / International Journal of Engineering and Technology (IJET) p-ISSN : 2319-8613 Vol 8 No 2 Apr-May 2016 860 authentication of public keys before key distribution. Implementing this public key cryptography solutions will require presence of a public key infrastructure in which certificate authorities authenticate public keys. II.Public Key Infrastructure Security of the Public-key encryption schemes are valid only if the authenticity of the public key is assured. This service is provided with the use of certificate schemes. In cryptography, a public key infrastructure is a methodology that connects public keys with corresponding user identities by means of a Certificate Authority. The main task of a PKI is to create, manage, store, distribute and revoke digital certificates. A typical public key infrastructure consists of: Certificate Authority (CA) third party which provides and verifies digital certificate Registration Authority (RA) –it acts as verifier for (CA)and performs initial authentication before the digital certificates was issued. Certificate repository there can be one or more directories where certificates (with their public keys) are stored together with Certificate Revocation Lists (CLRs); Certificate management system. In order to participate in a public key infrastructure, user A must first enroll or register with the Registration Authority. The registration authority validates the user’sidentity and forwards his public key to the Certificate Authority. Main aim of the Certificate Authority is to attach the public key and the identifying information and credentials supplied by the Registration Authority. Public key was generated at the end of this process.. The binding is declared when a trusted Certificate Authority digitally signs the public key certificate with its own private key. Certificate authority provides a digital certificate for each user that uniquely identifies each and every user. When we try to establish the public key infrastructure in wireless sensor networks In the context of wireless sensor networks we have to face many implementation concerns., In addition to the energy , resource , time and transmission constraints WSN also suffers from the lack of trusted infrastructure. Sensor nodes are generally deployed in adverse conditions and hence it is also difficult to deploy certificate authority. Even if we deploy certificate aut