One of the challenging issues in wireless sensor networks (WSNs) is to provide secure communication as the channel used is wireless. User authentication is a mechanism that is used to provide secure communication. The authors analyse the security of a recent authentication scheme for WSNs and show that it is not resistant to smart card loss, insider, and denial of service attacks besides the user traceability problem. Here, they design an improved user authentication scheme using the chaotic maps for WSNs. The chaotic maps-based public key cryptosystem helps a scheme to consider a large integer as the secret key rather than a large prime number and makes it fast. They show its formal security analysis using the random oracle model. They also analyse its security informally to show that it is resistant to various known attacks. They show that their scheme offers more security features than the existing schemes.
NomenclatureU i registered user DB database maintained by GWN SN j jth sensor node D id identity space D pw password space E attacker UID i identity of U i SC smart card of U i Pw i password of U i TC i /TC j temporal-credential of U i /SN j R i , K i random strings generated by U i K g random string generated by GWN K s random string generated by SN j n integer such that 2 4 ≤ n ≤ 2 8 TE i expiry time for TC i SK w − z session key between w and z x g − u / x g − s GWN's secret keys for users/SNs p large prime number En k ( . )/Dn k ( . ) encryption/decryption using key k ⊕ exclusive-OR operator f(.) one-way hash function ∥ concatenation operator In the last few years, many two-factor and three-factor authentication schemes have been proposed for WSNs. Based on the usage of the basic cryptographic techniques, existing authentication schemes for WSNs can be further classified as follows: i. Public key cryptography-based authentication: These types of schemes use public key cryptography such as Rivest-Shamir-Adleman (RSA). Watro et al. [12] discussed a scheme using the Diffe-Hellman [13] and RSA [14] mechanisms. This scheme is, however, not resistant to the node impersonation attack [15]. Xu et al. [16] designed a user authentication scheme based on the Diffie-Hellman key exchange protocol using RSA for providing mutual authentication. The main limitations of this scheme are that they require highcomputational cost and memory overhead as they keep all the public keys of the nodes and users. ii. Elliptic curve cryptography (ECC)-based authentication: These types of schemes are based on ECC and use point multiplication on ECC [17-20]. Le et al. [19] discussed an energy-efficient access control scheme for WSNs based on ECC after removing the limitations of the Wang et al.'s scheme