Recently, Om et al. proposed three-factor remote user authentication protocol using ElGamal cryptosystem and ensured that it is withstands to various kinds of security attacks. But, the authors review carefully Om et al.'s scheme and discover that it unable to resist three attacks (like password guessing; denial of service; and user impersonation). Moreover, their protocol is not facilitating user anonymity. To solve these security vulnerabilities, the authors devise a secure and robust anonymous identity based authentication scheme for multi-server environment. The authentication proof of the proposed scheme has validated using BAN (Burrows-Abadi-Needham) logic, which confirms the protocol facilitates mutual authentication and session-key negotiation securely. Informal security analysis also confirms that it is well protected against various security attacks. In addition, the proposed work is compared along with other schemes (in the context of smart card storage and computation costs as well as execution time).
