Biblio

A two-factor authenticated key-agreement scheme for session initiation protocol emerged as a best remedy to overcome the ascribed limitations of the password-based authentication scheme. Recently, Lu et al. proposed an anonymous two-factor authenticated key-agreement scheme for SIP using elliptic curve cryptography. They claimed that their scheme is secure against attacks and achieves user anonymity. Conversely, this paper's keen analysis points out several severe security weaknesses of the Lu et al.'s scheme. In addition, this paper puts forward an enhanced anonymous two-factor mutual authenticated key-agreement scheme for session initiation protocol using elliptic curve cryptography. The security analysis and performance analysis sections demonstrates that the proposed scheme is more robust and efficient than Lu et al.'s scheme.

Lo et al. (2011) proposed an efficient key assignment scheme for access control in a large leaf class hierarchy where the alternations in leaf classes are more frequent than in non-leaf classes in the hierarchy. Their scheme is based on the public-key cryptosystem and hash function where operations like modular exponentiations are very much costly compared to symmetric-key encryptions and decryptions, and hash computations. Their scheme performs better than the previously proposed schemes. However, in this paper, we show that Lo et al.’s scheme fails to preserve the forward security property where a security class can also derive the secret keys of its successor classes ’s even after deleting the security class  from the hierarchy. We aim to propose a new key management scheme for dynamic access control in a large leaf class hierarchy, which makes use of symmetric-key cryptosystem and one-way hash function. We show that our scheme requires significantly less storage and computational overheads as compared to Lo et al.’s scheme and other related schemes. Through the informal and formal security analysis, we further show that our scheme is secure against all possible attacks including the forward security. In addition, our scheme supports efficiently dynamic access control problems compared to Lo et al.’s scheme and other related schemes. Thus, higher security along with low storage and computational costs make our scheme more suitable for practical applications compared to other schemes.