Secure and efficient key assignment scheme for dynamic access control in a hierarchy

Abstract

The users belonging to an organization are often assigned different access permissions depending on their security class. In this situation, the users belonging to a higher security class are allowed access to the information accessible to the users belonging to a lower security class, but the opposite is not allowed. In the past two decades, many cryptographic solutions to the hierarchical access control problem have been proposed. This thesis classifies the existing schemes depending upon different properties such as type of hierarchy, key derivation method, the range of applications, etc. A comparative analysis of some prominent schemes is presented. Attacks are proposed on an existing scheme due to Yang and Li. A modification is proposed to avoid the attacks and improve the efficiency of the scheme. The modified scheme is proved to be secure using a security model proposed by Wu and Wei. A countermeasure is proposed to overcome an attack on an existing time-bound scheme due to Tzeng.