A SCHEME TO DETERMINE THE RELATIONSHIP BETWEEN 2 USERS IN A HIERARCHY

Security systems are often organized into a hierarchy. For example, the file access privileges of a file system are often organized hierarchically, so that a user may access all of the files of users who are below him in the hierarchy. In this paper, we propose an improved user hierarchy scheme which is inspired by Wu and Hwang's key-to-key (KTK) method. In Wu and Hwang's KTK schemes, each user is assigned a key vector, and the relationship between any two users can be revealed by computing the product of the two users' corresponding key vectors. Their method, however, has only theoretical interest due to the difficulty of finding key vectors for users, the amount of storage needed for the vectors, and the impossibility of adding new users without reconstructing all of the key vectors. Although our method also assigns keys to users, the amount of storage space is drastically reduced, and a new user can be easily added through simple operations, without affecting the existing keys.