Levelled attribute-based encryption for hierarchical access control

Attribute-based encryption (ABE) is an important primitive to address the problem of flexible one-to-many encryption. Attribute-based encryption has found many practical applications such as cloud storage systems, file sharing systems, e-Health, pay-TV systems, social networks, etc. However, in almost existing ABE schemes, the efficiency depends heavily on the number of attributes involved in the secret key and the ciphertext. This makes hierarchical access control in ABE, where attributes need to be hierarchically organized, could be inefficient.

This paper introduces a novel concept of Levelled Attribute-based Encryption (Levelled ABE) as a solution to address the inefficiencies of standard ABE for hierarchical access control systems, where scalability and key management are critical. Levelled ABE presents a hierarchical attribute framework where attributes are organized into classes, and each attribute is assigned a level number within its class. By introducing this hierarchical structure, Levelled ABE enables finer-grained access control, scalability and more efficient key management. As a proof of concept, this paper also proposes two concrete constructions of Levelled ABE, one for key-policy and the other for ciphertext-policy. These constructions are comparable to existing ABE schemes. The security of the proposed constructions is proved in the generic group model.