Accountable large-universe attribute-based encryption supporting any monotone access structures

Abstract

Ciphertext-policy attribute-based encryption (CP-ABE) is a promising cryptographic primitive for fine-grained access control on data outsourced to clouds. However, there still exists one critical functionality missing in existing CP-ABE schemes, which is the prevention of key abuse. Specifically, two kinds of key abuse problems are considered in this paper: malicious key sharing among colluding users, and key escrow problem of the semi-trusted authority. For a user, any malicious behaviour including illegal key sharing should be traced. For the semi-trusted authority, it should be accountable for its misbehavior including illegal key re-distribution. For better performance and security, it is also indispensable to support large universe and full security in CP-ABE. To the best of our knowledge, none of the existing traceable CP-ABE schemes simultaneously supports large universe and full security. In this paper, we construct a white-box traceable CP-ABE scheme with weak public user traceability, weak public authority accountability and weak public auditing in the sense that no additional secret keys are needed. The scheme supports large universe, and attributes do not need to be pre-specified during the system setup phase. Our scheme is proven fully-secure in the random oracle model and it can take any monotonic access structures as ciphertext policies.