Unbounded Attribute-Based Encryption Supporting Non-Monotonic Access Structure and Traceability without Key Escrow

Attribute-based encryption (ABE) can achieve data confidentiality as well as fine-grained access control of encrypted data in data outsourcing systems. However, we urgently need to address both decryption key escrow and key abuse problems, and enhance expressiveness of ABE in practice. We present a new ABE scheme, which supports high expressiveness, solves the key escrow and abuse issues and provides traceability simultaneously. Our scheme does not limit the size of the attributes set and access policies and supports non-monotonic access structures. There is no authority holds sufficient privileges to generate and fabricate the decryption keys. And only data users have their own complete decryption keys. Anyone can run the trace algorithm of our scheme to track the malicious user. Our key sanity check algorithm will check out if a decryption key is modified. Our scheme is resistant to key escrow, user key abuse and authorized key attacks. We implement and test our scheme on a personal laptop. The experimental results show that the running times of encryption and decryption algorithms are less than one second when it deals with access policy or attributes set with one hundred attributes. Implementation results and related comparisons show that our scheme is effective and efficient. Our scheme is based on the bilinear groups of prime order and is proved to be selectively secure under the n-(B) assumption.