Optimal Black-Box Traceability in Decentralized Attribute-Based Encryption

With the advent of Cloud-storages, secure sharing of encrypted data with fine-grained access control has become an important challenge. To enforce fine-grained access rights on encrypted data to different users, Attribute-Base Encryption (ABE) is a promising cryptographic tool. But in many situations, some pirate users sell their access privileges for monetary gain. Hence, an efficient Black-Box Traitor Tracing (BB-TT) system is vital to address the corresponding Pirate Decoders (PDs). But, in the existing BB-TTs, the tracing complexity is directly related to the maximum number of users in the system. This article proposes an ABE-based access control system that provides a new Relaxed BB-TT. Our Relaxed BB-TT addresses the complexity problem by exploring the pirate user with an optimal number of decryption queries on the PD. The optimal number of queries leads to the exciting capability of traceability of stateful decoders (i.e., the decoder that can save the states among the
Tracer
's queries). Finally, our system provides White-Box traceability and reduces the amount of trust in the authorities. We give formal security proofs and extensive experimental results on different classes of mobile devices, including a laptop and a smartphone.