Expressive data sharing and efficient data deletion are essential to drive the development of cloud-assisted IoT. But insecure transmission and the vulnerability of the cloud server may cause potential threats to IoT data, attribute-based encryption (ABE) is widely applied to ensure data confidentially. Nonetheless, the potential data exposure caused by the compromised long-term key and the contradiction between conventional access structures in ABE and the various demands of data owners are still two huge challenges. To overcome these challenges, this article designs an unbounded and puncturable ciphertext-policy ABE with arithmetic span program ($\mathcal {UP}$-$\mathcal {CP}$-$\mathcal {ABE}$-$\mathcal {ASP}$) scheme and presents an expressive data sharing and self-controlled fine-grained data deletion solution in cloud-assisted IoT, which allows data owners to efficiently encrypt and share data with various computable access policies, but also enables data owners and data users to independently delete specific data stored in the cloud. The designed$\mathcal {UP}$-$\mathcal {CP}$-$\mathcal {ABE}$-$\mathcal {ASP}$leverages unbounded ABE and puncturable encryption to support the flexible update of system parameters and the deletion of specific data. Also, the arithmetic span program access structure is combined to realize expressive data sharing. Moreover, the$\mathcal {UP}$-$\mathcal {CP}$-$\mathcal {ABE}$-$\mathcal {ASP}$is adaptively secure in the standard model, and comprehensive performance evaluations demonstrate its practicability and scalability in cloud-assisted IoT.

Existing conditional anonymous authentication protocols to secure the group communication in VANETs (Vehicular Ad hoc Networks) render challenges such as dynamically updating membership in a domain and achieving vehicle user’s privacy preservation. This article elegantly addresses these challenges by proposing a novel conditional privacy-preserving authentication with dynamic membership for VANETs depending on chinese remainder theorem (CRT). Specifically, the CRT is utilized by a trusted authority to securely disseminate a domain key for the authorized vehicles in the same domain, where each vehicle in this domain is able to obtain the domain key by only performing one modulo division operation in case of domain key updating. Distinct from the previous works in this field, our proposed protocol not only achieves message authentication, anonymity and conditional privacy-preserving, but also provides forward security and backward security of vehicles. Theoretical analysis and experiment simulation demonstrate that the proposed protocol is provably secure and highly feasible.