ACS-FIT: A Secure and Efficient Access Control Scheme for Fog-enabled IoT

The explosion of data generated by IoT devices encouraged the introduction of paradigm fog computing, which facilitates computation and analysis at the edge. Alongside fog, cloud computing co-exists for facilities such as massive storage, large processing capability, etc. However, storage and computation of data at different levels increase the risk of data security, which persuades the need for a proper access control scheme. Ciphertext-policy attribute-based encryption (CP-ABE) is a well-known cryptographic mechanism that provides data confidentiality and fine-grained access control. Unfortunately, the existing CP-ABE schemes are not well suited for the cloud-fog-IoT environment as they do not provide functionalities like key-escrow resistance, attribute update, attribute revocation, user revocation, and outsourcing of expensive operations with verifiable outsourced decryption, simultaneously in a single scheme. Therefore, this paper proposes a CP-ABE scheme named ACS-FIT, which supports key-escrow resistance, attribute update, user revocation, attribute revocation, and outsourcing of expensive operations with verifiable outsourced decryption functionalities altogether. The scheme is efficient as the expensive encryption and decryption operations are outsourced to fog nodes leaving only a small and constant amount of computation for the IoT devices. Additionally, the task of attribute update and revocation is also outsourced to a third party. The cost incurred during attribute update and revocation are also efficient as only those components are updated which are associated with the affected attributes. Meanwhile, the user holds a constant size key which remains unchanged during any update. The security analysis proves that the proposed scheme is secure against Chosen-Plaintext Attack under Decisional Bilinear Diffie-Hellman assumption. The performance analysis shows that the proposed scheme is efficient and suitable for IoT devices.