Privacy-preserving fully anonymous ciphertext policy attribute-based broadcast encryption with constant-size secret keys and fast decryption

Abstract

Cloud computing is admired as a notable computing terminology in which facilities of the computing framework are rendered as aid over Internet services. In the era of cloud computing, lightweight devices can be used to afford remote e-healthcare, which facilitates the development of remote healthcare consultations, monitoring of patients’ health reports, and medical research. The downside of the cloud environment is that it does not support direct revocation with fine-grained access control over encrypted data by specifying access policies among ciphertexts and consumers’ secret-keys. Ciphertext Policy Attribute-Based Broadcast Encryption (CP-ABBE) can be deployed in a cloud computing environment to ensure fine-grained access control of outsourced data. In a CP-ABBE, consumers’ secret-keys are associated with attributes. Broadcaster encrypts the data concerning a subscriber set and an access policy. Legitimate consumers can recover the correct data if and only if the data file access policy satisfies the attributes associated with the consumers’ secret-keys. However, existing CP-ABBE schemes fail to withstand social engineering attacks, meaning that those are incapable of accomplishing consumers’ full anonymity as well as privacy of access policy, which are highly sensitive information in e-healthcare scenario. To mitigate these deficiencies, we introduce a new CP-ABBE, called privacy-preserving fully anonymous CP-ABBE, by tweaking an identity-based encryption framework over the most advanced and secure Type-3 bilinear pairings. In addition to being adaptively secure, our construction endures indistinguishable chosen-plaintext attack security under standard asymmetric decisional bilinear Diffie–Hellman assumption without using the random oracle model. In particular, the design is very efficient both in terms of parameter sizes and computation costs, as consumer secret-key and decryption time both are constant, and ciphertext-size is independent of access policy. The implementation and performance analysis of the protocol in opposition to existing works illustrate its effectiveness in providing healthcare services in the cloud environment.