Revocable Certificateless Public Key Encryption with Equality Test

Traditional public key cryptography requires certificates as a link between each user's identity and her/his public key. Typically, public key infrastructures (PKI) are used to manage and maintain certificates. However, it takes a lot of resources to build PKI which includes many roles and complex policies. The concept of certificateless public key encryption (CL-PKC) was introduced to eliminate the need for certificates. Based on this concept, a mechanism called certificateless public key encryption with equality test (CL-PKEET) was proposed to ensure the confidentiality of private data and provide an equality test of different ciphertexts. The mechanism is suitable for cloud applications where users cannot only protect personal private data but also enjoy cloud services which test the equality of different ciphertexts. More specifically, any two ciphertexts can be tested to determine whether they are encrypted from the same plaintext. Indeed, any practical system needs to provide a solution to revoke compromised users. However, these existing CL-PKEET schemes do not address the revocation problem, and the related research is scant. Therefore, the aim of this article is to propose the first revocable CL-PKEET scheme called RCL-PKEET which can effectively remove illegal users from the system while maintaining the effectiveness of existing CL-PKEET schemes in encryption, decryption, and equality testing processes. Additionally, we formally demonstrate the security of the proposed scheme under the bilinear Diffie-Hellman assumption.