Server Aided Ciphertext-Policy Attribute-Based Encryption

Attribute-based encryption (ABE) is a type of public key encryption that allows users to encrypt and decrypt messages based on user attributes. One drawback is that encryption and decryption computational costs scale with the complexity of the access policy or number of attributes. In practice, this makes encryption and decryption a possible bottleneck for some applications. In this work, we aim to mitigate this problem for ciphertext-policy ABE (CP-ABE). We introduce the server-aided CP-ABE (SA-CP-ABE) system. In this system, users can precompute an intermediate ciphertext before actual encryption to improve efficiency, and stores it on its storage server. Before decryption, user can call its computing server to transform the ciphertext to the partially decrypted ciphertext. This is significant for mobile devices to save local storage resources and computational resources. Then, we propose an SA-CP-ABE scheme, and prove its security in the standard model.