A Key-policy Attribute-based Encryption Scheme with Constant Size Ciphertext

Attribute-based encryption (ABE) is a new cryptographic primitive which provides a promising tool for addressing the problem of secure and fine-grained data sharing and decentralized access control. Key-policy attribute-based encryption (KP-ABE) is an important class of ABE, where ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. KP-ABE has important applications in data sharing on untrusted cloud storage. However, the ciphertext size grows linearly with the number of attributes embedded in ciphertext in most existing KP-ABE schemes. In this paper, we describe our work on designing a KP-ABE scheme with constant size ciphertext for monotonic access structures. The downside of the proposed KP-ABE scheme is that private keys have multiple size growth in the number of attributes in the access structure. The proposed KP-ABE scheme is proved to be secure under the general Diffie-Hellman exponent assumption.