A secure channel free conjunctive keyword search without random oracle under simple assumption

The public key encryption scheme with conjunctive keyword search (PECKS) is one of the most important techniques used for sensitive users' data outsourced to the third party, especially the cloud storage. However, most existing PECKS schemes need to construct a secure channel, which is usually costly. To solve this problem, some scholars have proposed several secure channel-free PECKS schemes, however, most of these schemes either are provably secure in the random oracle model, or provably secure in the stand model under complicated security assumption. Therefore, the security of these schemes is questionable. In this article, we propose a security-enhanced SCF-PECKS scheme, which is provably secure under the simple Decisional Bilinear Diffie-Hellman (DBDH) assumption in the standard model. Then we give its computational consistency and full security proof. Finally, we improve our SCF-PECKS scheme to resist the keyword guessing attack (KGA) and give its security demonstration.