Research on oblivious keyword search protocols with CKA security

An oblivious keyword search (OKS) protocol allows a user to search and retrieve the data associated with a chosen keyword in an oblivious way. It has stronger security attributes than traditional searchable encryption schemes which suffer from keyword guessing attack. Whereas most of the existing OKS protocols are not satisfactory because they mainly have the following flaws: (1) Large ciphertext‐size, relatively low communication, and computation efficiency; (2) Do not protect both user and database's privacy simultaneity. To deal with the above two problems and to obtain strong privacy, we investigate new approaches to design efficient OKS protocols. Our OKS protocol mainly realizes three contributions: (1) Improving privacy for both users and database servers; (2) Realizing compact cipher‐size; and (3) Overcoming particular security flaws occurred in previous OKS protocols. To prove what precise security can be expected in our OKS protocol, a formal chosen keyword attack model is defined to incorporate real attackers' abilities. Chosen keyword attack model is also utilized to analyze and point out security flaws in current OKS protocols. Efficiency and security comparison with existing OKS protocols is described to indicate their appropriate applications.