SEPM: Efficient partial keyword search on encrypted data

Abstract

Searchable encryption (SE) in the public key setting is that anyone can encrypt data by using a public key and store this ciphertext on a server, and a client who has the corresponding secret key can generate search queries (say, trapdoor) in order to search for the encrypted data on the server. In this paper, we focus on partial matching in the public key setting in order to enhance usability. We call this “Searchable Encryption with Partial Matching (SEPM)”. Few previous works of SEPM employed a strategy that a client generates ciphertexts or trapdoors on all similar words closely related to a keyword in order to realize the partial matching functionality. This means that the client has to generate trapdoors for all partial matching varieties. Therefore, this approach is inefficient due to its trapdoor size. In order to overcome this disadvantage, we introduce a new concept of trapdoor conversion. When a client searches for ciphertexts on the server, he generates only one trapdoor tk and sends it to the server. Then, the server generates trapdoors related to tk by using a conversion secret key which is generated in the setup phase and stored in the server, and searches ciphertexts from them. Intuitively, this trapdoor generation process is achieved by moving locations of characters included in a searching keyword. In order to realize this situation, we introduce a new cryptographic primitive, inner-product encryption with trapdoor conversion (IPE-TC). We propose a specific construction of IPE-TC based on generalized inner-product encryption and basis conversion technique on a dual pairing vector spaces approach.