Token Open Secure and Post-quantum Updatable Encryption Based on MLWE

Updatable encryption (UE) allows a client to outsource ciphertexts to some untrusted server and periodically rotate the encryption key. Recently, a Token Open security model is presented, which is closer to the real attack scenario for UE. The existing post-quantum secure UE schemes are all based on the LWE assumption without engineering implementation. In this paper, we present a new model based on the Token Open security model which reflects the characteristics of UE. Then we construct an updatable encryption scheme based on the MLWE assumption by using the key switching technology and ciphertext masking technology to achieve backward-leak uni-directional key update and uni-directional ciphertext update. We show that the new scheme satisfies our new model. In addition, we present the practical safety analysis of the new scheme by engineering implementation.