On the Correctness of a Two-Round Multi-Keyword Top-k Ciphertext Retrieval

Yu et al. proposed a two-round multi-keyword ciphertext retrieval TRMCR) scheme by employing a vector space model and homomorphic encryption. A distinctive feature is to support top-k multi-keyword retrieval and hence TRMCR is an excellent choice for searching encrypted data over cloud with a desirable property of data privacy-preserving. Correct decryption is one of the fundamental requirements for the ciphertext retrieval. In this paper, we find that TRMCR can not achieve correct decryption, as we find that the underlying modified fully homomorphic encryption will result in a decryption error due to the growth of exponential noise. To solve the problem of incorrect decryption, we amend the original TRMCR by adjusting the parameter setup.