Comment on "An Efficient Privacy-Preserving Ranked Multi-Keyword Retrieval for Multiple Data Owners in Outsourced Cloud"

Protecting the privacy of keywords in the field of search over outsourced cloud data is a challenging task. In IEEE Transactions on Services Computing (Vol. 17 No. 2, March/April 2024), Li et al. proposed PRMKR: efficient privacy-preserving ranked multi-keyword retrieval scheme, which was claimed to resist keyword guessing attack. However, we show that the scheme fails to resist keyword guessing attack, index privacy, and trapdoor privacy. Further, we propose a solution to address the above said issues by correcting the errors in the important equations of the scheme.