ABSTRACTTo protect user privacy and data security in cloud computing, a secure k‐nearest neighbor computation‐enhanced scheme on encrypted database has been proposed by Wong, Cheung, Kao and Mamoulis. The scheme is proven resistant to the known‐plaintext attack. We show that contrary to claims, the enhanced asymmetric scalar‐product‐preserving encryption cannot resist known‐plaintext attack by directly solving a secret key from a set of known plaintext–ciphertext pairs. Copyright © 2014 John Wiley & Sons, Ltd.