  Blind quantum computation (BQC) protocol allows a client having partial
quantum ability to delegate his quantum computation to a remote quantum server
without leaking any information about the input, the output and the intended
computation to the server. Several BQC protocols have been proposed, e.g., Li
et al. in [1] proposed a triple-server BQC protocol and Xu et al. in [2]
proposed a single-server BQC protocol. Though both papers claimed that their
protocols can satisfy the requirement of privacy, this paper points out a
security loophole in their protocols. With that the server can reveal the
private information of the client.
