Recently, Liu et al. (Quantum Inf Process (2014) 13:491-502) proposed an arbitrated quantum signature (AQS) scheme, where a signature receiver (Bob) can verify the signer's signature through the help of a trusted arbitrator. However, this paper shows that a malicious Bob can perform the existential forgery of the signature under the chosen message attack without being detected.
@article{arxiv.1512.00714,
title = {Comment on "An arbitrated quantum signature scheme with fast signing and verifying"},
author = {Yi-Ping Luo and Tzonelih Hwang},
journal= {arXiv preprint arXiv:1512.00714},
year = {2015}
}