Comment on "An arbitrated quantum signature protocol based on the chained CNOT operations encryption"

In 2015, Li et al. (Quantum Inf Process (2015) 14:2171-2181) proposed an arbitrated quantum signature (AQS) scheme based on the chained controlled-NOT operations encryption. However, this paper points out that in their scheme an attacker can forge a signature without being detected. Therefore, Li et al.'s AQS scheme cannot satisfy the unforgeability and non-repudiation property.