  In this work, we exploit a serious security flaw in a code-based signature
scheme from a 2019 work by Liu, Yang, Han and Wang. They adapt the McEliece
cryptosystem to obtain a new scheme and, on top of this, they design an
efficient digital signature. We show that the new encryption scheme based on
McEliece, even if it has longer public keys, is not more secure than the
standard one. Moreover, the choice of parameters for the signature leads to a
significant performance improvement, but it introduces a vulnerability in the
protocol.
