Comment: cryptanalysis of Lee-Hwang-Li's key authentication scheme

Recently, Zhang and Kim proposed an improved key authentication scheme [Appl. Math. Comput., in press]. Zhang and Kim claimed that the proposed key authentication scheme achieves the non-repudiation service. However, we show that a dishonest user can forge his public key via the verification equation. Hence this scheme cannot achieve the non-repudiation service like the previous variants.