2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/144506Recently, Tian et al presented an article, in which they discussed some security weaknesses of Yoon et al's scheme and subsequently proposed two ``improved'' schemes. In this paper, we show that the Tian et al's schemes are insecure and vulnerable than the Yoon et al's scheme.Cryptography and Securitytext