Proposing a security system for the VPN through design and implementation of a scheme for android and IOS mobiles based on two-factor authentication. Periodicals of Engineering and Natural Sciences, [S. l.], v. 10, n. 2, p. 292–303, 2022. DOI: 10.21533/pen.v10.i2.607. Disponível em: https://pen.ius.edu.ba/index.php/pen/article/view/607. Acesso em: 10 jun. 2026.