Understanding security failures of multi-factor authentication schemes for multi-server environments

Revealing the security flaws of existing cryptographic protocols is the key to understanding how to achieve better security. Dozens of multi-factor authentication schemes for multi-server environments were successively proposed, yet most of them have been shortly found problematic. The research pattern of this area has fallen into the undesirable "break-fix-break-fix" cycle, in which lots of efforts have been devoted but little real progress has been made. In this paper, we revisit five leading two-factor authentication schemes for multi-server environments (i.e., Xu et al. scheme at ICICS'17, Wu et al. scheme at FC'17, Leu-Hsieh's scheme at IET IS'14, Zhou et al. scheme at WINET'18 and Roy et al. scheme at IEEE TII'19), and demonstrate that all of them suffer from critical security defects (e.g., no truly multi-factor security and temporary information leakage attack) or are short of important properties (e.g., no user anonymity). Our results invalidate any use of these five schemes for practical applications without further improvement, and underscore some new challenges (e.g., attacks arising from the leakage of session-specific parameters and from malicious insiders) in designing sound multi-factor schemes for multi-server environments. We also draw some useful lessons from the cryptanalysis results. (C) 2019 Elsevier Ltd. All rights reserved.