Cryptanalysis and the improvement of Kim et al.'s password authentication schemes

In 1999, Yang and Shieh proposed two authentication schemes with smart cards, one is timestamp-based password authentication scheme and other is nonce-based password authentication scheme. In 2002, Chan and Cheng pointed out that Yang and Shieh's timestamp-based password authentication scheme is insecure to vulnerable forgery attack. Further, in 2003, Sun and Yeh showed that Yang and Shieh's both schemes are insecure to vulnerable forgery attack. In 2005, Yang et a]. proposed the improvement of Yang and Shieh's password authentication schemes to withstand Sun and Yeh's forgery attack. In 2005, Kim et al. pointed out the security weaknesses to forgery attacks on Yang et al.'s schemes and they further proposed the improvement of Yang et al.'s schemes in order to resist their attacks. In this paper, we show that the Kim et al.'s password authentication schemes have security weaknesses to forgery attacks. Further, we propose the improvement of Kim et al.'s schemes in order to eliminate these weaknesses.