A note on the security of two improved RFID protocols

Recently, Baghery et al. [1, 2] presented some attacks on two RFID protocols, namely Yoon and Jung et al. protocols, and proposed the improved version of them. However, in this note, we show that the improved version of the Jung et al. protocol suffers from desynchronization attack and the improved version of the Yoon's protocol suffers from secret disclosure attack. The success probability of the desynchronization attack against the improved version of the Jung et al. protocol is (1-2-2n)2, where n is length of the protocol parameters. The attack can be accomplished with just three runs of the protocol. The success probability of the secret disclosure attack against the improved version of the Yoon's protocol is almost 1, while the complexity is just two runs of the protocol and doing 216 off-line evaluations of PRNG function.