Modadugu, Boneh and Kim proposed two RSA key generation protocols (MBK Protocols) to generate the RSA keys efficiently on a low-power handheld device with the help of the untrusted servers, and the servers do not get any useful information about the keys they helped generation. The security of MBK Protocols is based on the assumption that the two servers are unable to share information with each other. To resists a ”collusion attack” ,namely the attack which the two servers collude to share information in MBK Protocols, Chen et al. proposed two improved protocols and claimed that their protocols are secure against such collusion attack. This paper shows that Chen et al.'s standard RSA key generation protocol cannot resist collusion attack and then cannot be used in practice.