Applied sciences Article  
Formal Security-Proved Mobile Anonymous Authentication Protocols with Credit-Based Chargeability and Controllable Privacy +  
Footnote †: journal: Applied Sciences  
[PERSON] 1,*,* and [PERSON] 2,*  
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around [2]. The more information the eavesdroppers know, the less security and privacy the mobile users preserve. Sometimes the vicious insiders of the system operator would disclose the classified information of mobile users. Any system without maintaining user privacy will not be acceptable in the future [3; 4; 5]. There exist some weaknesses on user privacy in the existent 2G mobile network system. Each mobile user's alias, TMSI, can be linked to her/his real identity, IMSI, by attackers when the VLR requests her/him to retransmit her/his IMSI. The 2G mobile network also has no design for satisfying mutual authentication and protecting the users' privacy against the system operator. A mobile user may be cheated by some fake base stations in a mobile network system due to lack of mutual authentication. Although the 3G system has provided mutual authentication, the privacy or anonymity of mobile users has not been sufficiently considered yet. Most of the proposed authentication schemes [6; 7; 8; 9; 10; 11; 12] which emphasize the privacy of mobile users usually assign an anonymous identity to each user. A mobile user will obtain an anonymous identity after she/he is successfully authenticated by the system operator, and she/he will take this valid alias to roam over the mobile networks. The eavesdroppers do not know the relation between her/his real identity and alias, but the system operator can derive the relation. To protect the user's privacy perfectly, we hope that anyone else, even the system operator, cannot derive such relations either. Owing to the unlinkability property, the technique of _blind signatures_[13] can help us with realizing complete anonymity for mobile users. Another problem is that once a mobile user gets anonymity, how can the system operator charge her/him when she/he requests the mobile network services via an anonymous identity? Especially, how can the system charge the user via a credit-based way, which is the most commonly-used billing solution and has been accepted by almost all of the mobile users? Further more, if there is some mobile user who misused the anonymity property to commit crimes, how can the judge handle it? All of the current solutions cannot cope with all of the above problems at the same time. In our solution, every mobile user is anonymous from the system operator and any other person's point of view when she/he is accessing the mobile network resources. Furthermore, the system operator can charge the mobile user according to the communication time the user consumed via a credit-based way. Moreover, we also consider the issue of fair privacy. The privacy of the mobile users who misused the anonymity property can be revoked by the judge, and the police can trace the criminals who have gotten anonymity. This is the property of _fair privacy_.