Wireless metropolitan area sharing networks (WMSNs) are wide-area wireless networks with nodes owned and managed by independent wireless Internet service providers (WISPs). To support seamless roaming in emerging WMSNs, in this paper, we propose a localized and distributed authentication and billing architecture that aims at enabling efficient and privacy-preserving mutual authentication between mobile users (MUs) and WISPs. User anonymity and identity privacy can be protected, even in the

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... nce of collusion between WISPs and a roaming broker (RB), which is considered to be the strongest user privacy protection. An efficient billing architecture is introduced and performed in the same stage of roaming, where U-tokens are defined and can be purchased by MUs from an RB as authentication credentials for the MUs to access the wireless network. The WISPs, thus, can cash the collected U-tokens in the RB for payment. We show that the proposed authentication and billing architecture can support localized inter-WISP authentication through the divisible blind signature scheme and a local witness strategy. A detailed analysis on a number of performance metrics, such as computation time and power consumption, is given to validate the performance of the proposed architectures. Index Terms-Billing, partially blind signature, privacy protection, roaming, wireless metropolitan area sharing networks (WMSNs).