Pers Ubiquit Comput(2007)11: 157-169 6]. In this decentralized infrastructure, the mobile en- The most significant difference in ubiquitous com tity might have to make autonomous decisions with puting from traditional mainframe and personal com ly limited information available. All these aspects puting is that the environment and network is introduce the new issue which is trustworthiness in unpredictable and keeps changing. The biggest chal ubiquitous business computing. This issue is regarded lenge is that the mobile entity does not know which as the greatest barrier which may stop ubiquitous entity is trustworthy, including previously un-encoun computing success in the longer-term [7-9. Previous tered entities. However, here, we claim that the mobile studies show that trust plays a critical role in customer user usually will have a rough idea about which ser elations [10 and the importance of trust has also been vices they want to use and which group of entities they examined for e Commerce [11, 12] and mCommerce would like to interact with. So here we use the well known and proven passport concept, here migrated to In this paper, we propose an architecture named a mechanism to allow dynamic authentication and bipAss to build a trusted and flexible environment authorization, to convert this unpredictability into a for ubiquitous business computing. Our architecture predictable, trusted form aims to allow transaction entities to create trusted The new architecture is based on extending digital interaction without necessarily having prior knowledge certificate technologies of each other. By employing our architecture, mobile entities can interact safely with each other by enabling 2.2 Overview of the mobiPass architecture pre-set customized preferences. Our architecture adopts a user centric philosophy that delegates the final The infrastructure of the architecture utilizes a number decision to the user, still with reasonable flexibility and of existing technologies such as digital certificates, extensibility In our architecture, the mobile entity only certificate authorities (CAs)and asymmetric key talks with another trusted entity/environment which satisfies this customized access control rules encryption. There is some virtue in reusing existing This paper is structured as follows. Section 2 de- technology building blocks in the infrastructure of scribes the overall architecture of mobipass and mobile computing, as a large number of devices are interactions between different elements for establish already in the field. If the architecture is to build on top ing the trusted environment in mobile business com of existing and well-proven technologies, it can be puting. In Sect. 3, a representative case study is used to easily adopted and implemented The new elements introduced in this architecture to demonstrate our architecture. Section 4 discusses re- enable the specific MobiPass functionality are as fol lated work and Sect. 5 concludes the pape lows. Central Registry (not mandatory) 2 MobiPass architecture MobiPolicy Extended Certificate Authority(ECA) 2.1 Motivation Mobipass · Mobimanager As we have emphasized, to pursue success in ubiqui tous/mobile business a trusted environment must be All the new elements are shown in Fig. 1, and the established via a practical approach. As mobile com- following sections discuss how these elements inter puting is a user-centric business model. the approach operate to create a flexible and trusted mobile business for creating a trusted network must be straightforward platform. The architecture will be addressed as follows. Firstly, generally describe the elements in the and easily adoptable by end users and it must provide architecture respectively, and then we explain how fine-grained access control with an easily operable user these elements can establish the trusted mobile should not be exposed directly to the end user. In our other ht, i.e., how these elements interact with architecture, we have considered both technical factors and human factors and utilized the well-known pass- port concept combined with a preference wizard to 2.2. 1 Central registry allow users to easily set their customized rules to de cide which service they want to use and which trans- The central registry( CR) is a global, trusted service action entities they want to interact with in a flexible registry in our architecture. The purpose of introducing and understandable way the Cr into our architecture is to provide a solid base Spr6]. In this decentralized infrastructure, the mobile en￾tity might have to make autonomous decisions with only limited information available. All these aspects introduce the new issue which is trustworthiness in ubiquitous business computing. This issue is regarded as the greatest barrier which may stop ubiquitous computing success in the longer-term [7–9]. Previous studies show that trust plays a critical role in customer relations [10] and the importance of trust has also been examined for eCommerce [11, 12] and mCommerce [13, 14]. In this paper, we propose an architecture named MobiPass to build a trusted and flexible environment for ubiquitous business computing. Our architecture aims to allow transaction entities to create trusted interaction without necessarily having prior knowledge of each other. By employing our architecture, mobile entities can interact safely with each other by enabling pre-set customized preferences. Our architecture adopts a user centric philosophy that delegates the final decision to the user, still with reasonable flexibility and extensibility. In our architecture, the mobile entity only talks with another trusted entity/environment which satisfies this customized access control rules. This paper is structured as follows. Section 2 de￾scribes the overall architecture of MobiPass and interactions between different elements for establish￾ing the trusted environment in mobile business com￾puting. In Sect. 3, a representative case study is used to demonstrate our architecture. Section 4 discusses re￾lated work and Sect. 5 concludes the paper. 2 MobiPass architecture 2.1 Motivation As we have emphasized, to pursue success in ubiqui￾tous/mobile business, a trusted environment must be established via a practical approach. As mobile com￾puting is a user-centric business model, the approach for creating a trusted network must be straightforward and easily adoptable by end users and it must provide fine-grained access control with an easily operable user interface. For example, complex security protocols should not be exposed directly to the end user. In our architecture, we have considered both technical factors and human factors and utilized the well-known pass￾port concept combined with a preference wizard to allow users to easily set their customized rules to de￾cide which service they want to use and which trans￾action entities they want to interact with in a flexible and understandable way. The most significant difference in ubiquitous com￾puting from traditional mainframe and personal com￾puting is that the environment and network is unpredictable and keeps changing. The biggest chal￾lenge is that the mobile entity does not know which entity is trustworthy, including previously un-encoun￾tered entities. However, here, we claim that the mobile user usually will have a rough idea about which ser￾vices they want to use and which group of entities they would like to interact with. So here we use the well known and proven passport concept, here migrated to a mechanism to allow dynamic authentication and authorization, to convert this unpredictability into a predictable, trusted form. The new architecture is based on extending digital certificate technologies. 2.2 Overview of the MobiPass architecture The infrastructure of the architecture utilizes a number of existing technologies such as digital certificates, certificate authorities (CAs) and asymmetric key encryption. There is some virtue in reusing existing technology building blocks in the infrastructure of mobile computing, as a large number of devices are already in the field. If the architecture is to build on top of existing and well-proven technologies, it can be easily adopted and implemented. The new elements introduced in this architecture to enable the specific MobiPass functionality are as fol￾lows: • Central Registry (not mandatory) • MobiPolicy • Extended Certificate Authority (ECA) • MobiPass • MobiManager All the new elements are shown in Fig. 1, and the following sections discuss how these elements inter￾operate to create a flexible and trusted mobile business platform. The architecture will be addressed as follows. Firstly, we generally describe the elements in the architecture respectively, and then we explain how these elements can establish the trusted mobile envi￾ronment, i.e., how these elements interact with each other. 2.2.1 Central registry The central registry (CR) is a global, trusted service registry in our architecture. The purpose of introducing the CR into our architecture is to provide a solid base 158 Pers Ubiquit Comput (2007) 11:157–169 123