4.3.1 User Authentication Module to the JAVA Mobile Application 11.4.3.2 XKMS Module 11.4.3.3 XML-Security Module 11.4.3.4 WS-Security Module Service Delivery Platforms 11.4.3.5 STS Module 11.4.3.6 Time-Stamping Module 11.4.4 Implementation Aspects 11.4.4.1 Bouncy Castle APIs 11.4.4.2 Obfuscation Process 11.4.4.3 Security and Trust Services API 11.4.5 Java Mobile Client 11.4.5.1 Interface Description 11.5 Conclusions Acknowledgments Disclaimer References 11.1 Introduction This work is related to the consideration of some possible Service Oriented Architecture (SOA)-based e/m-government online systems, that is, about secure mobile communication between citizens and companies with the small and medium governmental organizations (SMGOs), such as municipalities, or other governmen- tal organizations and/or agencies. We have considered a general model of such systems consisting of three main parts: Secure mobile or desktop client application SOA-based e/m-government platform External entities, such as Public Key Infrastructure (PKI), STS, XML Key Management Specification (XKMS), Time-stamping Authority (TSA), and Universal Description Discovery and Integration (UDDI) Although the generic e/m-government model has been proposed and consid- ered, a main emphasis and contribution of the study is consideration of the Secure JAVA Mobile Web Service application communicating with the Web Service of the proposed platform. In other words, although the clients of the proposed platform could be desktop or mobile, as well as that mobile clients could be JAVA or .NET- based applications, we mainly considered the Secure JAVA Mobile Web Service application and all security aspects of its mobile communication with the Web Service of the proposed platform. The work presented and examples described are included in the general frame- work of the EU IST FP6 SWEB project (Secure, interoperable cross-border m-services contributing toward a trustful European cooperation with the non-EU member Western Balkan countries, SWEB) [1]. In a proces