The current Internet architecture hides a user's real identity by design, which is an important factor contributing to the Internet's great success. However, as the Internet is quickly moving towards the mainstream of the societies nowadays, it is also raising tremendous problems on a daily basis, simply because there are no effective means to enable "user accountability". In this work, I study the feasibility to build a "trust zone" on the Internet, in which Internet-wide user accountability can be enabled for applications where the trust and true collaboration among individuals far outweigh other values. Meanwhile, the solution is required to well preserve user privacy on the Internet. To this end, I propose "IDnetMesh", a distributed Internet-wide user authentication infrastructure that serves as the gateway to the trust zone. It offers to validate two types of user accountability as the basis of trust. The first type of accountability allows an anonymous user to be deanonymized to his or her real identity when a dispute ( e.g., a crime) arises; it can help to enforce global policies, including laws and other commonly accepted policies. The second type of accountability offers to counter Sybil attacks; it can help to enforce non-global policies, including subjective policies specific to each application provider. Meanwhile, to be qualified as a basic Internet-wide infrastructure, the IDnet Mesh is also designed to provide high service scalability and reliability, including: ( i ) to be scalable to serve potentially billions of Internet users, ( ii ) to withstand therefore high volumes of service requests, and ( iii ) to be resilient to distributed denial-of-service (DDoS) attacks. In addition, the deployment of the IDnet Mesh is fully incremental--no changes to the existing Internet infrastructure and protocols are required and all modifications stay at the application layer. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]