Sharing Private Data Over Public Networks
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Users share their sensitive personal data with each other through public services and applications provided by third parties. Users trust application providers with their private data since they want access to provided services. However, trusting third parties with private data can be risky: providers profit by sharing that data with others regardless of the user's desires and may fail to provide the security necessary to prevent data leaks. Though users may choose between service providers, in many cases no service providers provide the desired service without being granted access to user data. Users must make a choice: forego privacy or be denied service. I demonstrate that fine-grained user privacy policies and rich services and applications are not irreconcilable. I provide technical solutions to privacy problems that protect user data using cryptography while still allowing services to operate on that data. I do this primarily through content-agnostic references to data items and user-controlled pseudonymity. I support two classes of social networking applications without trusting third parties with private data: applications which do not require data contents to provide a service, and applications that deal with data where the only private information is the binding of the data to an identity. Together, these classes of applications encompass a broad range of social networking applications.