Privacy-preserving DRM

This paper describes and contrasts two families of schemes that enable a user to purchase digital content without revealing to anyone what item he has purchased. One of the basic schemes is based on anonymous cash, and the other on blind decryption. In addition to the basic schemes, we present and compare enhancements to the schemes for supporting additional features such as variable costs, enforcement of access restrictions (such as "over age 21"), and the ability of a user to monitor and prevent covert privacy-leaking between a content-provider-provided box and the content provider. As we will show, the different variants have different properties in terms of amount of privacy leaking, efficiency, and ability for the content provider to prevent sharing of encryption keys or authorization credentials.