The increasing amount of personal and sensitive information disseminated over the Internet prompts commensurately growing privacy concerns. Digital data often lingers indefinitely and users lose its control. This motivates the desire to restrict content availability to an expiration time set by the data owner. This paper presents and formalizes the notion of Ephemeral Publishing (EphPub), to prevent the access to expired content. We propose an efficient and robust protocol that builds on the Domain Name System (DNS) and its caching mechanism. With EphPub, sensitive content is published encrypted and the key material is distributed, in a steganographic manner, to randomly selected and independent resolvers. The availability of content is then limited by the evanescence of DNS cache entries. The EphPub protocol is transparent to existing applications, and does not rely on trusted hardware, centralized servers, or user proactive actions. We analyze its robustness and show that it incurs a negligible overhead on the DNS infrastructure. We also perform a large-scale study of the caching behavior of 900K open DNS resolvers. Finally, we propose Firefox and Thunderbird extensions that provide ephemeral publishing capabilities, as well as a command-line tool to create ephemeral files.
@cite_6: Online social networks increasingly allow mobile users to share their location with their friends. Much to the detriment of users’ privacy, this also means that social network operators collect users’ lo- cation. Similarly, third parties can learn users’ location from localization and location visualization services. Ideally, third-parties should not be given complete access to users’ location. To protect location privacy, we design and implement a platform-independent solution for users to share their location in a private fashion over online social networks. Our so- lution relies on encryption to enforce access control and uses dummy queries and caching to protect localization and location visualization.
Observe that the main flaw of Vanish design is that DHTs are assumed to be resistant to crawling. On the contrary, monitoring all DNS resolvers is realistically infeasible. Further, EphPub provides several improvements in terms of robustness and usability. First, it allows users to select the expiration time: by choosing domain names matching desired lifetime period, users assign their content a more precise expiration time (while in Vanish this is assigned by the specific DHT implementation and due to network churn, unless using a so-called refreshing proxy'' that re-pushes key shares). Also, as we show next, given its simple nature, EphPub does not require users to install any additional software (e.g., DHT client). Thus, it can be easily ported on any architecture and deployed even on mobile phones. Indeed, researchers are already advocating efficient solutions to guarantee retroactive privacy, for instance, in location sharing applications over smartphones @cite_6 .