Ephemeral Communications using the Domain Name System

The increasing amount of personal information disseminated over the Internet raises serious privacy concerns. Data may linger forever, and users often lose its control and ownership. This motivates the desire of binding availability of contents to expiration times set by the data owner. To this end, we discuss and formalize the notion of Ephemeral Data Systems (EDSs): EDSs protect privacy of past data and prevent malicious parties from accessing expired contents. We present EphCom, a practical EDS using only a primary Internet service --- the Domain Name Service (DNS) and its caching mechanism. EphCom does not rely on Trusted Platform Modules (TPM), centralized servers, peer-to-peer networks, or proactive actions of the users. It is transparent to existing applications and services, and allows users to tightly control data lifetime. We analyze its security and show that EphCom instantiates a secure and practical EDS, with a negligible overhead on the DNS infrastructure. In the process of testing EphCom's reliability, we performed extensive measurements on the caching behavior of Open DNS servers, which might be of independent interest this is to our knowledge the first such measurement. We found that 10% of the DNS servers follow IETF's recommended caching behavior. Finally, we present a proof-of-concept Firefox extension that provides ephemeral email capabilities and a command line tool for ephemeral files.