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.
Vanish. Similar to Vanish @cite_11 , EphPub aims at providing retroactive privacy, even if data storage is not trusted, compromised or stolen. However, as discussed in , the Vanish architecture is vulnerable to Sybil attacks @cite_27 . Authors of Vanish have proposed countermeasures to this specific attack @cite_26 . However, as discussed in @cite_27 , this has only raised the bar for the attacker, due to the vulnerability of DHTs to Sybil attack, thus, leaving as open question whether or not DHTs are the best choice for key-share storage.
@cite_27 @cite_26 @cite_11
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Researchers at the University of Washington recently proposed Vanish [20], a system for creating messages that automatically “self-destruct” after a period of time. Vanish works by encrypting each message with a random key and storing shares of the key in a large, public distributed hash table (DHT). DHTs expunge data older than a certain age; after this happens to the key shares, the key is permanently lost, and the encrypted data is permanently unreadable. Vanish is an interesting approach to an important privacy problem, but, in its current form, it is insecure. In this paper, we defeat the deployed Vanish implementation, explain how the original paper’s security analysis is flawed, and draw lessons for future system designs. We present two Sybil attacks against the current Vanish implementation, which stores its encryption keys in the million-node Vuze BitTorrent DHT. These attacks work by continuously crawling the DHT and saving each stored value before it ages out. They can efficiently recover keys for more than 99 of Vanish messages. We show that the dominant cost of these attacks is network data transfer, not memory usage as the Vanish authors expected, and that the total cost is two orders of magnitude less than they estimated. While we consider potential defenses, we conclude that public DHTs like Vuze probably cannot provide strong security for Vanish. Today's technical and legal landscape presents formidable challenges to personal data privacy. First, our increasing reliance on Web services causes personal data to be cached, copied, and archived by third parties, often without our knowledge or control. Second, the disclosure of private data has become commonplace due to carelessness, theft, or legal actions. Our research seeks to protect the privacy of past, archived data -- such as copies of emails maintained by an email provider -- against accidental, malicious, and legal attacks. Specifically, we wish to ensure that all copies of certain data become unreadable after a userspecified time, without any specific action on the part of a user, and even if an attacker obtains both a cached copy of that data and the user's cryptographic keys and passwords. This paper presents Vanish, a system that meets this challenge through a novel integration of cryptographic techniques with global-scale, P2P, distributed hash tables (DHTs). We implemented a proof-of-concept Vanish prototype to use both the million-plus-node Vuze Bit-Torrent DHT and the restricted-membership OpenDHT. We evaluate experimentally and analytically the functionality, security, and performance properties of Vanish, demonstrating that it is practical to use and meets the privacy-preserving goals described above. We also describe two applications that we prototyped on Vanish: a Firefox plugin for Gmail and other Web sites and a Vanishing File application. In the recent past we introduced two new security applications built on peer-to-peer systems and distributed hashtables (DHTs). First, we designed Adeona [18], which leverages DHTs to provide a privacy-preserving laptop tracking solution. Second, we designed the Vanish [10] selfdestructing data system, which uses DHTs to protect against retroactive attacks on archived data in the cloud. Both systems exploit intuitive properties of DHTs that dierentiate them from centralized solutions: e.g., complete or partial decentralization, giant scale, and geographic distribution. We implemented and made publicly available research prototypes of both Adeona and Vanish; the Adeona prototype uses OpenDHT as its underlying DHT and the Vanish prototype uses the Vuze DHT. While the properties of DHTs make them a tempting environment for new security-based systems, existing DHTs were never designed to support security or privacy applications, and such applications therefore stress DHTs in new ways. This paper provides a retrospective from our collective experience both designing and prototyping the two DHT-based security privacy applications, and operating and designing deployed DHTs (OpenDHT and Vuze). We discuss limitations and vulnerabilities of modern DHTs for security applications and propose very simple defenses that — perhaps surprisingly — greatly raise the bar for existing DHTs against certain privacy attacks. We also advocate for a hybrid approach that combines the best of both decentralized DHTs and centralized services for new security applications. Our goal is to inform the design of future DHTs and to strengthen the applicability of existing DHTs for supporting applications such as Adeona and Vanish. Releasing private data to the future is a challenging problem. Making private data accessible at a future point in time requires mechanisms to keep data secure and undiscovered so that protected data is not available prior to the legitimate release time and the data appears automatically at the expected release time. In this paper, we develop new mechanisms to support self-emerging data storage that securely hide keys of encrypted data in a Distributed Hash Table (DHT) network that makes the encryption keys automatically appear at the predetermined release time so that the protected encrypted private data can be decrypted at the release time. We show that a straight-forward approach of privately storing keys in a DHT is prone to a number of attacks that could either make the hidden data appear before the prescribed release time (release-ahead attack) or destroy the hidden data altogether (drop attack). We develop a suite of self-emerging key routing mechanisms for securely storing and routing encryption keys in the DHT. We show that the proposed scheme is resilient to both release-ahead attack and drop attack as well as to attacks that arise due to traditional churn issues in DHT networks. Our experimental evaluation demonstrates the performance of the proposed schemes in terms of attack resilience and churn resilience.