We introduce and analyze a general framework for authentically binding data to a location while providing strong assurances against cloud storage providers that (either accidentally or maliciously) attempt to re-locate cloud data. We then evaluate a preliminary solution in this framework that combines constraint-based host geolocation with proofs of data possession, called constraint-based data geolocation (CBDG). We evaluate CBDG using a combination of experiments with PlanetLab and real cloud storage services, demonstrating that we can bind fetched data to the location originally hosting it with high precision. We geolocate data hosted on the majority of our PlanetLab targets to regions no larger than 118,000 km 2 , and we geolocate data hosted on Amazon S3 to an area no larger than 12,000 km 2 , su ciently small to identify the state or service region.

Abstract-While solutions for file system encryption can prevent an adversary from determining the contents of files, in situations where a user wishes to hide the existence of data, encryption alone is not sufficient. Indeed, encryption may draw attention to those files, as they may likely contain information the user wishes to keep secret. Consequently, adversarial coercion may motivate the owner to surrender their encryption keys, under duress. This paper presents DEFY, a deniable file system following a log-structured design. Maintaining a log-structure is motivated by the technical constraints imposed by solid-state drives, such as those found in mobile devices. These devices have consequential properties that previous work largely ignores. Further, DEFY provides features not offered by prior work, including: authenticated encryption, fast secure deletion, and support for multiple layers of deniability. We consider security against a snapshot adversary, the strongest deniable filesystem adversary considered by prior literature. We have implemented a prototype based on YAFFS and an evaluation shows DEFY exhibits performance degradation comparable to the encrypted file system for flash, WhisperYAFFS.

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Abstract. We design communication efficient two-party and multi-party protocols for the longest common subsequence (LCS) and related problems. Our protocols achieve privacy with respect to passive adversaries, under reasonable cryptographic assumptions. We benefit from the somewhat surprising interplay of an efficient block-retrieval PIR (GentryRamzan, ICALP 2005) with the classic "four Russians" algorithmic design. This result is the first improvement to the communication complexity for this application over generic results (such as Yao's garbled circuit protocol) and, as such, is interesting as a contribution to the theory of communication efficiency for secure two-party and multiparty applications.