ObliviSync: Practical Oblivious File Backup and Synchronization

Oblivious RAM (ORAM) protocols are powerful techniques that hide a client's data as well as access patterns from untrusted service providers. We present an oblivious cloud storage system, ObliviSync, that specifically targets one of the most widely-used personal cloud storage paradigms: synchronization and backup services, popular examples of which are Dropbox, iCloud Drive, and Google Drive. This setting provides a unique opportunity because the above privacy properties can be achieved with a simpler form of ORAM called write-only ORAM, which allows for dramatically increased efficiency compared to related work. Our solution is asymptotically optimal and practically efficient, with a small constant overhead of approximately 4x compared with non-private file storage, depending only on the total data size and parameters chosen according to the usage rate, and not on the number or size of individual files. Our construction also offers protection against timing-channel attacks, which has not been previously considered in ORAM protocols. We built and evaluated a full implementation of ObliviSync that supports multiple simultaneous read-only clients and a single concurrent read/write client whose edits automatically and seamlessly propagate to the readers. We show that our system functions under high work loads, with realistic file size distributions, and with small additional latency (as compared to a baseline encrypted file system) when paired with Dropbox as the synchronization service.Comment: 15 pages. Accepted to NDSS 201

Developing and evaluating a gestural and tactile mobile interface to support user authentication

As awareness grows surrounding the importance of protecting sensitive data, stored on or accessed through a mobile device, a need has been identified to develop authentication schemes which better match the needs of users, and are more resistant to observer attacks. This paper describes the design and evaluation of H4Plock (pronounced “Hap-lock”), a novel authentication mechanism to address the situation. In order to authenticate, the user enters up to four pre-selected on-screen gestures, informed by tactile prompts. The system has been designed in such a way that the sequence of gestures will vary on each authentication attempt, reducing the capability of a shoulder surfer to recreate entry. 94.1% of participants were able to properly authenticate using H4Plock, with 73.3% successfully accessing the system after a gap of five days without rehearsal. Only 23.5% of participants were able to successfully recreate passcodes in a video-based attack scenario, where gestures were unique in design and entered at different locations around the interface

Towards Baselines for Shoulder Surfing on Mobile Authentication

Given the nature of mobile devices and unlock procedures, unlock authentication is a prime target for credential leaking via shoulder surfing, a form of an observation attack. While the research community has investigated solutions to minimize or prevent the threat of shoulder surfing, our understanding of how the attack performs on current systems is less well studied. In this paper, we describe a large online experiment (n=1173) that works towards establishing a baseline of shoulder surfing vulnerability for current unlock authentication systems. Using controlled video recordings of a victim entering in a set of 4- and 6-length PINs and Android unlock patterns on different phones from different angles, we asked participants to act as attackers, trying to determine the authentication input based on the observation. We find that 6-digit PINs are the most elusive attacking surface where a single observation leads to just 10.8% successful attacks, improving to 26.5\% with multiple observations. As a comparison, 6-length Android patterns, with one observation, suffered 64.2% attack rate and 79.9% with multiple observations. Removing feedback lines for patterns improves security from 35.3\% and 52.1\% for single and multiple observations, respectively. This evidence, as well as other results related to hand position, phone size, and observation angle, suggests the best and worst case scenarios related to shoulder surfing vulnerability which can both help inform users to improve their security choices, as well as establish baselines for researchers.Comment: Will appear in Annual Computer Security Applications Conference (ACSAC