DC-Area Anonymity, Privacy, and Security Seminar

Winter 2016 Seminar
Friday, February 19th, 2016
9:30 a.m. - 12:45 p.m.
Lunch afterward nearby

Location: AV Williams Building, Room 3258
University of Maryland, College Park
Host: Jonathan Katz

9:30 a.m. - 10:00 a.m.
Speaker: Yupeng Zhang (University of Maryland, College Park)
Title: Query Recovery Attacks against Searchable Encryption [slides]
Abstract: With the advent of cloud computing, techniques for outsourcing encrypted data with search capability are of significant interest. Searchable Encryption is proposed for such purpose. Searchable Encryption schemes achieves efficiency by allowing well-defined leakage. However, the practical consequence of the leakage has not been studied much in prior work. In this talk, I present query recovery attacks that exploit the leakage of Searchable Encryption and discuss potential countermeasures against these attacks.

10:00 a.m. - 10:30 a.m.
Speaker: Collin Anderson (Independent)
Title: Information Controls and Circumvention, A Contrived Action Involving Constant Pursuit [slides]
Abstract: The design and principles of networking protocols, cryptography tools and communications infrastructure can both positively and negatively impact the free flow of information in countries that control access to Internet. The consequences of these decisions, otherwise often far removed from the original decision-makers, are reflected in the real world history of efforts to provide, and concomitantly block, access to services that allow a user to bypass network restrictions. We will briefly review the landscape of censorship circumvention technologies, and then using historical examples narrate the feedback loop that exists between users that seek access to blocked content and the authorities that enforce such restrictions. The intention of this presentation is to demonstrate that the struggle between censors and users is often determined based on technical properties that would otherwise seem minor and start to identify hard limits to both actors.

10:30 a.m. - 11:00 a.m.
Speaker: Philip Kim (University of Maryland, College Park)
Title: Skor: IP tunneling through Skype video [slides]
Abstract: While many repressive regimes censor internet traffic, they commonly allow at least some communication with the outside world. We present Skor, a tool for tunneling arbitrary IP traffic over the video channel of Skype, a videotelephony application that is widely used and permitted around the world. Instead of modifying a covert transmission such that it mimics the behavior of the Skype protocol, Skor makes direct use of Skype as a carrier for the traffic. Prior work has used Skype to stream video from social networking sites, and demonstrated use of a software modem to send information through the audio channel of a Skype call. By using the video channel, Skor achieves higher throughput while still supporting arbitrary applications. I will present a prototype implementation of Skor as well as a preliminary analysis of its throughput and susceptibility to detection by statistical analysis.

11:00 a.m. - 11:45 a.m.
Coffee Break

11:45 a.m. - 12:15 p.m.
Speaker: Christine Task (Knexus Research)
Title: Differentially Private Statistical Significance Testing for Paired-Sample Data [slides]
Abstract: When looking at the practical application of differentially private data-mining to sets of sensitive human data, there are a few points that can be easily agreed upon: Having human data available to inform social policy decisions is a good idea. Preserving individual privacy is a good idea. Making erroneous policy decisions due to the added noise in privatized data is a bad idea.

In this work we present a privatization of the Wilcoxon Signed-Rank Test for statistical significance, which is applicable to paired-sample data and does not require the data to have a normal distribution (as data on social patterns often does not). Additionally, we demonstrate that added privatization noise can be factored into to the critical value table such that statistical significance can be determined reliably over the privatized statistic without increasing the risk of false-positives or false-negatives.

12:15 p.m. - 12:45 p.m.
Speaker: Farid Javani (University of Maryland, Baltimore County)
Title: cMix: Anonymization by High-Performance Scalable Mixing [slides]
Abstract: cMix is a cryptographic protocol for mix networks that uses pre-computations of a group-homomorphic encryption function to avoid all real-time public-key operations by the senders, mix nodes, and receivers. Like other mix network protocols, cMix can enable an anonymity service that accepts inputs from senders and delivers them to an output buffer, in a way that the outputs are unlinkable to the inputs. cMix's high-performance scalable architecture, which results from its unique pre-computation approach, makes it suitable for smartphone-to-smartphone use while maintaining full anonymity sets independently per round.

Each sender establishes a shared key separately with each of the mix nodes, which is used as a seed to a cryptographic pseudorandom number generator to generate a sequence of message keys. Each sender encrypts its input to cMix with modular multiplication by message keys. cMix works by replacing the message keys, which are not known in the pre-computation, in real time with a precomputed random value.

Our presentation includes a detailed specification of cMix and simulation-based security arguments. We also give performance analysis, both modeled and measured, of our working prototype currently running in the cloud.

cMix is the core technology underlying our larger PrivaTegrity system that allows smart devices to carry out a variety of applications anonymously (including sending and receiving chat messages), with little extra bandwidth or battery usage. This talk focuses on cMix.

Driving: There is a small paid visitors lot just south of the AV Williams building. You need to pay at the meter. There are other paid visitor parking lots on campus, but they are about a 10-minute walk from the building. See a campus map for those options.

Metro: Take the Metro to the College Park stop on Yellow/Green. Then take the free College Park Metro campus shuttle (#104), and get off at the stop at the Glenn L. Martin Wind Tunnel. You can find a detailed schedule and map for shuttle #104 here. Also, several public buses also bring you quite close to the A.V. Williams building, and they all take Metro Smart Cards.