DC-Area Anonymity, Privacy, and Security Seminar

Summer 2019 Seminar
Friday, June 28th, 2019
9:30 a.m. - 1:00 p.m.
Lunch afterward nearby

Location: Herman Room, Healey Family Student Center
(adjacent New South Hall, at Library Walk & Tondorf Rd)
Georgetown University
Host: Micah Sherr

9:30 a.m. - 9:55 a.m.
Speaker: Adam J. Aviv (U.S. Naval Academy)
Title: PIN Selection on Smartphones: Reconsidering Length and Blacklists
Abstract: Even though PINs are the dominant knowledge-based unlock authentication, there are few studies of this vital component of the authentication ecosystem. This talk will present our work on the first comprehensive study of user-chosen 4- and 6-digit PINs (n=1220) collected on smartphones that are explicitly primed and evaluated for situations of device unlocking. We find that against a throttled attacker (with 10 or 100 guesses, matching the smartphone unlock setting), using 6-digit PINs instead of 4-digit PINs provides little to no increase in security, and surprisingly may even decrease security.

We also study the effects of blacklists, where a set of "easy to guess" PINs is disallowed during selection. Two such blacklists are in use today by iOS, which we extracted via automated brute force. We evaluated the iOS 4-digit (274 PINs) and 6-digit (2910 PINs) blacklists in comparison with four other blacklists, including a small 4-digit (27 PINs), a large 4-digit (2740 PINs), and two placebo blacklists for 4- and 6-digit PINs that always excluded the first-choice PIN. We find that relatively small blacklists in use today by iOS offer little or no benefits against a throttled guessing attack. Only when the blacklist is much larger are security gains observed, at the cost of increased user frustration. Our analysis suggests that a blacklist at about 10% of the PIN space may provide the best balance between usability and security.

9:55 a.m. - 10:20 a.m.
Speaker: Sam Teplov (U.S. Naval Academy)
Title: Handoff All Your Privacy — A Review of Apple's Bluetooth Low Energy Continuity Implementation [slides]
Abstract: In recent versions of iOS, Apple has incorporated new wireless protocols to support automatic configuration and communication between devices. In this paper, we investigate these protocols, specifically Bluetooth Low Energy (BLE) "Continuity," and show that the price for this seamless user experience is substantial leakage of identifying information and users' behavioral data to a passive listening adversary. We start by reverse engineering Apple's proprietary protocol and identifying a number of data fields that are transmitted unencrypted. Plaintext messages are broadcast over BLE in response to user actions such as locking and unlocking a device's screen, using the copy/paste feature and tapping the screen while it is unlocked. We also demonstrate that the format and contents of these messages can be used to identify the type and OS version of a device. Finally, we show how the predictable sequence numbers of these frames can allow an adversary to track iOS devices from location to location over time, defeating existing anti-tracking techniques like MAC address randomization.

10:20 a.m. - 10:50 a.m.
Coffee Break

10:50 a.m. - 11:15 a.m.
Speaker: Chujiao Ma (Comcast)
Title: Crypto Agility
Abstract: Crypto agility refers to the ability of an entity to replace existing crypto primitives, algorithms, or protocols with a new more secure alternative quickly, inexpensively, and with minimum overhead. These changes may be driven by regulatory action; advances in computing, such as the production of a large enough quantum computer that can break existing public key crypto systems; and revealed vulnerabilities in older cryptography that require switching to a more secure alternative, e.g. transition from SHA1 to SHA2. Unfortunately, most organizations do not consider crypto agility, when deploying technology, designing processes, or developing products/services. Consequently changes are often performed in an ad hoc manner and the process is often specific to the threat in question. Thus, the transition from one crypto solution to another can take a long time, exposing organizations to unnecessary security risk. For this talk I'll present a framework to analyze and evaluate this risk that results from the lack of crypto agility. The framework can be used by organizations to determine the appropriate mitigation strategy commensurate with their exposure.

11:15 a.m. - 11:40 a.m.
Speaker: Micah Sherr (Georgetown University)
Title: Ephemeral Exit Bridges for Tor [slides]
Abstract: This talk describes a potentially existential threat to Tor—the increasing frequency at which websites block access to users who arrive via the Tor network. We show that approximately 8% of top Alexa websites (comprising an estimated 4.8% of Tor traffic) apply discriminatory behavior against Tor users.

We present the architecture, implementation, and evaluation of exit bridges for Tor. Exit bridges serve as alternative egress points for the Tor network and are designed to bypass server-side censorship of the network. They are inspired by domain fronting but have important architectural differences and implications to Tor's security and anonymity properties. Exit bridges are constructed as short-lived virtual machines on popular cloud service providers. Due in part to the proliferation of managed cloud-based desktop services (e.g., Amazon Workspaces), we show that there is already a surprisingly large fraction of web requests that originate in the cloud. Trivially disrupting exit bridges by blocking requests from the cloud would thus lead to significant collateral damage by indiscriminately blocking non-Tor (but still cloud-based) users.

Our experiments demonstrate that exit bridges effectively circumvent server-side blocking of Tor and do so with low overhead. Additionally, we perform a cost-analysis of exit bridges based on current cloud pricing models and show that even a large-scale deployment of Tor exit bridges can be done at low cost. Finally, we discuss the security and anonymity implications of using exit bridges.

11:40 a.m. - 12:10 p.m.
Coffee Break

12:10 p.m. - 12:35 p.m.
Speaker: Ryan Wails (U.S. Naval Research Laboratory)
Title: Guard Placement Attacks on Path Selection Algorithms for Tor [slides]
Abstract: Location-based Tor path selection algorithms have been proposed to defend against deanonymization attacks. However, adversaries can exploit these algorithms by strategically placing relays in locations that increase their chances of being selected as a client's guard. We rigorously define this guard placement attack and show that three state-of-the-art path selection algorithms — Counter-RAPTOR, DeNASA, and LASTor — are vulnerable to it, overcoming defenses considered by all three systems. Then we propose and evaluate a generic defense mechanism that provides a provable defense for any path selection algorithm.

12:35 p.m. - 1:00 p.m.
Speaker: Rahel Fainchtein (Georgetown University)
Title: The Hole in the Geo-Fence: Exploring the Operation of "Smart" DNS Services
Abstract: Newly-available "smart DNS" (DNS) services advertise access to restricted content (typically, video streaming sites such as Netflix or Hulu) that would normally be inaccessible within a prescribed geographic region (i.e., geo-fenced content). DNS is simple to use and involves no software installation. Instead, it requires only that users modify their DNS settings to point to a DNS resolver. The DNS resolver "smartly" identifies geo-fenced domains for which the user is outside the fence's geographic bounds. For these requests, the DNS resolver returns IP addresses of proxy servers located within the geo-fence. In so doing, DNS services allow the "unblocking" of restricted content via the returned proxies.

This talk presents an initial measurement study — and the first academic study — of DNS services. We catalog the techniques deployed and describe the risks such services pose to end-users. Additionally, we outline novel discoveries, such as the hidden proxying of domains not publicly advertised, and the potential that many DNS services are actually the same provider advertised under different company aliases.

Directions: The seminar will be held in the Herman Room of the Healey Family Student Center. The Herman Room is in the southeast corner of the building. It is marked as "Meeting room" in this floor plan.

Driving: Parking is limited on campus, but the official parking is at the Southwest Garage. It costs $5/hr., $25/day. There is also 2-hour street parking in the surrounding streets, although you stand a reasonable chance of being ticketed (~$30) for staying longer.

Metro: The best way to reach Georgetown is via public transportation. The nearest Metro stops are Rosslyn (on the Blue, Orange, and Silver lines) and Dupont Circle (on the Red line). These are 1.1 miles and 1.9 miles from the Healey Family Student Center, respectively. Georgetown University runs a regular shuttle service from each of these stops to campus: GUTS. The campus dropoff is near McDonough Arena, which is a short walk to the Healey Family Student Center. The shuttle is free, and riders should be prepared to show identification (university affiliation apparently not required). Several buses can also be used to get to campus, see details here.