National Institute of Standards and Technology における超伝導研究及び生活

We evaluate two decades of proposals to replace text passwords for general-purpose user authentication on the web using a broad set of twenty-five usability, deployability and security benefits that an ideal scheme might provide. The scope of proposals we survey is also extensive, including password management software, federated login protocols, graphical password schemes, cognitive authentication schemes, one-time passwords, hardware tokens, phone-aided schemes and biometrics. Our comprehensive approach leads to key insights about the difficulty of replacing passwords. Not only does no known scheme come close to providing all desired benefits: none even retains the full set of benefits that legacy passwords already provide. In particular, there is a wide range from schemes offering minor security benefits beyond legacy passwords, to those offering significant security benefits in return for being more costly to deploy or more difficult to use. We conclude that many academic proposals have failed to gain traction because researchers rarely consider a sufficiently wide range of real-world constraints. Beyond our analysis of current schemes, our framework provides an evaluation methodology and benchmark for future web authentication proposals.

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The Quest to Replace Passwords: A Framework for Comparative Evaluation of Web Authentication Schemes

The ubiquity of 802.11 devices and networks enables anyone to track our every move with alarming ease. Each 802.11 device transmits a globally unique and persistent MAC address and thus is trivially identifiable. In response, recent research has proposed replacing such identifiers with pseudonyms (i.e., temporary, unlinkable names). In this paper, we demonstrate that pseudonyms are insufficient to prevent tracking of 802.11 devices because implicit identifiers, or identifying characteristics of 802.11 traffic, can identify many users with high accuracy. For example, even without unique names and addresses, we estimate that an adversary can identify 64% of users with 90% accuracy when they spend a day at a busy hot spot. We present an automated procedure based on four previously unrecognized implicit identifiers that can identify users in three real 802.11 traces even when pseudonyms and encryption are employed. We find that the majority of users can be identified using our techniques, but our ability to identify users is not uniform; some users are not easily identifiable. Nonetheless, we show that even a single implicit identifier is sufficient to distinguish many users. Therefore, we argue that design considerations beyond eliminating explicit identifiers (i.e., unique names and addresses), must be addressed in order to prevent user tracking in wireless networks.

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802.11 user fingerprinting

Information technology can improve the quality, efficiency, and cost of healthcare. In this survey, we examine the privacy requirements of mobile computing technologies that have the potential to transform healthcare. Such mHealth technology enables physicians to remotely monitor patients' health and enables individuals to manage their own health more easily. Despite these advantages, privacy is essential for any personal monitoring technology. Through an extensive survey of the literature, we develop a conceptual privacy framework for mHealth, itemize the privacy properties needed in mHealth systems, and discuss the technologies that could support privacy-sensitive mHealth systems. We end with a list of open research questions.

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Privacy in mobile technology for personal healthcare

In mobile wireless networks, third parties can track the location of mobile nodes by monitoring the pseudonyms used for identification. A frequently proposed solution to protect the location privacy of mobile nodes suggests changing pseudonyms in regions called mix zones. In this paper, we propose a novel metric based on the mobility profiles of mobile nodes in order to evaluate the mixing effectiveness of possible mix zone locations. Then, as the location privacy achieved with mix zones depends on their placement in the network, we analyze the optimal placement of mix zones with combinatorial optimization techniques. The proposed algorithm maximizes the achieved location privacy in the system and takes into account the cost induced by mix zones to mobile nodes. By means of simulations, we show that the placement recommended by our algorithm significantly reduces the tracking success of the adversary.

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On the Optimal Placement of Mix Zones

We discuss ways to enhance the location privacy of Bluetooth. The principal weakness of Bluetooth with respect to location privacy lies in its disclosure of a device’s permanent identifier, which makes location tracking easy. Bluetooth’s permanent identifier is often disclosed and it is also tightly integrated into lower layers of the Bluetooth stack, and hence susceptible to leakage. We survey known location privacy attacks against Bluetooth, generalize a lesser-known attack, and describe and quantify a more novel attack. The second of these attacks, which recovers a 28-bit identifier via the device’s frequency hop pattern, requires just a few packets and is practicable. Based on a realistic usage scenario, we develop an enhanced privacy framework with stronger unlinkability, using protected stateful pseudonyms and simple primitives.

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Location privacy in bluetooth

Multichannel security protocols transmit messages over multiple communication channels, taking into account each channel's security properties. Our first intentional use of these protocols goes back to a 1999 article that proposed physical contact for imprinting as opposed to the wireless channel used in subsequent operations. Only later did we understand three key points. First, explicit use of multiple channels in the same protocol can offer significant advantages for both security and usability. Second, explicitly stating the properties of the channel on which each protocol message is transmitted is useful for understanding one's own protocol in greater depth and therefore for addressing subtle vulnerabilities early on. Third, multichannel protocols existed long before we recognized them as such - think of the courier handcuffed to the briefcase carrying the code book that will later protect postal or telegraphic traffic. The paper presents a security protocol that exploit additional transmissions over lower-capacity channels, typically found in ubicomp environments, that offer a different combination of security properties.

Multichannel Security Protocols

We examine several ad-hoc pairing protocols that strengthen their radio exchanges with additional transmissions over another channel, for example a screen showing graphically encoded information to a camera. Additional channels may have limited capacity and may still be subject to eavesdropping, but they may offer specific advantages over radio such as data origin authenticity. A single protocol may profitably use more than one channel, each with its own specific security properties, for different messages in its trace. Making this option explicit allows for further advances in protocol design.

We also present an intriguing asymmetric protocol that achieves results comparable to mutual authentication even though the verification happens only in one direction.

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Multi-channel protocols

We implement and demonstrate a passive attack on the Bluetooth authentication protocol used to connect two devices to each other. Using a protocol analyzer and a brute-force attack on the PIN, we recover the link key shared by two devices. With this secret we can then decrypt any encrypted traffic between the devices as well as, potentially, impersonate the devices to each other. We then implement an alternative pairing protocol that is more robust against passive attacks and against active man-in-the-middle attacks. The price of the added security offered by the new protocol is its use of asymmetric cryptography, traditionally considered infeasible on handheld devices. We show that an implementation based on elliptic curves is well within the possibility of a modern handphone and has negligible effects on speed and user experience.

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Repairing the bluetooth pairing protocol

Position localization of transmitters can be carried out by an adversary owning a network of pervasive receivers, which can pinpoint the victim mobile nodes' locations with high temporal and spatial accuracy, such that pseudonym changing and higher-layer obfuscation are insufficient to protect their location privacy. Our contribution is to consider covert beam patterns, generated using multiple antennas to do adaptive beamforming, and so reducing radio signature. We architect such a privacy-enhancing system, give an informal security analysis, and develop an evaluation framework to analyze its location privacy. We performed simulations using wireless LAN parameters, and found that signal-to-noise-ratios for successful direction-finding are more stringent than those required for mere communications. We composed an end-to-end integrated radio and mobility simulation, and compared location privacy performance of omnidirectional versus adaptive beamforming antennas. Our proposal is shown to perform better. In addition, our evaluation framework is flexible and extensible.

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Ford Long Wong

Papers

Location privacy in bluetooth

Multichannel Security Protocols

Multi-channel protocols

Repairing the bluetooth pairing protocol

Evaluation Framework of Location Privacy of Wireless Mobile Systems with Arbitrary Beam Pattern