We propose a novel location-based second-factor authentication solution for modern smartphones. We demonstrate our solution in the context of point of sale transactions and show how it can be effectively used for the detection of fraudulent transactions caused by card theft or counterfeiting. Our scheme makes use of Trusted Execution Environments (TEEs), such as ARM TrustZone, commonly available on modern smartphones, and resists strong attackers, even those capable of compromising the victim phone applications and OS. It does not require any changes in the user behavior at the point of sale or to the deployed terminals. In particular, we show that practical deployment of smartphone-based second-factor authentication requires a secure enrollment phase that binds the user to his smartphone TEE and allows convenient device migration. We then propose two novel enrollment schemes that resist targeted attacks and provide easy migration. We implement our solution within available platforms and show that it is indeed realizable, can be deployed with small software changes, and does not hinder user experience. Permission to freely reproduce all or part of this paper for noncommercial purposes is granted provided that copies bear this notice and the full citation on the first page. Reproduction for commercial purposes is strictly prohibited without the prior written consent of the Internet Society, the first-named author (for reproduction of an entire paper only), and the author's employer if the paper was prepared within the scope of employment.

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Smartphones can implement various security services from mobile banking to security tokens used for physical access control. System-wide trusted execution environments (TEEs), like ARM TrustZone, allow implementation of these services that withstand malware and operating system compromise. While researchers and developers have focused on secure storage and processing of credentials on such mobile TEEs, secure and practical bootstrapping of security services has been overlooked. The goal of this paper is to put forward the problem of secure user enrollment in the context of mobile system-wide TEEs. We explain why user identity binding to a mobile device is challenging on current smartphone platforms, and argue that current mobile device architectures do not facilitate secure enrollment and migration for such TEEs. We outline possible architecture changes that would enable the realization of secure and practical enrollment, and thus enable more widespread secure deployment of various mobile security services.

On primary storage systems content is often replicated, converted or modified, and the users quickly lose control over its dispersal on the system. Deleting content related to a particular project from the system therefore becomes a labor-intensive task for the user. In this paper we present IRCUS, a system that assists the user in securely removing project-related content, but does not require changes to the user's behavior or to any of the system components, such as the file system, kernel or applications. IRCUS transparently integrates within the user's system, operates in user-space and stores the resulting metadata alongside the files. We implemented and evaluated our system and show that its overhead and accuracy are acceptable for practical use and deployment.

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