Mobile wallets promise a future where users do not need to carry physical payment cards. However, the slow adoption of contactless point of sales (POS) terminals by merchants limits the potential of Near-Field Communication (NFC) based payment devices. In this paper, we present Wild Card, a secure and backward compatible solution for making mobile payments at conventional magnetic stripe based POS terminals. Our solution resembles a traditional credit card in its physical dimensions and stays in the phone case. It can be programmatically set by an NFC-enabled mobile phone to any card number that the user owns. The key technologies that enable Wild Card are a fully programmable magnetic stripe, an energy harvesting system that allows the card to be charged and programmed by the phone through NFC, and a security mechanism that makes card information resilient to attacks on mobile devices. With a prototype, we evaluate the feasibility of Wild Card in terms of functionality and energy budget.

This work analyzes the stochastic behavior of writing to embedded flash memory at voltages lower than recommended by a microcontroller’s specifications in order to reduce energy consumption. Flash memory integrated within a microcontroller typically requires the entire chip to operate on a common supply voltage almost twice as much as what the CPU portion requires. Our software approach allows the flash memory to tolerate a lower supply voltage so that the CPU may operate in a more energy-efficient manner. Energy-efficient coding algorithms then cope with flash memory writes that behave unpredictably. Our software-only coding algorithms ( in-place writes, multiple-place writes, RS-Berger codes , and slow writes ) enable reliable storage at low voltages on unmodified hardware by exploiting the electrically cumulative nature of half-written data in write-once bits. For a sensor monitoring application using the MSP430, coding with in-place writes reduces the overall energy consumption by 34%. In-place writes are competitive when the time spent on low-voltage operations such as computation are at least four times greater than the time spent on writes to flash memory. Our evaluation shows that tightly maintaining the digital abstraction for storage in embedded flash memory comes at a significant cost to energy consumption with minimal gain in reliability. We find our techniques most effective for embedded workloads that have significant duty cycling, rare writes, or energy harvesting.

In this paper we introduce a link layer security platform for wireless sensor networks. At the heart of this platform, lies our key management module facilitating an efficient scalable post-distribution key establishment that allows the platform to provide different security services. We have developed this framework under TinyOs and have tested it with MICA2 motes. To the best of our knowledge this is the first implemented security platform for sensor networks that provides acceptable resistance against node capture attacks and replay attacks. The provision of security services is completely transparent to the user of the framework. Furthermore, being highly scalable and lightweight, this platform is appropriate to be used in a wireless sensor network of hundreds of nodes.

We describe HyMAC, a new hybrid MAC layer protocol for wireless sensor networks that is, to the best of our knowledge, the first effort to combine the strengths of both TDMA and FDMA schemes in these constrained networks. While allowing the network to operate in an energy-efficient collision-free manner, HyMAC takes advantage of the multiple frequencies provided in the radio component of recent sensor node hardware platforms such as MICAZ, TELOS and FireFly. We show how HyMAC outperforms protocols such as B-MAC, RT-Link and MMSN achieving high throughput and small bounded end- to-end delay suitable for newer types of sensor network applications such as real-time voice streaming.