Energy expenditures represent approximately 10% of the global gross domestic product (GDP), second only to healthcare costs. Globally, the residential and commercial building sector accounts for 21% of total energy consumption. In the United States, the building sector accounts for a much larger share: 40% of the country's total energy consumption.With an increased global focus on energy conservation, the building sector presents a ripe target for introducing energy efficiency. While advancements have been made in building architecture and materials, the length of time needed for mass adoption of these technologies renders them ineffective in the short and medium term. Retrofitting existing buildings is a more desirable option, resulting in immediate energy savings while preserving the building structure. In this paper, we discuss several existing and ongoing efforts directed toward promoting energy efficiency in buildings, focusing specifically on building retrofits, and analyze their energy savings potential. This collection of building technologies spans several categories and represents various building energy end-uses. We also discuss the challenges involved in developing such energy-efficient building technologies.

Web services are increasingly adopting auxiliary authentication mechanisms to supplement the security provided by conventional password verification. In the domain of social network based web-services, Facebook has pioneered the use of social authentication as an auxiliary authentication mechanism. If Facebook detects a user login under suspicious circumstances, then users are asked to verify information about their friends (in addition to verifying their passwords). However, recent work has shown that Facebook's social authentication is insecure. In this work-in-progress, we propose to rethink the design of social authentication. Our key insight is that online social network (OSN) operators are privy to large amounts of private data generated by users, including information about users' online interactions. Based on this insight, we architect a system for social authentication that asks users to verify information about their social contacts and their interactions. Our system leverages information protected by privacy policies of OSNs to resist attacks, such as questions based on private user interactions including exchanging messages and poking social contacts. We implemented our system prototype as a Facebook application, and performed a preliminary user study to evaluate feasibility of the approach. Our initial experiments have been encouraging; we find that users have high rates of recall for information generated in the context of OSN interactions. Overall, our work provides a promising new direction for the secure and usable deployment of social authentication. 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.