HTTPS is the de facto standard for securing Internet communications. Although it is widely deployed, the security provided with HTTPS in practice is dubious. HTTPS may fail to provide security for multiple reasons, mostly due to certificate-based authentication failures. Given the importance of HTTPS, we investigate the current scale and practices of HTTPS and certificate-based deployment. We provide a large-scale empirical analysis that considers the top one million most popular websites. Our results show that very few websites implement certificatebased authentication properly. In most cases, domain mismatches between certificates and websites are observed. We study the economic, legal and social aspects of the problem. We identify causes and implications of the profit-oriented attitude of CAs and show how the current economic model leads to the distribution of cheap certificates for cheap security. Finally, we suggest possible changes to improve certificate-based authentication.

Peer-to-peer (p2p) video-on-demand (VoD) is increasingly popular with Internet users. Currently deployed pure p2p VoD systems provide poor general performance and they lack advanced features such as fast forward and seeking to arbitrary points. Peer-assisted VoD systems can provide such services, but they require very well provisioned source servers (or server farms).We propose BulletMedia, a system that uses proactive caching to attempt to provide advanced features without requiring a well provisioned server. In BulletMedia, blocks are altruistically replicated by peers not to aid immediate playback but to simply increase the number of replicas of each block. This helps ensure that blocks are available in-overlay and reduces dependence on the source. BulletMedia combines a traditional overlay mesh approach with a structured overlay. The overlay mesh is used to fetch blocks at a high rate, while the structured overlay is used to enable efficient block discovery and to control block replication. Initial experimental results from a prototype BulletMedia implementation demonstrate that it can both effectively control in-overlay block replication and can efficiently use these replicas to perform forward seeks.

Much of the Internet economy relies on online advertising for monetizing digital content: Users are expected to accept the presence of online advertisements in exchange for content being free. However, online advertisements have become a serious problem for many Internet users: while some are merely annoyed by the incessant display of distracting ads cluttering Web pages, others are highly concerned about the privacy implications-as ad providers typically track users' behavior for ad targeting purposes. Similarly, security problems related to technologies and practices employed for online advertisement have frustrated many users. Consequently, a number of software solutions have emerged that block online ads from being downloaded and displayed on users' screens as they browse the Web. We focus on these advertisement avoidance technologies for online content and their economic ramifications for the monetization of websites. More specifically, our work addresses the interplay between users' attempts to avoid commercial messages and content providers' design of countermeasures. Our investigation is substantiated by the development of a game-theoretic model that serves as a framework usable by content providers to ponder their options to mitigate the consequences of ad avoidance techniques. We complement our analytical approach with simulation results, addressing different assumptions about user heterogeneity.

Abstract. Location privacy has been extensively studied over the last few years, especially in the context of location-based services where users purposely disclose their location to benefit from convenient contextaware services. To date, however, little attention has been devoted to the case of users' location being unintentionally compromised by others. In this paper, we study a concrete and widespread example of such situations, specifically the location-privacy threat created by access points (e.g., public hotspots) using network address translation (NAT). Indeed, because users connected to the same hotspot share a unique public IP, a single user making a location-based request is enough to enable a service provider to map the IP of the hotspot to its geographic coordinates, thus compromising the location privacy of all the other connected users. When successful, the service provider can locate users within a few hundreds of meters, thus improving over existing IP-location databases. Even in the case where IPs change periodically (e.g., by using DHCP), the service provider is still able to update a previous (IP, Location) mapping by inferring IP changes from authenticated communications (e.g., cookies). The contribution of this paper is three-fold: (i) We identify a novel threat to users' location privacy caused by the use of shared public IPs. (ii) We formalize and analyze theoretically the threat. The resulting framework can be applied to any access-point to quantify the privacy threat. (iii) We experimentally assess the state in practice by using real traces of users accessing Google services, collected from deployed hotspots. Also, we discuss how existing countermeasures can thwart the threat.

Abstract-This paper presents a concrete and widespread example of situation where a user's location privacy is unintentionally compromised by others, specifically the location-privacy threat that exists at access points (public hotspots, FON, home routers, etc.) that have a single public IP and make use of network address translation (NAT). As users connected to the same hotspot share a unique public IP address, a single user's making a location-based request is enough to enable a service provider to map the IP address of the hotspot to its geographic coordinates, thus compromising the location privacy of all the other connected users. When successful, the service provider can locate users within a few hundreds of meters, thus improving over existing IP-location databases. Even in the case where IPs change periodically (e.g., by using DHCP), the service provider is still able to update a previous (IP, Location) mapping by inferring IP changes from authenticated communications (e.g., cookies). The contribution of this paper is three-fold: (i) We identify a novel location-privacy threat caused by shared public IPs in combination with NAT. (ii) We formalize and analyze the threat theoretically. In particular we derive and provide expressions of the probability that the service provider will learn the mapping and of the expected proportion of victims. (iii) We experimentally assess the state in practice by using real traces (collected from deployed hotspots over a period of 23 days) of users who accessed Google services. We also discuss how existing countermeasures can thwart the threat.