## 2 Related Work  
Even though Internet privacy is increasingly being covered in the media, many Internet users are still not aware of the attacks that threaten the privacy of their daily communication links. One important countermeasure against attacks on communication privacy is anonymization [11], the obfuscation of the identity of communication partners, especially of clients contacting a public server. As an important example, the Tor onion routing network provides privacy for Internet users by fundamentally enhancing their anonymity when using the Internet [2]. However, a fundamental problem associated with many of today's security and privacy solutions is not primarily that the level of security they provide is insufficient, but rather their lack of usability. If the usability for certain security features is too low, end users are not willing to apply them, increasing the users' personal risk of exposure to adversary attacks. Recent studies indicate that too complex security features are not applied unless they are mandatory, see for example the usage of security in banking scenarios [12]. The amount of time or money users are willing to spend for more security is restricted and differs individually. There exist two ways to foster a broader application of security mechanisms: either (i) to increase the awareness of security risks in order to raise the willingness to pay money or time; or (ii) to increase the usability of the security features. In the case of Tor, we argue that due to its poor usability in terms of network latency, Tor is not as frequently and intensively used as would be desirable. A larger user base--with proportionate number of additional Tor relays--could enhance the privacy of its users indirectly by making Tor traffic (_i.e._, connections to well-known relays) less rare and suspicious. This argument is supported by research on economic network effects and the role of usability in anonymity systems [4, 13]. Moreover, generalizing from current Tor adoption to future privacy infrastructures, if anonymity mechanisms are to be deployed to protect user privacy in a Future Internet [14], the performance expectations of average users need to be respected. An important aspect of usability is the latency overhead caused by anonymization systems. Classical anonymity systems are mix networks, which were invented by [PERSON] for anonymous email [15] and were later generalized to arbitrary anonymous communication [16]. In comparison to mix networks, Tor already provides much lower latency because traffic of different senders is not stored for a time and sent out in batches in order to counter timing attacks [2]. Recent studies provide a simulation analysis of the interrelation of network topology, additional synchronization and _dummy traffic_ against timing attacks, anonymity, and overhead [17]. Even though Tor does not (yet) apply these additional protection measures, end user latency is still high. Several authors have already qualitatively discussed why Tor is by design slow, or have proposed ideas how to improve the performance, e.g., [9] or [8]. An analysis of the number and the reported bandwidth of Tor relay servers from 2006 until 2008 gives an aggregated view on global Tor capacity and actual load [9]. Another study investigates the impact of different Tor path selection algorithms on anonymity and performance [18]. Further studies investigate the performance of Tor hidden services [19] and [20], which is different from our focus on accessing standard websites through Tor. Related research also includes demographic studies on Tor, e.g., number and countries of exit nodes or estimation of user numbers and origin [7]. In the Tor Metrics project [21], statistics such as number of users, relays, and bridges are collected. Furthermore, the duration and percentage of timeouts and failures of downloading files over Tor from a few data repositories are measured.