Abstract
Tor constitutes one of the pillars of anonymous online communication. It allows its users to communicate while concealing from observers their location as well as the Internet resources they access. Since its first release in 2002, Tor has enjoyed an increasing level of popularity with now commonly more than 2,000,000 simultaneous active clients on the network. However, even though Tor is widely popular, there is only little understanding of the large-scale behavior of its network clients. In this paper, we present a longitudinal study of the Tor network based on passive analysis of TLS traffic at the Internet uplinks of four large universities inside and outside of the US. We show how Tor traffic can be identified by properties of its autogenerated certificates, and we use this knowledge to analyze characteristics and development of Tor’s traffic over more than three years.
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Notes
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For the remainder of this paper, we will refer to either SSL or TLS as “TLS.”.
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Not counting Tor and Grid Computing certificates.
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Since we have extended our data collection script over time, information about older connections does not contain all the listed attributes.
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Acknowledgments
We thank Phillip Winter and David Fifield for their feedback during the writing of this paper. This work was supported by the National Science Foundation under grant numbers CNS-1528156 and ACI-1348077. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.
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Amann, J., Sommer, R. (2016). Exploring Tor’s Activity Through Long-Term Passive TLS Traffic Measurement. In: Karagiannis, T., Dimitropoulos, X. (eds) Passive and Active Measurement. PAM 2016. Lecture Notes in Computer Science(), vol 9631. Springer, Cham. https://doi.org/10.1007/978-3-319-30505-9_1
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