One Bad Apple Spoils the Bunch: Exploiting P2P Applications to Trace and Profile Tor Users

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Executive Summary

Tor is a popular low-latency anonymity network. However, Tor does not protect against the exploitation of an insecure application to reveal the IP address of, or trace, a TCP stream. In addition, because of the linkability of Tor streams sent together over a single circuit, tracing one stream sent over a circuit traces them all. Surprisingly, it is unknown whether this linkability allows in practice to trace a significant number of streams originating from secure (i.e., proxied) applications. In this paper, the authors show that linkability allows one to trace 193% of additional streams, including 27% of HTTP streams possibly originating from "Secure" browsers. In particular, they traced 9% of all Tor streams carried by their instrumented exit nodes.

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