How to Bypass Two Anonymity Revocation Schemes

Abstract

In recent years, there have been several proposals for anonymous communication systems that provide intentional weaknesses to allow anonymity to be circumvented in special cases. These anonymity revocation schemes attempt to retain the properties of strong anonymity systems while granting a special class of people the ability to selectively break through their protections. We evaluate the two dominant classes of anonymity revocation systems, and identify fundamental flaws in their architecture, leading to a failure to ensure proper anonymity revocation, as well as introducing additional weaknesses for users not targeted for anonymity revocation.

Introducing Accountability to Anonymity Networks

“…The system also introduces an external proxy to inspect all outbound traffic for correct signatures and protocol compliance. The inspector has been criticized for centralizing traffic flows, which enables DOS, censorship, and increases observability [29].…”

“…It is tailored to highlatency mix networks and requires a trusted authority to issue credentials-both impede deployability. Danezis and Sassaman [29] demonstrate a bypass attack on this and the Kopsell et al scheme [11]. The attack is based on the protocols' assumption that there can be no leakage of information from inside the channel to the world unless it passes through the verification step.…”

Enlisting ISPs to Improve Online Privacy: IP Address Mixing by Default

“…Since Chaum's seminal work, many researchers have developed re-routing based anonymity systems, including Crowds [26], Freedom [34], Tor [7], Tarzan [10], GAP/GNUnet [2], Herbivore [30], P5 [28], Hordes [16], Slicing [13], and JAP [12]. Over time, researchers have developed attacks of ever-increasing sophistication, involving techniques such as timing analysis [15,27,29] and broad spectrum traffic analysis [22,25], and have found weaknesses in systems designed to enable forensic support [5]. From a design perspective, AHP bears closest resemblance to CPP, a system that hierarchically encrypts IPv6 addresses to obtain privacy [32], and Anonymizer [1] and Proxify [24], which provide commercial application-level anonymization proxying.…”