Amir Houmansadr

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Many users face surveillance of their Internet communications and a significant fraction suffer from outright blocking of certain destinations. Anonymous communication systems allow users to conceal the destinations they communicate with, but do not hide the fact that the users are using them. The mere use of such systems may invite suspicion, or access to(More)
In response to the growing popularity of Tor and other censorship circumvention systems, censors in non-democratic countries have increased their technical capabilities and can now recognize and block network traffic generated by these systems on a nationwide scale. New censorship-resistant communication systems such as Skype Morph, Stego Torus, and Censor(More)
Open communication over the Internet poses a serious threat to countries with repressive regimes, leading them to develop and deploy censorship mechanisms within their networks. Unfortunately, existing censorship circumvention systems face difficulties in providing unobservable communication with their clients; this highly limits their availability as(More)
Linking network flows is an important problem in intrusion detection as well as anonymity. Passive traffic analysis can link flows but requires long periods of observation to reduce errors. Watermarking techniques allow for better precision and blind detection, but they do so by introducing significant delays to the traffic flow, enabling attacks that(More)
We analyze several recent schemes for watermarking network flows based on splitting the flow into intervals. We show that this approach creates time dependent correlations that enable an attack that combines multiple watermarked flows. Such an attack can easily be mounted in nearly all applications of network flow watermarking, both in anonymous(More)
We propose Stegobot, a new generation botnet that communicates over probabilistically unobservable communication channels. It is designed to spread via social malware attacks and steal information from its victims. Unlike conventional botnets, Stegobot traffic does not introduce new communication endpoints between bots. Instead, it is based on a model of(More)
A key challenge in censorship-resistant web browsing is being able to direct legitimate users to redirection proxies while preventing censors, posing as insiders, from discovering their addresses and blocking them. We propose a new framework for censorship-resistant web browsing called <i>CensorSpoofer</i> that addresses this challenge by exploiting the(More)
Decoy routing is a recently proposed approach for censorship circumvention. It relies on cooperating ISPs in the middle of the Internet to deploy the so called “decoy routers” that proxy network traffic from users in the censorship region. A recent study, published in an award-winning CCS 2012 paper [24], suggested that censors in highly connected countries(More)
Censorship circumvention systems such as Tor are highly vulnerable to network-level filtering. Because the traffic generated by these systems is disjoint from normal network traffic, it is easy to recognize and block, and once the censors identify network servers (e.g., Tor bridges) assisting in circumvention, they can locate all of their users.(More)