Re: [liberationtech] Browser-based Tor proxies
On 1/3/13 5:25 PM, Steve Weis wrote: I noticed a Stanford project for setting up browser-based, ephemeral Tor proxies. In their words, the purpose of this project is to create many, generally ephemeral bridge IP addresses, with the goal of outpacing a censor's ability to block them. I'm extremely worried by the client enumeration problem. Nothing could paint a brighter target on dissidents. Normalization is no defense here, since it applies to any scheme for circumventing a censorship system. (And with sufficient normalization, the political will to continue censorship evaporates anyway.) Either it's okay to identify clients to an adversary or it's not, and I'm under the impression that the consensus is that it's not. I also think the system could be easily rendered useless: I'm also not convinced that it's possible for the mass of ephemeral proxies to absorb the busywork created by the adversary: to twist an old aphorism, never get into a bandwidth competition with someone who buys 10GigE ethernet cards by the crate. While I do have to credit the authors with a good enumeration of the possible threats to the system, I think these threats simply make the system unworkable in practice. If the system becomes popular, it's easy to block, and if the system *isn't* popular, it's easy to identify who's using it. Remember that the adversary need not completely block all connections from ephemeral proxies: he need only impair usability to the point that users give up. -- Unsubscribe, change to digest, or change password at: https://mailman.stanford.edu/mailman/listinfo/liberationtech
Re: [liberationtech] Browser-based Tor proxies
Here's a perspective on the project and its current challenges from Jacob Appelbaum and Roger Dingledine's Tor ecosystem talk at 29C3: http://www.youtube.com/watch?v=Rnbc_9JnVtcfeature=youtu.bet=1h8s gf On 1/3/13 7:25 PM, Steve Weis wrote: I noticed a Stanford project for setting up browser-based, ephemeral Tor proxies. In their words, the purpose of this project is to create many, generally ephemeral bridge IP addresses, with the goal of outpacing a censor's ability to block them. The core idea is that volunteers outside a filtered region can embed an Internet Freedom badge on their web pages. Visitors browsing from outside a filtered region can become short-lived proxies that relay traffic to and from the filtered region. When visitors navigate away from a volunteer page, the proxy disappears. https://crypto.stanford.edu/flashproxy/ https://crypto.stanford.edu/flashproxy/flashproxy.pdf Note that flash is not a reference to Adobe Flash. It's based on Websockets and Javascript. Also, I am not endorsing this technology for real-world use yet nor can attest to its security. I haven't looked at it in enough detail yet. -- Gregory Foster || gfos...@entersection.org @gregoryfoster http://entersection.com/ -- Unsubscribe, change to digest, or change password at: https://mailman.stanford.edu/mailman/listinfo/liberationtech
Re: [liberationtech] Browser-based Tor proxies
Yes, the system is vulnerable to client enumeration if there are few facilitators and proxies. If there are many facilitators and proxies, then the adversary needs to discover facilitators, constantly poll them, and compete with legitimate proxies to learn client IPs. They won't discover every facilitator and cannot poll too aggressively without detection, but will certainly learn some client IPs. This may or may not be an acceptable risk. As the authors discussed, the adversary can already conduct traffic analysis, so it might be no worse than the status quo. On Thu, Jan 3, 2013 at 5:57 PM, Daniel Colascione dan...@dancol.org wrote: I'm extremely worried by the client enumeration problem. Nothing could paint a brighter target on dissidents. Normalization is no defense here, since it applies to any scheme for circumventing a censorship system. -- Unsubscribe, change to digest, or change password at: https://mailman.stanford.edu/mailman/listinfo/liberationtech
